Luteinizing hormone (LH), follicle-stimulating hormone, and testosterone responses to consecutive injections of D-leucine-6-LH-releasing hormone ethylamide in normal men.

Luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone (T) responses to three consecutive intravenous injections of D-Leu-6-LH-releasing hormone ethylamide (D-Leu-6-LH-RH-EA) at 3-hour intervals were studied in six healthy, fertile, male volunteers 34.2+/-1.6 years of age. Each man received three injections of 20 microng of D-Leu-6-LH-RH-EA at 6:00 A.M., 9:00 A.M., and 12:00 noon, respectively. Blood samples were obtained before the first injection and at 1, 2, 3 (before the second injection), 4, 5, 6 (before the third injection), 7, 8 and 9 hours after the beginning of the test. Serum levels of LH, FSH, and T were determined by radioimmunoassay with the double-antibody technique. The response to the first injection of D-Leu-6-LH-RH-EA confirmed the longer duration of the stimulation of LH and FSH release caused by this compound as compared with that caused by LH-RH. Serum T levels rose significantly, almost paralleling the variations experienced with gonadotropins. The second injection caused a slight increase in LH and T responses in relation to the first injection. Two and three hours after administration, the third stimulus resulted in hormone levels lower than those obtained with the first two injections. Possible explanations for this finding might be a reduction of pituitary responsiveness as a result of multiple stimulation with D-Leu-6-LH-RH-EA, or spontaneous circadian variation of the pituitary response, or a combination of factors.