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At least 919 records · Page 51Linked to original sources

PubMed1990

Heterogeneity of oxytocin receptors in the pregnant rat myometrium near parturition.

The contractile response of longitudinal and circular strips of rat myometrium to oxytocin (OT), [Arg8]vasotocin (AVT) and [Arg8]vasopressin (AVP) was examined in vitro in late pregnancy (controls at day 20, day 21, day 22) and 24 h after treatment with the antiprogestin, RU 486 (or mifepristone, given on day 20 or day 21 of gestation). In controls, the maximal effect (Emax) of OT in longitudinal strips increased with gestation, but there was no change in OT sensitivity in either myometrial layer. The pA2 values for the OT/AVP V1 antagonist, d(CH2)5[Tyr(Me)2]OVT, against OT, AVT and AVP on longitudinal strips and against AVT and AVP on circular strips were not different. However, the antagonist did not inhibit the effect of OT in circular strips, indicating that the receptor activated by OT is different from that in longitudinal strips. RU 486 treatment did not modify the characteristics of responses to AVT and AVP. RU 486 improved the response to OT in circular strips from rats treated at day 20, however the sensitivity to OT in longitudinal strips was decreased compared to that in the controls.

Animals↗

PubMed1993

Effects of central vasopressin administration to infant rats.

The neurohypophyseal peptide hormone arginine-vasopressin functions as a neuropeptide in several brain areas in addition to its role as a posterior pituitary hormone. Several studies indicate that arginine-vasopressin and arginine-vasopressin receptors appear early in the infant rat brain. To determine if arginine-vasopressin receptors in the infant were responsive to exogenous peptides, we compared the behavioral effects of central or peripheral administration of arginine-vasopressin, arginine vasotocin, the oxytocin precursor oxytocin-Gly-Lys-Arg, and arginine-vasopressin receptor antagonists in socially isolated rat pups. Central administration of arginine-vasopressin decreased the number of rat pup ultrasonic vocalizations, reduced locomotor activity and decreased the latency to express a response to negative geotaxis. Temperature was also reduced at all doses tested. Co-administration of arginine-vasopressin and receptor antagonists suggested that changes in vocal behavior were mediated by the V1 receptor subtype. Changes in core temperature appeared to be mediated by a V2 receptor subtype. Peripheral arginine-vasopressin administration increased calling and decreased core body temperature. Neither effect was blocked by central receptor antagonist administration. The results are consistent with the hypothesis that arginine-vasopressin receptors in the infant rat brain are functional.

Animals↗

PubMed1983

The role of hormones in regulation of carbohydrate metabolism in the Australian lungfish Neoceratodus forsteri.

Adrenaline, arginine vasopressin, arginine vasotocin, and glucagon, all at 10(-6) M, stimulate glycogen breakdown and glucose release from hepatic tissue of Neoceratodus forsteri cultured in vitro. Adrenaline acts via a beta-adrenergic receptor in this species. Gluconeogenesis from 2 mM lactate occurred at a rate of 680 +/- 39 nmol/g liver/h. This rate of gluconeogenesis was unaffected by the addition of 10(-6) M adrenaline.

Animals↗

PubMed1983

Adrenergic inhibition of uterine contractions and oviposition in the lizard Anolis carolinensis.

Injection of arginine vasotocin (AVT), which induces oviposition in several lizard species, fails to do so in Anolis carolinensis. We tested the hypothesis that epinephrine-induced activation of beta-adrenoreceptors in the uterus inhibits AVT action on uterine smooth muscle. Pretreatment of gravid females with the beta-adrenoreceptor antagonist dichloroisoproterenol 15 min before an AVT injection resulted in uterine sensitivity to AVT and subsequent oviposition. Furthermore, in vitro tests indicated that epinephrine as well as a beta-adrenoreceptor agonist (isoproterenol) inhibit uterine tonic and rhythmic contractions that normally follow exposure to AVT. These results suggest that stress-induced secretion of epinephrine can act as a short-term inhibitor of oviposition in this species.

Animals↗

PubMed1984

Effect of thyrotropin-releasing hormone and its metabolites on the secretion of sulfated polysaccharides by foot integument of a pond snail.

The effect of thyrotropin-releasing hormone (TRH), TRH metabolites, and a TRH analog on the secretion of 35S-labeled sulfated polysaccharides from in vitro incubated foot integument of the pond snail Lymnaea stagnalis palustris was assessed. Whereas TRH significantly inhibited the secretion of 35S-labeled polysaccharides, its metabolite deamido TRH significantly stimulated polysaccharide secretion. Histidyl-proline-diketopiperazine did not alter the secretion of 35S-labeled sulfated polysaccharides. Foot integument exhibited considerable TRH-peptidase activity in vitro. The principal proline-containing TRH metabolites were deamido-TRH and proline. The deamido-TRH content of the foot, mantle, and hemolymph was determined by radioimmunoassay. All tissues contained deamido-TRH. These findings suggest that the secretory activity of skin mucus glands of L. stagnalis palustris is the result of the stimulatory action of deamido-TRH and the inhibitory action of TRH. 3Methyl-2histidyl-TRH, TRH, vasotocin, and bombesin did not alter the polysaccharide secretion by in vitro incubated foot integument, indicating that the changes in mucus secretion after TRH and deamido-TRH administration are specific and that the gastropod "TRH receptors" may differ from the mammalian brain and anterior pituitary gland TRH receptors.

Animals↗

PubMed1984

Mating call phonotaxis in the female American toad: induction by hormones.

Gravid, female American toads are known to move toward conspecific mating calls. This behavior, as well as ovulation, often can be induced by the injection of human chorionic gonadotropin (HCG). It was found that HCG-induced phonotaxis could be terminated by the injection of indomethacin (an inhibitor of prostaglandin synthesis) and then reinstated by the injection of prostaglandin F2 alpha. A drug regimen was devised that allowed elicitation of phonotaxis, indistinguishable from that induced by HCG and in the absence of ovulation. This involved the administration of prostaglandin F2 alpha and arginine vasotocin (or mesotocin) following progesterone priming. It has not been determined whether the peptide is really essential.

Abdominal Muscles↗

PubMed1984

Correlation between cAMP in isolated frog skin epithelium and stimulation of sodium transport and osmotic water flow by antidiuretic hormone and phosphodiesterase inhibitors.

The cAMP level in isolated frog skin epithelia was stimulated by a range of concentrations of the antidiuretic hormone arginine vasotocin (AVT) and compared to active sodium transport measured as short-circuit current (SCC). The response of SCC and osmotic water flow (OWF) to AVT was investigated in a separate series. SCC was approximately three times more sensitive to AVT than OWF. Measurable increments of cAMP above the basal level were found only with AVT concentrations eliciting half-maximal response or more of SCC. Two models are offered to explain the findings: (A) Total SCC depends on epithelial cAMP with a sigmoidal relationship. (B) Epithelial cAMP exists in two separate pools of which only one is accessible to AVT, and SCC stimulation depends on cAMP in the AVT-controlled pool in a simple saturable fashion. Correlation between cAMP and SCC after stimulation with theophylline resembled that after AVT. Papaverine (10 microM) induced only small changes in SCC inspite of a substantial increase in cAMP level. Higher concentrations of papaverine inhibited both basal and AVT-stimulated SCC, while the cAMP level was further increased. This effect of papaverine may be due to a simultaneous block of another rate-determining process. Papaverine had no effect on basal or AVT-stimulated OWF despite a marked stimulation of the cAMP level. Thus, the role of cAMP as mediator of the hydroosmotic action of AVT must be questioned.

3',5'-Cyclic-AMP Phosphodiesterases↗

PubMed1984

Influence of estrogen and progesterone on the uterine sensitivity in vitro to neuropituitary hormones in the Brazilian marsupial Didelphis albiventris: comparison with lactating animals.

The influence of different neuropituitary hormones on the contraction of the Brazilian opossum uterus in vitro was studied in spayed adults injected with (i) peanut oil (ii) estrogen or (iii) estrogen plus progesterone, and in a fourth group of lactating animals. Two parameters were analyzed from the dose-response curve: pD2 and the relative contractile response compared to the maximal one induced by oxytocin. When oxytocin was administered to the bath, neither pD2 nor the contractile force was affected by any hormonal treatment or lactation. Oxytocin, however, remained in any hormonal status, the most powerful agonist to induce uterine contraction. Lysine vasopressin was the weaker agonist in any hormonal status. It binds slightly less to the isolated uterus than to the hormone-treated one. The maximal contractile force remains unchanged when the uterus is from ovariectomized or steroid-treated animals. However, after lysine vasopressin, uterus from lactating opossum develops a less intense contractility than that observed in other groups. Arginine vasopressin induces a contractile force comparable to that induced by oxytocin in any hormonal status. The affinity of this peptide for the uterine receptor is significantly lower in ovariectomized and estrogen-treated animals; after progesterone injection or in lactating animals the receptor affinity for this hormone is increased to the level of the affinity for oxytocin. Receptor affinity for arginine vasotocin is reduced in any hormonal state and brought to a level comparable to that for oxytocin only in lactating animals. On the other hand, progesterone reduced the maximal contractile force induced by this neuropeptide.(ABSTRACT TRUNCATED AT 250 WORDS)

Acetylcholine↗

PubMed1984

Adrenergic control of the anuran cutaneous hydroosmotic response.

Adrenergic effectors were shown to play a major role in increasing cutaneous water uptake (the hydroosmotic response) in dehydrated anurans. A beta-adrenergic antagonist, propranolol, blocked 61% of the cutaneous response to dehydration and 67% of the response elicited by salt loading in the toad Bufo cognatus. A beta-adrenergic agonist, isoproterenol, elicited a response in normally hydrated animals equal to the propranolol-sensitive portion of the cutaneous hydroosmotic response of dehydrated animals. The isoproterenol-induced cutaneous water balance response in hydrated animals greatly exceeded the response induced by arginine vasotocin, the endogenous antidiuretic hormone.

Animals↗

PubMed1985

Effects of prolactin, adrenocorticotrophin, neurohypophysial peptides, cortisol, and androgens on some osmoregulatory parameters of the hypophysectomized catfish, Heteropneustes fossilis (bloch).

Daily injections of ovine prolactin (PRL), cortisol acetate (FA), arginine vasotocin (AVT), and adrenocorticotrophic hormone (ACTH), at doses ranging from 0.1 to 500 mU/g, 0.2 to 25 micrograms/g, 0.01 to 0.02 micrograms/g, and 5 to 10 mU/g respectively, for 5 days elevated plasma osmolarity and plasma sodium levels in the 3-day hypophysectomized catfish, Heteropneustes fossilis maintained in tap water. PRL enhanced urine production and decreased urine osmolarity and sodium concentration. Administration of FA and AVT increased urine output as well as urine osmolarity and sodium concentration, thereby resulting in severe natriuresis. Simultaneous administration of PRL and FA to hypophysectomized catfish restored plasma osmolarity and sodium concentration to normal levels even in the presence of increased urinary salt loss. However, if the fishes were maintained in deionized water, administration of PRL and FA had no effect on plasma osmolarity or plasma sodium levels suggesting that these hormones increase plasma osmotic pressure by stimulating active uptake of salts from the external medium. Neither PRL nor AVT evoked any increase in plasma cortisol level indicating that their effects on catfish osmoregulation are not mediated through cortisol production. Isotocin, testosterone, and delta 4-androstenedione had no effect on any of the plasmatic or urinary parameters. It is concluded that prolactin, cortisol, and AVT are the principal hormones for osmoionic homeostasis in this catfish and that they act through independent mechanisms.

Adrenocorticotropic Hormone↗

PubMed1986

Cardiovascular responses to neurohormones in conscious chickens and ducks.

Cardiovascular responses (cardiac frequency, fH; mean arterial pressure, Pa; ischiatic arterial blood flow; Qi; ischiatic vascular resistance, Ri) to 1-norepinephrine (NE), acetylcholine (ACH), [Asp1, Val5]-angiotensin II (ANG II), and arginine vasotocin (AVT) were studied in conscious chickens (Gallus gallus) and Pekin ducks (Anas platyrhynchos). Age-dependent changes, in the cardiovascular variables and the responses to the native avian neurohormones, were also studied in ducks. NE injection caused larger increases in Pa and Ri, and a greater associated fall in fH, in ducks than in chickens. The pressor effect of ANG II was more persistent and developed at a slower rate than the response to NE in both species, although the pressor effect was greater in ducks. Interestingly, ANG II injection caused a tachycardia in these baroreceptor-intact birds. ACH and AVT produced similar rapid falls in Pa and a corresponding tachycardia in both species, although the fH response was greater in ducks. ANG II rapidly increased NE concentration in the arterial plasma of adult ducks, while AVT increased epinephrine (E) concentration. Resting Pa and hematocrit were lower, and fH was higher, in immature ducks. Immature ducks also were less responsive than adults to the cardiovascular actions of NE, ACH, AVT, and ANG II. The results demonstrate differences in the cardiovascular responses to neurohormones in chickens and ducks consistent with a higher level of cardioinhibitory nervous tone and a greater sensitivity to sympathetic stimuli in the aquatic species, which increase during maturation.

Acetylcholine↗

PubMed1987

Hormonal regulation of hepatic glycogenolysis in the toad, Xenopus laevis, is mediated by cyclic AMP and not Ca2+.

Hepatic glycogenolysis and glycogen phosphorylase a activity were stimulated by arginine vasotocin (AVT) in liver pieces from Xenopus laevis cultured in vitro. In each case, the EC50 was about l nM. The increased rate of glycogenolysis brought about by either AVT or adrenaline was maintained for at least 6 hr and was unchanged when Ca2+ salts were omitted from the medium or when 2.5 mM EGTA was added. Neither the Ca2+ ionophore, A23187, nor the Ca2+ channel blocker, verapamil, had any effect on the rate of glycogenolysis in the presence or the absence of either hormone. Tissue cyclic AMP levels were unchanged by addition of AVT alone but were doubled in the presence of AVT plus either of the phosphodiesterase inhibitors, isobutylmethylxanthine or RO20-1724. These findings suggest that hormones regulating hepatic glycogenolysis in X. laevis use cyclic AMP, and not Ca2+, as an intracellular messenger. We would argue that cytosolic Ca2+ may not have become involved in regulation of hepatic glycogenolysis until after the ancestors of present day amphibians separated from those of present day mammals.

Animals↗

PubMed1988

Peptidergic innervation of the adrenocorticotropic hormone (ACTH)- and growth hormone (GH)-producing cells in the pars distalis of the sea bass (Dicentrarchus labrax).

Due to its unique organization, the teleost pituitary is an ideal model in which to investigate the relationship of the nervous system with the pituitary endocrine cells. A light microscope immunocytochemical study of the sea bass pituitary revealed six different neuropeptides in nerve fibers which projected into the pituitary neurohypophysis and bordered the adenohypophysial cells. Double staining showed separate nerve fibers immunoreactive for corticotropin-releasing factor (CRF), vasotocin (VT), somatostatin (SRIF), growth hormone-releasing factor (GRF), and neurotensin (NT) in the vicinity of the adrenocorticotropic hormone-releasing cells (ACTH-cells) in the rostral pars distalis (PD). In the proximal PD cholecystokinin (CCK)-, SRIF-, GRF-, and VT-immunoreactive fibers penetrated between the growth hormone-releasing cells (GH-cells). These results suggest a possible role for CCK, GRF, SRIF, and VT in the modulation of GH-cell activity, while the synthesis and/or secretion of the ACTH-cells might be affected by the release of VT, CRF, SRIF, GRF, and NT.

Adrenocorticotropic Hormone↗

PubMed1989

Immunocytochemical demonstration of close relationships between neuropeptidergic nerve fibers and hormone-producing cell types in the adenohypophysis of the sea bass (Dicentrarchus labrax).

Light microscopic double immunocytochemical stainings, performed on sea bass hypothalamo-hypophysial sections, revealed the projection of different neuropeptide-immunoreactive neurons innervating the hormone-producing cell populations in the pituitary gland. In the rostral pars distalis (PD) the ACTH cells were found in close proximity to fibers immunoreactive for somatostatin (SRIF), growth hormone-releasing hormone (GRF), corticotropin-releasing hormone (CRF), vasotocin (VT), isotocin (IT), substance P (SP), neurotensin, and galanin (GAL), while the PRL cell zone seemed only innervated by nerve fibers immunopositive for GAL. In the proximal PD, fibers immunoreactive for SRIF, GRF, VT, IT, cholecystokinin, SP, neuropeptide Y, and GAL formed a close relationship with the growth hormone cells. The gonadotrophs were observed near nerve fibers immunostained for gonadotropin-releasing hormone, IT, and less obviously GRF and VT, while fibers positive for GRF, CRF, VT, IT, SP, and GAL penetrated between and formed a close association with the thyrotrophs. In the pars intermedia the MSH cells and the PAS-positive (PAS+) cells seemed both innervated by separate nerve fibers immunoreactive for GRF, CRF, melanin concentrating hormone, VT, IT, and SP. All these results suggest a functional role of the neuropeptides in the adenohypophysis of the sea bass, possibly in the synthesis and/or release of hypophysial hormones from the different cell types.

Animals↗

PubMed1990

The vasorelaxant effect of atrial natriuretic peptide in the frog.

The vasorelaxant effect of atrial natriuretic peptide (ANP) in two species of frogs, Rana catesbeiana and R. tigrina, were studied in vitro. Isolated arterial strips were prepared from the aortic loop, dorsal aorta, iliac, and femoral arteries in the frog. These were stimulated to contract with KCl, norepinephrine, or arginine vasotocin. When maximal contraction was attained, ANP was added to assess if it could relax the strips. Data show that ANP is vasorelaxant in these preparations. The sensitivity of these tissues depends on the contractile agents, e.g., KCl-stimulated preparations from R. catesbeiana did not respond to ANP. Data also suggest that ANP action elicited in the frog vascular tissue is due to an inhibitory effect on the mobilization of the intracellular calcium store and/or calcium influx from extracellular space to initiate contraction.

Animals↗

PubMed1990

Neurohypophysial hormones and cardiac activity in the frog, Rana tigrina, and in the snake, Ptyas mucosa.

The cardiac effects of neurohypophysial hormones (NH) in the frog, Rana tigrina, and in the snake, Ptyas mucosa, were studied in isolated atrial preparations. Arginine vasopressin (AVP), vasotocin (AVT), isotocin (ISN), mesotocin (MSN), and oxytocin (OXY) produced dose-related positive chronotropic and inotropic responses in the frog atria. AVT was the most potent. In the snake, AVP, AVT, MSN, and OXY produced dose-related positive inotropic but not chronotropic changes. OXY was the most potent. Data indicate that there is a direct action of NH on the heart in both animals, the atrial rate and tension responses to NH are not coupled, and judging by the efficacy, AVT and OXY might be the natural NH in the frog and snake, respectively, which may account for the high concentrations required of other NH to be cardiac stimulating.

Animals↗

PubMed1990

Neurohypophysial hormones and steroidogenesis in the interrenals of Xenopus laevis.

The influence of arginine vasotocin (AVT) on the interrenal secretion of the clawed toad (Xenopus laevis) was studied combining in vivo and in vitro experiments. In vivo: A single injection of 3 nmol AVT per 100 g body weight was given, and the concentrations of corticosterone and aldosterone in the serum were measured after 1, 3, 6, 12, and 24 hr. The serum levels of both steroids remained elevated over 6 hr and declined to normal levels within 12 hr. The increase of the aldosterone concentration was relatively stronger than that of corticosterone. In vitro: A perifusion system was used to study the influence of AVT concentrations ranging from 0.1 to 50 nM on the secretion rates of corticosterone and aldosterone. The response of the interrenals was dose dependent; corresponding to the in vivo results, the elevation rate was higher for aldosterone than for corticosterone. The effects of several nonapeptides were compared. AVT was most effective, followed by mesotocin and arginine vasopressin (AVP). Isotocin and oxytocin had less effect. The selective agonist of the mammalian V2 receptor (1-deamino-8-D-arginine)-vasopressin (DDAVP) did not stimulate the interrenals, while the V1 receptor-selective antagonist ((1-beta-mercapto-beta,beta-cyclopentamethylene propionic acid)-2-(O-methyl)-tyrosine)-AVP could not diminish the stimulation by AVT. Thus, the AVT receptor of the amphibian interrenal must be a special one and is different from the V1 and V2 types of mammals. In a comparison of the effects of AVT with other stimulators such as ACTH(1-28) or urotensin II, it was found that the sensitivity of the interrenals to AVT was similar to that of these peptides. The results indicate that AVT plays an important role in the osmomineral regulation of Xenopus laevis by acting on the corticosteroid secretion of the interrenals.

Adrenocorticotropic Hormone↗

PubMed1991

Interaction of atrial natriuretic factor and osmoregulatory hormones in the Pekin duck.

This study examined the influence of plasma atrial natriuretic factor (ANF) on the osmoregulatory hormones arginine vasotocin (AVT), angiotensin II (AII), aldosterone, and corticosterone in the blood of conscious Pekin ducks. Synthetic chicken ANF was iv infused at a nonhypotensive, natriuretic, and diuretic dose of 100 ng.kg-1.min-1 in normally hydrated ducks and birds in which the circulating levels of AVT, AII, aldosterone, and corticosterone were elevated by 24-hr dehydration. In normally hydrated animals the effect of ANF was limited to a reduction (P less than 0.05) in the basal concentration of aldosterone; in dehydrated birds both AII and aldosterone levels were reduced (P less than 0.05). ANF infusion was consistently without effect on plasma AVT or corticosterone concentrations. The iv infusions of AII with or without simultaneous infusion of ANF showed that ANF inhibited (P less than 0.05) the aldosterone response to AII. Autoradiographic and membrane binding techniques indicated that there were both AII and ANF receptors in the subcapsular zone of the duck adrenal gland and that ANF had no affinity for the AII binding sites. The results demonstrate that ANF is capable of modulating the duck angiotensin-aldosterone system and suggest a role for this peptide in avian salt and fluid homeostasis.

Aldosterone↗