Daily variations of FSH, LH and testosterone response to intravenous luteinizing hormone-releasing factor (LRF) in normal men.

The responses of FSH, LH and testosterone to acute stimulation with synthetic LRF were studied in 6 healthy, fertile men aged 33.4 plus or minus 1.6 yr (X plus or minus SE). Fifty mug of LRF were given, iv at 0600 h, 1200 h, 1800 h and 0000 h, at 1-week intervals, to all 6 volunteers simultaneously. Blood samples were collected by venipuncture before (-5 and 0 min) and 8, 16, 32, 64 and 128 min after LRF injection. Plasma levels of FSH, LH and testosterone were determined by double antibody radioimmunoassay techniques. The responses of FSH and LH to LRF injection showed a clear difference at the times studied. Maximal values were obtained at 0600 h and 1800 h while the response at noon was not significant for LH and absent for FSH. Testosterone secretion showed a clear-cut response to LRF in all the subjects. At three of the four studied times (0600 h, 1800 h, 000 h) plasma testosterone was already increased at 8 min reaching its maximum at 16 min and persisted high until the end of the study. The noon response reached its maximum at the end of the test period. The daily variations of FSH and LH responses to acute LRF stimulation should be taken into consideration in clinical practive and the increment in testosterone secretion makes this test a useful indicator for androgenic testicular reserve.