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PubMed2006

Influences of sex and saline intake on diurnal changes in plasma melatonin and osmoregulatory hormones of Pekin ducks (Anas platyrhynchos).

Melatonin (MT) inhibits salt gland secretion of Pekin ducks [Ching, A.C.T., Hughes, M.R., Poon, A.M.S., Pang, S.F., 1999. Melatonin receptors and melatonin inhibition of duck salt gland secretion. Gen. Comp. Endocrinol. 116, 229-240]. The present study examined simultaneous diurnal changes in plasma concentrations of MT and four osmoregulatory hormones of Pekin ducks to assess the possible interactions among these hormones that might contribute to inhibition of extrarenal salt secretion. The study compared diurnal changes in freshwater (FW) and saline-acclimated (SA) male and female ducks. We hypothesized plasma concentrations of osmoregulatory hormones: (1) differ between sexes (partially accepted); (2) vary diurnally (accepted, influenced by sex and treatment); (3) are correlated with MT (partially accepted); and their diurnal variation is affected by (4) sex (partially accepted); and (5) saline acclimation (partially accepted). We compared body mass, plasma osmolality (Osm(pl)), plasma volume, concentrations of plasma ions, and arginine vasotocin (AVT), angiotensin II (AII), prolactin, (PRL), and aldosterone (ALDO), in relation to plasma melatonin (MT). At night body mass increased in FW ducks and decreased in SA ducks. This likely reflects the higher plasma PRL concentration of female ducks and its middark increase only in SA ducks. Plasma volume increased at night in all but FW males. Plasma sodium and osmolality were higher in SA ducks and did not vary diurnally in either FW or SA ducks. Midday MT did not differ between males and females or between FW and SA ducks; at middark, all ducks, except FW females, increased MT. Midday AVT was higher in SA ducks. Only FW ducks increased AVT at middark. Changes in AVT and MT were positively correlated in males and negatively correlated in females. Males had higher AII and, at night, AII increased in SA ducks and decreased in FW ducks. AVT and AII were negatively correlated. ALDO was highly correlated with AII and unaffected by sex, saline, or time. At night, only AVT was elevated in FW ducks, while MT, AII, and PRL were elevated in SA ducks. FW and SA ducks appear to follow different, but equally effective, hormonal strategies to maintain osmotic homeostasis at night. We conclude that the effect of MT on salt gland secretion is probably a direct effect. These may be influenced by gender.

Aldosterone↗

PubMed2006

Seasonal changes in hypothalamic-pituitary-adrenal axis sensitivity in free-living house sparrows (Passer domesticus).

Recent evidence indicates that house sparrows (Passer domesticus) seasonally regulate corticosterone responses to capture, handling, and restraint. Responses during molt and in the fall are lower than responses in the winter and while breeding. This study tested whether changes in either adrenal tissue responsiveness to adrenocorticotropin (ACTH) or pituitary responsiveness to corticotropin releasing factor (CRF) or arginine vasotocin (AVT) could provide the mechanism regulating these seasonal changes. House sparrows were captured at two sites (Massachusetts and New Mexico, USA) and during the above four seasons and injected with exogenous ACTH, CRF, and AVT. ACTH stimulated further corticosterone release in all birds except Massachusetts birds in the winter, suggesting that reduced adrenal sensitivity to ACTH cannot explain reduced corticosterone release during fall and molt. However, exogenous ACTH was less effective during molt at both sites, implying that adrenal sensitivity does change. Pituitary sensitivity also changed seasonally, but these pituitary changes did not match the seasonal changes in corticosterone release. CRF and AVT only succeeded in elevating corticosterone in the spring in Massachusetts birds and in the winter in New Mexico birds, whereas CRF alone also stimulated corticosterone release in New Mexico birds in the fall. Taken together, these data indicate that house sparrows can alter the amount of corticosterone released from adrenal tissue, the amount of ACTH released from the pituitary, and the amount of CRF and AVT released from the hypothalamus, but that none of these changes correlate with seasonal changes in corticosterone release. Consequently, seasonal modulation of corticosterone release in house sparrows appear to result from a complicated mix of adrenal, pituitary, and hypothalamic changes that also vary seasonally.

Adrenocorticotropic Hormone↗

PubMed2004

Neural responses to territorial challenge and nonsocial stress in male song sparrows: segregation, integration, and modulation by a vasopressin V1 antagonist.

The present experiments were conducted to determine (1) which basal forebrain regions and/or their peptidergic components are responsive to social challenge and nonsocial stress, and (2) the influence of an arginine vasopressin V(1) antagonist (AVPa) on these responses. Experiments were conducted in wild-caught male song sparrows (Melospiza melodia) that were housed on seminatural territories (field-based flight cages). Subjects were each fitted with a chronic guide cannula directed at the lateral ventricle and exposed to one of five conditions before sacrifice and histochemistry: saline + simulated territorial intrusion (STI; consisting of song playback and presentation of a caged conspecific male), AVPa + STI, saline + empty cage, AVPa + empty cage, unhandled. Two tissue series were prepared and immunofluorescently double-labeled for ZENK (egr-1) protein and either arginine vasotocin (AVT; avian homologue of AVP) or corticotropin releasing factor (CRF). The results indicate that the neuronal populations that are sensitive to nonsocial stress (capture, handling and infusion) and STI are at least partially segregated. Increases in ZENK-immunoreactive (-ir) nuclei following handling and infusion were observed in a large number of areas, whereas neural responses that were specific to STI were more limited. However, multiple areas showed responses to both handling and STI. AVPa infusions significantly reduced or eliminated most experimental increases in ZENK-ir, suggesting a broad role for endogenous AVT in the modulation of baseline activity and/or stress responsivity, and a much more limited role in the specific response to social challenge. Particular attention is given to the numerous zones of the lateral septum (LS), which are differentially responsive to handling, STI, and V(1)-like receptor blockade. These data suggest that septal AVT modulates neural responses to general stressors, not social stimuli specifically. Thus, species differences in septal AVT function (as previously described in songbirds) likely reflect differences in the relationship of stress or anxiety to species-specific behaviors, or to behavior in species-typical contexts.

ADP-ribosyl Cyclase↗

PubMed2005

Neuroendocrine correlates of behavioral polymorphism in white-throated sparrows.

Interspecific differences in the neuropeptide systems of the lateral septum (LS) often parallel differences in social behavior. In rodents, some closely related species that differ in aggressive behavior also differ according to the level of vasopressin (VP) innervation of the LS. In songbirds, the neuropeptides vasotocin (VT) and vasoactive intestinal peptide (VIP) affect aggression when administered directly to the LS. Here, we tested whether the density of VT or VIP innervation of the LS reflects patterns of intraspecific behavioral polymorphism in male and female white-throated sparrows (Zonotrichia albicollis), in which the "white-stripe" (WS) morph behaves more aggressively than the "tan-stripe" (TS) morph. We found that the WS birds had more VT-immunoreactivity (IR) than the TS birds in the ventrolateral subdivision of the caudal LS (LSc.vl) and in the medial portion of the bed nucleus of the stria terminalis (BSTm). In addition, the TS birds had more densely stained VIP-IR in the LSc.vl than the WS birds. Males had more VT-IR than females in the LSc.vl and BSTm, and more VIP-IR in the LSc.vl. We also report sex and morph differences in VIP-IR in the basal hypothalamus, where VIP is synthesized and released into the portal vasculature. Males had nearly twice as many VIP-immunoreactive (ir) neurons in the infundibular nucleus than did females, and birds of the WS morph had more densely stained VIP-IR in the median eminence than TS birds. Our results support the hypothesis that differences in these neuropeptide systems underlie inter- and intraspecific differences in social behavior across vertebrates.

Animals↗

PubMed2005

Current research in amphibians: studies integrating endocrinology, behavior, and neurobiology.

Amphibian behavioral endocrinology has focused on reproductive social behavior and communication in frogs and newts. Androgens and estrogens are critical for the expression of male and female behavior, respectively, and their effects are relatively clear. Corticosteroids have significant modulatory effects on the behavior of both sexes, as does the peptide neuromodulator arginine vasotocin in males, but their effects and interactions with gonadal steroids are often complex and difficult to understand. Recent work has shown that the gonadal hormones and social behavior are mutually reinforcing: engaging in social interactions increases hormone levels just as increasing hormone levels change behavior. The reciprocal interactions of hormones and behavior, as well as the complex interactions among gonadal steroids, adrenal steroids, and peptide hormones have implications for the maintenance and evolution of natural social behavior, and suggest that a deeper understanding of both endocrine mechanisms and social behavior would arise from field studies or other approaches that combine behavioral endocrinology with behavioral ecology.

Adrenal Cortex Hormones↗

PubMed2006

Population divergence in plasticity of the AVT system and its association with aggressive behaviors in a Death Valley pupfish.

Behavioral differences can evolve rapidly in allopatry, but little is known about the neural bases of such changes. Allopatric populations of Amargosa pupfish (Cyprinodon nevadensis) vary in aggression and courtship behaviors in the wild. Two of these wild populations were recently found to differ in brain expression of arginine vasotocin (AVT)--a peptide hormone shown previously to modulate aggression in pupfish. These populations have been isolated for less than 4000 years, so it remained unclear whether the differences in behavior and neural AVT phenotype were evolved changes or plastic responses to ecologically dissimilar habitats. Here, I tested whether these population differences have a genetic basis by examining how aggressive behavior and neural AVT phenotype responded to ecologically relevant variation in salinity (0.4 ppt or 3 ppt) and temperature (stable or daily fluctuating). Pupfish from Big Spring were more aggressive than pupfish from the Amargosa River when bred and reared under common laboratory conditions. Morphometric analysis of preoptic AVT immunoreactivity showed that the populations differed in how the AVT system responded to salinity and temperature conditions, and revealed that this plasticity differed between parvocellular and magnocellular AVT neuron groups. Both populations also showed relationships between neural AVT phenotype and aggression in the rearing environment, although populations differed in how aggression related to variation in magnocellular AVT neuron size. Together, these results demonstrate that the pupfish populations have diverged in how physical and social conditions affect the AVT system, and provide evidence that the AVT system can evolve quickly to ecologically dissimilar environments.

Aggression↗

PubMed2006

Neuropeptide binding reflects convergent and divergent evolution in species-typical group sizes.

Neuroendocrine factors that produce species differences in aggregation behavior ("sociality") are largely unknown, although relevant studies should yield important insights into mechanisms of affiliation and social evolution. We here focused on five species in the avian family Estrildidae that differ selectively in their species-typical group sizes (all species are monogamous and occupy similar habitats). These include two highly gregarious species that independently evolved coloniality; two territorial species that independently evolved territoriality; and an intermediate, modestly gregarious species that is a sympatric congener of one of the territorial species. Using males and females of each species, we examined binding sites for (125)I-vasoactive intestinal polypeptide (VIP), (125)I-sauvagine (SG; a ligand for corticotropin releasing factor, CRF, receptors) and a linear (125)I-V(1a) vasopressin antagonist (to localize receptors for vasotocin, VT). VIP, CRF and VT are neuropeptides that influence stress, anxiety and/or various social behaviors. For numerous areas (particularly within the septal complex), binding densities in the territorial species differed significantly from binding in the more gregarious species, and in most of these cases, binding densities for the moderately gregarious species were either comparable to the two colonial species or were intermediate to the territorial and colonial species. Such patterns were observed for (125)I-VIP binding in the medial bed nucleus of the stria terminalis, medial septum, septohippocampal septum, and subpallial zones of the lateral septum; for (125)I-SG binding in the infundibular hypothalamus, and lateral and medial divisions of the ventromedial hypothalamus; and for the linear (125)I-V(1a) antagonist in the medial septum, and the pallial and subpallial zones of the caudal lateral septum. With the exception of (125)I-SG binding in the infundibular hypothalamus, binding densitites are positively related to sociality.

Amphibian Proteins↗

PubMed1997

Proconvulsive effect of vasopressin; mediation by a putative V2 receptor subtype in the central nervous system.

Subcutaneously (s.c.) administered [Arg8]vasopressin (AVP) potentiated seizures induced by intracerebroventricular (i.c.v.) injection of 1.95 mg pilocarpine (a muscarinic cholinergic agonist). A bell-shaped relation between dose and effect was found. I.c.v. pretreatment with a V1, V2 or oxytocin receptor antagonist was performed to determine whether and what type of receptor is involved in this proconvulsive effect of vasopressin. For these experiments a higher dose of pilocarpine (2.4 mg i.c.v.) was injected. This caused seizures in a slightly but not significantly higher percentage of the rats. A dose-dependent protective action of the V2 receptor antagonist d(CH2),[D-Ile2,Ile4]AVP (effective doses were 25 and 125 ng) on seizures was found. A reduction was observed in the number of animals that developed tonic-clonic convulsions. Neither the V1 receptor antagonist d(CH2)5[Tyr(Me)2]AVP nor the oxytocin receptor antagonist desGly(NH2)9d(CH2)5[Tyr(Me)2Thr4]OVT possessed anti-convulsive activity. Subsequently the type of receptor was studied in detail with fragments of AVP with either V1 or V2 activity. AVP (with V1 and V2 affinity) (1 and 3 microg s.c.) potentiated pilocarpine (1.95 mg) induced seizures. Vasotocin and oxytocin were without effect. Interestingly neither s.c. nor i.c.v. administration of the selective kidney type vasopressin receptor (V2) agonist dDAVP potentiated pilocarpine induced seizures. Several selective antidiuretic agonists (V2), such as d[Val4]AVP, d[Phe2,Val4,D-Arg8]vasopressin (3 microg), [Val4,D-Arg8]vasopressin (3 microg) and d[Val4,D-Arg8]vasopressin (3 microg) were active. Other selective antidiuretic compounds, such as [Val4]AVP, dAVP, d[Tyr(Me)2]AVP and HO[D-Arg8]vasopressin (3 microg) did not influence seizures. These results demonstrate that a combination of substitution of aminoacid 4 (Gln) by Val and to a lesser extent deamination and the D-arginine form yield an active molecule, which can potentiate pilocarpine induced seizures and suggest the existence of a V2 receptor subtype in the brain.

Animals↗

PubMed2000

EP 60761 and EP 50885, two hexarelin analogues, induce penile erection in rats.

The effect of hexarelin and four related peptide analogues, EP 40904, EP 40737, EP 50885 and EP 60761, injected into the paraventricular nucleus of the hypothalamus of male rats in doses between 2 and 2000 ng on spontaneous penile erection was studied. Of these peptides, EP 60761 and EP 50885, but not hexarelin, EP 40904 or EP 40737, increased dose-dependently the number of spontaneous penile erections. EP 60761 was active already at the dose of 20 ng, which induced the sexual response in 70% of the treated rats. The maximal response was induced by 200 ng of the peptide. EP 50885 was less potent than EP 60761, with 1000 ng being the minimal effective dose and 2000 ng as the dose required to induce the maximal response. At the doses used, both peptides also increased slightly the number of spontaneous yawning episodes. EP 60761- and EP 50885-induced penile erection was prevented by the oxytocin receptor antagonist [d(CH(2))(5)Tyr(Me)(2)-Orn(8)]vasotocin (0.1-1 microg) given intracerebroventricularly (i.c.v.), but not into the paraventricular nucleus (0.1-1 microg), by the competitive nitric oxide (NO) inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) given either into the paraventricular nucleus (10-20 microg) or i.c.v. (75-150 microg), by the N-type Ca(2+) channel blocker omega-conotoxin-GVIA (2-5 ng) or by the opiate morphine (1-10 microg), but not by the dopamine receptor antagonist (Z)-4-[3-[2-(trifluoromethyl)-9H-thioxanthen-9-ylidene]propyl]-1-p ipe razine-ethanol (cis-flupenthixol) (10 microg) or by the N-methyl-D-aspartic acid (NMDA) receptor antagonist (5R, 10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-imine ((+)-MK-801) (1 microg), all given into the paraventricular nucleus before either peptide. The present results show that EP 60761 and EP 50885 induced penile erection by increasing central oxytocin transmission, possibly by activating NO synthase in the cell bodies of oxytocinergic neurons located in the paraventricular nucleus that control penile erection.

Animals↗

PubMed2003

Neurochemical correlates of male polymorphism and alternative reproductive tactics in the Azorean rock-pool blenny, Parablennius parvicornis.

In the common Azorean rock-pool blenny, Parablennius parvicornis, males exhibit alternative reproductive morphologies: (1) larger males defend nest sites, provide parental care, have anal glands (involved in pheromone release), testicular glands, and low gonad:body weight ratio (GSI) and (2) smaller, younger, males do not defend nests, have reduced glands and high GSI. These smaller non-nesting males behave as satellites (associated with nests) or sneakers (moving among nests), attempting to achieve parasitic fertilizations via sperm competition. In non-mammals, arginine vasotocin (AVT) is a key hypothalamic peptide involved in the control of reproductive behavior and physiology, and several fish species that exhibit alternative male reproductive morphs show polymorphism in AVT brain chemistry. We conducted an immunocytochemical study to generate comparative data on this intertidal blenny. Our analysis showed no difference in AVT-immunoreactive cell number or size between the male morphs, which is consistent with studies on other fish, including blennies. The number of AVT cells was positively correlated to fish body mass, while cell size showed no such relation. If corrected for body mass, the smaller non-nesting males have significantly more cells than the large nesting males. Our data suggest that the size and number of forebrain AVT cells develops initially to allow for reproduction in the young non-nesting males and this pattern does not appear to change when males take on the nesting morphotype later in life. This result appears to be consistent in many fishes with alternative male morphotypes.

Animals↗

PubMed1998

Characterization of vasopressin receptor in rat lung.

This study characterized rat lung membrane arginine vasopressin (AVP) receptors in detail. Specific binding of [3H]AVP to rat lung membranes was dependent upon time, temperature and membrane protein concentration. Scatchard plot analysis of equilibrium binding data revealed the existence of a single class of high-affinity binding sites with a Kd of 0.45 nM and a Bmax of 76.6 fmol/mg protein. Competitive inhibition of [3H]AVP binding showed that neurohypophysial hormones as well as their synthetic analogues displaced [3H]AVP in a concentration-dependent manner. The order of potencies for the native peptides was: AVP > lysine vasopressin = arginine vasotocin > oxytocin. Furthermore, potent V1A receptor antagonists, d(CH2)5Tyr(Me)AVP and dPTyr(Me)AVP, showed high affinity for lung membranes. In contrast, the V2 receptor agonist, dDAVP, and the specific oxytocin receptor agonist, [Thr4,Gly7]oxytocin, did not affect AVP binding. These results suggest that the lung contains the V1A receptor subtype. The lung membrane AVP receptor characterized in this study may play an important role in mediating the physiological effects of AVP in the lung.

Animals↗

PubMed2001

Steroid-induced plasticity in the sexually dimorphic vasotocinergic innervation of the avian brain: behavioral implications.

Vasotocin (VT, the antidiuretic hormone of birds) is synthesized by diencephalic magnocellular neurons projecting to the neurohypophysis. In addition, in male quail and in other oscine and non-oscine birds, a sexually dimorphic group of VT-immunoreactive (ir) parvocellular neurons is located in a region homologous to the mammalian nucleus of the stria terminalis, pars medialis (BSTm) and in the medial preoptic nucleus (POM). These cells are not visible in females. VT-ir fibers are present in many diencephalic and extradiencephalic locations. Quantitative morphometric analyses demonstrate that, in quail, these elements are expressed in a sexually dimorphic manner (males>females) in regions involved in the control of different aspects of reproduction: i.e., the POM (copulatory behavior), the lateral septum (secretion of gonadotropin-releasing hormone [GnRH]), the nucleus intercollicularis (control of vocalizations), and the locus coeruleus (the main noradrenergic center of the avian brain). In many of these regions, VT-ir fibers are closely related to aromatase-ir, GnRH-ir, or estrogen receptor-expressing neurons. This dimorphism has an organizational nature: administration of estradiol-benzoate to quail embryos (a treatment that abolishes male sexual behavior) results in a dramatic decrease of the VT-immunoreactivity in all sexually dimorphic regions of the male quail brain. Conversely, the inhibition of estradiol (E2) synthesis during embryonic life (a treatment that stimulates the expression of male copulatory behavior in adult testosterone (T)-treated females) results in a male-like distribution of VT-ir cells and fibers. Castration markedly decreases the immunoreactivity in both the VT-immunopositive elements of the BSTm and the innervation of the SL and POM, whereas T-replacement therapy restores the VT immunoreactivity to a level typical of intact birds. These changes reflect modifications of VT mRNA concentrations (and probably synthesis) as demonstrated by in situ hybridization and they are paralleled by similar changes in male copulatory behavior (absent in castrated male quail, fully expressed in CX+T males). The aromatization of T into estradiol (E2) also controls VT expression and, in parallel limits the activation of male sexual behavior by T. In castrated male quail, the restoration by T of the VT immunoreactivity in POM, BSTm and lateral septum could be fully mimicked by a treatment with E2, but the androgen 5alpha-dihydrotestosterone (DHT) had absolutely no effect on the VT immunoreactivity in these conditions. At the doses used in this study, DHT also did not synergize with E2 to enhance the density of VT immunoreactive structures. Systemic or i.c.v. injections of VT markedly inhibit the expression of all aspects of male sexual behavior. VT, presumably, does not simply represent one step in the biochemical cascade of events that is induced by T in the brain and leads to the expression of male sexual behavior. Androgens and estrogens presumably affect reproductive behavior both directly, by acting on steroid-sensitive neurons in the preoptic area, and indirectly, by modulating peptidergic (specifically vasotocinergic) inputs to this and other areas. The respective contribution of these two types of actions and their interaction deserves further analysis.

Animals↗

PubMed1996

In the trout, CRH and AVT synergize to stimulate ACTH release.

Anterior pituitaries of the rainbow trout (Oncorhynchus mykiss) were incubated with graded concentrations of arginine vasotocin (AVT) or synthetic rat corticotrophin-releasing hormone (rCRH-41), alone or in combination, and the ACTH secreted into the medium was measured by a sensitive cytochemical bioassay. The aim was to determine the relative potencies of the two secretogogues and whether, in this fish species, they act synergistically. Rat CRF-41 and AVT both produced concentration-dependent increases in ACTH release. The minimum effective concentration for both peptides was approximately 1 nM but, at higher concentrations, the efficacy of CRF-41 was greater than that of AVT. Clear evidence of synergy between the two peptides was obtained. The response of the trout thus falls in line with observations in mammals and contrasts with findings for the goldfish.

Adrenocorticotropic Hormone↗

PubMed2000

Hormonal control of urodele reproductive behavior.

Hormonal control of expression of courtship behavior and of development of structures related to the reproductive behavior in two species of Japanese newts, Cynops pyrrhogaster and Cynops ensicauda, was described. Prolactin (PRL) and androgen were essential factors for eliciting courtship behavior. In addition, arginine vasotocin markedly enhanced the expression of courtship behavior. PRL induced migration to water, in which courtship and oviposition take place, and converted the integument from the terrestrial type to the aquatic one. PRL also stimulated the growth of the tail fin, which was blocked by estrogen. Cellular and nuclear size and number of synapses on the somata of Mauthner cells, which are involved in tail movement, were also increased by PRL and androgen. Synthesis of sodefrin, a female-attracting pheromone, in the abdominal gland as well as that of mucopolysaccharides constituting the sac of sperm in the lateral gland was enhanced by PRL and androgen. Structural development of oviducts was elicited by estrogen or PRL to a certain extent, and full oviducal development by the combination of these two hormones, PRL being indispensable for the oviducal jelly secretion.

Animals↗

PubMedDate not supplied

Forebrain AVT and courtship in a fish with male alternative reproductive tactics.

In this paper, we present the results of cellular and molecular studies on the neuroendocrine correlates of male sexual polymorphism in a population of the blenniid fish Salaria pavo (Risso). Bigger and older males defend nests, whereas smaller and younger males mimic female nuptial coloration and behavior to gain access to nests and sneak fertilizations. In this population, sex-role reversal in courtship also occurs (i.e., females are the courting sex). Immunocytochemistry and in situ hybridization were used to examine the production of arginine vasotocin (AVT) peptide and messenger RNA, respectively. The expression of AVT mRNA on a per-cell basis was correlated with mating behavior, rather than with sex morphotype, which suggests that the greater level of AVT mRNA expression in females and sneakers is correlated with the production of courtship behavior. On the other hand, the number and size of AVT peptide-producing cells in both male types is higher or larger, respectively, than in females, which suggests that it is correlated with sex morphotype, rather than with mating behavior.

Animals↗

PubMed1998

Effects of homologous natriuretic peptides in isolated skin of the bullfrog, Rana catesbeiana.

The effects of frog atrial (fANP), brain (fBNP) and C-type natriuretic peptide (fCNP) on transepithelial ion transport were investigated in the bullfrog, Rana catesbeiana. The transepithelial potential difference (PD) and short-circuit current (Isc) of the abdominal skin were measured according to the technique of Ussing and Zerahn. When the abdominal skin was exposed to homologous natriuretic peptides (NPs) at concentrations ranging from 4 x 10(-13) to 5 x 10(-7) M, no significant changes in PD or Isc were observed. The influence of the NPs on the arginine vasotocin (AVT)-induced increase in Isc was then examined. Treatments with ANP and BNP (4 x 10(-9)-4 x 10(-8) M) inhibited the increase in the AVT (10(-8) M)-induced Isc. Furthermore, fCNP I and fCNP II (5 x 10(-13)-5 x 10(-7) M) did not significantly inhibit the increase in the AVT-induced Isc. The cyclic GMP analog, 8-BrcGMP, (> 10(-4) M) with AVT inhibited the increase of AVT-induced ISc, as well as fANP and fBNP. HS-142-1, an inhibitor of particulate guanylyl cyclase, (10(-5) g ml-1) significantly reduced the inhibitory action of fANP on the increase of AVT-induced Isc. These results suggest that fANP and fBNP act through the guanylyl cyclase systems to increase cellular cGMP and modulate AVT-induced epithelial transport in a concentration-dependent manner. It is also suggested that fCNPs have no effect on the natriferic response in the skin of the bullfrog.

Animals↗

PubMed2001

Effect of AVT antisense oligodeoxynucleotides on AVT release induced by hypertonic stimulation in chicks.

In birds, arginine vasotocin (AVT) and mesotocin (MT) are the neurohypophyseal hormones. AVT is known to be an avian antidiuretic hormone and is released from the neurohypophysis by dehydration or hyperosmotic stimulation. The purpose of this study was to determine whether the mechanism of AVT synthesis is related to the mechanism of hormone release from the neurohypophysis. Four-day-old chicks received an AVT antisense oligodeoxynucleotide (ODN) injection into the cerebral ventricle (icv). Following antisense administration, the chicks received hypertonic saline stimulation. Plasma levels of AVT and MT were measured by radioimmunoassays. In control birds, a hypertonic saline injection resulted in the increase of plasma AVT level. The administration of a high dose (50 microg) of antisense ODN inhibited the increase of plasma AVT level induced by the hypertonic saline stimulation. Plasma levels of MT did not change with the administration of hypertonic saline or antisense ODN. These results suggest that the mechanisms that regulate the secretion of AVT from the neurohypophysis may be coupled to the mechanisms that regulate the synthesis of AVT.

Animals↗

PubMed1998

Changes of AVT levels in plasma, neurohypophysis and hypothalamus in relation to oviposition in the laying hen.

Arginine vasotocin (AVT) is a neurohypophysial hormone involved in the reproductive function in avian species. We measured AVT concentrations in the neurohypophysis and plasma in relation to indomethacin blocked oviposition and to prostaglandin (PG) E2-induced premature oviposition in the hen. In addition, AVT concentration in the hypothalamus was measured in relation to spontaneous oviposition. In the control group the concentration of AVT decreased in the neurohypophysis and increased in plasma at oviposition. In hens that were administrated indomethacin, oviposition was delayed for several hours and no changes in the levels of AVT in neurohypophysis and plasma were observed at the predicted time of oviposition. Premature oviposition was induced within 5 min after the administration of PGE2. The levels of AVT decreased in the neurohypophysis and increased in plasma at the PGE2-injected premature oviposition. The increases of AVT levels in paraventricular and supraoptic nuclei were observed 2 and 5 h after spontaneous oviposition. The results indicate that oviposition causes an increase in the release of AVT from neurohypophysis and suggest that the synthesis of hypothalamic AVT may be stimulated by oviposition.

Animals↗