Peripheral testosterone in boars after administration of hCG, ACTH and testosterone at three ages

Forty-four purebred Yorkshire boars, reared outdoors on concrete, were randomly assigned to one of three age groups (150 +/- 7, 200 +/- or 250 +/- 7 days of age) for the purpose of examining endogenous testosterone concentration in response to one of four exogenously administered treatments. Four boars from each age group were administered either human chorionic gonadotrophin (hCG; 1000 U.S.P. units intravenous), adrenocorticotrophin (ACTH; 100 IU intravenous), or testosterone proprionate (TP; 25 mg intramuscular). The remaining boars served as controls and were given saline (S; 5 ml IV). Blood samples were collected from each boar at -120, -90, -60, -30, and 0 min pre-treatment and at 15, 30, 45, 60, 75, 90, 105, 120, 150, 180, 210, 240, 270, 300, 330, and 360 min post-treatment via an indwelling anterior vena cava catheter. Plasma testosterone was quantified by radioimmunoassay. Within treatment, boars receiving hCG, ACTH or S responded similarly (P>.10) across the three age groups for measured testosterone. Plasma testosterone was elevated (P<.05) by 30 min (4.7 +/- .5 ng/ml; X +/- SEM) and 15 min (5.5 +/- 1.1 ng/ml) post-treatment in boars administered hCG and ACTH, respectively, when compared with the S (1.0 +/- .3 ng/ml) group. Testosterone in hCG treated boars peaked by 90 min (21.8 +/- 1.8 ng/ml) post-treatment, declined slightly until 210 min (18.8 +/- 1.8 ng/ml) post-treatment and increased thereafter. Hormone levels in ACTH treated boars plateaued by 45 min (7.5 +/- 1.4 ng/ml) post-treatment and began to decline by 90 min post-treatment. Plasma testosterone for TP treated boars differed (P<.05) over time among the three age groups. Boars 150 +/- 7 and 200 +/- 7 days of age had an increase in plasma testosterone at 150 and 240 min post-treatment with TP, respectively. Results suggest that the testosterone biosynthetic and secretory capabilities of the boar testes are fully operational by 150 days of age.