Prolactin, AVP, angiotensin II, corticosterone and aldosterone in the rat during weaning.

In the rat significant changes in the control of body water and electrolyte homeostasis take place during the weaning period (16-24th day of life). This study was performed to analyse how the serum levels of hormones that are known to modulate body water homeostasis change during that period. The serum levels of aldosterone, corticosterone and prolactin increased significantly from 10 to 20 days, whereas those of arginine vasopressin were the same between 10 days and 20 days but increased significantly from 10 to 40 days. Serum levels of angiotensin II increased significantly from 10 to 20 days but decreased from 20 to 40 days, at which time they were significantly lower than in 10-day-old rats. In prolonged-suckling rats, that is, rats which suckled until the 20th day of life, the serum levels of corticosterone, aldosterone and prolactin were somewhat lower than in control rats and those of prolactin were not detectable at 16-20 days. It is concluded that important changes in the serum levels of hormones that regulate body water and electrolyte homeostasis take place during weaning. The postnatal increase in the serum levels of corticosterone and aldosterone is independent of weaning to solid food. The prolactin serum levels seem to be influenced by the length of the nursing period.