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PubMed1986

Oxytocin in human follicular fluid and its possible role in the ovulatory process as studied in vitro.

Oxytocin immunoreactivity was determined in follicular fluid from human follicles at different stages of development. The concentration of oxytocin was highest in pre-ovulatory follicles. The measured oxytocin was found to co-elute with synthetic oxytocin in an h.p.l.c. system. The influence of oxytocin on the incorporation of [3H]proline into isolated human follicular wall was studied in vitro. Oxytocin induced a decrease of radiolabelling in both unripe and pre-ovulatory follicles, indicating an inhibitory effect on collagen synthesis. This effect of oxytocin was not affected by indomethacin. An oxytocin analogue, 1-deamino-2-D-Tyr(OEt)-4-Thr-8-Orn-vasotocin, did not inhibit the incorporation of [3H]proline. The pre-ovulatory augmentation of oxytocin concentration in follicular fluid might reflect a physiological role for oxytocin in the ovulatory process. This assumption is strengthened by the observation that oxytocin may influence follicular collagen metabolism in vitro and by this means participate in the regulation of follicular rupture in the human.

Adult↗

PubMed1997

Mesotocin receptor binding of cortical and medullary kidney tissues of the hen.

[125I]Mesotocin (MT) binding of membrane fractions of the cortical tissue and the medullary tissue (medullary cone) of the kidney of nonlaying hens was measured by the use of radioligand binding assays to determine the distribution of two distinct MT receptors within the hen kidney. The binding to [125I]MT in the medullary tissue was found to be highly competitive with unlabeled MT. In the cortical tissue, the binding was competitive with both unlabeled MT and arginine vasotocin. Kinetic and Scatchard analyses of specific binding revealed that the binding affinity was higher in the cortical tissue than in the medullary tissue, but the binding capacity was less in the cortical tissue. The localization of two distinct MT receptor having different binding properties may be related to the biphasic action of MT within the tissue of the kidney of the hen.

Animals↗

PubMed2004

Changes in prostaglandin F concentration in the uterus (shell gland) of the hen oviduct in relation to oviposition and estrogen.

The prostaglandin F (PGF) concentration of the uterus (shell gland) of the hen oviduct, measured by a radioimmunoassay, was found to increase slightly 6 h before oviposition and steeply immediately after oviposition. An intravenous injection of arginine vasotocin (AVT) caused the increase in the uterine PGF concentration and induced oviposition. When indomethacin was injected before the injection of AVT, the uterine PGF concentration was not increased, and the incidence of oviposition was reduced. Estrogen injection caused an increase in the uterine PGF concentration at 1 and 2 h after injection. Specific binding of the estrogen receptor of the uterine tissue increased 9 and 7 h before oviposition. The slight increase in the uterine PGF concentration 6 h before oviposition may be due to the action of estrogen via its receptor, and the steep increase immediately after oviposition may be caused by AVT released at the time of oviposition.

Animals↗

PubMed1987

Antigonadal activity of the neurohypophysial hormones: in vivo regulation of testicular function of hypophysectomized rats.

The "antigonadal" potential of the neurohypophysial hormones, previously demonstrated in vitro, was evaluated in vivo using hypophysectomized male rats. This approach minimizes the likelihood that the in vivo "antigonadal" effect of the neurohypophysial hormones may be due to their ability to attenuate the release of pituitary gonadotropins. Given that the identity of the putative endogenous occupant of testicular pressor-selective neurohypophysial receptors remains uncertain, use was made of a substitute probe, arginine vasotocin (AVT), the utility of which has been demonstrated in vitro. Concurrent in vivo treatment of follicle-stimulating hormone (FSH; 5 micrograms/rat/day)-maintained immature hypophysectomized rats with increasing doses of AVT (0.25-25 microgram/rat/day) produced significant (P less than 0.05) dose-dependent inhibition of the testicular luteinizing hormone/human chorionic gonadotropin (LH/hCG) receptor binding capacity (but not affinity; Kd = 1.8 X 10(-10) M) from 8.8 +/- (standard error; SE) 0.4 ng/testis to a level (3.2 +/- 0.2 ng/testis) lower than that of controls (64% reduction). This AVT-induced decrease in the testicular LH/hCG receptor content of FSH-maintained immature hypophysectomized rats was associated with significant (P less than 0.05) decrements in the hCG- and N6, 2'-O-dibutyryladeosine cyclic 3',5'-monophosphate [( Bu]2cAMP)-stimulated accumulation of 3 alpha-hydroxy-5 alpha-androstan-17-one (androsterone; 52% and 42% inhibition, respectively), with virtual elimination (98% inhibition) of the forskolin-stimulated accumulation of extracellular cAMP by testicular incubates in vitro, as well as with profound suppression of spermatogenesis. Taken together, these observations indicate that the "antigonadal" effect of the neurohypophysial hormones previously demonstrated in vitro, can be fully reproduced in vivo, and that the "antigonadal" activity of the neurohypophysial hormones may be accounted for, in large part, by decreased testicular LH/hCG binding capacity, stimulable adenylate cyclase activity, and cAMP-supported androgen biosynthesis.

Adenylyl Cyclases↗

PubMed1989

Development of the inhibitory guanine nucleotide-binding regulatory protein in the rat testis.

The functional development of the inhibitory guanine nucleotide-binding regulatory protein (Gi) and anti-diuretic hormone (ADH) activity was investigated in rat testes. Adult (90-day-old), adolescent (40-day-old), prepubertal (23-day-old), and fetal (20.5 days of gestation) testis cells were cultured with 100 ng/ml pertussis toxin for 24 h. The cells were then cultured with human chorionic gonadotropin (hCG), the ADH agonist arginine vasotocin (AVT), or a combination of the two. Testis cells from rats 23, 40, and 90 days of age that were incubated with hCG increased testosterone production when compared with controls. Preincubation of the cells from postnatal rats with pertussis toxin significantly increased hCG-stimulated testosterone secretion when compared to cells preincubated in medium only at all three ages. AVT suppressed hCG-stimulated testosterone secretion, but this suppression was partially reversed in cells from all postnatal ages preincubated with pertussis toxin. Fetal testis cells showed no response to preincubation with pertussis toxin, even when levels were increased to 400 ng/ml or when pertussis toxin treatment was continued throughout the culture period. AVT also had no effect on fetal testis cells. These results indicate that the Gi protein and AVT are not functional in fetal testes but are active from prepubertal stages of development through maturity.

Animals↗

PubMed1993

Demonstration of oxytocin receptors in porcine corpora lutea: effects of the cycle stage and the distribution on small and large luteal cells.

Recent investigations have demonstrated an inhibitory effect of oxytocin (OXT) on luteal cell progesterone (P) release under in vitro conditions. This inhibitory effect was counteracted by an OXT antagonist, indicating that it was receptor-mediated. In the present investigation, we demonstrated the presence of OXT binding sites in porcine luteal tissue using a radioiodinated OXT antagonist, [1-(beta mercapto-beta,beta-cyclopentamethylene propionic acid),2-(ortho-methyl)-Tyr2-Thr4-Orn8-Tyr-NH2] vasotocin (OTA), as ligand. For membrane fractions of porcine luteal tissue, Kd values of 0.7-0.8 nM were obtained; these are comparable to those of porcine myometrial fractions, measured under the same experimental conditions. Competition studies with luteal membrane fractions yielded a Ki(OXT) of 10(-9) M. This is a dose of OXT that exerts inhibitory effects on P release under both in vitro and in vivo conditions. To evaluate putative variations of luteal OXT receptor concentrations during the estrous cycle, membrane fractions prepared from corpora lutea (CL) of the early or midluteal (Days 2-6) and late luteal phase (Days 9-11) were used. While no differences in Kd values were observed, OXT binding capacities were significantly (p < 0.05) higher in CL from the early/midluteal phase (Bmax(E/M) = 116 +/- 12 fmol/mg protein) compared to CL from the late luteal phase (Bmax(L) = 65 +/- 10 fmol/mg protein). OXT binding sites were present in both small (SLC) and large luteal cells (LLC). SLC but not LLC responded to hCG with a significant increase of OXT binding sites, whereas E2 augmented OXT receptor binding in SLC as well as in LLC.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1996

Serial adult sex change involves rapid and reversible changes in forebrain neurochemistry.

Species with multiple sexual phenotypes provide novel insights into neuroendocrine mechanisms underlying vertebrate sexuality. Many fish species are capable of socially mediated sex reversal: the marine goby (Trimma okinawae) is one of only four species known to change sex more than once and in either direction. We have demonstrated that socially mediated serial sex change involves significant and reversible changes in the size of arginine vasotocin-producing forebrain cells. Sex-specific mating and parental behavior also change during sex reversal: both are regulated by the vasotocin/vasopressin peptide family in vertebrates. These neural and behavioral changes are correlated with modifications in gonad form and function, the form of the sexually dimorphic genital papilla, and the presence of an active male accessory gonadal structure. The speed, reversibility, and extent of these changes in adult sexual phenotype is remarkable relative to the rigid nature of these characteristics in many vertebrates.

Animals↗

PubMed1984

A mechanism of mania and the chemistry of dreams: a hypothesis.

A suggested cause of mania is asynchrony of two biologic clocks that are involved with the sleep-waking mechanism. Increased norepinephrine in the synaptic clefts of the locus ceruleus could quicken the pace of one clock. That same increase in norepinephrine is a possible inducer of euphoria and hyperactivity in mania. The action of melatonin and/or vasotocin on the dorsal raphe nucleus may induce the hallucinatory behavior in mania. Lithium corrects the psychosis by inhibiting adenylate cyclase and slowing the circadian rhythm.

Biological Clocks↗

PubMed1990

Complete amino acid sequence of goose VLDV-neurophysin. Traces of a putative gene conversion between promesotocin and provasotocin genes.

Goose VLDV-neurophysin (mesotocin-associated neurophysin) has been purified from posterior pituitary glands through molecular sieving on Sephadex G-75 and high-pressure reverse-phase liquid chromatography on Nucleosil C-18 columns. Despite apparent molecular mass of unreduced VLDV-neurophysin measured by polyacrylamide gel electrophoresis with sodium dodecylsulfate appeared near 17 kDa, this value fell to 11 kDa after reduction with mercaptoethanol, suggesting the existence of a homodimer. Complete amino acid sequence (93 residues) of goose VLDV-neurophysin has been determined. N- and C-terminal sequences of the protein have been established by Edman degradation (microsequencing) and use of carboxypeptidase Y, respectively. Peptides derived from oxidized or carboxamidomethylated neurophysin by trypsin or staphylococcal proteinase hydrolyses have been isolated by high-pressure liquid chromatography and microsequenced, allowing determination of the complete sequence. Comparison within the vertebrate VLDV-neurophysin lineage, namely goose VLDV-neurophysin to mammalian VLDV-neurophysins and to deduced toad VLDV-neurophysin, reveals a residue insertion between positions 66 and 67 in the nonmammalian VLDV-neurophysins. When goose MSEL-neurophysin (vasotocin-associated neurophysin) and goose VLDV-neurophysin are compared to their bovine counterparts, identical substitutions are found in positions 17 (Asn in both goose neurophysins instead of Gly in both ox neurophysins), 18 (Arg instead of Lys), 35 (Tyr instead of Phe), and 41 (Thr instead of Ala). Identity of the sequences 10-74 in both ox neurophysins has been explained by partial gene conversion between oxytocin and vasopressin genes, and identical substitutions in both goose neurophysins might reveal a similar gene conversion between mesotocin and vasopressin genes in birds.

Alkylation↗

PubMed1999

Regulation of Cl- secretion in seawater fish (Dicentrarchus labrax) gill respiratory cells in primary culture.

1. Primary cultures of sea bass (Dicentrarchus labrax) gill cells grown on permeable membranes form a highly differentiated tight epithelium composed of respiratory-like cells. This preparation was also found to provide a functional model for investigating the hormonal regulation of Cl- secretion. 2. In control conditions, i.e. in the absence of hormones or other stimuli, the cultured epithelium showed a short-circuit current (Isc) of 8.8 +/- 0.4 microA cm-2, a transepithelial potential (Vt) of 28.6 +/- 0.6 mV (serosal side positive), and a transepithelial resistance (Rt) of 5026 +/- 127 Omega cm2. Addition of 50 nM PGE2 caused a stimulation of Isc, Vt and transepithelial conductance, Gt. The increase in Isc was probably due to the elevation in Cl- secretion, since it could be correlated with the stimulation of serosal to mucosal 36Cl- flux. Application of the neurohypophyseal peptide arginine vasotocin (AVT; 50 nM) or the beta-adrenergic agonist isoproterenol (isoprenaline; 0. 5 microM) evoked a stimulation in Cl- secretion, as was shown by the increases in Isc and Gt. The excitatory effect of isoproterenol followed by the inhibitory action of propranolol, a beta-adrenergic antagonist, suggested the presence of beta-adrenergic receptors. Noradrenaline (0.1 microM) elicited a reduction in Isc, Vt and Gt, which was counterbalanced by the addition of phentolamine, an alpha-adrenergic antagonist. This suggested an activation of alpha-adrenergic receptors. 3. This study provides evidence for hormonal control of the Cl- secretion in sea bass gill respiratory cells in culture, involving AVT, prostaglandin (PGE2), and beta- and alpha-adrenergic receptors.

Animals↗

PubMed1982

Theophylline-induced stimulation of sodium transport in frog skin by a mechanism different from the antidiuretic hormone activated pathway.

Theophylline (theo) induced a marked increase in the short circuit current (SCC) after maximal stimulation by the antidiuretic hormone, arginine vasotocin (AVT). The stimulation amounted to 20-70% of the AVT-stimulation. Practically no effect was seen on osmotic water flow after maximal AVT-stimulation. A concentration dependence of the SCC stimulation was found from 0.04 to 4 mM theo, 16 mM inhibited the SCC. The response to theo was independent of the time of preincubation with AVT. The theo induced increase of SCC was accounted for by active sodium transport. Theo did induce an increase in the cyclic AMP level after stimulation with a maximal concentration of AVT, but so did a supramaximal dose of AVT. This indicates that the mechanism, by which theo stimulated the SCC additional to maximal AVT stimulation, is different from that by which AVT works. This effect of theo may be unrelated to cAMP or it may be explained by differences in cellular specificity of theo and AVT.

Animals↗

PubMed1995

Correlation between chloride flux via the mitochondria-rich cells and transepithelial water movement in isolated frog skin (Rana esculenta).

The coupling between net transepithelial Cl- influx and net water flow was investigated. Experiments were performed on isolated frog skin bathed in isotonic Cl- Ringer's solution in the presence of the Na+ channel blocking agent amiloride in the mucosal solution. The skins were voltage-clamped at -80 or -100 mV (with the serosal solution as reference). Under these conditions the current across the skin is carried by an influx of Cl-. In the absence of antidiuretic hormone the correlation between current and net water flow was low, but in the presence of the antidiuretic hormone, arginine vasotocin, there was a highly significant correlation between current and net water flow. The data presented here indicate that under steady state conditions about 70 molecules of water follow each Cl- ion across the skin. If the water influx is driven by electroosmosis one would expect that a change in current should result in an immediate change in the water flow. There was, however, a considerable time delay between the change in current and water flow. This indicates that the observed coupling between Cl- flux and water flow is caused by current-induced local osmosis and not electroosmosis.

Amiloride↗

PubMed1977

The permeability of the skin of a neotenous urodele amphibian, the mudpuppy Necturus maculosus.

1. The permeability of the isolated skin of a neotenous urodele amphibian, the mudpuppy Necturus maculosus, to Na, Cl, urea and water was measured. 2. Unidirectional transcutaneous flux measurements and the action of ouabain and amiloride, showed that there was normally no active Cl or Na transport, nor a Cl/Cl exchange diffusion process. 3. Amphotericin B initiated a transcutaneous potential difference and short-circuit current, which could be inhibited by ouabain. 4. The short-circuit current was nearly equivalent to the net Na Transport and this was also inhibited by ouabain. 5. A transcutaneous active Na transport mechanism thus appears to be incipient in the mudpuppy but is limited by a low permeability of the outer barrier of the cells. 6. Vasotocin increased the skin's diffusion permeability for water but had no effect on the influx of Na or urea. 7. The function of Necturus skin is in several respects unique compared to that of other amphibians.

Amiloride↗

PubMed1984

Circulatory and osmoregulatory effects of angiotensin II perfusion of the third ventricle in a bird with salt glands.

In Pekin ducks adapted to salt water, 1Asp - 5Val -angiotensin II, 1Asp - 5Ile -angiotensin II and 1Asp - 5Ile -tetradecapeptide were applied intracerebroventricularly (I.C.V.) during steady-state conditions evoked by continuous intravenous loading with 200 mosmol kg-1 saline. Each of the angiotensin II (AII) analogues caused a dose-dependent antidiuresis with a concomitant rise in urine osmolality and electrolyte concentration. Antidiuresis was linearly correlated with plasma arginine vasotocin (AVT). The elevation of plasma AVT occurred rapidly during I.C.V. stimulation with AII and declined exponentially to the pre-stimulation level. Under conditions of salt loading with 1000 mosmol kg-1 saline in which the ducks excreted the salt and water by their supraorbital salt glands, AII applied I.C.V. in a concentration of 1 nmol ml-1, inhibited the NaCl excretion via the salt glands. Arterial blood pressure and heart rate increased after I.C.V. microperfusion with 1 nmol ml-1 AII. This was not due to leakage of I.C.V. AII into the circulation because systemic application of AII required a 100-fold higher dose to elicit similar effects. Respiration rate remained constant. Systemically applied AVT which produced plasma levels similar to, or greater than, those caused by centrally acting AII resulted in the same antidiuretic responses but did not mimic the circulatory effects of I.C.V. AII. Specific AVT antiserum, injected intravenously, totally suppressed the renal response to I.C.V. AII and reduced the rise in blood pressure and heart rate by more than 50%. The anterior part of the third ventricle was more sensitive than the posterior part in eliciting the antidiuretic responses to I.C.V. applied AII. The particular combination of effects on renal excretion, salt gland secretion and cardiovascular function of centrally applied AII in the duck supports the idea that AII plays a major role as a central modulator of volume homeostasis.

Angiotensin II↗

PubMed1991

Partial uncoupling of salt gland blood flow and secretion in the Pekin duck (Anas platyrhynchos).

1. The aim of this study was to investigate the relationship between the blood flow through and the secretion by the salt glands of conscious, salt-water-adapted Pekin ducks. 2. Intravenous loading with hypertonic saline induced a steady-state secretion from the salt glands with a concomitant increase in whole-organ blood flow. The distribution of elevated local glandular blood flow was, however, uneven and in addition demonstrated vasomotor patterns that ranged from constant to rhythmic. 3. During on-going salt gland secretion, the infusion of three vasoactive agents, 5Val-angiotensin II (ANG II), 8Arg-vasotocin (AVT) and noradrenaline, via the carotid artery had differential effects on salt gland blood flow and secretion. 4. ANG II (80 pmol min-1 (kg body wt)-1) had no effect on mean arterial blood pressure (MABP), produced a transient 30% decrease in glandular blood flow and strongly diminished salt gland secretion (retention of 6.4 mosmol NaCl). 5. AVT (20 pmol min-1 (kg body wt)-1) had no effect on MABP and did not alter salt gland secretion despite a 35% reduction in blood flow. 6. Noradrenaline (20 nmol min-1 (kg body wt)-1) elevated MABP by 15 mmHg, reduced salt gland blood flow by more than 50%, but diminished salt gland secretion only slightly (retention of 2.7 mosmol NaCl). 7. Using ANG II, AVT and noradrenaline as hormonal tools, integrated changes in blood flow rate did not correspond with integrated changes in salt gland excretion. The partial dissociation between both parameters shows that control of secretion by the salt gland is more complex than simply being linearly dependent upon blood flow through it.

Angiotensin II↗

PubMed1968

Abnormal water balance in a mutant strain of chickens.

Polydipsia and polyuria are pronounced in chickens of a selected strain and this diabetes insipidus is inherited. The kidneys of such birds are capable of an antidiuretic response when lysine vasopressin or arginine vasotocin is injected. Osmotic pressure and sodium concentration of the plasmas of normal and mutant chickens are identical. Chicks predicted to have diabetes insipidus on the basis of parental pedigree are polydipsic.

Animals↗

PubMed1987

Catecholamine and blood pressure regulation by gonadotropin-releasing hormone analogs in amphibians.

Analogs of gonadotropin-releasing hormone (GnRH) occur in the brain, plasma, and sympathoadrenal system of anuran amphibians. The present experiments studied the effects of GnRH and [Trp7, Leu8]-GnRH on plasma catecholamines and cardiovascular function in conscious adult bullfrogs (Rana catesbeiana) and cane toads (Bufo marinus). Both GnRH analogs elicited dose-dependent (0.1-1 nmol.kg-1) increases in arterial norepinephrine, epinephrine, and blood pressure levels when injected intravenously into toads. In bullfrogs, [Trp7, Leu8]-GnRH (1 nmol.kg-1) increased arterial norepinephrine concentration approximately 10-fold without affecting the concentrations of norepinephrine sulfate, norepinephrine glucuronide, epinephrine, epinephrine sulfate, or epinephrine glucuronide. The noradrenergic response of bullfrogs to [Trp7, Leu8]-GnRH was specific to the neurohormone because it could be inhibited by [D-pGlu1, D-Phe2, D-Trp3,6]-GnRH. The sympathomimetic activities of the GnRH analogs did not depend on changes in temperature, which occur seasonally in natural habitats, because similar noradrenergic responses were observed at 4 and 22 degrees C. GnRH and [Trp7, Leu8]-GnRH (0.01-10 nmol.kg-1) did not raise arterial blood pressure in bullfrogs despite their pressor actions in toads. This interspecific difference was remarkable because cardiovascular responses to norepinephrine, angiotensin II, and vasotocin in bullfrogs were similar to those in toads. The parallels between catecholamine and blood pressure responses suggest that epinephrine is the principal mediator of the blood pressure response to native GnRH analogs in toads. In bullfrogs, [Trp7, Leu8]-GnRH mobilizes norepinephrine but not epinephrine, and the noradrenergic effect is insufficient to raise blood pressure. These observations are consistent with a physiological role for native GnRH analogs in the regulation of the sympathoadrenal system in anuran amphibians.

Angiotensin II↗

PubMed1986

Downregulation of vasopressin receptors in toad bladder.

Binding of tritium-labeled vasopressin [( 3H]AVP) to a broken epithelial cell preparation of the toad's urinary bladder has been related to hormonal action on water and urea transport across the intact tissue. Hormone binding to receptor sites and permeability changes were initiated at the same concentration of hormone (0.4 nM). Half-maximal urea and water permeability responses were observed with 3.1 and 5.6 nM AVP, respectively, although half-maximal receptor saturation required considerably higher concentrations of hormone (less than 500 nM). Because maximal permeability responses were obtained with occupation of approximately 200 fmol/mg protein receptor sites and the total receptor density was in excess of 2,000 fmol/mg protein, there is apparently a receptor reserve in this tissue. The antidiuretic hormone employed by the toad is vasotocin (AVT). This compound was 60-fold more effective than AVP in displacing [3H]AVP from receptor sites. Preincubation of bladders with AVT resulted in downregulation of receptor sites. Although the magnitude of receptor loss was equivalent in the presence or absence of a transmembrane osmotic pressure gradient, the capacity of AVT to induce permeability changes was more markedly reduced in the presence of an osmotic gradient. This observation suggests that the negative-feedback signal initiated by water flow through the hormone target cell diminishes sensitivity to hormone by a mechanism other than by a reduction in the number of surface receptors or by a decrease in their affinity for the hormone.

Animals↗