Androgen and estrogen dynamics in the female baboon ( Papio anubis)

Abstract

Androgen and estrogen dynamics were studied in 5 female baboons ( Papio anubis) using constant infusions of [ 3H]androstenedione/[ 14C]estrone and [ 3H]testosterone/[ 14C]estradiol. Blood samples were obtained prior to the infusions and both blood and plasma was used for measurements of androstenedione (A), testosterone (T), dihydrotestosterone (DHT), estrone (E 1), estradiol (E 2). Plasma was used for measurements of sex-hormone binding globulin (SHBG), and the percents of T and E 2 free, bound to SHBG, and to albumin. Blood samples obtained during the infusions were analyzed for radioactivity as purified androgens and estrogens. Metabolic clearance rates (MCR), and transfer factors ([ρ] BB; fraction of steroid infused which is converted to and measured in blood as product) and blood production rates were calculated from whole blood data. All urine was collected for 96 h and an aliquot analyzed for radioactivity as the glucuronides of estrone and estradiol and the % peripheral aromatization calculated. The MCR's, calculated in whole blood, of A, E 1, E 2 and T were 53 ± 6 I/day/kg, 39.3 ± 31/day/kg, 29.9 ± 5.21/day/kg and 10.1 ± 2.31/day/kg, respectively. Each MCR was different ( P < 0.05) from the others. The P b of E 1 was 15± 2μg/day and was not different from that of E 2 (12 ± 3 μg/day). The P B of A, 231 ± 55μg/day, was greater than that of T, 13± 5μg/day. The interconversions of both the androgens (18.9 ± 3.4% vs 3.9 ± 1.0%) and the estrogens (48.8 ± 10.7% vs 4.0 ± 0.8%) favored the oxidative pathway, i.e. conversion of 17-OH to 17-oxo steroids. The conversion ratio of A to DHT was greater than that of T to DHT (16.4 ± 2.1% vs 5.3 ± 0.7%), and A is a more important source of DHT than is T. The percent of T bound to SHBG (80.7 ± 0.9%) was greater than percent of E 2 (36.9 ± 9.8%) and inversely the percents of T bound to albumin and free (17.5 ± 0.8% and 1.65 ± 0.16%) were less than the respective percents for estradiol (60.5 ± 9.5% and 2.40 ± 0.27%). The mean SHBG concentration was 54 ± 6 nM. The peripheral aromatization of androstenedione, 1.36 ± 0.05%, was greater than of testosterone, 0.18 ± 0.02%. This difference is, in part, due to the lack of SHBG-binding of androstenedione. The general pattern of androgen and estrogen dynamics is similar to that in women. This similarity is due, in part, to the presence of SHBG in both baboons and women.