SEXUAL DIMORPHISM OF GROWTH HORMONE (GH) SECRETION BY CULTURED PITUICYTES OF YOUNG GONADECTOMIZED RATS

Abstract

To study the sexual dimorphism of GH secretion, 22-day-old rats, 8 female (F) and 8 male (M), were gonadectomized and their pituitaries dispersed 10 days later. Plated at 5 × 104 cells in 1-ml wells, the cultured monolayers were incubated for 4 h with 1-40 human GH-releasing factor (hGRF, 0.2-60 nM), and rat GH (rGH) was measured. F cells were more sensitive to hGRF than M cells, and rGH increased with 0.2 nM hGRF by 110±30 (SD)%, and with 20 nM hGRF to a peak of 500±40% of controls. M cells responded more vigorously than F cells, with a threshold increase at 1 nM hGRF by 105±33% and a peak of 780±60% at 60 nM hGRF. Thus, dimorphism of GH secretion persisted in pituicytes of prepubertal rats deprived of sex steroids (SS). To determine the role of SS, cultured pituicytes of gonadectomized rats were incubated with 5 nM estradiol (E2) or testosterone (T) for 9 days. In the F cells, T augmented basal secretion by 53±12% and de-decreased its sensitivity to hGRF; while in the M cells, basal secretion, sensitivity and potency of hGRF were unaffected by T. E2 augmented basal secretion by 62±12% in F cells and by 28±7% in M cells. It decreased hGRF sensitivity and potency in F cells, while in M cells it increased potency but not sensitivity. We conclude that the sexual dimorphism of rGH secretion at the pituitary is partly inherent in the respective sex before pubertal hormone changes and is partly induced by SS through their effect on GRF sensitivity and potency.