Serum concentrations of
arginine vasotocin (AVT),
mesotocin and
prolactin were determined by radioimmunoassay in Rhode Island Red chickens during and after
dehydration, haemorrhage and oviposition. During
dehydration increased circulating levels of AVT,
mesotocin and
prolactin were found. As water deprivation proceeded, marked differences were observed. After an initial rise in serum AVT,
mesotocin and
prolactin levels during mild and moderate
dehydration, concentrations of both AVT and
prolactin tended to normalize during continued water deprivation, while those of
mesotocin remained high throughout the whole
dehydration experiment with the highest at the end of the water-deprivation period. Removal of 5 ml blood at intervals of 10 min during six consecutive time-periods did not affect serum osmolality and circulating levels of AVT and
prolactin, but slightly increased
mesotocin. These results suggest an osmoregulatory role for AVT and
prolactin, whereas
mesotocin may be involved in volume control. Finally, 1 min after oviposition, control values of 19.5 +/- 3.4 pmol AVT/1 (n = 9) were raised more than sevenfold to 142.9 +/- 12.5 pmol/l (n = 11). Thereafter, a decline occurred with a half-life for AVT of 13 min with raised serum levels up to 31 min after oviposition. In contrast, the serum concentrations of
mesotocin and
prolactin remained unaffected by oviposition.