Twenty-four-hour patterns in serum prolactin and cortisol after partial and complete isolation of the hypothalamic-pituitary unit in rhesus monkeys.

Abstract

Serum concentrations of PRL and cortisol (F) exhibited dissimilar 24-h patterns in adult rhesus females subjected to 4-h sequential blood sampling for either 24 or 48 h. The changes in PRL concentrations appeared to show circadian rhythmicity, with daytime (0800-1600 h) levels of PRL (14.1 ± 2.6 ng⁄ml) being approximately half (27.8 ± 3.7 ng⁄ml) those found during the night (1900-0400 h). The variations in serum concentrations of F also showed a circadian rhythm; the zenith (36.5 ± 4.6 jug⁄100 ml) o ccurred near 0300-0400 h and the nadir (12.1 ± 3.2 ⁄xg⁄100 ml) occurred near 1900-2000 h. The influence of the brain on these hormonal patterns was examined by destroying various neural connections contributing to the hypothalamic- pituitary axis. After pituitary stalk transection (n = 4), both PRL and F 24-h rhythms were abolished. These losses in rhythmicity were accompanied by a 10-fold elevation in serum PRL levels and a decline in serum F to levels below those at the nadir in intact monkeys. Females (n = ...