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At least 523 records · Page 29Linked to original sources
PubMed1999

The oxytocin antagonist d(CH2)5Tyr(Me)2-Orn8-vasotocin reduces non-contact penile erections in male rats.

Male rats show four to six penile erection episodes when put for 80 min in the presence of an inaccessible receptive female. These non-contact penile erections were reduced dose-dependently by d(CH2)5Tyr(Me)2-Orn8-vasotocin, a potent and selective oxytocin receptor antagonist, when given into the lateral ventricles (0.1, 0.5 and 1 microg), but not when given into the paraventricular nucleus of the hypothalamus (0.1 and 1 microg). In contrast, non-contact erections were reduced by N(G)-nitro-L-arginine methyl ester, a competitive inhibitor of nitric oxide synthase, given into the lateral ventricles (50, 100 and 200 microg), or into the paraventricular nucleus (10 and 20 microg). The present results show that central oxytocin is involved in the expression of penile erection induced not only by drugs but also by sexual physiological stimuli.

Animals↗
PubMed1980

Renal and peripheral vascular responsiveness to arginine vasotocin in bullfrog, Rana catesbeiana.

Arginine vasotocin (AVT), the amphibian neurohypophysial hormone, has pressor and antidiuretic actions in bullfrogs (Rana catesbeiana). Much higher doses of exogenous AVT were required for the pressor response than those for the antidiuretic response. When bullfrog legs and kidneys were perfused under constant pressure simultaneously, the kidney vasculature was more sensitive to bolus injection of AVT than was the leg vasculature. The same was true when the tissues were perfused with different concentrations of hormone. AVT constricts preglomerular vessels in the bullfrog. We suggest that the preglomerular vasculature of the bullfrog is more sensitive to AVT than is the peripheral vasculature. This may explain in part the antidiuretic action of the hormone at nonpressor doses. Evolutionary speculations are discussed.

Animals↗
PubMed1995

Cardiovascular effects of arginine vasotocin, atrial natriuretic peptide, and epinephrine in freshwater eels.

The effects of 150 ng/kg iv injections of arginine vasotocin (AVT), eel atrial natriuretic peptide (ANP), and epinephrine (Epi) on the cardiovascular dynamics of resting freshwater eels, Anguilla rostrata were studied. Injection of AVT into the caudal vein significantly increased cardiac output (CO) from 15.3 to 23.6 ml.min-1.kg-1 primarily by increasing stroke volume. Mean dorsal aortic pressure (PDA) also increased. Estimated branchial shunting (2.54 ml.min-1.kg-1) was elevated by 130% because of an increased proportion of CO, indicating a vasoconstriction of the branchial arterioarterial pathway. In contrast, Epi reduced the fraction of CO perfusing the arteriovenous pathway. Epi also produced a positive chronotropic effect, increased CO and systemic vasoconstriction, resulting in a vasopressor response. These changes occurred earlier than those of AVT and ANP. Pressor responses triggered by AVT and Epi preceded the increases in CO. Injections of 150 and 200 ng/kg ANP caused a reduction in PDA due to a decrease in CO (and SV) but failed to modulate systemic resistance. The change in CO was the primary contributor to the pressor (and depressor) responses elicited by the three hormones.

Animals↗
PubMed1984

Opioid and dopamine involvement in prolactin release induced by arginine vasotocin and vasopressin in the male rat.

The potential involvement of the endogenous opioid and dopamine (DA) systems in the mechanism(s) mediating arginine vasotocin (AVT)- and arginine vasopressin (AVP)-induced prolactin (PRL) release was investigated in vivo. The injection of AVT (5 micrograms) into unanesthetized male rats resulted in a 2-fold stimulation of PRL release 15 min later, followed by an inhibition of PRL release 30 min thereafter; both the stimulatory and inhibitory PRL responses to AVT were obviated by naloxone (NAL) (200 micrograms). Similarly, the administration of either AVT or AVP (5 micrograms) to urethane-anesthetized rats led to a 3- and 5-fold increase in plasma PRL levels, respectively, 10 min after injection. The PRL stimulatory response to both peptides was completely blocked by pretreating the animals with apomorphine (APO) (5 mg); however, the injection of APO by itself had no effect on PRL secretion in these animals. Both AVT and AVP were also effective in stimulating PRL release 10 min after injection in estrogen (50 micrograms)-progesterone (25 mg) (EP)-treated rats anesthetized with urethane. APO negated the PRL stimulatory response to these compounds in the EP-treated rat as well. Normal, urethane-treated rats experienced a 7- to 8-fold increase in PRL levels 20 min following the injection of methysergide (MET) (250 micrograms). Both AVT and AVP caused approximately a 2.5-fold greater PRL response in MET-treated animals than in AVT and AVP controls, respectively; however, only in the MET + AVT-treated rats was the PRL stimulatory response greater than in the MET controls. MET probably stimulated PRL through its DA antagonistic properties.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1997

Cardiovascular effects of arginine vasotocin in the rainbow trout Oncorhynchus mykiss.

The physiological functions of the neurohypophyseal hormone arginine vasotocin (AVT) in teleosts are not clear. In the present studies, the sites and mechanisms of action of AVT on the rainbow trout Oncorhynchus mykiss cardiovascular system were examined in unanesthetized instrumented fish, perfused organs and isolated vessels. Injection of AVT (1, 10 or 100 pmol kg-1 body mass) into trout with dorsal aortic cannulas produced a modest, but dose-dependent, increase in dorsal aortic pressure (PDA). Bolus injection of AVT (100 pmol kg-1 body mass), or continuous infusion (6.7 pmol kg-1 min-1), into trout instrumented with dorsal aortic, ventral aortic and central venous cannulas and a ventral aortic flow probe significantly increased PDA as well as ventral aortic (PVA) and central venous (PVEN) blood pressure. Bradycardia accompanied the rapid rise in PVA while gill resistance (RG) increased. Maximum response to the AVT bolus was reached within 13­21 min and the response decayed slowly over the ensuing 90 min. AVT infusion (6.7 pmol kg-1 min-1) significantly increased PVEN and mean circulatory filling pressure and decreased unstressed blood volume, whereas venous compliance was unaffected. These in vivo studies indicate that AVT increases venous tone, thereby mobilizing blood from the unstressed compartment into the stressed compartment. This increases PVEN, which increases venous return and helps maintain, or slightly elevate, cardiac output. This, combined with an elevated RG and slightly elevated systemic resistance (RS), increases both PVA and PDA; however, the rise in PDA is mitigated by a disproportionate increase in RG relative to RS. In vitro, the effects of AVT are consistent with in vivo responses. AVT increased vascular resistance in the perfused gill and perfused trunk and contracted isolated vascular rings from both rainbow and steelhead trout. The general order of sensitivity of isolated vessels to AVT was (in decreasing order): anterior cardinal vein, celiacomesenteric artery, ductus Cuvier, efferent branchial artery, ventral aorta and coronary artery. Extracellular Ca2+ accounted for over 70 % of the tension in the AVT-contracted efferent branchial artery, but only 57 % of the tension in the anterior cardinal vein. Vascular AVT receptor sensitivity (EC50) in vitro ranged from 0.3 to 6 nmol l-1 and was similar to the estimated ED50 for the dose-dependent increase in PDA in vivo (approximately 1 nmol l-1). AVT was not inotropic in paced ventricular rings nor did it exhibit vasorelaxant activity in perfused organs or vascular rings. These results show that AVT is a potent vasoconstrictor in trout and that its two primary cardiovascular targets are the systemic veins and the branchial vasculature.

Journal Article↗
PubMed1979

Neurotransmitter regulation of arginine vasotocin release from rat pineal glands in vitro.

Studies were performed to determine the effects of neurotransmitters on arginine vasotocin (AVT) release in vitro. Rat pineal glands were incubated with 10(-8)M or 10(-6)M norepinephrine (NE), dopamine (DA), serotonin (5HT), and acetylcholine (ACH) for eight h after which the concentrations of AVT in the media were determined by radioimmunoassay. With the exception of ACH, none of the neurotransmitters had a significant effect on AVT release. ACH significantly (P less than 0.05) elevated AVT release in vitro at the 10(-6)M concentration but not at the 10(-8)M concentration. The data indicate that ACH may play a role in the regulation of rat pineal gland secretion of AVT in vitro.

Acetylcholine↗
PubMed1995

Influence of arginine-8-vasotocin and indomethacin on in vitro progesterone secretion by porcine granulosa cells.

The effect of the nonapeptide hormone arginine-8-vasotocin (AVT) and indomethacin on progesterone (P) production by cultured granulosa cells (GCs) from porcine preovulatory follicles was investigated. AVT dose-dependently stimulated the release of P by GCs. Basal and AVT-stimulated P secretion was inhibited when cultures were pretreated with the cyclooxigenase inhibitor indomethacin. These results suggest that AVT is involved in the local control of porcine follicle functions and that the effects of AVT on the P release are dependent on the endogenous production of prostaglandins (PGs) in the GCs.

Journal Article↗
PubMed2001

Vasotocin and mesotocin in the brains of amphibians: state of the art.

Immunohistochemical studies during the last decade have revealed elaborate systems of vasotocinergic (AVT) and mesotocinergic (MST) neuronal elements in the brain of a variety of amphibians including anurans, urodeles, and gymnophionans. Apart from a well-developed hypothalamo-hypophysial system, the antibodies demonstrated the existence of extrahypothalamic AVT- and MST-immunoreactive cell groups as well as extensive extrahypothalamic networks of immunoreactive fibers. The wide distribution of AVT- and MST-immunoreactive fibers throughout the brains of amphibians suggests that the two neuropeptidergic systems are involved not only in hypothalamo-hypophysial interactions, but also in a variety of other brain functions. Moreover, there is now evidence that sex-related differences occur in amphibians as previously shown for amniotes. It should be noted, however, that substantial variation occurs in the relative densities of AVT- and MST-immunoreactive fibers and number of cells between species, even within a single order of amphibians. Similar observations have been made in other classes of vertebrates and prompt us, therefore, to critically evaluate conclusions with respect to specific functions of AVT and MST in the central nervous system of vertebrates.

Amphibians↗
PubMed1996

Arginine vasotocin: locus of action along the nephron of the ornate dragon lizard, Ctenophorus ornatus.

The first measurements of AVT-sensitive adenylate cyclase activity in specific segments of the nephron of the Australian arid-zone agamid lizard, Ctenophorus (=Amphibolurus) ornatus, are reported. All sections of the collecting-duct system of this lizard were found to be sensitive to AVT at a concentration of 1 x 10(-6) M. In addition, receptors to AVT were located in the thin-intermediate segment linking proximal and distal convoluted tubules. No significant response to AVT was detected in the glomeruli, in either proximal or distal convoluted tubules, or in the ureter. The physiological significance of these particular segments is discussed in terms of the action of AVT in stimulating water and salt reabsorption in the lizard kidney.

Adenylyl Cyclases↗
PubMed1985

Vasotocin-immunoreactive elements and neuronal typology in the suprachiasmatic nucleus of the chicken and Japanese quail.

A Golgi study of the suprachiasmatic nucleus (SCN) of the chicken and Japanese quail revealed in this area a complex neuronal pattern and typology, including specialized dendritic patterns. Immunocytochemical studies provided evidence for the existence of a vasotocinergic system within the SCN, mainly in its rostral portion. Other clusters of immunoreactive elements are located in the lateral and dorsal divisions of this nucleus; they show a different distribution in the chicken and Japanese quail. The present results confirm, in birds, the existence of a morphologically defined SCN, the complex cytoarchitecture of which suggests specialized functions.

Animals↗
PubMedDate not supplied

Blood pressure and arginine vasotocin in normonatremic and hypernatremic ducks.

As a model to study effects of chronic, excessive salt loading on circulation, Pekin ducks were adapted to 2% saline solution as their sole water supply, while fresh-water-adapted animals were used as controls. Due to the development of salt-eliminating glands, salt-adapted ducks are able to cope indefinitely with this salt stress which means a daily ingestion of 5-6 g NaCl per kg body weight per day, associated with a chronic elevation of plasma osmolality and plasma sodium by 5-8% above normal and an up to 3-fold increase of antidiuretic hormone concentration in comparison to animals maintained on fresh water. Salt loading for up to 14 months did neither increase arterial mean, nor diastolic, nor pulse pressure. On the contrary, arterial mean and diastolic pressure were slightly lower in the salt-adapted than in the fresh-water-adapted animals, while pulse pressure and heart rate did not differ. Circulatory adaptation to removal and reinfusion of 10% of the estimated blood volume was identical in salt-water and fresh-water-adapted ducks. It is concluded that even excessive chronic salt loading resulting in chronic hyperosmolality with high plasma levels of sodium and antidiuretic hormone does not alter hemodynamic adaptation, provided that efficient compensating mechanisms are at the animal's disposal.

Animals↗
PubMed1990

Invertebrate neuropeptides resembling vasotocin and some analogues: synthesis and pharmacological properties.

The solid phase synthesis of three invertebrate vasopressin-oxytocin homologs: AVP-like factor, F1(1), ([Leu2, Thr4] AVT)2 isolated from subesophageal and thoracic ganglia of Locusta migratoria3, Arg-conopressin-S4. ([Ile2, Arg4] AVT), Lys-conopressin-G4 ([Phe2, Arg4] LVT), both isolated from the venom of fish-hunting marine snails of the genus Conus and six of their analogues is reported. These analogues are: [Arg4] AVT, [Ile2] AVT, [Leu2] AVT, [Phe2, Arg4] AVT, [Arg4] LVT and [Ile2, Arg4] LVT. All peptides were tested for antidiuretic and vasopressor activities.

Animals↗