Gonadotrophin releasing hormone causes a biphasic secretion of luteinizing hormone and follicle stimulating hormone by cultures of rat anterior pituitary cells.

Primary monolayer cultures of adult male rat anterior pituitary cells secreted both LH and FSH in a biphasic manner when incubated with gonadotrophin releasing hormone (GnRH). The peaks of secretion of LH and FSH were coincident: the first occurred between 15 and 30 min and the second between 1 and 3 h after the addition of GnRH. Approximately 20% of the total amount of gonadotrophins secreted in the 6 h treatment with GnRH was contained in the first peak. Inhibitors of the secretion of gonadotrophins affected LH and FSH secretion differently. Inhibin suppressed the secretion of FSH to a greater extent than that of LH, whereas testosterone and cycloheximide had a greater effect on LH. Neither phase of secretion of LH or FSH was reduced preferentially by inhibin or testosterone but the greater effect of cycloheximide was on the second phase of secretion.