Plasma hormones (arginine vasotocin, prolactin, aldosterone, and corticosterone) in relation to hydration state, NaCl intake, and egg laying in fowls.

This review surveys our latest research dealing with the involvement of arginine vasotocin (AVT), the avian antidiuretic hormone, and other hormones in the regulation of water and salt balance in fowl. We examined the effect of dehydration, salt loading, high- and low-salt diets, and oviposition on plasma hormone levels and analyzed them in light of our knowledge of avian osmoregulatory responses to changes in water and salt balance. Gradual dehydration and hyperosmotic loading in domestic fowl revealed consistent differences in the AVT response between groups adapted to low- and high-NaCl diets. In birds on a low-NaCl diet the sensitivity of the AVT release was significantly higher than in birds on a high-NaCl diet. These results support the concept that the link between osmotic and volume regulation is established via varying sensitivity of the AVT release. We determined the half-life of the AVT in fowls (6.3 min), a value similar to that of ADH in mammals. We found that during oviposition, plasma AVT increases by a factor of four over the normal level, a magnitude consistent with the maximal responses revealed in osmotic stimulations. We have shown that as long as drinking water is available, heat exposure has no effect on the plasma osmotic constituents and the regulatory hormones. However, combined dehydration and heat exposure resulted in pronounced osmoregulatory responses integrated with the thermoregulatory responses to maintain water and salt balance without jeopardizing the birds' ability to cope with the thermoregulatory demands.(ABSTRACT TRUNCATED AT 250 WORDS)