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At least 253 records · Page 14Linked to original sources

PubMed1988

Effects of arginine vasotocin on water balance of three leiopelmatid frogs.

The effects of arginine vasotocin (AVT) on water movements in three frogs of the anatomically primitive genus Leiopelma were compared in vivo and in vitro. Treatment with AVT in vivo (7 x 10(-13) mol/g body weight) led to significant water retention in the terrestrial species L. archeyi and L. hamiltoni, but not in the semiaquatic species L. hochstetteri. All three species showed increasing water retention over some part of the dose range 7 x 10(-15)-7 x 10(-11) mol/g. Isolated pelvic skin from L. archeyi and L. hamiltoni increased in osmotic water flow (OWF) in response to AVT, whereas that from L. hochstetteri did not. Dorsal skin from all three species, as well as pectoral skin from L. archeyi and L. hochstetteri, showed no hydroosmotic response to AVT. Isolated bladders of all species are small and showed small increases in OWF in response to AVT. Glomerular filtration rate in vivo was reduced significantly by AVT in L. archeyi and L. hamiltoni, but not in L. hochstetteri. These results show that water balance responses to AVT among the three species are correlated with habitat, and indicate that the absence of a cutaneous hydroosmotic response in L. hochstetteri is not a characteristic, primitive feature of the entire genus.

Animals↗

PubMed1989

Increased levels of arginine vasotocin and neurophysin during nesting in sea turtles.

Arginine vasotocin (AVT) and neurophysin (NP) levels were measured by radioimmunoassay in two species of sea turtle, the olive ridley, Lepidochelys olivacea, and the loggerhead, Caretta caretta, during the brief period of nesting and oviposition. In both species, AVT was low in animals which were not reproductively active. AVT was also low at the time animals emerged from the surf to nest, but increased significantly during oviposition and then declined as the animals returned to the water. NP increased in concert with AVT, also reaching highest levels during oviposition. In both species, however, NP levels remained elevated over prenesting levels at the time of return to the water. These findings are consistent with the hypothesis that an AVT-neurophysin complex is released from the neurohypophysis during nesting, and that AVT is a physiological regulator of oviducal contractions in sea turtles.

Animals↗

PubMed1989

Control of plasma arginine vasotocin in Kelp gulls (Larus dominicanus): roles of osmolality, volume, and plasma angiotensin II.

The physiological roles of plasma osmolality, volume, and angiotensin II (AII) in the control of plasma arginine vasotocin (AVT) have been evaluated in the Kelp gull. Plasma AVT (measured by radioimmunoassay) consistently followed the changes in plasma osmolality induced by dehydration, intravenous (iv) infusion of hypertonic saline, or iv infusion of hypotonic glucose solution. Osmoreceptor control of AVT was further characterized by the stimulatory effect of iv hypertonic mannitol but lack of effect of iv hypertonic urea. A direct volume effect on AVT release was demonstrated during hemorrhage, but blood volume reductions in excess of 10% were required. However, the volume of the extracellular fluid (ECF) compartment does have an important role in modulating the osmotic release of AVT in a way that enables contraction or expansion of ECF to be more expeditiously corrected than would occur if osmoreceptors alone regulated plasma AVT. Any physiological role of plasma AII in the control of plasma AVT is doubtful because after the iv infusion of AII for 60 min at 10, 25, 50, and 100 ng.min-1, only the two highest doses of AII, which produced supraphysiological plasma AII levels, caused elevations of plasma AVT. In addition, the osmotic reactivity of AVT release was not altered by exogenous administration of AII.

Angiotensin II↗

PubMed1990

Immunohistochemical localization of corticotropin-releasing factor- and arginine vasotocin-like immunoreactivities in the brain and pituitary of the American bullfrog (Rana catesbeiana) during development and metamorphosis.

Immunoperoxidase staining for corticotropin-releasing factor (CRF) in the median eminence was sparce or absent from premetamorphic tadpoles, but increased dramatically by late prometamorphosis. Quantitative photometry revealed that CRF-like immunostaining material in the median eminence was most dense in metamorphic climax tadpoles. Arginine vasotocin (AVT)-like immunostaining material was visualized in perikarya of the magnocellular nucleus, with extensive fiber staining seen in the medial basal and infundibular hypothalamus as well as in the median eminence and pars nervosa of the pituitary. AVT-like immunoreactive perikarya were virtually absent in premetamorphic tadpoles, but their number increased greatly by Taylor-Kollros stage XII and continued to increase after this stage. Quantitative photometry revealed that AVT-like immunoreactivity in the pars nervosa increased greatly at Taylor-Kollros stage XII and remained intense after this stage. AVT-like immunoreactivity did not appear in the median eminence until Taylor-Kollros stage XVI. Localization of AVT-like immunoperoxidase staining around portal vessels in the median eminence suggests an anatomical mechanism for delivery of AVT to anterior pituitary corticotropes. These results indicate that both CRF and vasotocinergic neuronal systems develop just before the activation of interrenal steroidogenesis which occurs during the later stages of metamorphosis in this species.

Adrenocorticotropic Hormone↗

PubMed1990

Arginine vasotocin and mesotocin levels in theca and granulosa layers of the ovary during the oviposition cycle in hens (Gallus domesticus).

Neurohypophysial hormones in mammals are synthesized by the ovary and may influence reproductive function. Although arginine vasotocin (AVT) can induce premature oviposition in chickens, the gonadal content of AVT or mesotocin (MT) has not been examined in this species. Ovarian follicles were removed 2 hr before oviposition (-2 hr), immediately after oviposition (0 hr), and 5 hr after oviposition (+5 hr). The theca and granulosa layers of the three largest preovulatory and postovulatory follicles were isolated, extracted, and assayed for immunoreactive AVT and MT. AVT content in the theca and granulosa layers was lowest at -2 hr and increased to maximum levels at +5 hr. Pre- and postovulatory follices contained similar amounts of AVT. Maximum AVT levels in the theca and granulosa layers were 2.5 +/- 0.6 and 1.3 +/- 0.2 ng/tissue, respectively. In contrast, theca content of MT was maximal at 0 hr and the highest peptide levels were observed in the largest preovulatory follicle (0.24 +/- 0.02 ng/tissue). The results demonstrate that, compared with circulating levels of the hormones, the ovary of the chicken contains high concentrations of AVT and MT. The ovarian content of AVT and MT varies in a different manner in relation to the oviposition cycle.

Animals↗

PubMed1990

Effect of pharmacological adrenalectomy on corticotropin-releasing factor-like and arginine vasotocin immunoreactivities in the brain and pituitary of the eel: immunocytochemical study.

Metopirone, a blocker of the 11 beta-hydroxylase, was used to suppress cortisol synthesis in the eel, producing a pharmacological adrenalectomy. After 1 and 2 days, corticotropin-releasing factor (CRF) immunoreactivity was reduced in the preoptic nucleus (PON) and was increased in the rostral neurohypophysis (NH) where CRF fibers ended in close proximity to ACTH cells. After 4 days, immunoreactive (ir) CRF increased in the PON or was similar to that of controls, and was reduced in the rostral NH. It was not affected in the caudal NH among intermediate lobe (IL) ramifications. Arginine vasotocin (AVT) immunostaining was often slightly increased in the PON, but changes were not apparent in the pituitary and AVT-ir fibers remained very scarce in the rostral NH. Metopirone significantly increased the cross-sectional area of CRF- and AVT-ir perikarya in the parvocellular region and the number of these perikarya as well as the ratio of CRF to AVT cell bodies in the totality of the PON. Colocalization of CRF and AVT, barely detected in control eels, occurred in 9.6% of CRF perikarya after 1-2 days, but in only 2.4% after 4 days. ACTH cells were rapidly and markedly stimulated. These immunocytochemical studies suggest that CRF synthesis, axonal transport, and release are increased in metopirone-treated eels, acting on the pituitary to stimulate ACTH release and interrenal cell activity. The participation of AVT in ACTH cell stimulation is less clear. These data are compared to those reported in mammals.

Adrenal Glands↗

PubMed1990

Antagonism of responses to arginine vasotocin by its structural analogs in the bullfrog, Rana catesbeiana.

Antagonism of arginine vasotocin (AVT) actions in vivo by synthetic AVT analogs was studied in bullfrogs. In addition, one analog was examined for its in vitro effect on water flux in the urinary bladder and on vascular contraction in a dorsal aortic preparation. AVT and its analogs were injected into conscious bullfrogs while blood pressure and urine flow rate were recorded simultaneously. d(CH2)5Tyr(Me)AVT induced a slight, but not statistically significant, antidiuresis and a clear vasopressor response. d(CH2)5Tyr(Et)OVT and d(Et2)Tyr(Et)OVT did not show any intrinsic effects. These analogs partially blocked the antidiuretic effects of AVT and completely blocked the pressor effects of AVT. In studies in vitro, 1 microM d(Et2)Tyr(Et)OVT antagonized AVT-stimulated water flux, whereas 10 nM competitively inhibited (by about 50%) the vasocontraction induced by AVT. These results suggest that d(Et2)Tyr(Et)OVT has no intrinsic activity but retains a relatively high receptor affinity, thereby producing effective antagonism of AVT in target cells of vascular smooth muscle. On the other hand, this antagonist showed no detectable intrinsic activity and appeared to be a weaker antagonist in target cells of the urinary bladder. This suggests that there might be two types of AVT receptors in bullfrogs.

Animals↗

PubMed1991

In vitro effects of arginine vasotocin on testosterone production by testes of rainbow trout (Oncorhynchus mykiss).

The objective of this study was to investigate the effect of arginine vasotocin (AVT) on testosterone (T2) production by the rainbow trout testis in culture. AVT increased T2 production in a dose-dependent manner in immature testes. The maximum response (10 nM AVT) increased T2 production 6-fold over basal (3-6 pg/mg tissue protein). Mature testes did not respond to AVT. Salmon gonadotropin (2.5 nM sGtH, SGA-GtH) stimulated T2 production by both juvenile (5-fold) and mature (11-fold) testes. When AVT (100 nM) was added in addition to salmon gonadotropin (sGtH; from 0.1 to 100 nM), AVT had a stimulatory effect at the submaximal doses of sGtH, but T2 production did not exceed the maximum level obtained with sGtH (100 nM) alone. Isotocin also increased T2 production although to a lesser degree than AVT. The maximum response at 10 nM increased T2 production 4-fold over basal. beta-Endorphin had no effect on T2 production.

Animals↗

PubMed1991

Arginine vasotocin (AVT) and AVT-related peptide are major aldosterone-releasing factors in the bullfrog neurointermediate lobe.

Two major components which stimulate aldosterone release from Xenopus adrenocortical tissue were isolated from an acid-acetone extract of the neurointermediate lobes of the bullfrog (Rana catesbeiana) using C18 Sep-Pak cartridges, Sephadex G-50, and reverse-phase HPLC columns. One of the components was identified as arginine vasotocin (AVT) from its HPLC profile and amino acid sequence analysis. The other was an AVT-like decapeptide with an extra glycine residue at the C-terminus of nonamidated AVT, which was recently termed hydrin 2. The yields of these two peptides were almost the same. They also showed equipotent activity in stimulating water flux from the isolated urinary bladder of the toad (Bufo japonicus).

Aldosterone↗

PubMed1991

Pituitary and plasma arginine vasotocin levels in teleost fish.

The role of arginine vasotocin (AVT) in teleostean osmoregulation is unclear. Its administration may produce dose-dependent effects on renal fluid loss though the physiological significance of such effects is unknown due to the paucity of data on the normal range in pituitary and plasma AVT levels. The present study addresses these questions by examining the pituitary AVT activity in the flounder and plasma AVT concentrations in the flounder, trout, and carp following alterations in environmental tonicity. Flounder pituitary AVT content, measured by bioassay, was elevated in freshwater (FW)-acclimated compared to seawater (SW)-acclimated fish and rapidly fell or rose, respectively, following transfer from FW to SW or from SW to FW to attain a new steady state. Plasma levels of AVT were higher in FW than in SW in both flounder and trout and it would, therefore, appear that the synthesis, storage, and secretion of AVT may be enhanced in FW. In the stenohaline carp plasma levels of AVT were unchanged on acclimation from FW to 40% SW. In SW flounder there was a significant positive correlation between plasma osmolality and plasma AVT concentration. Such a relationship was not apparent in FW fish, which may reflect differing roles for the hormone in these two extremes of osmotic environment.

Animals↗

PubMed1991

Changes in arginine vasotocin content in the pituitary of the Medaka (Oryzias latipes) during osmotic stress.

Changes in the arginine vasotocin (AVT) neurons of the medaka, Oryzias latipes, during osmotic stress were studied by means of immunohistochemistry and radioimmunoassay. AVT neurons were identified by their immunoreactivity to anti-arginine vasopressin serum, which crossreacts with AVT. When freshwater (FW)-adapted fish were transferred to seawater (SW), the number of immunoreactive magnocellular neurons decreased, while the cell nuclear size increased. AVT content in the pituitary significantly decreased 2 hr or 1 day after transfer to SW, but returned to approximately the initial level 1 week after transfer. However, when SW-adapted fish were transferred to FW, the number of immunoreactive magnocellular neurons increased from 1 hr after readaptation to FW, but the cell nuclear size failed to show significant changes. AVT content in the pituitary significantly increased 1 or 2 hr after transfer. These results seem to indicate that AVT secretion in the medaka was temporarily accelerated by exposure to SW and inhibited immediately after transfer to FW.

Adaptation, Physiological↗

PubMed1991

Inositol phosphate formation in uterine tissue from two species of reptiles is stimulated by arginine vasotocin and influenced by stage of reproduction.

Phosphoinositide hydrolysis, resulting in inositol trisphosphate (IP3) and diacylglycerol (DG) formation, has been implicated in oxytocin-stimulated pulsatile secretion of prostaglandin F2 alpha (PGF2 alpha) from uterine endometrium of sheep and other mammals. In reptiles, arginine vasotocin (AVT) stimulates uterine secretion of PGF2 alpha. These studies investigated the ability of AVT to stimulate incorporation of [3H]inositol into inositol mono-, bis-, and trisphosphates in two reptilian species. In Experiment 1, AVT stimulated (P less than 0.01) IP formation in uterine from late-gravid (150 to 291%) and postpartum (104 to 363%) Yarrow's spiny lizards (Sceloporus jarrovi). Inositol phosphate formation, in response to AVT, was greater (P less than 0.01 for IP3 and P less than 0.05 for total IP) for gravid (stage 40 embryos) and postpartum (1-2 days) lizards near the time of parturition than for lizards at other stages (stage 38-39 embryos or 7 days postpartum). Inositol phosphate formation was greater (P less than 0.05) in uterine tissue from gravid than from postpartum lizards. In Experiment 2, basal IP formation and the response to AVT were the greatest (P less than 0.01) in endometrium from late-gravid American alligators (Alligator mississippiensis). AVT stimulated (P less than 0.02) IP synthesis in uterine endometrium from vitellogenic (136 to 394%), early-gravid (7 to 270%), late-gravid (315 to 1002%), postpartum (86 to 313%), and nonreproductive (292 to 322%) alligators. Results indicate that (1) AVT stimulates IP formation in the uterus of reptiles; (2) uterine IP formation increases in late-gravid reptiles; and (3) increased responsiveness to AVT may occur at parturition or oviposition.

Animals↗

PubMed1991

Plasma arginine vasotocin, progesterone, and luteal development during pregnancy in the viviparous lizard Tiliqua rugosa.

The relationship between plasma levels of arginine vasotocin (AVT), progesterone, and corpus luteum formation and degeneration was studied in the viviparous lizard Tiliqua rugosa. Hormone levels were monitored in free-ranging, pregnant females which were located for sampling by means of attached radio transmitters. There was an increase in plasma AVT levels in the 30 days immediately prior to parturition. Concurrent with this event was a decline in plasma progesterone levels from relatively high levels in mid-term to basal levels prior to parturition. This is associated with degenerative changes in the corpus luteum which include pyknosis of the nuclei of the cells of the cell mass and increasing prevalence of intercellular spaces, while the thecal layer became increasingly compacted. Ovariectomy experiments indicate that the major source of progesterone during pregnancy in T. rugosa is ovarian.

Animals↗

PubMed1992

Effects of arachidonic acid, prostaglandin F2 alpha, prostaglandin E2, and arginine vasotocin on induction of birth in vivo and in vitro in a viviparous lizard (Sceloporus jarrovi).

The ability of arachidonic acid (AA) and prostaglandins of the two series to induce parturition in vivo and oviducal contraction in vitro was studied in the viviparous lizard Sceloporus jarrovi. Injection of PGF2 alpha, PGE2, or AA during late pregnancy stimulated parturition within 2 hr in a threshold-dependent fashion. In contrast, during mid pregnancy, females did not respond. Surgically removed and cultured oviducts from females in late pregnancy gave "birth" in response to AA, PGF2 alpha, and PGE2. Oviducts from S. jarrovi in mid pregnancy responded to PGF2 alpha but not to AA. Addition of arginine vasotocin, a potent stimulator of PG synthesis, either alone or with AA to oviduct cultures stimulated rapid and complete birth in vitro from oviducts obtained from late, but not mid pregnant, females. Stage of pregnancy mediates the response of the lizard oviduct to prostaglandin stimulation.

Analysis of Variance↗

PubMed1992

Effect of breeding state, moulting, dehydration, exposure to saturated atmosphere, and arginine vasotocin on cutaneous water permeability in the toad Bufo bufo.

Cutaneous water permeability was assessed in hydrated male toads under a variety of conditions, including dehydration and rehydration, and the effects of exogenous arginine vasotocin (AVT) were determined. Cutaneous water permeability (the rate of water uptake by toads in water) was high in toads collected in the breeding pond and declined steeply during the first week, coincident with reduced activity of the cutaneous mucus glands. The slopes of the dose-response curves relating AVT to cutaneous water influx were about the same at the transition from the breeding to the nonbreeding state, but the level of influx was higher in the breeding state. The dose-response relationship in long-term terrestrial-acclimated toads was similar to that in water-acclimated toads. The threshold dose for effect on the cutaneous water permeability was about 1 ng AVT. Dehydration had a substantially greater effect on the cutaneous water permeability than AVT. The ratio between dehydration and AVT responses tended to increase with increasing water transport capacity of the skin. Moulting and acclimation to a saturated atmosphere in fully hydrated toads more than doubled the water permeability and abolished the response to AVT. It is suggested that AVT and other factors increase the cutaneous water permeability by similar mechanisms, such as insertion of water channels in the apical membrane of the epidermal cells. The effect of AVT on the toad skin is interpreted as reflecting the general high potency of neurohypophysial hormones in stimulating the water permeability of membranes of variable permeability.

Acclimatization↗

PubMed1992

In vivo studies on the effects of ovine corticotrophin-releasing hormone, arginine vasotocin, arginine vasopressin, and haloperidol on adrenocortical function in the racing pigeon (Columba livia domestica).

This study investigates the effects of in vivo administration of pituitary stimulants in racing pigeons (Columba livia domestica). Plasma corticosterone concentrations were measured following intravenous administration of ovine corticotrophin-releasing hormone (oCRH) (0.1, 1, 10, and 100 micrograms/kg), arginine vasopressin (AVP) (0.01, 0.1, 1, and 10 micrograms/kg), arginine vasotocin (AVT) (0.01, 0.1, 1, and 5 micrograms/kg), and haloperidol (0.05, 0.5, and 5 micrograms/kg). Compared with mammals the pituitary-adrenocortical system of the pigeon appeared to be less sensitive to stimulation with oCRH, although high doses were well tolerated and gave a clear response. Both AVP and AVT stimulated corticosterone secretion, AVT in a more pronounced dose-dependent manner than AVP. The natural neurohypophysial peptide in birds, AVT, was less well tolerated in high doses than AVP. The clear response to haloperidol indicates that the hypothalamo-pituitary-adrenocortical system is under dopaminergic inhibition. Of the pituitary stimulants tested AVP (10 micrograms/kg) and oCRH (100 micrograms/kg) are the most appropriate for testing the integrity of the pituitary-adrenocortical system in the pigeon.

Adrenal Cortex↗

PubMed1986

Correlation between immunoreactive vasotocin in optic tectum and seasonal changes in reproductive behaviors of male rough-skinned newts.

Previous studies have shown that intracranial administration of the amphibian neuropeptide arginine vasotocin (AVT) to male rough-skinned newts (Taricha granulosa) can stimulate masculine sexual behaviors. The present study was conducted to determine whether concentrations of endogenous AVT in specific brain areas are correlated with seasonal changes in sexual behavior. Immunoreactive (ir) AVT was measured in the dorsal preoptic area and in the optic tectum throughout the course of the reproductive cycle. In the optic tectum, irAVT levels were low throughout the summer, fall, and winter, but rose over fivefold in the spring when sexual behaviors are most prevalent in male newts. In contrast, irAVT levels in the dorsal preoptic area were high in the summer, but declined in the fall and fluctuated widely during the winter and spring. Thus, there are site-specific changes in irAVT concentrations in the brain of male newts during the seasonal reproductive cycle. The finding that irAVT concentrations in the optic tectum are seasonally correlated with newt sexual behaviors provides further evidence that AVT in this brain area may be important in the expression of sexual behavior.

Animals↗

PubMed1988

Brain arginine vasotocin concentrations related to sexual behaviors and hydromineral balance in an amphibian.

Arginine vasotocin (AVT), a potent stimulator of sexual behaviors and regulator of hydromineral balance in male rough-skinned newts (Taricha granulosa), was measured in 11 brain areas using microdissection and radioimmunoassay procedures. A 60-min test for sexual behaviors was used to segregate males into two groups: sexually responsive (initiated amplectic clasping behaviors) and sexually unresponsive (exhibited no sexual behaviors). Compared to sexually unresponsive males, sexually responsive males had significantly higher concentrations of immunoreactive (ir) AVT in the dorsal preoptic area, optic tectum, ventral infundibular nucleus, and cerebrospinal fluid. These results provide evidence for a behavioral action of endogenous AVT in T. granulosa. In another study, irAVT was measured in normal males (control newts maintained in water) and males that were dehydrated for 6 hr. Compared to normal males, dehydrated males had significantly lower concentrations of irAVT in the ventral preoptic area, but not in the other 10 areas of the brain. That different brain areas are associated with sexual behaviors and hydromineral balance suggests that there are some neuroanatomical separations between the behavioral and hydromineral aspects of the vasotocinergic system in this amphibian.

Animals↗