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PubMed1995

A new neurohypophysial peptide, seritocin ([Ser5,Ile8]-oxytocin), identified in a dryness-resistant African toad, Bufo regularis.

From the pituitary neurointermediate lobe of the African toad Bufo regularis, vasotocin, hydrin 2 (vasotocinyl-Gly) and a mesotocin-like peptide have been isolated by HPLC and characterized by mass spectrometry, amino acid sequence and chromatographic coelution with synthetic peptides. The mesotocin-like peptide has been identified as [Ser5,Ile8]-oxytocin in place of mesotocin ([Ile8]-oxytocin) found in all other amphibians investigated to date. The name seritocin is suggested. The molecule is virtually devoid of oxytocic activity on rat uterus in contrast to mesotocin. On the other hand, the molar ratio of hydrin 2 to vasotocin in the pituitary reaches 2, whereas it is about 1 in toads and frogs from temperate regions. B. regularis is an anuran species able to withstand a hot and dry season by burrowing. The possible relationship between occurrence of seritocin and adaptation to arid environment remains to be demonstrated.

Amino Acid Sequence↗

PubMed1975

Circular-dichroic spectra of vasopressin analogues and their cyclic fragments.

The circular dichroic spectra of [Arg8]vasopressin, [Mpr1, Arg8]vasopressin, [Mpr1, D-Arg8]-vasopressin, pressinamide, deaminopressinamide, tocinamide, deaminotocinamide, [Leu4, D-Arg8]-vasotocin, [Mpr1, Leu4, D-Arg8]vasotocin and [Phe2, Lys8]vasopressin have been studied. All these substances showed a characteristic positive dichroic band at about 225 nm due to the presence of tyrosine in sequence position 2. The intensity of this band was affected by interactions between the tyrosine side-chain and other structural elements in the molecule, such as the Na-amino group, the side-chain of phenylalanine in position 3 and the linear C-terminal peptide. Analysis of the response of this band to structural modifications of the molecule and change in the solvent (particularly comparing neutral aqueous solutions with hexafluoroacetone solutions) allowed some conformational conclusions. The linear C-terminal tripeptide is probably situated over the cyclic portion of the molecule both in vasopressin and oxytocin substances. Its steric interaction with the tyrosine side-chain seems to be particularly efficient in molecules containing D-arginine in position 8. In the vasopressin series the stacking interaction of neighbouring aromatic amino acid residues furthermore limits the conformational freedom of the tyrosine side-chain and also probably distorts the dihedral angles of residues 1-3 in comparison with oxytocin. The interactions of phenylalanine and arginine with tyrosine relatively decrease the conformational effects of the primary amino group. Consequently the local conformation of vasopressin in the region of the tyrosine residue is more rigid and less sensitive to changes in medium than that of oxytocin. The circular dichroic spectra did not show any basic conformational differences in the backbone peptide chain of oxytocin and vasopressin substances. A weak negative disulphide band at about 290 nm could be observed in the spectra of both series of substances.

Arginine Vasopressin↗

PubMed1985

Magnesium ions and oxytocin sensitivity of the male mouse anococcygeus.

The sensitivity of the mouse anococcygeus to contraction by oxytocin was shown to be Mg2+-dependent. Decreasing [Mg2+]0 from the optimal concentration of 1 to 0 mM caused a 20-fold parallel rightward displacement of the oxytocin dose-response curve. Contractions to oxytocin-related peptides (Arg-vasotocin, Arg-vasopressin and Lys-vasopressin) were also Mg2+-dependent, but those to other drugs (carbachol, methoxamine and thyrotrophin releasing hormone) were not. The onset of the potentiating effect of Mg2+ was rapid, full potentiation occurring within 70 s. 1-Deaminopenicillamine 8-ornithine-vasotocin produced competitive antagonism of responses to oxytocin, but was more potent in the absence (pA2 = 8.01) than in the presence of Mg2+ (1 mM; pA2 = 7.52). Thus, physiological concentrations of [Mg2+]0 enhanced oxytocin agonist potency but decreased oxytocin antagonist potency; possible mechanisms are discussed.

Animals↗

PubMed1972

Permeability of urinary bladder of Rana cancrivora to urea in the presence of oxytocin.

1. When Rana cancrivora collected from fresh water had been exposed for 3 days to saline solutions having osmolalities from 280 to 690 m-osmole/kg, urea concentrations in plasma and urine appeared to come into equilibrium, and were from 70 to 200 m-mole/l.2. Plasma urea level of fresh water R. cancrivora (48 m-mole/l.) was doubled (82 m-mole/l.) after 8 hr of exposure to 270 m-osmolal saline. It continued the same after 24 hr of exposure.3. When isolated urinary bladders of R. cancrivora were exposed to Ringer on the serosal aspect and one-fifth Ringer on the mucosal aspect, then in response to this osmotic difference of 190 m-osmole/kg, the rate of fluid movement (mucosa to serosa), which was 10.3(+/-2) mul./cm(2).hr, was not significantly altered when up to 60% of the NaCl of the Ringer solution was substituted by urea.4. Under the same circumstances, when oxytocin (50 m-u./ml.) was present in the serosal solution, the rate of fluid movement (mucosa to serosa) was 133.2(+/-7.9) mul./cm(2).hr in the absence of urea; it was progressively decreased by the presence of urea until, when 80% of the NaCl had been substituted by urea, the rate of fluid movement was reduced to 14.5(+/-4.0) mul./cm(2).hr.5. The diminished rate of fluid movement under the above circumstances could not be correlated with serosal urea concentration, with serosal availability of Na(+), nor with Na(+) concentration difference across the bladder wall. It appeared to be directly related to the ;non-urea osmotic difference' across the bladder wall provided by solutes other than urea.6. When isolated bladders were exposed to an osmotic difference of 190 m-osmole/kg, but having 25 mM urea present in the mucosal solution, then fluid moved from mucosa to serosa at a rate of 10.4(+/-1.3) mul./cm(2).hr in the absence of oxytocin and 124(+/-9) mul./cm(2).hr when oxytocin (50 m-u./ml.) was present. In the former case no urea passed across the bladder wall, but in the latter case urea passed from mucosa to serosa at a rate of 3.16(+/-0.3) mumole/cm(2).hr. The fluid moving from mucosa to serosa thus contained urea 25.5 m-mole/l.7. Vasotocin (10(-9)M), which is equipotent with oxytocin (50 m-u./ml.) in affecting permeability of the isolated urinary bladder to water, was also equipotent in producing a reduced rate of water fluid movement in the presence of 40% urea (vasotocin, 63 mul./cm(2).hr; oxytocin, 59 mul./cm(2).hr).8. When groups of frogs were cystectomized, and other groups of frogs were sham-operated, then after 48 hr of exposure to fresh water or to 300 m-osmolal saline the sham-operated frogs had plasma urea level raised from 20 m-mole/l. (fresh water) to 42 m-mole/l. (saline), while the cystectomized frogs had 20 m-mole/l. (fresh water) and 26 m-mole/l. (saline).9. The hypothesis is presented that hormone-induced permeability of the urinary bladder to urea contributes to the immediate adjustment of plasma urea level by which R. cancrivora survives when exposed to high environmental salinity.

Animals↗

PubMed1976

Active sodium uptake by the skin of foetal sheep and pigs.

1. Simultaneous measurements of unidirectional sodium fluxes across foetal skin incubated in vitro with identical solutions ([Na] = 150 mM) bathing either side showed a flux ratio (influx/efflux) of 1-40+/-0-08 in twenty-seven sheep skins, which was significantly different from unity (P less than 0-001). The gestational ages ranged from 47 to 98 days (term = 147 days). Similar experiments on eight foetal pig skins at 58 days gestation (term = 114-118 days) gave a mean flux ratio of 1-10 +/- 0-03 (P less than 0-02). 2. Unidirectional sodium fluxes measured with dilute Ringer solution on the outside (mucosal) surface ([Na]0 = 100mM) gave influx to efflux ratios of 0-86 +/- 0-09 in seventeen sheep (P less than 0-05) and 1-07 +/- 0-26 in five foetal pigs; the value predicted for passive movement was 0-67. 3. Incubation with inhibitors, ouabain (10-4 M) or dinitrophenol (DNP) (10-4 M) gave a flux ratio for sodium which was not significantly different from unity in the absence of a gradient, or from 0-67 when the concentration gradient was applied. 4. Sequential measurement of unidirectional diffusional fluxes of tritiated water across foetal skin gave flux ratios of 0-98 +/- 0-02 in six sheep skins and 1-06 +/- 0-11 for four pig skins in control conditions. When the outside solution was diluted to give an osmotic gradient of 100 m-osmole. kg-1 across the skin a flux ratio of 0-95 +/- 0-07 was obtained for seven sheep and was not measured in pig skin. Hormones and inhibitors had no effect on the diffusional flux ratio for water in the presence or absence of an osmotic gradient. 5. Lysine vasopressin (ADH) (200 mu./ml.) increased influx and efflux of water in the presence and, to a lesser extent in the absence of an osmotic gradient in sheep skin. In pig skin prolactin (1 u./ml.) increased both influx and efflux, but ADH had no effect on diffusional water fluxes. 6. ADH increased sodium influx in sheep skin slightly but vasotocin (5-5 mu./ml.) was more potent, particularly in the presence of an opposing diffusion gradient. Vasotocin (55 mu./ml.) reduced sodium influx in pig skin ADH had no effect on influx or efflux and prolactin reduced sodium influx and efflux. Ouabain and DNP generally reduced permeability to both sodium and water in sheep skin but had no effect in pig skin.

Animals↗

PubMed1976

The effect of hormones and of an osmotic gradient on the structure and properties of mammalian foetal urinary bladder in vitro.

1. Water and isotope fluxes were measured by incubating urinary bladders of foetal pigs and sheep in vitro in the presence and absence of a concentration and osmotic gradient. The structure of the urinary bladder of foetal pigs under various conditions was studied by electron microscopy. Its ultrastructure was found to be closely similar to that of foetal sheep. 2. Antidiuretic hormone (ADH) (0-2 U. ml-1) enhanced the enlargement of intercellular spaces caused by dilute mucosal medium in pig bladders; prolactin (1 u. ml-1) prevented osmotic dilatation of the intercellular spaces. 3. The hydraulic conductivity, Lp, was estimated to be 0-5 X 10 (-7) cm.s-1atm-1 in sheep and pigs at about 100 days gestation; the ratio of osomotic to diffusional permeability, (LpRT/VW)/PD, in the presence and absence of ADH, was 2-1 and 1-6 respectively. These are similar to the values found in fish gills. 4. Prolactin reduced bulk flow of water to zero in seven out of eight bladders investigated. Incubation with ADH or vasotocin (55 mu. ml-1) in the presence of prolactin restored water flux to 22% and 45% of control values respectively. 5. There was no significant net flux of sodium from mucosa to serosa in pig bladder except in the presence of prolactin. No net flux of sodium occurred from mucosal to serosal side of pig or sheep bladders in the presence of an adverse electrochemical gradient, although in sheep the permeability ratio was significantly greater than one. 6. The diffusional flux ratio for water remained unity under all conditions; vasotocin increased unidirectional fluxes and prolactin reduced them. The flux ratios were unaffected by the direction of bulk fluid flow, probably because diffusion was rapid compared to flow: the ratio of diffusional flux to volume flow was between 11 and 18.

Animals↗

PubMed1987

In vivo apparent peptide-receptor dissociation rate constants for arginine vasopressin analogs estimated from inhibition of rat pressor responses.

Apparent pressor receptor dissociation rate constants for arginine vasopressin, arginine vasotocin, oxytocin, oxypressin, and [1-deamino, 9-D-alanineamide]arginine vasopressin were estimated by the following method. Two minutes after injection of a moderate dose of agonist into urethane-anesthetized rats prepared for recording mean blood pressure, a large dose of inhibitor was injected. Under these conditions, in the first few moments after inhibitor injection, there should be no rebinding of the agonist after it dissociates, because vacant receptors should be immediately occupied by inhibitor. The rate of the blood pressure drop at the initiation of inhibition was calculated and used as an estimate of the dissociation rate of the agonist. Apparent dissociation rate constants thus estimated were 1.1, 1.1, 6.9, 5.8, and 13.9 min-1 for arginine vasopressin, arginine vasotocin, oxytocin, oxypressin, and [1-deamino, 9-D-alanineamide]arginine vasopressin, respectively. These rate constants were inversely related to the pressor potencies (435, 250, 5, 3, and 0.7 U/mg, respectively) of these five compounds. Such a relationship is to be expected if decreased potency is in part due to a faster "off" rate from pressor receptors.

Animals↗

PubMed1986

Disk method for measuring effects of neurohypophysial hormones on urea permeability of toad bladder.

This study describes a precise and sensitive method for the bioassay of 8-arginine vasotocin (AVT). The technique is based on the observation that AVT increases the permeability to urea of the isolated toad bladder and that this effect can be measured with minute quantities of AVT by suspending bladders in humid air and applying hormone on small paper disks. The hormone diffuses from the disk to the underlying epithelium where it increases permeability to urea. The bladder is filled with Ringer's fluid containing [14C]urea and the label diffuses across the bladder wall into the disk at the serosal surface. Disks are removed at timed intervals for scintillation counting. Disks containing 0.25 pg AVT accumulated 232 +/- 8 cpm of [14C]urea in 30 min, whereas control disks without hormone at a distance of 3-4 mm on the same bladder wall accumulated only 12 +/- 2 cpm. The minimal sensitivity during the summer was 0.1 pg AVT. Average values (+/- SE) for induction of a half-maximal urea permeability response in toads from all seasons were 1.4 +/- 0.3 X 10(-10) M for AVT, 7.4 +/- 1.5 X 10(-9) M for 8-arginine vasopressin, and 2.9 +/- 0.6 X 10(-8) M for oxytocin. Plasma from a hydrated toad (255 mosm/kg H2O) showed AVT-like activity of 1.53 X 10(-11) M and from a dehydrated toad (342 mosm/kg H2O) 4.86 X 10(-11) M. Because this bioassay is specific and as sensitive as the radioimmunoassay, it may serve as a useful tool for studying the physiology of vasotocin.

Animals↗

PubMed1993

V2-like vasopressin receptor mobilizes intracellular Ca2+ in rat medullary collecting tubules.

Cytosolic free calcium concentration ([Ca2+]i) was measured in single microdissected rat medullary collecting tubules [outer (OMCD) and inner (IMCD)] to identify receptors involved in vasopressin (AVP)-induced [Ca2+]i increases. In both segments, [Phe2,Orn8]vasotocin ([Phe2,Orn8]VT), a specific V1 agonist, as well as the V2 agonist 1-desamino-8-D-AVP (dDAVP) triggered [Ca2+]i variations. In OMCD, the mean response to 10 nM AVP roughly corresponded to the sum of V1 and V2 agonists effects. In IMCD, dDAVP (10 nM) alone reproduced the calcium response to AVP (delta[Ca2+]i = 243 +/- 34 nM, n = 6, and 248 +/- 27 nM, n = 8, with dDAVP and AVP, respectively). Furthermore, in the same experiments V1 and V2 maximal effects were not additive ([Phe2,Orn8]VT = 154 +/- 21 nM, n = 6; dDAVP + [Phe2,Orn8]VT = 233 +/- 23 nM, n = 9). As AVP, dDAVP released intracellular calcium (delta[Ca2+]i in calcium-free medium = 182 +/- 24 nM, n = 8, vs. 182 +/- 14 nM, n = 6 with 10 nM dDAVP and AVP, respectively). Neither 8-(4-chlorophenyl-thio)-adenosine 3',5'-cyclic monophosphate nor forskolin modified [Ca2+]i. A cross-reaction of dDAVP with an oxytocin (OT) receptor can be excluded since 1) the specific OT agonist [Thr4,Gly7]OT (10 nM) increased only slightly [Ca2+]i (delta-[Ca2+]i = 20 +/- 5 nM, n = 11); 2) the dDAVP response was not altered by the specific OT antagonist [1-(beta-mercapto-beta,beta-cyclopentamethylene propionic acid),2-(O-methyl)tyrosine,4-threonine, 8-ornithine,9-tyrosylamide]vasotocin [d(CH2)5(1),O-Me-Tyr2,Thr4,Tyr-NH2(9)]OVT; 3) it was insensitive to V1 antagonists but was totally blocked by the V1/V2 antagonist [d(CH2)5(1),O-Et-Tyr2,Val4]AVP ([delta[Ca2+]i = 18 +/- 4 nM, n = 6). These results indicate that in IMCD AVP increases [Ca2+]i via both V1 and V2 receptors. [Ca2+]i variations due to V2 receptors involve a mechanism independent of adenylate cyclase and coupled to the same intracellular calcium pool as V1 and V2 receptors.

Animals↗

PubMed1985

Oxytocin release induced by melatonin in the ewe.

The pineal gland indolamine melatonin now appears to be a primary mediator of the timing of estrus in mammals. Because the neurohypophyseal nonapeptides arginine vasotocin and oxytocin have recently been identified in the pineal glands of several species, we sought to assess the possibility of an interaction between melatonin and the neurohypophyseal hormones. An acute melatonin infusion (216 mumol) was administered to pregnant and nonpregnant ewes. Although plasma arginine vasopressin and arginine vasotocin levels did not change, melatonin produced a significant increase in plasma oxytocin in the nonpregnant though not the pregnant ewe. These data suggest a possible interaction between melatonin and oxytocin in the integration of mammalian reproduction cycles.

Animals↗

PubMed1981

Effects of prostaglandins on sexual receptivity in the female lizard, Anolis carolinensis.

Prostaglandins (PGs) have been implicated in the mediation of sexual behavior in vertebrates. In this study, the effects of administered PGs on sexual receptivity were examined in the ovariectomized female green anole lizard (Anolis carolinensis). Injection (ip) of 15 microgram PGF2 alpha failed to induce sexual receptivity in nonreceptive females which were either untreated or estrogen primed. On the other hand, PGF2 alpha treatment of sexually receptive estrogen-pretreated females inhibited sexual receptivity 1 h post injection. A dose of 7.5 microgram PGF2 alpha was as effective as 15 microgram in inhibiting sexual receptivity, while a dose of 1.5 microgram was near the minimum effective level. Treatment with 15 microgram PGE2 and, to a lesser extent, PGE1 also reduced sexual receptivity. In contrast, arginine-8-vasotocin, a neuropeptide capable of stimulating smooth muscle contractions in reptiles, did not decrease sexual receptivity. The inhibitory effects of PG treatment observed at 1 h were diminished by 3 h and were no longer present 6 and 24 h post injection, with females, again, being fully receptive. Inhibition of sexual receptivity occurs very rapidly after PGF2 alpha treatment. When tested 5 min post injection, all females treated with 15 microgram arginine-8-vasotocin were sexually receptive. The oviducts were not required for PGF2 alpha inhibition of sexual receptivity, as sexual receptivity was inhibited in oviductectomized females 1 h after the injection of 15 microgram PGF2 alpha. The inhibitory action of PGF2 alpha was also observed when sexually receptive females were injected intracranially rather than ip. Intracranial injection of 3.8 microgram PGF2 alpha inhibited sexual receptivity in females tested 1 h post injection. These results indicate that exogenous PGs, possibly acting centrally within the brain, inhibit sexual receptivity in female A. carolinensis, a species with a rapid mating-induced termination of sexual receptivity.

Animals↗

PubMed1988

Role of oxytocin on prolactin secretion during proestrus and in different physiological or pharmacological paradigms.

The present study was designed to evaluate the possible physiological role of oxytocin (OXY) on PRL release by examining the effect of administration of potent pharmacological antagonists of OXY on the stimulation of PRL secretion observed in vitro from anterior pituitary (AP) cells in response to OXY administration or in a number of in vivo paradigms. OXY caused a dose-related increase in PRL release from dispersed AP cells and short term AP cell cultures which was blocked by administration of the OXY antagonists [1-deaminopenicillamine, 2-O-methyltyrosine, 8-ornithine]vasotocin (dPOMeOVT) or [1-(beta-mercapto-beta,beta-cyclopentamethylene propanoic acid)2-O-methyltyrosine, 8-ornithine]vasotocin (MPOMeOVT), respectively. The antagonists were given in vivo in a dose that completely blocked suckling-induced milk let-down for up to 90 min. Injection of the antagonists did not alter the 5-hydroxytryptophan-induced increase in plasma PRL or the increase associated with acute ether stress or acute suckling stimuli, suggesting that OXY is not a major component involved in the neuroendocrine mechanisms responsible for those particular increases. On the other hand, iv administration of dPOMeOVT or MPOMeOVT prevented the increase in plasma PRL normally observed on the afternoon of proestrus in the cycling female rat. The characteristic surge of LH was also blocked by high doses of these antagonists. These data demonstrate that PRL secretion undergoes a differential regulation, in that OXY appears to play a major role in regulating the increase in plasma PRL observed on the afternoon of proestrus, but apparently provides little, if any, contribution toward the neuroendocrine regulation of the increases in PRL associated with 5-hydroxytryptophan administration, acute ether stress stimulus, or acute suckling stimulus. The data also suggest that OXY receptors located in the AP that are involved in the OXY-induced increase in PRL release may be similar to those OXY receptors located in mammary and uterine tissue, since specific biological effects of OXY in those tissues are effectively blocked by the OXY antagonists dPOMeOVT and MPOMeOVT. A possible role of OXY neurons in the neural mechanisms triggering the LH surge during proestrus is also suggested.

Animals↗

PubMed1993

Oxytocin receptor subtypes in the pregnant rat myometrium and decidua: pharmacological differentiations.

Oxytocin (OT) has a dual action in the uterus: a uterotonic action on myometrial cells and a prostaglandin (PG)-releasing action on endometrial/decidual cells. It had not been determined whether the OT-binding sites or receptors on the myometrial and the endometrial/decidual membranes are of the same type or may represent two subtypes. Our studies presented in this paper show that isolated day 19-22 pregnant rat uterine horns and myometrial tissues (uterine horns with decidual tissues removed) incubated in Kreb's buffer at 37 C released PGF2 alpha in sustained quantities into the bathing medium. OT stimulated PG release over the basal release rate in a dose-dependent manner in the whole uterine horn but not in the myometrial tissue. Two OT antagonists, P[Phe(Me)2,Thr4]ornithine vasotocin (antagonist A) and desGly-NH2(9),d(CH2)5(1)[Tyr(Me)2,Thr4]ornithine vasotocin (antagonist B) were found to have different effects on the PG-releasing action of OT. At antiuterotonic doses, antagonist A had no antagonism of the PG-releasing action of OT. On the contrary, antagonist A was found to stimulate uterine PG release. Antagonist B was a full OT antagonist. At equivalent antiuterotonic doses, antagonist B inhibited both the uterotonic action and the PG-releasing action of OT. These findings suggest that OT-sensitive PGs are synthesized/released principally in the endometrium/decidua. The myometrial uterotonic OT receptors and the endometrial/decidual PG-releasing OT receptors are two distinct subtypes and can be differentiated. The existence of two OT receptor subtypes in the uterus has important implications in the clinical application of OT antagonists as tocolytics for preterm labor. To be efficacious, OT antagonist therapy needs to block both the uterotonic and the PG-releasing action of OT.

Animals↗

PubMed1977

Asymmetrical permeability of the integument of tree frogs (Hylidae).

The skin from four species of North American tree frogs (Hylidae) was found in vitro, to be remarkably permeable to water in the presence or absence of the neurohypophysial hormone vasotocin. This property was, however, only seen in preparations from the ventral integument; osmotic water movement across the dorsal skin was negligible. The ionic permeability, reflected by the electrical resistance, was also much greater in the ventral skin. Unidirectional fluxes of 22Na, 36Cl, 14C-urea and tritiated water were measured in vitro in a single species, Agalychnis dacnicolor Cope. The ventral skin was 10-20 times more permeable to these molecules than the dorsal skin. The short-circuit current (usually reflecting active transmural Na transport) across the ventral skin was increased by aldosterone and vasotocin but these responses were absent on the dorsal side. The lipid content of the dorsal skin was four times greater than that on the ventral surface.

Aldosterone↗

PubMed1978

The permeability of the skin of the aquatic anuran Xenopus laevis (Pipidae).

The undirectional transcutaneous fluxes of Na, Cl, water and urea were measured, in vitro, in the pipoid anuran Xenopus laevis. An active uptake (outside to inside) of Na was observed but Cl movements appeared to be passive. The effluxes of Na and Cl were low compared to those measured in other species of amphibians. The active Na transport was less than that of more terrestrial species and, although it could be stimulated by vasotocin, aldosterone was ineffective. The permeability of the skin to water was also low and although it was increased in the presence of vasotocin the magnitude of the response was much less than seen in more terrestrial anurans. The skin was permeable to urea but the movement of this solute was not remarkable when compared to that in other amphibians. These properties of the skin are discussed in relation to the animal's aquatic manner of life.

Animals↗

PubMed1998

[The role of prostaglandin E2 and its receptors in the regulation of osmotic permeability of the frog bladder epithelium].

Arginine-vasotocin-induced enhancement of osmotic water flow was inhibited by PGE2, sulprostone, M&B 28767 and 17-phenyl-omega-trinor PGE2. The inhibitory action of these agents except M&B 28767 was more obvious when the osmotic water flow was activated by dibutyryl-cAMP. The findings suggest that, in the frog urinary bladder, the inhibitory effect of the PGE2 on arginine-vasotocin-induced water flow appears to be mediated via two receptor subtypes coupled with different secondary messengers. The inhibition-sensitive targets are localised both on pre- and post-cAMP steps of the hormonal signal transduction pathway.

Animals↗

PubMed1992

[Effect of Asu-AVT on electroacupuncture (EA) analgesia].

The Asu-AVT (1,6-aminosuberic acid -8-arginine-vasotocin) in an analogue of 8-arginine-vasotocin (AVT) which is one of pineal hormones. The effect of Asu-AVT on the pain threshold and EA analgesia was studied in rats. An increase of 16.2-41.5% in pain threshold was observed within 70 min. after ivc of Asu-AVT (75ng), while the Asu-AVT injection in combination with EA produced a significant increase of 164.6-309.1% in pain threshold, which was much higher than that in the saline-EA group (p < 0.05-0.01). The effect of Atu-AVT is analogous to that of oxytocin and arginine-vasopressin. The data indicate ivc of ASu-AVT not only elevates the pain threshold, but also enhances the EA analgesia. These results suggest that the pineal hormone, AVT may play a role in the EA analgesia.

Acupuncture Analgesia↗

PubMedDate not supplied

Vascular action of natural vasopressin-like peptides in isolated rat tail artery.

The literature data regarding the vasoconstriction potency of natural vasopressin-like peptides are contradictory. The cumulative concentration-response curve for arginine-vasopressin (AVP), lysine-vasopressin (LVP), arginine-vasotocin (AVT), lysine-vasotocin (LVT) and phenypressin (PHP) on the isolated rat tail artery was determined. The potency rank of these peptides on the vascular smooth muscle of the rat tail artery was the following: AVP greater than LVP greater than AVT = LVT greater than PHP. The results are discussed in comparison to the data in the literature.

Animals↗