Estradiol increases growth hormone secretion in rats exposed to swimming stress or reserpine treatment.

The secretory pattern of growth hormone (GH) in female rats differs from that in males with respect to e.g. the inter-peak baseline levels being higher in females. In the present study the influence of sex steroids on plasma GH levels was investigated in male rats under various conditions. Administration of estradiol, but not testosterone, was found to increase GH release in rats with suppressed levels induced by exposure to swimming stress or by treatment with the monoamine depleting agent reserpine. In line with previous studies, administration of estradiol was found to increase also inter-peak GH levels in adult male rats; i.e. to cause a feminization of the secretory pattern. In stressed and in reserpinized animals as well as in normal male rats, the effect of estradiol is similar to that earlier demonstrated for somatostatin antiserum, and hence it is suggested that estradiol may act antagonistic to the GH inhibiting factor.