- The present study compared the effect of D-Ser(tBU)6-des-Gly-LHRH-ethylamide in the form of a nasal spray, D-Trp6-LHRH, which is applied in daily intramuscular injections, and the long-acting preparation, D-Trp6-LHRH, which is given as a monthly intramuscular injection, on the function of the pituitary-ovarian axis. Forty spontaneously menstruating women not belonging to the PCOD group participated in the study, the results of which indicate that the three LH-RH agonists used are similarly effective in their ability to down-regulate the pituitary-ovarian axis. The time required for the appearance of the suppressive effect, as measured by reduced levels of gonadotropins and estradiol as well as by the abolishment of the hypophyseal response to rising estrogens, usually does not exceed 14 days and is never more than 28 days. The immunoreactive LH-reducing effect of the LH-RH agonists was true only if the basic levels of the hormone were higher than 11 mIU/ml. This fact might be particularly significant in patients with polycystic ovarian disease or in perimenopausal women.