Daytime titers of testosterone, LH, estrone, estradiol, and testosterone-binding protein: acute effects of LH and LH-releasing hormone in men

Abstract

Four normal 18-20 yr-old men were studied on 3 occasions, from 0830 h to 1500 h. The baseline for each study consisted of 3 or 4 measurements of the respective hormone obtained between 0830 and 0900 h. In the control studies mean testosterone (T) fell by 43% (P less than 0.01) during the final 30 min. The fall was gradual throughout the day and was significant by 1100 h (P less than 0.05). Administration of LH and LH-releasing hormone (LHRH) at 0900 h resulted in 9-fold (5 min) and 3-fold (30 min) higher concentrations of LH respectively. LH declined more slowly after LHRH. Titers of T rose to the 0830-0900 h mean 130 min after LH but were never significantly elevated; the occurrence of a significant drop in mean T was delayed for 70 min. After LHRH there was a nonsignificant 24% increase of the mean T followed by a slow decline; however, T did not fall significantly below the mean baseline level. In contrast, in 2 of the 4 subjects LHRH resulted in rises in T levels (P less than 0.05) above the basal titers. Testosterone-binding globulin (TeBG) mean titers showed no diurnal rhythm in the control studies. There were statistically significant elevations of mean TeBG 150 min after LH and 340 to 370 min after LHRH, as well as sustained increases during the final 30 to 210 min of 1 or 2 individuals in each group. The reason for these increases in TeBG is not presently known. Estrogen analyses performed in all studies on 2 of the subjects revealed: 1) afternoon titers of estrone were lower than baseline in all 6 studies, 2) there was no diurnal rhythm for estradiol in control studies, and 3) estradiol increased during the final 2.5 to 3 h after LHRH (P less than 0.01), but after LH it was not altered in 1 man and was lower in the other.