Short-term regulation of LH and FSH secretion in cyclic women. I. Altered pituitary response to a second of two LH-RH injections at short intervals.

The effects of two iv 25 microgram LH-RH injections (180 tests) at different intervals (30 min to 24 h) on radioimmunoassay serum LH and FSH levels were investigated in 30 women in the midfollicular or midluteal phase of the menstrual cycle. The pituitary LH and FSH response to the second LH-RH injection at time-intervals of 30 and 360 min was significantly lower than the response elicited after the first injection. The second response was significantly higher at 60 to 180 min intervals. The maximum increment occurred at 120 min. No significant differences between the two pituitary responses to LH-RH were found at intervals of 240 min and 24 h. A theory with regard to intracellular processes of hormone synthesis and degradation is proposed to explain these time-dependent differences in the pituitary LH and FSH response.