Sex differences in beta-adrenergic stimulation of growth hormone secretion in vitro

In previous in vitro studies we have shown that the amounts of GH released by pituitary cells in response to human GH-releasing factor -40 (hGRF-40) are significantly related to the sex and gonadal hormone environment of the donor animals. The present studies were designed to determine whether the beta-adrenergic stimulation of GH release is sex related and to compare the response to that observed after hGRF-40. Dispersed pituitary cells from male or female rats were exposed to sequential pulses of isoproterenol (ISO) and epinephrine (EPI), followed by a single pulse of 10 nM hGRF-40. In a second series of experiments, the cells were exposed to sequential pulses of norepinephrine (NE), followed by a single pulse of 10 nM hGRF-40. ISO and EPI stimulated GH secretion at concentrations as low as 10(-8) M, but NE required a concentration of 10(-6) M to cause significant GH release. GH release after ISO, EPI, and NE was concentration dependent, and the order of potency was ISO greater than EPI greater than NE. The amounts of GH secreted by pituitary cells from male rats were significantly greater than those from female rats, and the magnitude of the difference was directly comparable to that observed in response to hGRF-40. These results confirm the beta-adrenergic stimulation of GH release, and the order of potency is consistent with mediation by a beta 2-adrenergic receptor. The significantly greater capacity for pituitary cells from male rats to secrete GH supports the possibility that individual somatotropes in the pituitaries of male rats might have a greater responsiveness and/or sensitivity to beta-adrenergic and hGRF-40 stimulation.