Modulation of LH-RH stimulated gonadotropin release by progestagens and 17 beta-estradiol in primary pituitary cell culture.

Simple trypsination procedure for rat anterior pituitary gland which permits a high yield of viable cells was described. Primary cell cultures set up by this method was characterized for their ability to release gonadotropic hormones into the culture medium with or without stimulation by hypothalamic extracts and a synthetic LH-RH, maximal sensitivity to the latter being found at 3--4 days after plating. Gonadotropin secretion was maximal after 4 hr of incubation with LH-RH, its maximal effective dose (ED50) being between 10(-11) and 10(-10) mol 1(-1). Such a dose stimulated rLH release into the medium by a factor of about 6 and rFSH secretion by a factor of 3 over controls. The preincubation of cultures wih progesterone, D-norgestrel and delta 15-D-norgestrel resulted in a progestagen dose-dependent desensitization of the cell cultures against LH-RH for both gonadotropic hormones. This effect of progestagens was found to be time-dependent and maximal inhibition was found after 12-20 h. However, more effective inhibition of LH-RH stimulated rLH release was caused by preincubation with cycloheximide suggesting the importance of protein synthesis in the course of LH-RH augmented gonadotropin release. A dissociation of sensitivity of cultured cells against LH-RH concerning their rLH and rFSH release was also found after preincubation with a mixture of progesterone and estradiol. Present data and previous observations strongly suggest the modulatory influence of steroid hormones on LH-RH provoked gonadotropin release at the pituitary level.