Pituitary responsiveness to LHRH during Norplant use.

Norplant contraceptive implants were inserted during the 1st 7 days of the menstrual cycle in the upper arm of 16 regularly menstruating women of proven fertility. Pituitary responsiveness to LH-RH was carried out before (as a control) and after 3 and 12 months of implant use. Serum FSH and LH values were determined by radioimmunoassay techniques after 30 60 and 90 minutes of LH-RH administration. Comparisons between the mean serum values of the 2 gonadotropins at the basal level and following LH-RH administration before and after 3 and 12 months of Norplant use showed no statistically significant changes for all the values after 30 60 or 90 minutes of LH-RH injection. However the % increase of both FSH and LH mean values from initial concentrations following LH-RH administration were found to increase after 3 months of Norplant use and to decrease after 12 months. Statistical analysis of the maximum increase in both FSH and LH levels from initial concentrations regardless of time after LH-RH administration was undertaken but there were no statistically significant changes observed. There was however some delay in the achievement of maximum response following LH-RH injection as the interval from insertion increased to 12 months. These data indicate that Norplant use does not suppress the pituitary response to LH-RH for up to 1 year of use. The steroid release rate for the Norplant implant is approximately 50 mcg/day for the 1st year 30 mcg/day for the 2nd year and then remains constant for the next 4 years. The present investigation was planned with the objective of evaluating the capacity of the pituitary to release LH and FSH in response to LH-RH stimulation. (authors modified)