Showing papers on "Oxytocin published in 1977"
TL;DR: Extracellular action potentials were recorded from forty antidromically identified single units in the supraoptic nucleus of lactating, urethane‐anaesthetized female rats during reflex milk ejection and during an increase of plasma osmotic pressure induced by intraperitoneal injection of 1 ml.
Abstract: 1 Extracellular action potentials were recorded from forty antidromically identified single units in the supraoptic nucleus of lactating, urethane-anaesthetized female rats The activity was monitored both during reflex milk ejection and during an increase of 10-15 m-osmole/kg in plasma osmotic pressure induced by intraperitoneal injection of 1 ml of 15 M-NaCl solution
2 About half (eighteen) the cells showed a burst of activity before reflex milk ejection and were dubbed oxytocin cells Oxytocin cells responded to a hypertonic injection with a smooth sustained threefold increase in firing rate
3 The remainder (twenty-two) showed no burst of activity before reflex milk ejection and were dubbed vasopressin cells Vasopressin cells doubled their firing rate as plasma osmotic pressure increased Neither cell type increased its firing rate after injections of isotonic NaCl
4 A phasic firing pattern was rarely seen in slow firing vasopressin cells (< 2 spikes/sec) but was seen in almost all vasopressin cells (twelve out of fourteen) firing between 3 and 8 spikes/sec Above 8 spikes/sec, some vasopressin cells fired continuously Phasic firing was only once encountered in an oxytocin cell
5 The firing rate of both oxytocin and vasopressin cells decreased when plasma osmotic pressure was reduced 10-15 m-osmole/kg by an intragastric water load of 10 ml
6 Hypothalamic cells lying just outside the supraoptic nucleus did not show a consistent response to injection of hypertonic NaCl
7 Clearly, both oxytocin and vasopressin cells are osmoresponsive, but phasic firing is characteristic of stimulated vasopressin cells Thus, osmotic activation allows discrimination between oxytocin- and vasopressin-secreting neurones
278 citations
TL;DR: Data provide support for the hypothesis that the neurohypophysial peptides (vasopressin and oxytocin) and neurophysins are derived from the post- translational clevage of protein precursors synthesized in the SON, and that the conversion process can occur in the neurosecretory granule during axonal transport.
Abstract: 35S-cysteine injected adjacent to the supraoptic nucleus (SON) of the rat is rapidly incorporated into proteins. These 35S-cysteine-labeled proteins in the SON (1-24 h after injection) were separated by polyacrylamide gel electrophoresis, and the distribution of radioactive proteins on the gels was analyzed. 1 h after injection, about 73% of the radioactivity appeared in two peaks (both about 20,000 mol wt). With time, these peaks (putative precursors of neurophysin) decreased, as a 12,000 mol wt peak (containing two distinct neurophysins) increased in radioactivity. Both the 20,000- and 12,000-mol wt proteins are transported into the axonal (median eminence) and nerve terminal (posterior pituitary) regions of the rat hypothalamo-neurohypophysial system. Conversion of the larger precursor protein to the smaller neurophysin appears to occur, in large part, intra-axonally during axonal transport. Six distinct 35S-cysteine-labeled peptides (less than 2500 mol wt), in addition to arginine vasopressin and oxytocin, are also synthesized in the SON and transported to the posterior pituitary where they are released together with labeled neurophysin by potassium depolarization in the presence of extracellular calcium. These data provide support for the hypothesis that the neurohypophysial peptides (vasopressin and oxytocin) and neurophysins are derived from the post-translational clevage of protein precursors synthesized in the SON, and that the conversion process can occur in the neurosecretory granule during axonal transport.
254 citations
TL;DR: It was shown that the human suprachiasmatic nuclei contain numerous neurophysin-vasopressin-producing neurons, and it was demonstrated in the human hypothalamus, as well as in the hypothalamus of other mammals, that vasoppressin and oxytocin are synthesized in separate neurons.
Abstract: The human hypothalamic-neurohypophysial hormone-producing nuclei were investigated with the unlabeled antibody peroxidase-antiperoxidase complex (PAP) technique at the light microscopic level. The size, shape and location of the supraoptic, paraventricular, accesssory supraoptic and suprachiasmatic nuclei were determined. It was demonstrated in the human hypothalamus, as well as in the hypothalamus of other mammals, that vasopressin and oxytocin are synthesized in separate neurons. In each of the nuclei of the magnocellular neurosecretory system, the distribution, ratios and structural features of the vasopressinergic and oxytocinergic neurons were determined. It was shown that the human suprachiasmatic nuclei contain numerous neurophysin-vasopressin-producing neurons.
146 citations
TL;DR: Tissue sections of the hypothalamus were examined by immunoperoxidase technique and light microscopy using antisera to oxytocin and arginine vasopressin, and an antiserum which reacts with all rat neurophysins.
Abstract: Adrenal regulation of the vasopressincontaining fibers to the portal capillary system in the zona externa of the median eminence was studied in the rat. Tissue sections of the hypothalamus were examined by immunoperoxidase technique and light microscopy using antisera to oxytocin and arginine vasopressin, and an antiserum which reacts with all rat neurophysins. These peptides were localized in the intact normal rat and after adrenalectomy, glucocorticoid replacement with dexamethasone, and after dehydration. The effect of adrenalectomy was also examined in the homozygous Brattleboro rat with diabetes insipidus (DI rat) which lacks arginine vasopressin and, arginine vasopressinneurophysin. In the zona externa of the normal rat a small number of arginine vasopressin and neurophysin- containing fibers, and an occasional one containing oxytocin were traced to the portal capillary bed. The zona externa of the unoperated DI rat contained only an occasional neurophysin- and oxytocin-reactive fiber. In the normal...
126 citations
TL;DR: Vasopressin-induced barrel rotation was accompanied by pathological symptoms indicating a disturbance of muscle tone regulation and is considered to be a non-specific and toxic effect.
Abstract: Intraventricular injection of arginine-8-vasopressin and its analogues vasotocin and lysine-8-vasopressin into rat brain evoked a special rotational behavior resembling somatostatin-induced barrel rotation [1]. Oxytocin and oxypressin were less active while vasopressin fragments had no effect. Vasopressin-induced barrel rotation was accompanied by pathological symptoms indicating a disturbance of muscle tone regulation and is considered to be a non-specific and toxic effect. This rotational behavior was not prevented by atropine, propranolol, phentolamine, methysergide or haloperidol but was reduced by chlorpromazine, probably due to the latter's muscle relaxing activity.
118 citations
TL;DR: These and subsequent studies have revealed that vasopressin is not the corticotropin-releasing factor(s) (CRF) and a number of peptide structures have been proposed for CRF but its struc-like structure is not confirmed.
Abstract: A physiologic role for vasopressin in the regulation of ACTH secretion has been debated for more than 20 years.'-'< In the 1950s it was shown that a deficient adrenal response to stress in rats with experimental diabetes insipidus could be corrected by the administration of posterior pituitary extracts containing vasopre~sin.~, s However, the exogenous systemic dose of vasopressin required to release ACTH was a 1000-fold greater than the amount that produced antidiuresis.6 In addition, endogenous release of the hormone stimulated by intracarotid hypertonic saline was not associated with activation of the adrenal cortex.6 Unless vasopressin was secreted into the hypophyseal portal system in the zona externa of the median eminence in very high concentrations by a separate pathway from the one to the posterior pituitary, it did not seem likely that the hormone had any normal role in the regulation of ACTH.4j Such a pathway was doubted because Gomori-positive fibers like those transporting vasopressin to the posterior pituitary were often reported to be absent or scarce in the zona externa, although some were found by Scharrer, particularly in young dogs.' Furthermore, other preparations of peptides extracted from the hypothalamus and posterior pituitary gland were much more active and gave different dose-responses in releasing ACTH than did vasopressh8 These and subsequent studies have revealed that vasopressin is not the corticotropin-releasing factor(s) (CRF) .9-11 A number of peptide structures have been proposed for CRF but its struc-
99 citations
TL;DR: Threonine substitution has brought about a substantial enhancement in oxytocic activity and a fivefold enhancement in O/A selectivity in these peptides, which might offer a greater margin of safety than oxytocin in those clinical stiuations in which the latter is currently employed.
Abstract: [4-Threonine, 7-glycine]oxytocin and [1-(L-2-hydroxy-3-mercaptopropanoic acid), 4-threonine, 7-glycine]oxytocin (hydroxy[Thr4, Gly7]oxytocin) were synthesized by a combination of solid-phase and classical methods of peptide synthesis. A protected octapeptide was synthesized by the solid-phase method and following ammonolysis and purification 1 + 8 couplings in solution were employed to furnish the required key nonapeptide and acyl octapeptide intermediates, respectively. [7-Glycine]oxytocin was prepared from a sample of the protected nonapeptide intermediate used in the original synthesis of this peptide. [7-Glycine]oxytocin has an oxytocic potency (O) of 93 +/- 4 units/mg and an antidiuretic potency (A) of 0.0056 +/- 0.0003 units/mg. It has an O/A ratio of 16 000. [4-Threonine, 7-glycine]oxytocin has an oxytocic potency of 166 +/- 4 units/mg and an antidiuretic potency of 0.002 +/- 0.0004 units/mg. Its O/A ratio is 83 000. Threonine substitution has thus brought about a substantial enhancement in oxytocic activity and a fivefold enhancement in O/A selectivity. Hydroxy [Thr4, Gly7]oxytocin has an oxytocic potency of 218 +/- 8 units/mg and antidiuretic potency of 0.0040 +/- 0.0005 units/mg. Its O/A ratio is thus 54 500. All three 7-glycine-substituted analogues exhibit a marked sensitivity to Mg2+ on the rat uterus assay ststem and in the presence of 0.5 mM Mg2+ had oxytocic potencies in the range of 900-1000 units/mg. Should these peptides exhibit enhanced oxytocic selectivity in humans, they might offer a greater margin of safety than oxytocin in those clinical stiuations in which the latter is currently employed.
88 citations
TL;DR: A comparative study of the proton and carbon-13 nuclear magnetic resonance spectral parameters of the peptide hormone oxytocin and of its competitive inhibitor [1-L-penicillamine]oxytocin has been made, and the results indicate that Oxytocin has a flexible conformation, while [1
Abstract: A comparative study of the proton and carbon-13 nuclear magnetic resonance spectral parameters of the peptide hormone oxytocin and of its competitive inhibitor [1-L-penicillamine]oxytocin has been made, and the results analyzed in terms of comparative conformational and dynamic properties. The results indicate that oxytocin has a flexible conformation, while [1-L-penicillamine]oxytocin has a more restricted conformation. The results provide a framework for understanding the mechanism of peptide hormone agonism and antagonism for these compounds, and an approach for understanding some features of the interaction of the hormone and related compounds with their receptor.
85 citations
TL;DR: The results indicate that pituitary hormones are physiologically involved in heroin self-administration, and treatment with oxytocin or human growth hormone antiserum fails to influence this behavior, while prolactin antisersum exhibits similar effects as observed with antivasopressin serum.
67 citations
TL;DR: Various storage conditions of the blood before centrifugation and freezing produced significant differences in plasma levels of endogenous PGF, but storage experiments with added labelled PGF-2alpha indicated that the PG was stable in plasma and whole blood.
Abstract: Six heifers with normal oestrous cycles were treated i.m. with 100 i.u. oxytocin on 3 consecutive days, commencing on Days 1-6 after oestrus, and the levels of prostaglandin (PG) F in posterior vena cava plasma were compared with pretreatment values. An increase of PGF in response to oxytocin was significantly influenced by day, with the greatest response occurring on Day 3 after oestrus. In an ovariectomized heifer the levels of PGF in posterior vena cava plasma increased 24 h after priming with oestradiol, but no further increase occurred after oxytocin injection. Peak levels of PGF were higher in the plasma of the posterior vena cava than in the jugular vein. Various storage conditions of the blood before centrifugation and freezing (--20 degrees C) produced significant differences in plasma levels of endogenous PGF, but storage experiments with added labelled PGF-2alpha indicated that the PG was stable in plasma and whole blood.
62 citations
01 May 1977
TL;DR: It appears that oxytocin binding sites on the plasma membrane of target cells constitute the recognition part of oxytoc in receptors, which is specific to the target tissue or cell as well as to the ligand.
Abstract: High affinity binding sites for 3[H] oxytocin have been demonstrated in particulate fractions from rat uterus and oviduct, myometrium from the sow, ewe and human, ewe endometrium, and mammary gland from the lactating rat. The binding activity has been localized to enriched plasma membrane fractions from the rat uterus and mammary gland; cells isolated from the mammary gland also bind oxytocin. The apparent dissociation constant (Kd) for the interaction of oxytocin with its binding sites in a variety of tissue preparations is in the nanomolar range. The concentration of oxytocin eliciting half-maximal contraction of the rat isolated uterus corresponds to the apparent Kd of oxytocin interaction with uterine particulate fractions. Binding is specific with respect to the target tissue or cell, as well as to the ligand. The affinity of binding sites for oxytocin analogues corresponds generally to their potencies as agonists or antagonists. Factors that affect the binding of oxytocin affect the biological response in the same way. For example, certain divalent metal ions, which increase oxytocin binding activity, enhance the sensitivity of the contractile response of the uterus and mammary gland to oxytocin. Estrogen administration, which increases the uterine binding of oxytocin, increases the sensitivity of the myometrium to oxytocin. The myometrium binds the most oxytocin at estrus and is most sensitive to oxtocin at that time. The dgree of stimulation by oxytocin of prostaglandin F2alpha synthesis by ewe endometrium is paralleled by an increased concentration of oxytocin binding sites. The marked increase in sensitivity to oxytocin of the rat uterus occurring on the day of parturition also is reflected by the amount of oxytocin bound by the uterus. Because of the many correlations between oxytocin binding and bioactivity, it appears that oxytocin binding sites on the plasma membrane of target cells constitute the recognition part of oxytocin receptors.
Journal Article•
TL;DR: In this article, a theoretical scheme for the mechanism of labor in the human subject is presented, which permits the identification of four possible points of attack: (1) replacement of progesterone to reduce the myometrial sensitivity to oxytocin, (2) administration of beta-mimetic agents to relax the uterus and make it unresponsive to stimuli, (3) treatment with ethanol, and (4) anti-inflammatory drugs to inhibit prostaglandin synthesis.
Abstract: Although only about 8 per cent of pregnancies end prematurely, as much as 75 per cent of perinatal deaths are due to prematurity. Since it is difficult to identify the predisposing factors in individual cases and to prevent the premature onset of labor, it is necessary to try to arrest such labor when it occurs. A theoretical scheme for the mechanism of labor in the human subject is presented. This permits the identification of four possible points of attack: (1) replacement of progesterone to reduce the myometrial sensitivity to oxytocin, (2) administration of beta-mimetic agents to relax the uterus and make it unresponsive to stimuli, (3) administration of ethanol to block oxytocin secretion, and (4) administration of anti-inflammatory drugs to inhibit prostaglandin synthesis. Results obtained with ritodrine, a beta-mimetic agent, and with ethanol are presented as illustration. Ritodrine gave somewhat better results than ethanol, possibly because the treatment was continued after discharge of the patients.
TL;DR: In this article, the distribution of oxytocin and vasopressin together with neurophysin in the hypothalamo-neurohypophysial system of the rat was studied.
Abstract: Antisera, with cross reactive antibodies removed by affinity chromatography, were used in the immunoperoxidase-bridge technique to study the distribution of oxytocin and vasopressin together with neurophysin in the hypothalamo-neurohypophysial system of the rat. The hormones were demonstrated in different areas of the supraoptic nucleus (SON) and paraventricular nucleus (PVN), in neurosecretory fibres of the hypothalamo-neurohypophysial tract, median eminence, and in nerve terminals of the neurohypophysis. Intact normal and rats with hereditary hypothalamic diabetes insipidus (Brattleboro strain), and rats dehydrated by the administration of oral hypertonic saline were studied. In dehydrated rats the hormone concentration in the neurons, and the number of neurons containing hormone varied according to the time of dehydration stress. The observations support the hypotheses that: 1) oxytocin and oxytocin-neurophysin, and vasopressin and vasopressin-neurophysin are synthesised in different neurons and are transported along different axons; 2) the SON and PVN are functionally indistinguishable in that neurons containing oxytocin or vasopressin are present in both nuclei; and 3) the two types of neurons respond to osmotic stimulation in a way that is qualitatively the same but quantitatively different.
TL;DR: Data support the association of NSN with vasoppressin although changes in NSN were found only with potent stimuli for vasopressin release, and ESN may be associated with oxytocin but demonstration of this awaits knowledge of oxytocIn physiology in humans.
Abstract: Two human neurophysins, nicotine stimulated neurophysin (NSN), and estrogen stimulated neurophysin (ESN) were assayed during physiologic maneuvers and pathologic states in man. NSN is thought to be associated with vasopressin and was elevated in some subjects by volume depletion, surgical stress, hypotension and hypertonic saline infusion. Overnight dehydration did not elevate NSN in spite of urinary concentration. NSN was elevated in some subjects with the syndrome of inappropriate secretion of antidiuretic hormone and when tested was unresponsive to administered water, alcohol or nicotine. ESN was elevated during estrogen administration, in pregnancy, in newborns and in patients with cirrhosis. NSN was also acutely increased at parturition. These data support the association of NSN with vasopressin although changes in NSN were found only with potent stimuli for vasopressin release. ESN may be associated with oxytocin but demonstration of this awaits knowledge of oxytocin physiology in humans.
TL;DR: It was found that the C-terminal tripeptide of oxytocin, prolyl-leucyl-glycinamide, was the most potent oligopeptide in this respect.
TL;DR: It is suggested that neuro-intermediate lobe opiate peptides may modulate the release of neurohypophysial antidiuretic peptides.
TL;DR: Evidence is presented that the putative neurophysin precursors and intermediates bind specifically to anti-rat neurophysins antiserum.
Abstract: NEURONES in the supraoptic and paraventricular nuclei of the hypothalamus synthesise two peptide hormones, vasopressin and oxytocin. These hormones and their neurophysin ‘carrier’ proteins are stored in (and released from) nerve endings in the posterior lobe of the pituitary1–3. On the basis of extensive studies of the synthesis of vasopressin in vivo and in vitro, Sachs et al.4–8 have suggested that vasopressin and its associated neurophysin are synthesised as parts of a common precursor by a ribosomal mechanism. We have also presented evidence that the neurophysins are synthesised as parts of larger precursor molecules9,10. These 20,000 molecular weight precursors seem first to give rise to 17,000 molecular weight intermediates which, in turn, yield the 12,000 molecular weight neurophysins. The following data show that the putative neurophysin precursors and intermediates bind specifically to anti-rat neurophysin antiserum.
TL;DR: Plasma sodium and urine flow were studied in two further patients given high‐dose oxytocin infusions and the findings are related to previously published observations.
TL;DR: Antisera, with cross reactive antibodies removed by affinity chromatography, were used in the immunoperoxidase-bridge technique to study the distribution of oxytocin and vasopressin together with neurophysin in the hypothalamo-neurohypophysial system of the rat, which supports the hypotheses that they are synthesised in different neurons and are transported along different axons.
Abstract: Synthetic oxytocin and [8-arginine]-vasopressin conjugated to bovine thyroglobulin were used to induce specific antibodies in rabbits. The specificity of the anti-oxytocin serum, and the suitability of the anti-[8arginine]-vasopressin serum for the detection of [8-lysine]-vasopressin, was evaluated by immunofluorescent studies of the respective hormones bound to Sepharose 4B particles. Oxytocin and [8-lysine]-vasopressin were specifically localized in the paraventricular (PVN) and supraoptic (SON) nuclei of the pig hypothalamus using the immunoperoxidase staining technique.
TL;DR: Data would seem to support the hypothesis that the introduction of unsatuation into binding element of a peptide hormone can enhance the affinity of the hormone for some of its receptors and thereby its selectivity.
Abstract: The side chain of the proline residue in position 7 of oxytocin has been proposed as a binding site of the hormone for the uterotonic receptor. This is the first in a series of studies in which the possibility is explored that amino acid residues located at such sites and bearing unsaturated side chains may contribute more strongly to binding than neutral, aliphatic side chains. To test this hypothesis [7-(L-3,4-dehydroproline)]oxytocin, [1-beta-mecaptopropionic acid,7-(L-3,4-dehydroproline)]oxytocin, and [1-L-alpha-hydroxy-beta-mercaptopropionic acid,7-(L-3,4-dehydroproline)]oxytocin were prepared by the solid-phase technique of peptide synthesis. Some of the pharmacological properties of the analogues were determined, and the following specific activities, respectively, were found: rat uterotinic, 1071 +/- 59, 1066 +/- 95, 880 +/- 180; avian vasodepressor, 548 +/- 10, 1008 +/- 42, 1295 +/- 62; rat antidiuretic 5.9 +/- 0.2, 23.3 +/- 1.1, 76.7 +/- 2.3. All analogues possess a lower rat pressor activity than ocytocin. Compared to oxytocin, [7-(L-3,4,-dehydroproline)]oxytocin exhibits a parallel displacement of the cumulative uterotonic log dose vs. response curve toward lower concentration (pD2 = 9.26 vs. 8.63) but elicits the same maximum response. These data would seem to support the hypothesis that the introduction of unsatuation into binding element of a peptide hormone can enhance the affinity of the hormone for some of its receptors and thereby its selectivity.
TL;DR: The hormonal surge at the spontaneous onset of labour may affect fetal enzyme induction, but other factors, such as methods of infant feeding and oral contraceptive use, were found not to be significant.
Abstract: In a prospective study of 196 consecutive single births a significant increase in serum bilirubin concentrations was found in infants born after low amniotomy induction and oxytocin infusion compared with those born spontaneously. This relationship was not dose-dependent and may have been associated with artificial interruption of pregnancy rather than the oxytocin itself. Infants delivered after spontaneous labour accelerated by oxytocin showed no such increase. The hormonal surge at the spontaneous onset of labour may affect fetal enzyme induction, but other factors, such as methods of infant feeding and oral contraceptive use, were found not to be significant.
01 May 1977
TL;DR: The "cooperative model" for the biologically active conformation of oxytocin is discussed and an approach to conformation-activity analysis is described, highlighting the importance of determining the peptide backbone conformation and the functional contribution of peptides backbone and amino acid side chains to hormone receptor interactions.
Abstract: Following a brief review of the preferred three-dimensional structured proposed for oxytocin in dimethylsulfoxide and in aqueous medium, the "cooperative model" for the biologically active conformation of oxytocin is discussed. An approach to conformation-activity analysis is described. The importance of determining the peptide backbone conformation and the functional contribution of peptide backbone and amino acid side chains to hormone receptor interactions are analyzed. Sites are proposed that are thought to be involved in the binding process of oxytocin to the smooth muscle receptor in rat uterus, as well as sites that are thought to be responsible for receptor activation.
Journal Article•
TL;DR: The spontaneous contractility of the epididymis in the rat was recorded in vivo and the effects of the neurohypophyseal hormones were studied.
Abstract: The spontaneous contractility of the epididymis in the rat was recorded in vivo and the effects of the neurohypophyseal hormones were studied. Oxytocin (50 muU and 500 muU/100 g body weight) produced a progressive increase in tonus together with an increase in amplitude and frequency of the contractions. Vasopressin (100 muU and 1000 muU/100 g body weight) showed similar effects. No differences were apparent at the doses studied.
01 Jan 1977
TL;DR: The results when corticotropin or neurohypophysial hormones were injected directly into human anencephalic fetuses in utero, and data obtained from 147 clinical records of such fetuses, seemed to show that the fetal brain does not trigger the onset of parturition, pointing to the likelihood that fetal neurohypophysical hormones stimulate the course of labour.
Abstract: The possibility that the fetal brain or pituitary either initiates parturition or influences the course of labour was studied in human and rat. The results when corticotropin or neurohypophysial hormones were injected directly into human anencephalic fetuses in utero, and data obtained from 147 clinical records of such fetuses, seemed to show that the fetal brain does not trigger the onset of parturition. On the other hand, the course of labour was seriously protracted in anencephalic fetuses. Gestation length of brain-aspirated rat fetuses was not significantly longer than in sham-operated controls. However, the course of labour was protracted in the brain-aspirated fetuses. A similarly protracted expulsion pattern was observed in Brattleboro rats homozygous for a hypothalamic form of diabetes insipidus. These data all pointed to the likelihood that fetal neurohypophysial hormones stimulate the course of labour. Neither oxytocin nor vasopressin could be demonstrated in the rat fetus on the last day of pregnancy, when specific immunofluorescence was used. However, a closely related compound was found that was identified as most probably being vasotocin. The hypothesis is put forward that this fetal hormone normally stimulates the course of labour.
TL;DR: The results indicate that oxytocin and vasopressin bind with greater affinity to the neurophysin dimer than the monomer and that the binding of oxytoc in and vasOPressin in neurophys in dimer more than double that of the monomers at pH 7.4.
Abstract: The interaction between bovine neurophysins I and II and oxytocin and vasopressin was measured using temperature-jump relaxation. A single relaxation time in the 10 to 90 ms range was noted for each solution. This time depended upon the concentration of both neurophysin and hormone and increased with increasing pH. The formation rate constants (+/- SE) for the interaction of neurophysin I dimer with the protonated form of oxytocin and vasopressin at pH 7.4 in 0.1 M KNO3 and 25 degrees C were 2.8 (+/- 0.4) x 10(6) and 2.3 (+/- 0.5) x 10(6) M-1 s-1, respectively; the dissociation rate constants were 11 and 15 s-1, respectively.For neurophysin II dimer, formation rate constants were 6.0 (+/- 0.2) x 10(6) and 2.4 (+/- 0.3) x 10(6) M-1 s-1; dissociation rate constants were 24 and 16 s-1 for oxytocin and vasopressin, respectively. Formation rate constants for the interaction of neurophysin monomer with protinated hormone were approximatley an order of magniment with circular dichorism and pH titration studies which indicate that this interaction occurs between a negatively charged carboxyl group on the neurophysin and a protonated alpha-amino group on the hormone. Our results indicate that oxytocin and vasopressin bind with greater affinity to the neurophysin dimer than the monomer and that the binding of oxytocin and vasopressin in neurophysin dimer than the monomer and that the binding of oxytocin and vasopressin in neurophysin dimer at pH 7.4 and concentrations between 10(-4) and 10(-5) M is nearly identical for each hormone.
TL;DR: In the range tested, the effects of synthetic AVT appear dose-dependent since 10−5 pg caused a more pronounced effect than 10−6 PG, and 10−7 pg only slightly decreased plasma cortisol levels.
Abstract: A single injection of 10−6 pg synthetic arginine vasotocin (AVT), corresponding to about 600 molecules AVT, into the third ventricle of urethane-anesthetized cats, significantly decreased plasma cortisol levels between 15 and 60 min after the injection. A partially purified bovine pineal AVT injected into the third ventricle in an equivalent amount, produced the same effects. After incubation with trypsin, pineal AVT completely lost its ability to decrease plasma cortisol levels. In the range tested, the effects of synthetic AVT appear dose-dependent since 10−5 pg caused a more pronounced effect than 10−6 PG, and 10−7 pg only slightly decreased plasma cortisol levels. Neither synthetic arginine vasopressin nor oxytocin, injected into the third ventricle in the amount of 10−6 pg, was able to affect plasma cortisol levels. When 10−6 pg of synthetic AVT was injected into the lateral ventricle of the brain, infundibular recess, or into the pituitary, no effect on plasma cortisol levels could be detected. Also...
TL;DR: It is demonstrated that isolated mammary cells possess oxytocin receptors with properties comparable to those found in broken mammary cell preparations, consistent with a single-step model for the interaction of Oxytocin with binding sites on the cells.
Abstract: More than 90 percent of the cells isolated from the mammary gland of lactating rats with 0.1 percent collagenase were viable by dye exclusion. Myoepithelial cells comprised about one-third of the mammary cells and appeared to be morphologically intact in electron micrographs. [(3)H]Oxytocin-binding activity was localized in an enriched myoepitheial cell fraction obtained by density gradient centrifugation of the isolated cells. The amount of [(3)H] oxytocin bound at 20 degree C and pH 7.6 was proportional to the concentration of oxytocin and the number of cells, reaching a steady state by 40 min. About 0.45 fmol of oxytocin were bound per 10(6) cells. There was a single class of independent binding sites with an apparent K(d), estimated from equilibrium conditions, of 5 nM. This value agrees within experimental error with the value calculated from the ratio of reverse to forward rate constants (5.8 x 10(-4)s(-1) and 2.2 x 10(5) M(-1)s(-1), respectively), consistent with a single-step model for the interaction of oxytocin with binding sites on the cells. Erythrocytes bound only 3.5 percent of the amount of oxytocin bound by an equal number of mammary cells. Oxytocin analogues competed with [(3)H]oxytocin for binding sites in the following order: [deamino]oxytocin > [4-threonine]oxytocin > oxytocin > [O- methyltyrosine]oxytocin > [8-lysine]vasopressin; [lysine]-bradykinin and [4-proline]oxytocin were not inhibitory in the dose ranges tested. These results demonstrate that isolated mammary cells possess oxytocin receptors with properties comparable to those found in broken mammary cell preparations.
01 May 1977
TL;DR: Analysis of the pharmacological data from over 300 analogs of oxytocin and vasopressin allows the delineation of those structural modifications that can optimize selectivities, and the potential and limitations of this approach for the design of peptides possessing desired agonistic or antagonistic selectivity are discussed.
Abstract: Within the spectrum of the characteristic pharmacological activities (oxytocic (O), milk-ejecting (ME), antidiuretic (A), pressor (P) associated with the known natural and synthetic analogs of oxytocin and vasopressin it is possible to discern patterns of selectivity of these types: 1) interpeptide-like (a) O/A, (b) O/P; 2) intraoxytocin-like (a) O/ME; (b) ME/O; 3) intravasopressinlike (a) A/P, (b) P/A. Consideration of structural modifications of oxytocin or vasopressin, which individually or in combination give rise to peptides possessing enhanced selectivity of a given type, can in some cases provide a rational basis for the design of peptides with even greater selectivity. [1-Deamino-4-valine-8-D-arginine]vasopressin, the most highly specific antidiuretic peptide known to date, was designed in this fashion. By contrast, intraoxytocin-like selectivity, is manifested to only a minor degree in all peptides studied to date. Enhanced interpeptide-like selectivity of the type 1a (O/A; O/P) is readily attainable by specific single substitutions at positions 4 or 7 in oxtocin. Substitution of threonine in the 4 position of the oxytocic antagonist [1-deaminopenicillamine]oxytocin brought about a threefold enhancement in oxytocic inhibitory activity. Thus [1-deaminopenicillamine-4-threonine]oxytocin (dPTOT) is the most potent antagonist of the in vitro oxytocic response to oxytocin known to date. Thus analysis of the pharmacological data from over 300 analogs of oxytocin and vasopressin allows the delineation of those structural modifications that can optimize selectivities. The potential and limitations of this approach for the design of peptides possessing desired agonistic or antagonistic selectivity for potential clinical use and for studies on oxytocin and vasopressin receptors is discussed.
01 Jul 1977