Corticosterone secretion in response to suckling at various stages of normal and prolonged lactation in rats

In an earlier study, it was observed that the weight of adrenal glands of lactating rats decreased greatly when the period of lactation was prolonged for more than 20 or 25 days (Tomogane, 1969). Although Thatcher & Tucker (1968, 1970a, b) suggested that adrenal gland function may be a factor limiting milk synthesis during prolonged lactation in rats, they found no significant differences in plasma corticosteroid concentrations at the resting stage in rats between normal and prolonged lactation. Therefore, the magnitude of secretion of corticosteroid in response to the suckling stimulus was studied in rats at various stages of normal and prolonged lacta-tion. Grosvenor and his colleagues have demonstrated that the relative importance of the suckling stimulus in inducing the release of prolactin decreased along with the advancement of lactation in rats (Grosvenor & Turner, 1958; Grosvenor, Maiweg & Mena, 1970; Mena & Grosvenor, 1972). Thus, whether a similar phenomenon could be observed for adrenal function was another problem in the present experiment. Primiparous Wistar-Imamichi strain rats, weighing 250-310 g at parturition, were used. They were housed singly in wooden cages and kept in an animal roo