Sex steroid hormone binding globulin levels and free 17β-estradiol and testosterone in cynomolgus monkeys during different reproductive states

Abstract

The effect of differences in sex hormone binding globulin (SHBG) levels associated with reproductive status on free 17β-estradiol (E 2) and testosterone (T) was characterized in cynomolgus monkeys. Cycling female cynomolgus monkeys had higher SHBG levels than males, pregnant and lactating females ( P < 0.05). Ovariectomized females were not different than control females, suggesting no hypoestrogenic effect. The percentage of free T was elevated in pregnant animals ( P < 0.05) compared to normal males and females, but the percentage of free E 2 was similar between these groups. Although a gender difference in the percentages of free E 2 and T was not detected, there was a gender difference in the free T and E 2 concentrations due to endogenous secretion. Increased free E 2 concentrations during pregnancy were the result of endogenous secretion rather than the decreased binding capacity of SHBG; the increased percentage of free T during pregnancy significantly increased free T concentrations. These data suggest that the gender difference in SHBG levels in cynomolgus monkeys is due to androgenic influences and that estrogens have minimal influence. Furthermore, the decrease in SHBG levels during pregnancy and lactation may not be entirely dependent on these androgenic influences.