Showing papers on "Oxytocin published in 1978"

Intra- and extrahypothalamic vasopressin and oxytocin pathways in the rat

Abstract: Vasopressin and oxytocin pathways were specifically localized in glutaraldehyde-paraformaldehyde fixed rat brains, with the use of the unlabelled antibody enzyme method and purification of the first antiserum. Vasopressin and oxytocin containing pathways were traced from the paraventricular nucleus towards the dorsal and ventral hippocampus, the nuclei of the amygdala, substantia nigra and substantia grisea, nucleus tractus solitarius, nucleus ambiguus and to the substantia gelatinosa of the spinal cord. In addition, a vasopressin containing pathway between the suprachiasmatic nucleus and the lateral habenular nucleus was demonstrated. The possible nature (axons or dendrites) and role of these extrahypothalamic fibres is discussed in relation to water balance, milk ejection and avoidance behaviour.

Intra- and extrahypothalamic vasopressin and oxytocin pathways in the rat. Pathways to the limbic system, medulla oblongata and spinal cord.

Abstract: Vasopressin and oxytocin pathways were specifically localized in glutaraldehyde-paraformaldehyde fixed rat brains, with the use of the unlabelled antibody enzyme method and purification of the first antiserum. Vasopressin and oxytocin containing pathways were traced from the paraventricular nucleus towards the dorsal and ventral hippocampus, the nuclei of the amygdala, substantia nigra and substantia grisea, nucleus tractus solitarius, nucleus ambiguus and to the substantia gelatinosa of the spinal cord. In addition, a vasopressin containing pathway between the suprachiasmatic nucleus and the lateral habenular nucleus was demonstrated. The possible nature (axons or dendrites) and role of these extrahypothalamic fibres is discussed in relation to water balance, milk ejection and avoidance behaviour.

Oxytocin release following osmotic activation of oxytocin neurones in the paraventricular and supraoptic nuclei.

Abstract: 1. Recordings were made from a total of 35 antidromically identified neurones in the paraventricular (PV) and supraoptic (SO) nuclei of urethane-anaesthetized lactating rats. During recording plasma osmotic pressure was raised by 12 m-osmole/kg by injection of hypertonic solutions of NaCl, LiCl, or mannitol.2. Nine PV neurones (mean firing rate 4.2 +/- 1.0 (S.E.) spikes/sec) were classified as oxytocin cells because they gave a burst of activity before reflex milk-ejections. None of these showed a bursting (phasic) firing pattern. Ten PV neurones (mean firing rate 1.8 +/- 0.2 spikes/sec) fired phasically either before or after injection of hypertonic NaCl and were classified as vasopressin cells. The remaining six PV cells (mean firing rate 1.6 +/- 0.9 spikes/sec) showed no bursts of firing related to milk ejection and did not fire phasically.3. Increasing plasma osmotic pressure by injection of hypertonic NaCl increased the mean firing rate of PV oxytocin cells to 7.0 +/- 1.0 spikes/sec. Vasopressin cells in the PV nucleus were much less responsive and the mean firing rate after injection was 2.9 +/- 0.4 spikes/sec. The third group of PV neurones was unresponsive.4. Plasma oxytocin concentration (determined by radioimmunoassay) increased from 2.1 +/- 0.3 muu./ml. in the control period to 10.9 +/- 2.8 muu./ml. 30 min after I.P. injection of 1 ml. 1.5 M-NaCl and to 14.8 +/- 2.8 muu./ml. following injection of a second 1 ml. 1.5 M-NaCl.5. The responses of oxytocin and vasopressin neurones in the SO nucleus to an increase in plasma osmotic pressure following injections of hypertonic solutions of LiCl or mannitol were similar to those observed when plasma osmotic pressure was raised by NaCl.6. It may be concluded that both oxytocin and vasopressin cells in the neurohypophysical system are responsive to the osmotic pressure of the blood plasma rather than to Na(+) or Cl(-) concentration, that osmotic activation of oxytocin cells releases sufficient oxytocin to increase its plasma concentration, and that there may be a functional difference between the SO and PV nuclei.

Opposing effects of estradiol and progesterone on oxytocin receptors in rabbit uterus.

Abstract: Estradiol-17β administration to young (10- to 12-week-old) rabbits to produce the “estrogen-dominated” uterus increased the uterine contractile response to both oxytocin and methacholine in vitro. In “progesterone-dominated” uteri, obtained from rabbits that received progesterone for 4 days after estrogen pretreatment, the contractile response to oxytocin in vitro was selectively abolished; the response to methacholine was unaffected. Parallel changes were observed in the concentration (but not affinity) of specific sites in uterine microsomal membranes that bind [3H]oxytocin with selectivity features expected for oxytocin receptors. Thus, estrogen-dominated uteri have an increased number of specific [3H]oxytocin binding sites per mg of membrane protein relative to untreated controls, whereas specific oxytocin binding sites are reduced to barely detectable levels in the progesterone-dominated uterus. Similar results are obtained when binding sites are measured in membranes from the myometrium of estrogen- or progesterone-dominated uteri. Short-term (24-hr) progesterone administration to estrogen-pretreated rabbits decreased, but did not abolish, specific [3H]oxytocin binding; the concentration of specific [3H]oxytocin binding sites was reduced without influence on the affinity of these sites. A sublethal dose of actinomycin D, administered over a 24-hr period to rabbits pretreated with estradiol for 4 days, likewise reduced specific oxytocin binding; additive effects were not observed when progesterone and actinomycin D were administered together. These results suggest that the regulatory effects of estrogens and progesterone upon the rabbit uterine contractile response to oxytocin are achieved, at least in part, by the opposing actions of these steroids in regulating the number of oxytocin receptors in smooth muscle cells. Estradiol increased the concentration of uterine oxytocin receptors; the maintenance of high receptor levels appears to depend upon the continuous de novo synthesis of oxytocin receptors. In contrast, progesterone, like actinomycin D, appears to act at the nuclear locus to repress synthesis of oxytocin receptors.

The Effect of Hemorrhage and Hypertonic Saline upon Plasma Oxytocin and Arginine Vasopressin in Conscious Dogs

Abstract: Sensitive and highly specific RIAs for arginine vasopressin (AVP) and oxytocin (OT) were utilized to assess the specificity of neurohypophyseal hormone release after hemorrhage or infusion of hypertonic saline to trained conscious dogs. Phlebotomy of 12.5 and 25 ml/kg produced increases in plasma AVP from 1.0 +/- 0.2 to 7.8 +/- 2.1 and 41.6 +/- 9.7 (SEM) microunit/ml respectively, and both responses differed significantly from values in control experiments (P less than 0.01 after the first phlebotomy and P less than 0.001 after the second phlebotomy). Plasma OT concentrations rose from baseline values of 1.1 +/- 0.4 to 3.3 +/- 0.6 and 8.3 +/- 1.7 microunit/ml (P less than 0.005 and P less than 0.001 compared to controls); plasma osmolality and sodium concentrations were unchanged. Both log AVP and log OT were highly correlated with the quantity of blood removed (r = 0.92 and -0.82, each P less than 0.001). Infusion of hypertonic (20g/dl) NaCl (3.4 meq/kg) over 20 min caused plasma osmolality and sodium to rise from 304 +/- 1.0 mosm/kg and 143 +/- 3.0 meq/liter to 316 +/- 1.0 mosm/kg and 150 +/- 3.0 meq/liter (each P less than 0.001). Plasma AVP rose from 1.5 +/- 0.2 to 2.4 +/- 0.2 microunit/ml (P less than 0.0025) and OT rose from 1.2 +/- 0.5 to 2.6 +/- 0.7 microunit/ml (P less than 0.005). The stimulus response ratios (change in log hormone concentration divided by the rise in plasma osmolality) were comparable for both hormones (0.024 +/- 0.006 for AVP and 0.031 +/- 0.008 for OT; P less than 0.4). The data indicate that hemorrhage or hypertonic saline stimulate release of both AVP and OT. After hemorrhage, there is greater stimulation of AVP than OT, whereas there is comparable stimulation of both peptides after hypertonic saline.

Stimulation by vasopressin, angiotensin and oxytocin of gluconeogenesis in hepatocyte suspensions.

Abstract: 1. In hepatocytes from starved rats, vasopressin, angiotensin (angiotensin II) and oxytocin stimulated gluconeogenesis from lactate by 25--50%; minimal effective concentrations were about 0.02pM, 1 nM and 0.2 nM respectively. 2. Vasopressin and angiotensin also stimulated gluconeogenesis from alanine, pyruvate, serine and glycerol. EGTA decreased gluconeogenesis from these substrates. 3. Hormonal stimulation of gluconeogenesis from lactate was abolished in the absence of extracellular Ca2+. 4. Insulin did not prevent stimulation of gluconeogenesis by vasopressin or angiotensin. 5. The potency of the stimulatory effects of vasopressin and angiotensin on hepatic gluconeogenesis suggests they are operative in vivo. Also, the data suggest that Ca2+ plays a role in the stimulation by these hormones.

Demonstration that progesterone 'blocks' uterine activity in the ewe in vivo by a direct action on the myometrium.

Abstract: Intrauterine pressure was monitored in vivo in oestrogen-treated ovariectomized ewes before, during and after treatment with progesterone (50 mg s.c./day for 3 days). Progesterone reversibly reduced the frequency and amplitude of myometrial activity and abolished uterine reactivity to oxytocin (i.v.) and PGF-2alpha (intrauterine infusion). The rate of rise of intrauterine pressure during active pressure cycles was significantly reduced. These results confirm that the action of progesterone on the ovine myometrium is comparable to the classic progesterone 'block'. The intrauterine infusion of PGF-2alpha (10 microgram/min), which elicited a marked mechanical response in the control animals, failed to stimulate the progesterone-'blocked' uterus, suggesting that the inhibition produced by progesterone is due to a direct action of the hormone on the uterine muscle and not to an indirect mechanism operating through endometrial prostaglandin output.

Rapid stimulation by vasopressin, oxytocin and angiotensin II of glycogen degradation in hepatocyte suspensions.

Abstract: 1. The hormonal control of glycogen breakdown was studied in hepatocytes isolated from livers of fed rats. 2. Glucose release was stimulated by [8-arginine]vasopressin (10pm–10nm), oxytocin (1nm–1μm), and angiotensin II (1nm–0.1μm). These responses are all at least as sensitive to hormone as is glucose output in the perfused rat liver. 3. The effect of these three hormones on glucose release was critically dependent on extracellular Ca2+, unlike that of glucagon. Half-maximal restoration of the vasopressin response occurred if 0.3mm-Ca2+ was added back to the incubation medium. 4. Glycogen breakdown was more than sufficient to account for the glucose released into the medium, in the absence or presence of hormones. Lactate release by hepatocytes was not affected by vasopressin, but was inhibited by glucagon. 5. If Ca2+ was omitted from the extracellular medium, vasopressin stimulated glycogenolysis, but not glucose release. 6. The phosphorylase a content of hepatocytes was increased by vasopressin, oxytocin and angiotensin II; minimum effective concentrations were 0.1pm, 0.1nm and 10pm respectively. This response was also dependent on Ca2+. 7. These results demonstrate that hepatocytes can respond to low concentrations of vasopressin and angiotensin II, i.e. these effects are likely to be relevant in the intact animal. The role of extracellular Ca2+ in the effects of these hormones on hepatic glycogenolysis and glucose release is discussed.

Arginine vasotocin as a pineal hormone.

Abstract: The pineal nonapeptide hormone arginine vasotocin (AVT) is synthesized by the ependymal cells of the pineal recess and subcommissural organ and stored in so far undefined cells of the pineal gland proper AVT is first released into the cerebrospinal fluid (CSF) and reaches the blood only secondarily after its absorption from CSF It displays a diurnal rhythm in the pineal and CSF, suggesting its release into the CSF during the night in the dark Melatonin represents its releasing hormone AVT exerts both its endocrine and non-endocrine effects by a unique mechanism involving the activation of serotonin neurotransmission in the brain with resultant inhibition of release of hypothalamic releasing and inhibiting hormones and induction of sleep It produces both its endocrine effects and sleep at concentrations equivalent to only several hundreds of molecules, being thus by far the most active hormone so far known Midbrain raphe nuclei or some structures intimately correlated with these cell bodies, most contain the extremely sensitive and specific AVT receptors in the mammalian brain In contrast with its natural analogues arginine vasopressin and oxytocin which are mainly blood hormones, AVT is a CSF hormone whose major if not the sole site of action is the brain itself

The hypothalamic magnocellular system of the rhesus monkey: An immunocytochemical study

Abstract: The hypothalamic magnocellular system of the adult female rhesus monkey is studied here, using immunoperoxidase technique and antisera to estrogen stimulated neurophysin (ESN), nicotine stimulated neurophysin (NSN), oxytocin (OT) and vasopressin (VP). These observations confirm and enlarge previous descriptions by others using Gomori techniques. It is apparent from this study that the magnocellular system spreads through a broader area than is generally accepted. A group of cells ventral to the head of the caudate nucleus and medial to the internal capsule is described. The general orientation of the nuclei and their tracts can only be appreciated when coronal, horizontal and sagittal sections are compared. Our observations suggest that the supraoptic nucleus is made up of a single group of cells that straddles the optic pathways, and is not divided in three segments, as it is generally described. It is also shown that the rostral extensions of the paraventricular and supraoptic nuclei merge above the optic chiasm. Cells containing ESN/OT and NSN/VP are evenly dispersed in the paraventricular nucleus but a topographical arrangement is present in the supraoptic nucleus. The magnocellular nuclei project to the organum vasculosum of the lamina terminalis, zona externa of the median eminence and pars nervosa of the pituitary gland. Reactive fibers were also seen within islets of cells from the pars in termedia located inside the pars nervosa. A globular structure containing small blood vessels surrounded by positive fibers was noticed protruding into the floor of the third ventricle, at the level of the median eminence.

Radioimmunoassay of oxytocin.

Abstract: The evaluation of a radioimmunoassay of oxytocin is described. The method involved careful collection and transportation of blood at 4 degrees C, acidification of the plasma, extraction with Fuller's earth and radioimmunoassay using antisera raised in rabbits immunized against oxytocin conjugated to bovine serum albumin and 125I-labelled oxytocin. The antisera showed insignificant cross-reaction with a variety of small peptides including vasopressin and vasotocin. The limit of detection of the assay was 2.5 pg with intra-assay and interassay coefficients of variation of 7-15% and 12-18% respectively. Seventy-seven per cent (88 out of 116) of the pregnant women tested had detectable maternal plasma oxytocin. Serial samples of maternal plasma showed a significant increase in oxytocin from the first to the second stage of labour and a significant decrease in the third stage. Oxytocin concentrations in the umbilical arterial plasma were significantly higher in patients in labour. The significance of these findings is discussed.

Characterization of rat stalk median eminence vasopressin and its involvement in adrenocorticotropin release.

Abstract: The perfused isolated rat anterior pituitary cell column was used as a bioassay for corticotropinreleasing factor (CRF). The system responded to arginine vasopressin (AVP) in a dose-dependent manner with a minimum effective dose of 10-10 M. Log doseresponse curves for AVP and crude stalk median eminence extract (SME) were statistically significantly nonparallel (P < 0.05) and similar results were found for lysine vasopressin, arginine vasotocin (AVT), oxytocin, and human posterior lobe extract. Vasopressin and its analogs had no effect on LH release. Using RIA for AVP, SME was found to contain 10.83 ng (7.7–14.3 ng, n = 12) AVP, which could account for no more than 30% of its CRF activity. The CRF activity of both SME and AVP was totally quenched by incubation overnight with vasopressin antisera. Partial quenching was obtained with higher dilutions of the antisera. Vasopressin-stimulated ACTH release was affected in a similar way to SME-stimulated ACTH release by the presence of corticosterone (0.2 μg/ml)...

Structure—Activity Relations of the Fibrinolytic Response to Vasopressins in Man

Abstract: 1. The systemic plasminogen activator response has been examined after intravenous infusion of the following peptides related to neurohypophyseal hormones in approximately equimolar dosages into informed, consenting human volunteer subjects: (a) the natural nonapeptides: lysine- and arginine-vasopressin, oxytocin and arginine-vasotocin, (b) the N- and C-terminal tripeptide fragments of vasopressin and (c) four vasopressin analogues without pressor activity, altered at the N-terminus, the disulphide bridge and/or sequence position 8 in the C-terminal tripeptide. In addition, angiotensin II and adrenaline were infused. 2. It was observed that some of the cyclic nonapeptides resulted in high and prolonged increases in amounts of plasminogen activator in venous blood, in the following order, both for amplitude and duration: 1-desamino-6-monocarba-[8-d-arginine]-vasopressin > 1-desamino-[8-d-arginine]-vasopressin ≫ arginine-vasopressin = lysine-vasopressin > Nα-glycyl-glycyl-glycyl-lysine-vasopressin. 3. No plasminogen activator responses followed infusions of vasopressin tripeptide fragments, oxytocin, angiotension II, 1-desamino-[8-N-MeArg]-vasopressin or 9-desglycineamide-lysine-vasopressin octapeptide. 4. Mole for mole, the four most active substances were approximately two orders of ten more potent than adrenaline by amplitude comparison alone. 5. Intra-arterial adrenaline, in one-tenth the systemic dose, stimulated a release of plasminogen activator from the infused local vascular bed only, This did not occur with equivalent doses of arginine-vasopressin and 1-desamino-[8-d-arginine]-vasopressin. 6. It is concluded that plasminogen activator release arising from catecholamine-responding and vasopressin-responding receptors are both molecule-specific and different in anatomical location. The molecular structural requirements for triggering the latter hypothetical receptor type and potential clinical applications are discussed.

[1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid),4-valine,-8-D-arginine]vasopressin, a potent and selective inhibitor of the vasopressor response to arginine-vasopressin.

Abstract: As part of a program in which we are attempting the design and synthesis of an antagonist of the antidiuretic response to arginine-vasopressin (AVP) [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid),4-valine,8-D-arginine]vasopressin [d(CH2)5VDAVP] was synthesized and assayed for antidiuretic, vasopressor, and oxytocic activities. The required protected intermediate was synthesized by a combination of solid-phase synthesis and an [8 + 1] coupling in solution. d(CH2)5VDAVP has an antidiuretic potency of 0.10 +/- 0.02 unit/mg, less than 1/10000 that of its parent [deamino,4-valine,8-D-arginine]vasopressin (dVDAVP). d(CH2)5VDAVP is a specific antagonist of the vasopressor responses to AVP. It has an antivasopressor pA2 value of 7.68 +/- 0.05 when tested against AVP. It is also an antagonist of the in vitro oxytocic response to oxytocin (pA2 value = 6.62 +/- 0.07). With its negligible antidiuretic activity, absence of oxytocic activity, and its potent and specific ability to antagonize the vasopressor effects of AVP, d(CH2)5VDAVP is one of the most potent and selective vasopressor antagonists reported to date. It should thus be a useful tool with which to probe the possible role(s) that AVP may play in cardiovascular regulation under normal and pathological conditions.

Effects of chounoceptor antagonists on the suckling-induced and experimentally evoked release of oxytocin

Abstract: 1 In the anaesthetized lactating rat, the suckling of the young causes the regular release (about every 7 min) of brief pulses of oxytocin (0.5 to 1.0 mu), which each produce a single transient increase in intramammary pressure.2 The effects of several cholinoceptor antagonists were studied in relation to this natural reflex, and also the release of oxytocin evoked by the intraventricular injection of cholinomimetics.3 Reflex milk ejection was blocked by the nicotinic antagonists mecamylamine and hexamethonium, and the inhibition was dose-dependent (ED(50) of 1 mg/kg i.v. and 5 mg/kg i.v., respectively). Despite the use of high doses, the muscarinic antagonists atropine (200 mg/kg), hyoscine (90 mg/kg) and benzhexol (30 mg/kg) all failed to prevent the reflex release of oxytocin.4 Acetylcholine (20 to 100 mug), bethanechol (0.2 to 4.0 mug) and carbachol (0.01 to 0.2 mug) injected into the cerebral ventricals stimulated a sustained release of oxytocin, which produced multiple increases in intramammary pressure. Nicotine (200 mug) was relatively ineffective by this route.5 The release of oxytocin by intraventricular bethanechol or carbachol was abolished by atropine (0.1 to 1.0 mg/kg) but not by mecamylamine (5 mg/kg) or hexamethonium (5 mg/kg).6 None of the antagonists used significantly affected either the release of oxytocin following electrical stimulation of the neurohypophysis or the mammary sensitivity to endogenous or exogenous oxytocin.7 The results suggest that the neural pathway controlling the reflex release of oxytocin during suckling in the rat contains a cholinergic component, which acts through nicotinic receptors. A second cholinergic pathway, of the muscarinic type, may also exist. The role of these two pathways is discussed.

Localization of the Oxytocin Receptor in the Plasma Membrane of Rat Myometrium

Abstract: The distribution of [3H]oxytocin binding sites among various subcellular fractions of rat myometrium paralleled the distribution of 5′-nucleotidase, a plasma membrane marker enzyme, but not of NADPH-cytochrome c reductase or succinate-cytochrome c reductase, which are endoplasmic reticulum and mitochondrial marker enzymes respectively. [3H]Oxytocin binding to the most enriched plasma membrane fraction showed the degree of selectivity with respect to hormone analogues that is expected for the oxytocin receptor. The binding of oxytocin to this fraction showed an apparent Kd of 1.98 × 10−9 M and a capacity of 1.28 pmol mg−1. It is concluded that the oxytocin receptor is located on the plasma membrane of the smooth muscle cells of the rat uterus.

Plasma half-lives of vasopressin and oxytocin analogs after iv injection in rats.

Abstract: SummaryThe curve-fit method for estimating plasma half-lives from vasopressor responses in rats (2) was used to estimate the plasma half-lives of vasopressin and oxytocin analogs substituted in the 1, 1 and 6, and 8 positions. Deamino-vasopressin and 1-hydroxy-oxytocin did not seem to be long-acting. Deamino-dicarba analogs of arginine-vasopressin and arginine-vasotocin were long-acting to the same degree, respectively, as deamino-vasopressin and deamino-vasotocin. Three 8-substituted analogs of oxytocin, [8-ornithine]-oxytocin, [8-glutamine]-oxytocin, and [8-proline]-oxytocin, were also long-acting.