Showing papers on "Oxytocin published in 1976"
TL;DR: The results suggest that the endometrium is a target for Oxytocin, synthesis of PGF2alpha by the uterus may involve interaction between oxytocin and its endometrial receptors and ovarian steroids may influence uterine PG synthesis by regulating the availability of these receptors.
Abstract: Endometrial and myometrial tissues, obtained from Merino ewes on 5 different days of the estrous cycle, were incubated at 37 C in 30 ml of gassed (95% O2:5% CO2) Krebs-bicarbonate buffer containing 0, 10, 100 or 1,000 μ, U/ml oxytocin. Aliquots of the medium were removed at 10 min intervals and examined for prostaglandin F2α (PGF2α) content by radioimmunoassay. Fresh-frozen (-70 C) samples of endometrial and myometrial tissue were homogenized in Tyrode's solution. Particulate fractions from each tissue, sedimenting between 1,000 × g for 10 min and 165,000 × g for 30 min, were prepared and assayed for ‘3H’oxytocin-binding activity. Endometrium incubated in vitro released PGF.2α spontaneously and oxytocin enhanced this release in a dose-dependent manner. The degree of enhancement with low doses of oxytocin appeared to increase as estrus approached, reaching a maximum on the day of estrus. High-affinity binding sites (K2d = 5 to 7 × 10−10M) were found in both myometrium and endometrium. The number of highaff...
263 citations
TL;DR: The hormone release induced in vivo by dopamine could be prevented by the prior administration of haloperidol or phentolamine and these antagonists were equally effective in blocking the hormone release due to noradrenaline.
Abstract: 1. The rat hypothalamus (containing the supra-optic nuclei, paraventricular nuclei, median eminence and proximal pituitary stalk) has been incubated in vitro and shown to be capable of releasing the neurohypophysial hormones, oxytocin and arginine vasopressin, at a steady basal rate about one twentieth that of the rat neural lobe superfused in vitro. 2. The hypothalamus and neural lobe in vitro released both hormones in a similar arginine vasopressin/oxytocin ratio of about 1-2:1. However, when release was expressed relative to tissue hormone content, the hypothalamus was shown to release about three times as much arginine vasopressin and six times as much oxytocin as the neural lobe. 3. Dopamine in a concentration range of 10(-3)-10(-9)M caused graded increases in hormone release from the hypothalamus in vitro to a maximum fivefold increase over preceding basal levels. The demonstration that apomorphine also stimulated hormone release whereas noradrenaline was relatively ineffective suggested that a specific dopamine receptor was involved. A separate cholinergic component in the release process was indicated by the finding that acetylcholine stimulated release to a maximum fivefold increase in concentrations of 10(-3)-10(-9)M. 4. The fact that the isolated hypothalamus can be stimulated by dopamine and acetylcholine to release increased amount of oxytocin and arginine vasopressin raises the question of the origin and fate of the hormones released in this way. The possibility that they could be released into the hypophysial portal circulation from median eminence to affect the anterior lobe of the pituitary is discussed. 5. In similar doses, both dopamine and noradrenaline injected into the lateral cerebral ventricles of the brain of the anaesthetized, hydrated, lactating rat caused the release of arginine vasopressin and oxytocin. Apomorphine release both hormones but at a higher dose level and to less effect than the catecholamines. 6. The hormone release induced in vivo by dopamine could be prevented by the prior administration of haloperidol or phentolamine and these antagonists were equally effective in blocking the hormone release due to noradrenaline. The involvement of a specific dopamine receptor was more clearly implicated by the use of pimozide which completely inhibited the hormone release due to dopamine and apomorphine but not that due to noradrenaline. 7. It is suggested that the release of neurohypophysial hormones can be stimulated via a dopaminergic nervous pathway in addition to a cholinergic one. The possibility that the osmoreceptor mechanism for the release of antidiuretic hormone from the neural lobe of the pituitary may involve such a dopaminergic pathway is discussed.
169 citations
TL;DR: In normal rats and in heterozygous Brattleboro rats, VP appeared to be present in both OT-positive and OT-negative neurons suggesting that some cells may have the capacity to synthesize two hormones.
Abstract: The cellular distribution of neurophysin was examined in hypothalami and neural lobes of normal Long-Evans rats and Brattleboro rats deficientin vasopressin and a major neurophysin.Tissue sections were treated with antisera to bovine,human, and rat neurophysins, using immunoperoxidasebridge techniques. Antisera to oxytocin (OT)and vasopressin (VP) were applied to adjacent sections.Two distinct cell populations were discerniblein both magnocellular nuclei on the basis of theintensity of cytoplasmic staining. About half of themagnocellular neurons in the supraoptic (SON) andparaventricular (PVN) nuclei of homozygous Brattlebororats with diabetes insipidus (DI) were devoid ofimmunoreactive neurophysin, OT, and VP. Thesecells were presumably the defective counterparts ofthose neurons that produce VP and its associatedneurophysin in normal and heterozygous Brattlebororats. The cells in homozygous DI rats which werestained with immunoreaction products to NP and OTwere more concentrated in the dorsal part of the...
144 citations
TL;DR: Oxytocin given as a dilute solution produced no circulatory change; hence, it is suggested that this drug be administered in such fashion rather than by bolus injection.
Abstract: Oxytocin, 5 to 10 units, is frequently given as a bolus injection following term delivery or elective termination of pregnancy. It is not general knowledge that this has any untoward effects. In the present study in young, healthy women undergoing elective termination of pregnancy, mean arterial blood pressure decreased approximately 30% and the total peripheral resistence 50%, 40 seconds after injection. However, heart rate increased 30% and stroke volume 25%, so that the cardiac output was elevated more than 50% above control. Oxytocin given as a dilute solution produced no circulatory change; hence, we suggest that this drug be administered in such fashion rather than by bolus injection.
133 citations
TL;DR: It was found that the C-terminal tripeptide of oxytocin, prolylleucyl-glycinamide, was the most potent oligopeptide in this respect.
119 citations
TL;DR: Serial blood samples were obtained from 97 women in spontaneous labor, and oxytocin levels were determined by a sensitive and highly specific radioimmunoassay, finding the frequency of spurt release increases as labor progresses.
88 citations
TL;DR: The two neurosecretory systems studied have two common features: magnocellular perikarya containing the neurohypophysial peptides and smaller elements containing Gn-RH are found near and appear to terminate around the fine vessels of the OVLT.
Abstract: Immunoperoxidase technique and light microscopy have been used to localize neurosecretory systems forming vasopressin, oxytocin and related neurophysins (neurohypophysial peptides) and gonadotropin-releasing hormone (Gn-RH) in the rhesus monkey brain. All the neurohypophysial peptides were found in the magnocellular nuclei (suproptic and paraventricular) of the hypothalamus and in their projections to the posterior pituitary gland, the zona externa of the median eminence and the organum vasculosum of the lamina terminalis (OVLT). Gn-RH was found in smaller cell bodies which were widely scattered in the hypothalamus. Some of these were found in the medial-basal hypothalamus in the infundibular nucleus and lateral and dorsal to it, while others were found in dorsal hypothalamus. Numerous cells were also located in the preoptic area close to the OLVT. Gn-RH-contaming fibers projected to the OVLT and the zona externa of the median eminence. The two neurosecretory systems studied have two common features: magnocellular peri.karya containing the neurohypophysial peptides and smaller elements containing Gn-RH are found near and appear to terminate around the fine vessels of the OVLT. In addition, cells of both systems send fibers to the hypophysial portal capillary system in the zoha externa of the median eminence. Many more vasopressin- than oxytocin-containing fibers end in the ebtire expanse of the zona externa, where they are mainly concentrated in the anterior and middle parts, while Gn-RH fibers project to all portions. In the last few years immunocytochemical methods have become available to localize specifically pathways in the brain containing neurosecretory peptides. This new approach to the study of neurosecretion began 5 years ago with the localization of neurophysins (intragranular proteins associated with oxytocin and vasopressin) in the magnocellular system by immunofluorescence (18). In the following years immunoperoxidase techniques were used to study neurophysins (35, 40). Although other biological functions for these proteins other than “carrier” roles for vasopressin and oxytocin are at present uncertain, the study of neurophysins has been particularly fruitful for three main reasons.
87 citations
TL;DR: It is concluded that while increased contractile activity is not a sine qua non for OT-induced synthesis of PGF20, neither is increased synthesis ofPGF20 an essential intermediate step in the activation of the myometrium by OT.
Abstract: The role of prostaglandin F20 (PGF20) in the oxytocic response to oxytocin (OT) was investigated by infusing OT directly into the uterine artery of the sheep and recording changes in both the pattern of uterine motility and the rate of secretion of PGF20 at different stages of the estrous cycle. On Day 3 (estrus = Day 0), OT infused from 0.1 to 5.0 mU/mm produced a dose-related increase in the rate of secretion of PGF20 but increased intrauterine pressure (IUP) and the frequency of contractions only at intermediate (1 mU/mm) or high (5 mU/mm) doses. Although exogenous PGF20 infused at 15 Mg/h mimicked OT, the myometrium responded normally to OT when the production of endogenous PGF20 was suppressed with indomethacin. On Day 8, an intermediate dose of OT changed neither the pattern of uterine motility nor the rate of secretion of PGF20. On Day 14, OT infused at rates as low as 0.025 mU/mm increased the secretion of PGF20 4-fold but induced no change in IUP or frequency of contraction. At 0.1 mU/mm, OT increased the rate of secretion of PGF20 nearly 10-fold within 3 mm but changed IUP only slightly and after a delay of 5 mm. Even at higher doses, OT invariably elevated PGF20 secretion but did not consistently raise IUP. We conclude that while increased contractile activity is not a sine qua non for OT-induced synthesis of PGF20, neither is increased synthesis of PGF20 an essential intermediate step in the activation of the myometrium by OT.
80 citations
TL;DR: Investigation of the magnocellular system of the hypothalamus suggests that vasopressin may play a role in the hypothalamic anterior pituitary adrenal axis and the cerebral spinal fluid pathway may be important in man if vasopression is found to have the memory consolidating effects which have been investigated in other animals.
76 citations
TL;DR: In vivo experiments in the cat suggested that both the glycinamide-releasing enzyme and post-proline cleaving enzyme are present and effective in inactivating neurohypophyseal hormones in the intact animal.
75 citations
TL;DR: Observations strongly support the hypotheses that (1) vasopressin and its associated neurophysin are formed via a common precursor, and (2) the initial point of intracellular appearance of the hereditary defect in the Brattleboro rat lies in the synthesis of this precursor, which occurs on ribosomes.
Abstract: Immuno-enzyme cytochemical investigations have shown that, (1) the hypothalamic supraoptic and paraventricular nuclei of the Brattleboro rat, as in the normal rat, contain separate neurons which produce oxytocin + neurophysin; (2) the hereditary inability of the Brattleboro rat to synthesize vasopressin and its associated neurophysin is due to a biochemical defect of separate “neurophysin-vasopressin” neurons in the supraoptic and the paraventricular nuclei. These observations strongly support the hypotheses that (1) vasopressin and its associated neurophysin are formed via a common precursor, and (2) the initial point of intracellular appearance of the hereditary defect in the Brattleboro rat lies in the synthesis of this precursor, which occurs on ribosomes.
TL;DR: Supraoptic, paraventricular, and arcuate hypothalamic nuclei and the retrochiasmatic area had decreased concentration of one or both hormones following hypertonic saline, while hormone concentration in the suprachiasmatic nucleus and median eminence was unaffected.
Abstract: Vasopressin and oxytocin were measured by radioimmunoassay in rat posterior pituitary and microdissected hypothalamic areas after 3 and 10 days of oral 2 percent sodium chloride in place of drinking water. There was a significant decrease in concentration of both hormones in posterior pituitary and in specific areas of the hypothalamus. Supraoptic, paraventricular, and arcuate hypothalamic nuclei and the retrochiasmatic area had decreased concentration of one or both hormones following hypertonic saline, while hormone concentration in the suprachiasmatic nucleus and median eminence was unaffected.
TL;DR: Findings on the subcellular distribution of these peptides are related to current theories on transport and release of neurohormones.
Abstract: Neurophysin, vasopressin and oxytocin were localized in different portions of the supraopticohypophysial tract (SHT) using the unlabeled antibody enzyme technique at the ultrastructural level. In vasopressin-positive supraoptic perikarya, vasopressin and neurophysin were present in all neurosecretory granules. Within the zona interna of the median eminence, vasopressin and neurophysin were present in two populations of axons, one with granules of 1300-1500 A and one with granules of 900-1300 A. Following exposure of thin sections of median eminence to antiserum to neurophysin, reaction products were present in granules and in the extragranular cytoplasm in the axons with larger granules; in all other cases reaction product was confined to the granules. Vasopressin-positive fibers were also presented in large numbers of the zona externa of the median eminence and many terminated on the pituitary primary portal plexus. A few oxytocin fibers were present on the portal capillaries in the infundibular stalk. In the posterior pituitary all axon profiles were neurophysin positive. Neurophysin was present as both a granular and cytoplasmic pool. Vasopressin-containing axons account for 90% of the neuronal elements in the posterior pituitary and oxytocin for the remaining 10%. Findings on the subcellular distribution of these peptides are related to current theories on transport and release of neurohormones.
TL;DR: The increased frequency of the rhythmic activity after oxytocin administration may also result in increased contractility by summation, and may be explained by the increase in the intensity of the inward current.
Abstract: The influence of oxytocin on the electrical and mechanical activity of uterine smooth muscle strips was studied under voltage-clamp conditions.
1.
At a concentration of 0.1 mU/ml, oxytocin caused a slight depolarization of the resting potential and also increased the amplitude of the action potential. The maximal frequency of the rhythmic activity, which can be produced by depolarizing current pulse, is increased by about 20%.
2.
Oxytocin increased the peak of the inward current without modification of the reversal potential. This effect is enhanced in a sodium-free solution. With oxytocin the steady-state inactivation of the inward current is not modified and the increase in the current intensity can be related to an increase in the maximal conductance. The amplitude of the outward current is not affected.
3.
The first component (phasic-like) of the contractile response obtained for brief depolarizations is increased by oxytocin. This effect may be explained by the increase in the intensity of the inward current. The second component (tonic-like) of the contraction associated with long-lasting depolarizations and obtained in manganese-containing solution is not modified. The increased frequency of the rhythmic activity after oxytocin administration may also result in increased contractility by summation.
TL;DR: Observations of the effects of hormone binding on the reversible monomer in equilibrium dimer equilibrium of bovine neurophysins I or II in solution suggest that each neurophysin molecule possesses two structurally distinct hormone binding sites.
TL;DR: Results indicate that suckling releases TSH as well as prolactin in the urethaneanaesthetized rat, however, the absence of prolact in release after injections of TRH makes it unlikely that both endocrine responses are regulated solely by the actions of this one releasing hormone.
Abstract: Plasma levels of prolactin and TSH were determined by radioimmunoassay in urethaneanaesthetized lactating rats during suckling. Oxytocin release was monitored by recording intramammary pressure. Application of ten pups, 3 h after administration of urethane (1-1 g/kg, i.p.), evoked a parallel rise in prolactin and TSH concentrations which reached a maximum during the 3rd hour of suckling and then declined. Peak hormone concentrations represented a 25-fold increase in prolactin and a ten-fold increase in TSH. Suckling also elicited a pulsatile (every 5-10 min) release of 0-5--1-0 mu. oxytocin. The gradual rise in prolactin and TSH occurred between the 1st and 20th oxytocin pulses. Intravenous injection of thyrotrophin-releasing hormone (TRH) into unsuckled, anaesthetized lactating rats resulted in a 7- to 30-fold increase in TSH concentration, whereas prolactin levels showed no substantial change. These results indicate that suckling releases TSH as well as prolactin in the urethaneanaesthetized rat. However, the absence of prolactin release after injections of TRH makes it unlikely that both endocrine responses are regulated solely by the actions of this one releasing hormone.
TL;DR: It is concluded that vasopressin exerts a potent influence on the glomersulosa, in contrast with the prevalent view that the glomerulosa is little affected by the hypophysis.
Abstract: Injection of posterior pituitary powder induces an intense mitotic stimulation in the zona glomerulosa of the adrenal gland of young rats. This effect is much more pronounced in females than in males. It is maximal at two days treatment. Longer periods result in a hypertrophied zona glomerulosa and lower mitotic activity. A search for the hormone responsible for the stimulation shows that vasopressin, and to a lesser extent oxytocin, are mitogenic. ACTH, α-MSH, β-MSH and the pineal hormones have no effect. Renin (but not angiotensin) induces a significant stimulation. It is concluded that vasopressin exerts a potent influence on the glomerulosa. This is in contrast with the prevalent view that the glomerulosa is little affected by the hypophysis.
TL;DR: An 18-year-old primipara developed acute hypertension leading to cerebral edema and convulsions following the IV injection of a bolus of 10 units of oxytocin with 0.2 mg methylergonovine maleate.
Abstract: An 18-year-old primipara developed acute hypertension leading to cerebral edema and convulsions following the IV injection of a bolus of 10 units of oxytocin with 0.2 mg methylergonovine maleate. Oxytocin in a dose of more than 2 units should not be administered IV in a single injection, as severe hypotension may result. If oxytocin is required, it can be injected either IM, or by IV pump or drip. The use of ergot in obstetrics should be limited to the treatment of life-threatening postpartum hemorrhage and be given only by the IM route. Ergot should not be administered to patients with cardiac, renal, or hypertensive disease, or in association with a vasoconstrictor.
TL;DR: Blood loss and the incidence of emetic sequelae were assessed in 148 patients undergoing midcavity forceps delivery under continuous lumbar extradural analgesia and oxytocin was found to be as effective as ergometrine 0.5 mg i.v. in reducing blood loss at delivery.
Abstract: SUMMARY Blood loss and the incidence of emetic sequelae were assessed in 148 patients undergoing midcavity forceps delivery under continuous lumbar extradural analgesia. Five units of oxytocin i.v. was found to be as effective as ergometrine 0.5 mg i.v. in reducing blood loss at delivery. Nausea, retching or vomiting occurred in 35 (46%) of the mothers who received ergometrine and in none of those who received i.v. oxytocin. The cardiovascular side-effects of ergometrine and oxytocin are reviewed and compared with special reference to patients with hypertension and heart disease. It is suggested that 5 units of oxytocin i.v. should be preferred in these high-risk patients. Because of the absence of an emetic action, i.v. oxytocin is preferable to i.v. ergometrine for patients receiving extradural analgesia.
TL;DR: The results show that the sensitivity of the myometrium to PGE2 and oxytocin during the early and early‐middle stages of gestation can be simulated by progesterone treatment, but the sensitivity during the last stage of gestation and during parturition cannot be simulate by oestradiol and progester one treatment.
Abstract: The effects of prostaglandin E2 (PGE2) and oxytocin on the electrical activity of rat myometrium at various stages of gestation and following hormonal treatment have been investigated. 1. PGE2 and oxytocin produce an excitation of the myometrial membrane under all experimental conditions. The sensitivity of the myometrium markedly increases during the last stage of gestation, and at parturition is more than one thousand times greater than in the mid-pregnant rat. The sensitivity of the myometrium to oxytocin increases rapidly during the last stage of gestation but to PGE2 the increase is gradual, beginning in the late middle stage of gestation. 2. During the early middle stage of gestation, the sensitivity of the myometrium to PGE2 and oxytocin is lower than in the non-pregnant myometrium. 3. After oestradiol treatment, the sensitivity to PGE2 and oxytocin increases but the sensitivity is much weaker than that during the parturition. On the other hand, after progesterone treatment, the sensitivity is reduced below that of the castrated rat. 4. Differences in the sensitivity of progesterone-treated and oestradiol-treated myometria to PGE2 and oxytocin are compared to those of the pregnant and post-partum myometrium. The results show that the sensitivity of the myometrium to PGE2 and oxytocin during the early and early-middle stages of gestation can be simulated by progesterone treatment, but that the sensitivity during the last stage of gestation and during parturition cannot be simulated by oestradiol and progesterone treatment.
Journal Article•
TL;DR: The data suggest that vasopressin and oxytocin have an opposite effect on self-stimulation and this action is not mediated through the brain serotoninergic or pituitary-adrenocortical axis.
Abstract: Oxytocin (500 mu u) and vasopressin (50 mu u) were injected into the lateral ventricle and its effect on hypothalamic self-stimulation has been studied. Oxytocin increased, while vasopressin decreased the self-stimulation rate tested 10-20 min following application. The hypothalamic and mesencephalic serotonin content decreased slightly while plasma corticosterone content did not change 20 min after oxytocin and vasopressin administration compared to the injected control animals. The data suggest that vasopressin and oxytocin have an opposite effect on self-stimulation and this action is not mediated through the brain serotoninergic or pituitary-adrenocortical axis.
TL;DR: The concept that oral PGE2 administration is a safe and effective alternative to intravenous oxytocin for induction of labor in normal and high-risk pregnancies is supported.
TL;DR: The concentration of oxytocin in the median eminence was more than three times that in either the supraoptic or the paraventricular nuclei, and significant amounts of Oxytocin were also found in the arcuate nucleus and in tow anterior hypothalamic nuclei.
Abstract: Oxytocin content has been measured by radioimmunoassay in microdissected hypothalamic nuclei. Equal concentrations of oxytocin were found in the supraoptic and the paraventricular nuclei, indicating that both are major sources of the hormone. The concentration of oxytocin in the median eminence was more than three times that in either the supraoptic or the paraventricular nuclei, and significant amounts of oxytocin were also found in the arcuate nucleus and in two anterior hypothalamic nuclei. (Endocrinology 98: 1430, 1976)
TL;DR: In this paper, it was shown that the hypothalamo-neurohypophysial complex produces Oxocin and vasopressin in the mammalian hypothalamo and hypothalamus, respectively, in separate perikarya and axons.
Abstract: OXYTOCIN and vasopressin, the hormones of the mammalian hypothalamo–neurohypophysial complex, are synthesised in the supraoptic (SON) and paraventricular (PVN) nuclei and are secreted into the blood stream from the neuro-hypophysis. It is now thought that the two hormones are produced in both nuclei, but are stored, together with their corresponding neurophysins, in distinct neurosecretory granules located in separate perikarya and axons, on the basis of data from various species including fish, reptiles, birds and mammals1–4. This study describes cytochemical experiments carried out on tissue from normal rats and from rats homozygous for hereditary diabetes insipidus (Brattle-boro strain) that support this view and allow a tentative identification of the two granule types.
TL;DR: The hypertrophic response of the in situ ovary in adult mice following unilateral ovariectomy (UO) was inhibited in a dose-related manner by a single intraperitoneal injection of freshly prepared AVT.
Abstract: When AVT (arginine vasotocin) was given neonatally during the period when the brain is undergoing sexual differentiation, increased growth of the reproductive organs was observed in adulthood. Injection of AVT after this neonatal period in immature animals led to diminished growth of the accessory organs and in some cases the gonads themselves. The hypertrophic response of the in situ ovary in adult mice following unilateral ovariectomy (UO) was inhibited in a dose-related manner by a single intraperitoneal injection of freshly prepared AVT. Much less AVT was required for this response when injected into the third ventricle. After intraperitoneal injection, arginine vasopressin (AVP), lysine vasopressin (LVP), and 4-leucine vasotocin (4-leu-AVT) also inhibited compensatory ovarian hypertrophy whereas oxytocin did not. The commonality in die structure of these antigonadotrophic peptides include a closed ring and a basic amino acid in position 8. After opening the disulfide bond of these nonapeptides with mercaptoethanol, a single injection of the reduced AVT, AVP, LVP, or 4-leu-AVT into UO mice causes exaggerated hypertrophy of the remaining ovary. When added with leuteinizing hormone-releasing hormone (LRH) to culture medium containing hemipituitaries from castrated estrogen-progesterone primed female rats, AVT significantly increased the release of radioimmunoassayable LH above that due to LRH alone. AVT might interact at all levels of the hypothalamo-hypophysealgonadal axis.
TL;DR: The results indicate that under conditions of low protein concentration and high temperature, the glycinamide residues of oxytocin and arginine vasopressin bound to neurophysin possess significant internal motion, while lowering the temperature and/or raising the protein-hormone concentration reduces this internal motion.
TL;DR: The release of antidiuretic hormone in response to the introduction of an osmotic stimulus into the cerebral circulation of the fetal sheep and lamb is described.
Abstract: The release of antidiuretic hormone in response to the introduction of an osmotic stimulus into the cerebral circulation of the fetal sheep and lamb is described. Infusion of 1.0 M
TL;DR: The methyl-acceptor activities of bovine neurophysins I and II for the enzyme protein carboxymethylase (EC 2.1.24) were found to be similar and as high as for other previously identified, biologically active protein substrates.
TL;DR: Homogenates of bovine neural lobe tissue were fractionated by differential centrifugation at 20°C or at 4°C and the distribution of activities of vasopressin and oxytocin among the fractions was compared.
Abstract: — Homogenates of bovine neural lobe tissue were fractionated by differential centrifugation at 20°C or at 4°C and the distribution of activities of vasopressin and oxytocin among the fractions was compared. The ratio of total hormone to protein (mg) in the homogenate was similar at the two temperatures. At 20°C a much smaller proportion of the total hormone was recovered in the soluble fraction (100,000 gav supernatant), than at 4°C with a corresponding increase in recovery in the nerve-ending fraction (800–3000 g sediment).
Nerve endings isolated at 4°C did not, when incubated, release hormone in response to changes in temperature. Nerve endings isolated at 20°C released hormone when the temperature was reduced below 15°C. Gradual reduction in temperature led to hormone release unaccompanied by lactate dehydrogenase release. Incubation of nerve endings for 10 min at 10°C increased the release of vasopressin and of neurophysin without any increase in lactate dehydrogenase. These results demonstrate that release of vasopressin by cold stimulation occurs by way of exocytosis.
Journal Article•
TL;DR: The findings reveal that the effect of 4-leucine substitution may not be to enhance the natriuretic activity but rather to abolish the antidioretic activity of oxytocin.
Abstract: The substitution of the 4-glutamine of oxytocin by a lipophilic aliphatic amino acid leucine yields [4-Leu] oxytocin which possesses natriuretic-diuretic anti-arginine-vasopressin (anti-ADH) activities. Alkyl substitutions of the beta-carbon of the 1 half-cystine of oxytocin yield a series of antioxytocin analogs which inhibit the uterotonic response to oxytocin. In this paper, the results of our further investigations on the molecular requirements for natriuretic, anti-ADH and antioxytocic activities of these peptides are reported. A total of 12 analogs of oxytocin and lysine-vasopressin (LVP) with leucine and/or beta-carbon alkyl substitutions were studied. Our findings reveal that the effect of 4-leucine substitution may not be to enhance the natriuretic activity but rather to abolish the antidiuretic activity of oxytocin. The lack of antidiuretic activity of these 4-leucine analogs makes it possible to unmask the intrinsic natriuretic activity of these peptides at the high dose level. Structure-activity correlations suggest that the oxytocin molecule may be the optimal requirement for natriuretic activity of these peptides. Substitution of 4-glutamine by lipophilic aromatic phenylalanine yields [4-Phe] oxytocin which possesses anti-ADH activity with little or no natriuretic activity. The "hybrid" antioxytocin and anti-ADH molecules, beta-carbon alkyl and 4-leucine substituted analogs did not possess enhanced antihormone activity. Although they had antioxytocic and antipressor activities, they were less potent than their respective singly alkyl substituted analogs. Furthermore, they had no demonstrable anti-ADH activity. The single alkyl substituted oxytocin and LVP also had no anti-ADH activity. It therefore appears that beta-carbon alkyl substitution had different effects on activities depending on the morphological features and the functions of the target cell. In target cells of contractile smooth muscles (uterus and vascular), the alkyl substituted analogs had no intrinsic activity but retained a relatively high receptor affinity to become effective antagonists to the natural hormone. On the other hand, in target cells of the renal tubule which are noncontractile epithelial cells, both intrinsic activity and receptor affinity were reduced or abolished. Thus none of these alkyl substituted analogs possessed more than very slight antidiuretic activity, and none had any natriuretic or anti-ADH activity.