Endogenous testosterone enhances growth hormone (GH)-releasing factor-induced GH secretion in vitro.

The influence of endogenous gonadal steroids in male and female rats on basal and growth hormone-releasing factor (GRF)-stimulated GH secretion from perifused anterior pituitaries was studied. After 75 min of perifusion with basal medium, freshly dissected pituitaries were exposed to human GRF(1-44) (10 nmol/l) for 15 min. Neonatal (day 1-2) or prepubertal (day 25) gonadectomy of male rats suppressed baseline GH release (ng/min per mg dry weight) as well as GRF-stimulated GH release by 40-70%. This effect was slightly more pronounced in neonatally gonadectomized animals. In prepubertally gonadectomized male rats, the suppression of GH release was completely reversed by testosterone replacement therapy. In female rats, prepubertal gonadectomy did not affect GH secretion from perfused pituitaries. However, treatment of ovariectomized female rats with oestradiol reduced baseline and GRF-induced GH release to levels lower than those observed in sham-operated or vehicle-treated ovariectomized animals. The data suggest that testicular androgen secretion in adult male rats increases the pituitary GH release in response to GRF in vitro, whereas ovarian oestrogen secretion is of less importance for the GRF responsiveness of female rat pituitaries.