Distribution of immunoreactive mesotocin and vasotocin in the brain and pituitary of chickens.

The distribution of vasotocin and mesotocin in the pituitary and central nervous system in male chickens was determined using radioimmunoassays. Neither peptide was detected in the pineal. Mesotocin, but not vasotocin, was detected in the cerebellum. Both peptides were found in the septal area, archistriatum, paleostriatum, optic lobe, anterior, medial and posterior hypothalamus, midbrain, pons, medulla oblongata, and the anterior and posterior pituitary. Equal amounts of the 2 peptides were present in the septal area, archistriatum and anterior hypothalamus whereas vasotocin was more abundant (2- to 10-fold) in the paleostriatum, optic lobe, midbrain, and pituitary. The amount of mesotocin was about twice that of vasotocin in the medulla oblongata and the medial and posterior hypothalamus. The wide distribution of vasotocin and mesotocin in extrahypothalamic sites in the central nervous system suggests that the peptides may, as in mammals, have a role in a variety of autonomic and endocrine regulatory processes in chickens.

Absence of sodium appetite in cyclophosphamide and DOCA treated house mice.

Intraperitoneal administration of cyclophosphamide 100 mg/kg and 200 mg/kg significantly lowered plasma sodium and significantly increased plasma potassium but did not result in saline preference in a strain of wild-derived house mice given a choice between water and saline (0.15M) to drink. Deoxycorticosterone acetate treatment in dosages up to 1.5 mg for four days also failed to increase salt intake, The data suggest a possible absence of a sodium appetite mechanism in this species.

Distribution of immunoreactive vasotocin and mesotocin in the chicken gastrointestinal tract.

Immunoreactive arginine vasotocin (AVT) and mesotocin (MT) were measured in heart, breast muscle, adrenals, testes, and different parts of the gastrointestinal tract in adult male chickens. Neither of the peptides were detected in liver, testis, heart and breast muscle. The amounts of AVT and MT in the adrenals were 167 +/- 25 and 669 +/- 198 pg/gland, respectively. Considerable amounts of immunoreactive peptides were found in the gastrointestinal tract with the highest concentration in the proventriculus (4.18 +/- 0.31 ng AVT and 16.58 +/- 0.86 ng MT per organ). Dose-response curves of duodenal and proventriculus extracts were parallel with synthetic AVT and MT standards.

Arginine vasotocin (AVT) release in relation to uterine contractility in the hen.

The relationship between plasma levels of arginine vasotocin (AVT) and factors associated with increases in uterine contractility was studied in the domestic hen. Plasma AVT levels increased from 3.3 +/- 0.3 microU/ml 15 min before a midsequence oviposition (OP) to 14.8 +/- 0.6 microU/ml at OP and then decreased to 5.2 +/- 0.6 microU/ml 15 min following OP. A ninefold increase in plasma AVT concentration was observed in hens laying a terminal egg of a sequence, which is not immediately followed by ovulation (OV). AVT levels also increased approximately 1 hr before the time of the first ovulation (C1OV) of the next sequence in association with an increase in uterine contractility. When OP was induced 2 hr before an expected OP by intrauterine administration of prostaglandin F2 alpha (PGF2 alpha, 1.0 microgram), plasma AVT levels immediately increased threefold (P less than 0.001) and then returned to basal levels within 30 min. In PGF2 alpha-treated hens AVT levels rose at the expected time of OP (P less than 0.05) in association with an increase in uterine contractility without OP actually occurring. When C1OV was induced by LH-RH (25 micrograms, iv), a small but significant increase of AVT similar to levels during spontaneous C1OV was observed. These results suggest that plasma AVT levels increase with every ovulation and oviposition in the absence of an egg in the uterus and that AVT is released in association with induced ovulation and oviposition.

Plasma volume and electrolytes during progressive water deprivation in chickens (Gallus domesticus).

1. Studies were performed to examine the effects of progressive water deprivation in the fowl (Gallus domesticus). 2. A reduction in plasma volume and an increase in capillary permeability to protein were observed only after 3 or 4 days of dehydration. 3. Moderate changes in arterial blood pressure and heart rate were noted in dehydrated birds but respiratory rate and body temperature remained unchanged. 4. Dehydration was associated with increases in the concentration of total solutes, sodium and chloride in plasma but no changes were noted in plasma potassium levels or arterial pH. 5. The results indicate that the chicken can maintain volume more effectively during water deprivation than several mammalian species.

Plasma concentrations of arginine vasotocin and mesotocin following pentobarbital anaesthesia and carotid cannulation in domestic fowl.

1. Plasma concentrations of arginine vasotocin (AVT) and mesotocin (MT), arterial pH and pCO2, body temperature, respiratory rate, heart rate, mean arterial blood pressure, packed cell volume and plasma osmolality were monitored in birds for 28 h following anaesthesia and carotid cannulation. 2. Plasma MT concentration decreased after 6 h of surgical recovery but there were no differences between 6 and 28 h of recovery. 3. In contrast, plasma AVT concentration was raised only after 27 h, but no differences were observed between 3 and 28 h of recovery. 4. Anaesthesia and/or carotid cannulation apparently suppressed AVT and enhanced MT release, but no significant change in either hormone was observed after 6 h of surgical recovery under the conditions specified in this study.

Arginine vasotocin and mesotocin in the anterior hypothalamus, neurohypophysis, proventriculus and plasma of White Leghorn cockerels, during dehydration.

1. The effect of 96 hrs of water deprivation on plasma electrolytes, osmolarity, arginine vasotocin (AVT), mesotocin (MT), and on AVT and MT content in the neurohypophysis, anterior hypothalamic area (AHA) and proventriculus, was studied at 24 hrs intervals, in adult White Leghorn cockerels. 2. Plasma AVT increased three fold during the first 24 hrs but there was no further change during the next 48 hrs. In the last 24 hrs, plasma AVT decreased in about 25%. Plasma MT did not change during the entire period of dehydration. 3. Plasma sodium and osmolarity gradually increased during that time. 4. Neurohypophysial AVT content was depleted by 95% during the period of dehydration while MT content did not change. 5. In the AHA there was no change in AVT levels during dehydration while the levels of MT increased while in the proventriculus there was no change in either AVT or MT levels. 6. For the data collected during the entire experimental period, no correlation was found between plasma osmolarity and plasma AVT, but there was a highly significant negative correlation between plasma osmolarity and neurohypophysial AVT content. 7. It may be suggested that the depletion in AVT content in the neurohypophysis during progressive water deprivation resulted in an insufficient level of AVT in circulation to enable the cockerels to counter the dehydration. This may explain the death of those cockerels which were dehydrated for a further 24 hr period.

Effect of acute and chronic cardiac denervation on osmotic release of vasotocin in chickens.

Hypo- and hyperosmotic NaCl were infused intravenously to examine osmotic release of arginine vasotocin (AVT) in anesthetized, acutely cardiac-denervated chickens and in conscious, chronically denervated birds. Mean arterial blood pressure was consistently higher in denervated compared to sham-operated chickens but heart rates were similar in experimental and control groups. Plasma AVT concentrations (pAVT) were significantly higher than controls in acutely, but not chronically, denervated chickens. The slope of the regression line relating pAVT to plasma sodium concentration was higher in denervated birds indicating that removal of cardiac receptor activity increases the osmotic sensitivity of the AVT system. The results suggest that cardiac end-net receptor activity may participate in the regulation of blood pressure and can modulate the release of antidiuretic hormone in the chicken.

Peripheral angiotensin II stimulates release of vasotocin in conscious chickens.

In mammals, intracranial or peripheral administration of angiotensin II (ANG II) has a number of actions, including the release of antidiuretic hormone (ADH). Relatively little is known of the interactions between the renin-angiotensin and ADH systems in birds. In the present study [Asp1, Val5]ANG II (fowl ANG II) was infused intravenously into conscious White Leghorn cockerels to determine whether peripheral ANG II influences the release of arginine vasotocin (AVT), the avian ADH. Cannulas were inserted into a wing artery and vein under local anesthesia. ANG II was dissolved in 0.154 M NaCl and administered intravenously at 0, 2, 20, and 200 ng X kg-1 X min-1. In a second series of experiments, ANG II was infused in 0.1 and 1.0 M NaCl (200 ng X kg-1 X min-1) to examine the effect of the peptide on osmotic release of ADH. In the three groups administered ANG II in 0.154 M NaCl, plasma AVT before intravenous infusion averaged between 1.8 +/- 0.46 to 2.6 +/- 0.30 microU/ml. In these birds, infusion of ANG II at 2, 20, and 200 ng X kg-1 X min-1 caused plasma AVT to increase over preinfusion means by 39, 78, and 300%, respectively. The changes in AVT occurred in the absence of differences in plasma osmolality, electrolyte composition, or arterial blood pressure among the groups. In chickens that were administered ANG II in 0.1 and 1.0 M NaCl, significantly higher plasma AVT levels were observed compared with a control group receiving the saline infusions alone.(ABSTRACT TRUNCATED AT 250 WORDS)

An antiserum that recognizes mesotocin and isotocin: development of a homologous radioimmunoassay for plasma mesotocin in chickens (Gallus domesticus).

This report presents characteristics of an antiserum raised in a rabbit immunized with synthetic mesotocin (MT) conjugated to bovine thyroglobulin. Cross-reactivity studies indicate that the antiserum (Kl-II) recognizes the carboxyl-terminal "tail" of MT and isotocin (IT). A homologous, disequilibrium radioimmunoassay (RIA) for MT has been developed that can detect less than 1 pg of peptide. Plasma was extracted with octadecasilyl-silica. Recovery of MT from plasma was correlated with the amount added and averaged 70%. Different volumes of plasma and posterior pituitary extract, when measured in the assay system, yielded inhibition curves that were parallel with standard MT. Immunoreactive MT and AVT of plasma and neural lobe coeluted with synthetic standards after gel filtration. The ED50 of a heterologous, sequential saturation RIA for IT was 17.4 pg, suggesting that the MT antiserum may be useful for measuring the oxytocin-like principle in bony fishes. Immunoreactive MT in plasma of cockerels increased and decreased with iv infusion of hypo- and hyperosmotic saline, respectively. The changes in plasma MT were inversely related to osmolality. Hyperosmotic saline infusion resulted in correlated increases in plasma AVT and osmolality. The data suggest that MT may be released by dilution and/or expansion of extracellular fluid in chickens.

Relationships between renal hemodynamics and plasma levels of arginine vasotocin and mesotocin during hemorrhage in the domestic fowl (Gallus domesticus).

1. Renal tissue blood flow (renal perfusion) and plasma levels of arginine vasotocin (AVT) and mesotocin (MT) were measured in anesthetized chickens before and during hemorrhage. 2. Renal perfusion did not decrease (P less than 0.05) until nearly 50% of the blood volume had been removed. The decrease in renal perfusion was not related to arterial blood pressure but was concomitant with an increase (P less than 0.05) in plasma AVT levels. 3. Renal perfusion during hemorrhage was positively correlated with plasma MT levels by the regression equation: renal perfusion = 0.091 (MT)-1.1459 which was highly significant (P less than 0.001, r2 = 0.95). 4. The results of this study suggest that MT as well as AVT may participate in regulating blood flow in the avian kidney.

Effect of heat stress on plasma levels of arginine vasotocin and mesotocin in domestic fowl (Gallus domesticus).

1. The effect of an acute heat stress on plasma arginine vasotocin (AVT) and mesotocin (MT) levels were determined in non-heat-acclimated domestic fowl. 2. Heat increased (P less than 0.05) AVT and decreased MT (P less than 0.05) levels but had no affect on plasma osmolality. Changes in MT were correlated with body temperature (-0.40) and blood pCO2 (0.32). However, changes in AVT were not correlated with any physiological variable, including MT. 3. During thermoneutral recovery, with the exception of hematocrit which remained lower (P less than 0.05), all monitored variables returned to values which were not different (P greater than 0.05) from those observed prior to heat stress. 4. These results indicate that in non-heat-acclimated birds, acute heat stress elevated plasma AVT and suppressed the release of MT and that changes in these hormones occurred independent of any change in plasma osmolality.

Effects of sex and gonadal steroids on arginine vasotocin and mesotocin in the pineal gland and neurohypophysis of White Leghorn fowls.

1. Pineal and neurohypophysial arginine vasotocin (AVT) and mesotocin (MT) were measured in White Leghorn hens, cockerels and castrated males treated with either testosterone propionate (TP) or oestradiol benzoate (EB) (n = 10/group). The lighting regimen was 14 h light: 10 h dark, supplied by natural diffused sunlight and incandescent bulbs. 2. Both AVT and MT were detected in the pineal gland of all the chickens. 3. There was no significant effect of either sex or treatments on pineal MT. 4. Females had about 4 times more pineal AVT than males, regardless of their treatment. There was no effect of the treatments on pineal AVT in the males. 5. No sexual difference in neurohypophysial AVT was detected, but the neurohypophysis of the castrated males treated with EB contained less AVT than the neurohypophysis of the intact males. 6. Intact males had about twice as much MT in the neurohypophysis as females. Castrated males treated with either TP or EB had similar concentrations of neurohypophysial MT, which were lower than that of the intact males, but higher than that of the females.

Effect of intrahypothalamic injections of norepinephrine and serotonin on plasma arginine vasotocin and mesotocin in the White Leghorn cockerel.

1. Saline (10 microliters), norepinephrine (NE) and Serotonin (5-HT), 500 nmol each, were injected into the anterior third ventricle (A3V; n = 7) or the posterior third ventricle (P3V; n = 11) of ananesthetised, unrestrained White Leghorn cockerels. Plasma arginine vasotocin (AVT) and mesotocin (MT) were measured 20, 60 and 120 min after injection. 2. Injection of NE into both the A3V and P3V had no significant effect on either plasma AVT or plasma MT at any of the sampling times. 3. Administration of 5-HT into the A3V significantly increased plasma MT about two-fold 20 min following injection. At 120 min time, plasma MT returned to normal. 4. In P3V birds, 5-HT had no effect on plasma MT in the first 20 min, but a significant increase in plasma MT occurred 60 to 120 min after injection. The magnitude of the response was lower than in the A3V cockerels. 5. Plasma AVT was not affected by 5-HT administration into the A3V at any of the sampling times, but 5-HT administration into the P3V caused significant rises in plasma AVT at 120 min. 6. Serotonergic, but not noradrenergic, induction of neurohypophysial peptide secretion was demonstrated.

Physiological effects of arginine vasotocin and mesotocin in cockerels.

1. The effects of continuous infusion of 0.1, 1.0 and 10.0 mU/min/kg body weight of arginine vasotocin (AVT) or mesotocin (MT) on cardiovascular and thermoregulatory responses, on plasma osmolality and ionic composition and on plasma concentrations of AVT, MT, prolactin and aldosterone, were investigated in conscious White Leghorn cockerels. 2. Neither of the peptides, at any dose, affected cardiovascular functions, plasma ions and osmolality. Infusion of MT at the rate of 10 mU/min/kg body weight increased respiratory rate. Both peptides at doses of 1 and 10 mU/min/kg reduced the temperatures of the comb and shank but had no effect on the skin and cloaca. 3. Doses of 0.1 and 1.0 mU MT/min/kg reduced plasma aldosterone and at 10 mU/min/kg increased plasma AVT. At any given dose MT had no effect on plasma prolactin. AVT at 0.1 and 1.0 mU/min/kg of AVT reduced plasma MT. AVT at 1.0 mU/min/kg increased plasma prolactin and at 10 mU/min/kg reduced plasma aldosterone. 4. During saline infusion, plasma MT was positively correlated with plasma AVT and negatively correlated with respiratory rate and cloacal temperature. Plasma AVT showed a positive correlation with plasma MT and aldosterone and a negative correlation with respiratory rate and skin temperature. 5. During saline infusion, there was no significant correlation between cardiovascular functions, or plasma osmolality and ionic composition and plasma MT or AVT. 6. The present study suggests that interrelationships between circulating concentrations of AVT and MT do exist and that AVT affects aldosterone secretion. These neurohypophysical peptides are involved in thermoregulation.