Changes in plasma concentrations of arginine vasotocin after intrauterine injections of prostaglandin F-2 alpha and acetylcholine at various times during the oviposition cycle of the domestic hen (Gallus domesticus)

Prostaglandin F-2 alpha (PGF-2 alpha, 1 microgram) and acetylcholine (10 mg) were injected into the uterus of chickens 23, 21, 16, 8 or 4 h before expected oviposition. Plasma concentrations of immunoreactive arginine vasotocin and PGF were measured in relation to the time of administration of PGF-2 alpha or acetylcholine or to the premature oviposition that was induced. PGF-2 alpha or acetylcholine administration caused premature oviposition and a marked increase in plasma arginine vasotocin levels only when an egg was present in the uterus. Changes in plasma PGF concentrations were not observed. After premature oviposition was induced, plasma values of PGF and arginine vasotocin increased at the expected time of oviposition. Manual stimulation of the uterus 4 h after oviposition also stimulated arginine vasotocin release. During spontaneous oviposition, a rise in plasma PGF concentration preceded increases in uterine contractility and plasma arginine vasotocin concentration. These results suggest that PGF may stimulate uterine contractility which in turn causes the release of arginine vasotocin to provide an additional contractile stimulus during oviposition.     

Contractions of amphibian Wolffian duct in response to acetylcholine, norepinephrine, and arginine vasotocin

The regulation of sperm transport through the Wolffian duct of male amphibians is poorly understood. These experiments were conducted using rough-skinned newts (Taricha granulosa) to determine if Wolffian ducts are capable of contracting in vitro and, if so, to characterize the contractile responses to acetylcholine (ACh), norepinephrine (NE), and neurohypophysial hormones. Dose-response curves for NE and ACh, which were prepared by measuring isometric contractions, are similar to those reported for mammalian vas deferens. For NE, the minimum effective dose and ED50 were found to be 1 X 10(-5)M and 4.17 X 10(-5)M, respectively. For ACh, the minimum effective dose was 3.2 X 10(-8)M and the ED50 was 1.37 X 10(-5)M. Alpha-adrenoreceptors appear to mediate the contractile responses to NE because phentolamine (10(-5)M) blocked or attenuated the response to NE (10(-6)M, 10(-5)M or 10(-4) M). Beta-adrenoreceptors appear to mediate relaxation because dichloroisoproterenol (10(-5)M) enhanced the response to 10(-5)M NE. The contractile response to three neurohypophysial hormones were also investigated. Arginine vasotocin was more effective in eliciting contractions than oxytocin. The effect of lysine vasopressin was intermediate between arginine vasotocin and oxytocin. These experiments demonstrate that amphibian (Taricha) Wolffian ducts contract in vitro in response to neurotransmitters and neurohypophysial hormones. The contractile response to neurotransmitters occurs in a dose-dependent manner; the response to neurohypophysial hormones is hormone specific.     

Osmoregulatory Functions of Neurohypophysial Hormones in Fishes and Amphibians

The renal effects of neurohypophysial hormones in fishes andamphibians are discussed. Injections of arginine vasotocin (AVT)elicit diuresis in fishes, but antidiuresis in amphibians. However,the physiological significance of these hormonal responses remainsto be demonstrated. Studies with bioassays and radio-immunoassayson circulating levels of AVT indicate that hypovolemia may bea very potent stimulus for the release of the hormone. Hyperosmoticstimuli may not be as important. In anurans, mesotocin has aglomerular diuretic effect. This neurohypophysial hormone appearsto dilate, while AVT constricts, the afferent glomerular circulationin bullfrogs, Rana catesbeiana.     

Molecular evolution of the neurohypophysial hormones: The active peptides of a primitive bony fish Polypterus bichir

Neurohypophysial hormones have been so far identified in Neopterygii and Crossopterygii but not in species of the bird sub-class of bony fishes, the Palaeopterygii. Isolation and chemical characterization of the active principles of a primitive bony fish, Polypterus bichir, have been performed. Isotocin (Ser(4)-Ile(8)-oxytocin) and arginine vasotocin (Arg(8)-oxytocin) have been identified. Because the same peptides were found in the recent Neopterygii, it can be deduced that neurohypophysial hormones have displayed a peculiar stability in the course of the evolution of bony fishes. However isotocin and vasotocin are replaced by oxytocin and vasopressins in mammals and therefore might be regarded as "old" molecules.     

Sequence and organization of coelacanth neurohypophysial hormone genes: Evolutionary history of the vertebrate neurohypophysial hormone gene locus

Background  

The mammalian neurohypophysial hormones, vasopressin and oxytocin are involved in osmoregulation and uterine smooth muscle contraction respectively. All jawed vertebrates contain at least one homolog each of vasopressin and oxytocin whereas jawless vertebrates contain a single neurohypophysial hormone called vasotocin. The vasopressin homolog in non-mammalian vertebrates is vasotocin; and the oxytocin homolog is mesotocin in non-eutherian tetrapods, mesotocin and [Phe²]mesotocin in lungfishes, and isotocin in ray-finned fishes. The genes encoding vasopressin and oxytocin genes are closely linked in the human and rodent genomes in a tail-to-tail orientation. In contrast, their pufferfish homologs (vasotocin and isotocin) are located on the same strand of DNA with isotocin gene located upstream of vasotocin gene separated by five genes, suggesting that this locus has experienced rearrangements in either mammalian or ray-finned fish lineage, or in both lineages. The coelacanths occupy a unique phylogenetic position close to the divergence of the mammalian and ray-finned fish lineages.     

Neurohypophysial hormones and renal function in fish and mammals

The two major basic neurohypophysial peptides, arginine vasopressin (AVP) of mammals and arginine vasotocin (AVT) of all non-mammalian vertebrates, share common structure and major roles in regulating renal function. In this review the complexity of AVP actions within the mammalian kidney is discussed and comparisons are made with the emerging picture of AVT's renal effects in fish. It has become apparent that the antidiuretic action of the neurohypophysial hormones is an ancient phylogenetic phenomenon, although this is based upon reduced glomerular filtration in fish by comparison with predominant tubular effects in mammals. Nonetheless, there appears to be retention of AVP effects upon the functional heterogeneity of nephron populations in mammals. Preliminary evidence for the possible existence of V(2)-type (tubular) neurohypophysial hormone receptors in fish, implies possible AVT actions which parallel those in mammals on tubular ion transport. Further insight from recent mammalian tubule microperfusion studies suggests that in teleost fish both apical (tubular lumen) and basolateral (blood borne) AVT have the potential to modulate renal function, though this remains to be examined.     

Direct regulation of rat testicular steroidogenesis by neurohypophysial hormones. Divergent effects on androgen and progestin biosynthesis

The direct regulation of testis androgen and progestin biosynthesis by neurohypophysial hormones was investigated in a primary culture of rat testis cells. Treatment with arginine vasotocin (AVT; 10(-6) M) over a 10-day period inhibited the human chorionic gonadotropin (hCG)-stimulated testosterone accumulation while enhancing hCG-stimulated progesterone accumulation. Furthermore, treatment with increasing doses (10(-11) - 10(-6) M) of AVT by itself led to dose-dependent increases in the accumulation of pregnenolone (ED50: 8.0 +/- 0.2 X 10(-9) M) and progesterone (ED50: 1.6 +/- 0.3 X 10(-8) M) but not testosterone. Under blockade of pregnenolone metabolism using cyanoketone and spironolactone, AVT, like hCG, stimulated pregnenolone accumulation with an ED50 dose of 5.8 +/- 0.3 X 10(-9) M. Similar effects were observed with several related neurohypophysial hormones, but not with nine unrelated peptides. AVT, arginine vasopressin, and lysine vasopressin were about 100-fold more potent than mesotocin, valitocin, and oxytocin. Pressor (but not antidiuretic or oxytocic)-selective agonists of the neurohypophysial hormones also exerted dose-dependent stimulation of pregnenolone accumulation. Potent pressor (but not oxytocic)-selective antagonistic analogs of the neurohypophysial hormones prevented the AVT-stimulated accumulation of pregnenolone. Thus, the neurohypophysial hormones may exert a direct stimulatory effect on testis pregnenolone and progesterone biosynthesis via putative, pressor-selective recognition sites, and this progestin-stimulatory activity may be partly due to stimulation of steroidogenic steps preceding pregnenolone formation. Since the effective doses of neurohypophysial hormones in vitro are higher than the serum hormone levels, the present results suggest an intratesticular paracrine role for these peptides.     

Neurohypophysial hormones of the 1-month-old bovine fetus: absence of vasotocin during mammal development

The neurohypophysial hormones of the 1-month-old bovine fetus have been identified by their positions in ion-exchange chromatography and their retention times in high-pressure reverse-phase partition chromatography. Arginine vasopressin and oxytocin have been recognized. The molar ratio vasopressin/oxytocin in neurohypophysis is about 6 in the 1-month-old fetus compared with 4 in the 3-month-old fetus, 2.7 in the 7-month-old fetus and 1 in the adult. Vasotocin is virtually absent even in the early fetus (less than 0.1% of arginine vasopressin). The occurrence of a vasotocin gene expressed in the fetus but silent in the adult appears unlikely.     

Phylogeny of neurohypophyseal hormones in birds: microidentification of mesotocin and vasotocin in the ostrich (Struthio camelus)

Ostrich (Struthio camelus) neurohypophysial hormones have been isolated from 5 freeze-dried posterior pituitary glands. Purification has involved three steps: a first molecular sieving on Sephadex G-75 for eliminating proteins, a second molecular sieving on Bio-Gel P4 for separating the two active principles and a high pressure reverse-phase liquid chromatography (HPLC) on Nova-Pak C 18 with an 10 mM acetate-acetonitrile gradient for isolating each hormone. The active peptides have been identified by their retention time in HPLC and their amino acid composition. Mesotocin and vasotocin have thus been characterized. Although the phylogeny of Ratites is disputed, in particular their possible common origin with Carinates, which include most of the living birds, species of the first sub-class seem to have the same neurohypophysial hormones as those of the second.     

Divergent neuropeptide evolutionary drifts between American and Australian marsupials

Present-day marsupials, which are supposed to have arisen from a single stem diverging from the placental stem some 130 million years ago, exist only in the American and Australian continents. Comparison of the homologous genes and their protein products, which evolved under different environmental conditions, may provide arguments for either selective or neutral evolution. In contrast to Australian Macropodidae, which have pecuIiar neurohypophysial peptides, namely mesotocin and two pressor peptides, lysine vasopressin and phenypressin, the South American oppossum,Didelpbis marsupialis, has oxytocin, lysine vasopressin, and arginine vasopressin. Because placental mammals have oxytocin and usually arginine vasopressin, and nonmammalian tetrapods have mesotocin and arginine vasotocin, it is assumed that (1) selective change of arginine vasotocin into arginine vasopressin occurred in mammalian ancestors and a subsequent gene duplication in the marsupial line gave rise to two pressor peptides with divergent neutral drifts in American and Australian groups, and (2) mesotocin of nonmammalian tetrapods has been preserved in Australian marsupials and reclaimed for milk-ejecting function whereas it has been converted into oxytocin in South American oppossums. The change of mesotocin into oxytocin seems neutral rather than selective.     

Effect of estrogen and its antagonist on the expression of arginine vasotocin (AVT) and its oxytocic-like receptor VT3 in the shell gland of Japanese quail, Coturnix coturnix japonica

Avian neurohypophysial hormone arginine vasotocin (AVT) is known to regulate shell gland contractility during oviposition. While studying the role of estrogen in the expression and regulation of AVT and its oxytocic-like receptor VT3, using in situ hybridization and immunohistochemistry, it was observed that the expression of AVT and its receptor was not detected in the shell gland of sexually immature Japanese quail. However, administration of estrogen to these birds not only stimulates the growth and activity (as assessed by increased mucosal fold length, total protein content and alkaline phosphatase level) of the shell gland but also upregulates the expression of AVT and VT3. Further, administration of estrogen antagonist tamoxifen to sexually mature bird shows opposite results. On the other hand, localization of ir-AVT, observed in the ovary of sexually mature bird, was not detected in the estrogen treated sexually immature quail. It is concluded that estrogen not only affects the growth and differentiation of avian oviduct, but also regulates the expression of shell gland AVT and its receptor VT3. Present findings suggest that the locally synthesized AVT acts in a paracrine way to upregulate VT3 receptor and thus facilitates the endocrine function of neurohypophysial AVT during oviposition.     

Mesotocin and vasotocin, two neurohypophysial hormones in the ostrich, Struthio camelus

Two neurohypophysial hormones have been isolated from an avian species, the ostrich, Struthio camelus. Both have been characterized by amino acid analysis and sequence determination. The data obtained suggest that the oxytocin-like hormone is [Ile8-oxytocin] (mesotocin) and the vasopressin-like hormone is [Ile3-vasopressin] (vasotocin). Bioactivity measurements based on urinary conductivity showed vasotocin to be about five times as active as mesotocin.     

Galanin immunoreactivity increased in chicken supraoptic neurons after activation of the vasotocin system at oviposition

The avian arginine vasotocin (AVT) synthesized in the hypothalamic magnocellular neurons and released from the posterior pituitary is known to be involved in the regulation of uterine contractions for oviposition in chickens. However, regulation of AVT synthesis and release within the magnocellular hypothalamus has not been elucidated. Galanin, the oviposition inducing factor in the oviduct of the hen, has been demonstrated to have sexually dimorphic stimulatory action in oxytocin- and vasopressin neurons in the mammalian hypothalamus. In this study, galanin and AVT immunoreactivity was investigated around the time of oviposition in the supraoptic nucleus (SON) to determine if galanin modulates AVT synthesis and/or release. Within SON neurons increased AVT immunoreactivity before oviposition and the decreased AVT immunoreactivity after oviposition implied function-related peptide release. The significantly increased number of galanin neurons co-localizing with AVT immediately after oviposition suggests that galanin is involved in the negative feedback to limit AVT release in the SON. Thus, these data support the idea that AVT in the SON is involved in central regulation of oviposition and that AVT release could be modulated by the neuropeptide galanin.     

Comparative Physiology of the Vasomotor Effects of Neurohypophysial Peptides in the Vertebrates

The neurohypophysial peptides are vasopressor or depressor inaction depending on the species. Isotocin, mesotocin and oxytocinconstrict the branchial vessels in fish and induce a reflexvasodilation in the systemic vasculature. The vasodilation haspersisted in some higher vertebrates and is particularly prominentin the snakes and birds where vasotocin and arginine vasopressinalso are vasodepressor but are much less potent than mesotocinand oxytocin. In other vertebrates including fish, vasotocinand vasopressin are pressor and exert their effects mainly onthe peripheral resistance. The newt, toads and soft-shell turtlegave pressor responses to all neurohypophysial peptides, withvasotocin showing the highest potency. The frogs, big-headedturtle and lizards were intermediate with vasotocin being pressor,mesotocin being pressor and oxytocin exhibiting a dual effect.     

Galanin immunoreactivity increased in chicken supraoptic neurons after activation of the vasotocin system at oviposition.

The avian arginine vasotocin (AVT) synthesized in the hypothalamic magnocellular neurons and released from the posterior pituitary is known to be involved in the regulation of uterine contractions for oviposition in chickens. However, regulation of AVT synthesis and release within the magnocellular hypothalamus has not been elucidated. Galanin, the oviposition inducing factor in the oviduct of the hen, has been demonstrated to have sexually dimorphic stimulatory action in oxytocin- and vasopressin neurons in the mammalian hypothalamus. In this study, galanin and AVT immunoreactivity was investigated around the time of oviposition in the supraoptic nucleus (SON) to determine if galanin modulates AVT synthesis and/or release. Within SON neurons increased AVT immunoreactivity before oviposition and the decreased AVT immunoreactivity after oviposition implied function-related peptide release. The significantly increased number of galanin neurons co-localizing with AVT immediately after oviposition suggests that galanin is involved in the negative feedback to limit AVT release in the SON. Thus, these data support the idea that AVT in the SON is involved in central regulation of oviposition and that AVT release could be modulated by the neuropeptide galanin.     

Molecular Variation and Possible Lines Of Evolution of Peptide and Protein Hormones

The widespread distribution of certain steroids and amino acidderivatives with hormonal properties is considered evidencein support of the dictum that "it is not the hormones that change,but rather the uses to which they are put." However, analysesof the distributions, biological activities, immunological cross-reactivities,and sequences of amino acids of five representative peptideand protein hormones or groups of hormones—lactogenichormone, growth hormone, the corticotropin-MSH-ß lipotropinfamily, insulin, and the neurohypophysial hormones—supporta concept of change and of molecular evolution of these polypeptidicmolecules. When analyzed in terms of the genetic code, the aminoacid interchanges which have been revealed by determinationof sequences of amino acids can, most often, be explained bysingle base mutations in the appropriate codons. In two instanceswhere two base mutations within a single codon are required,intermediate replacements of amino acid have been suggested;one of these would lead to a 2-ALA-ß MSH, and theother to a 4-PRO, 8-ILE oxytocin.     

Different sensitivities of arteries and veins to vasoactive drugs in a hagfish, Eptatretus cirrhatus

We used myography on five different arteries and three veins of the hagfish, Eptatretus cirrhatus, to test the response of vessels to vasoactive drugs. Concentration-response curves were generated for carbachol, endothelin-1, arginine vasotocin and the adrenergic agonists, phenylephrine and isoprenaline. pEC50 values indicated that veins were more sensitive to endothelin-1 than were arteries, but the arteries were more sensitive to the cholinergic agonist, carbachol. Segmental arteries did not react to arginine vasotocin, but all other vessels did, and on a molar basis it was the most potent agonist tested. That ventral and dorsal aortas were more sensitive to arginine vasotocin than smaller vessels might indicate that this neurohypophysial peptide has the potential to exert a profound influence on branchial vascular resistance and cardiac output in hagfishes. The results also demonstrate the potential for a variety of endogenous peptides to contribute to central venous tone.     

Neurophpophysial hormones and the emission of semen in rabbits.

To elucidate the importance of the neurohypophysial hormones for the emission of semen, several neurohypophysial peptides were tested in male rabbits and the sperm density in the ejaculates was determined. Besides oxytocin and vasopressin, vasotocin and one oxytocin analogue (de-amino1-oxytocin) were used. Only vasopressin, in a dose as low as 10 mU, increased the number of spermatozoa in the ejaculates. It is suggested that vasopressin is of physiological significance for the emission of semen, at least in rabbits.