PLASMA CONCENTRATIONS OF TESTOSTERONE, ANDROSTENEDIONE, DIHYDROTESTOSTERONE, 5α-ANDROSTANE-3α, 17β-DIOL, 5α-ANDROSTANE-3β, 17β-DIOL, AND ANDROSTERONE IN BULL CALVES: RESPONSE TO hCG

Abstract

Plasma androgen concentrations were measured in bull calves sampled weekly from birth to 30 wk of age and in calves sampled every 30 min for 8 h at 6, 14, 22 and 30 wk of age, before and after administration of hCG (5 IU kg−1, i.v.). Mean plasma concentrations of testosterone rose to 20 wk of age and then fell, but were variable. Mean plasma concentrations of androstenedione rose to 14 wk of age and then declined. Mean plasma concentrations of 5α-androstane-3α, 17β-diol and 5α-androstane-3β,17β-diol did not change with age, but dihydrotestosterone and androsterone were elevated at 14 and 22 wk of age, respectively. The overall means were 0.9 ± 0.08 ng mL−1 for testosterone, and 0.6 ± 0.07 ng mL−1 for dihydrotestosterone. Other androgens were present at concentrations of < 0.3 ng mL−1. However, the total concentration of the 5α-reduced androgens exceeded that of testosterone in bull calves from birth to 28 wk of age. Changes in mean androgen concentration with age and in response to hCG appeared to be reflected primarily in changes in the amplitude of pulses in plasma androgen concentration. Significant increases in pulse amplitude for testosterone and androstenedione occurred in response to hCG in 14-, 22- and 30-wk-old bull calves and for 5α-androstane-3α,17β-diol in 30-wk-old calves. The developing bull calf differs from laboratory rodents in that there is no period of time during reproductive development when individual 5α-reduced androgens circulate in concentrations greater than testosterone. Key words: Bull calf, sexual maturation, androgens