Stress-Induced Suppression of Testicular Function in the Wild Baboon: Role of Glucocorticoids*

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Abstract
In an ongoing study of endocrine function in wild olive baboons living freely in Kenya, sustained social stress was associated with suppressed testosterone (T) concentrations in males. The acute stressor of rapid capture and immobilization caused profound and rapid suppression of T concentrations in these individuals. Elevation of cortisol concentrations preceded, and was at least partially responsible for, the declining T concentrations, as dexamethasone (DEX) administration produced a similar suppression. DEX inhibited T secretion, but did not alter its clearance. The testes appeared to be the principal site of this inhibition; DEX did not alter LHRH-induced pituitary secretion of LH [luteinizing hormone], it somewhat attenuated LH bioactivity, but it caused a complete suppression of LH-induced testicular secretion of T. Considerable individual variation occurred in sensitivity to stress-induced suppression of T concentrations. Some individuals had transient elevations of T concentrations during the poststress hour, although concentrations ultimately declined significantly. These males were also least sensitive to DEX inhibition of LH-induced T secretion. Acute stress-induced suppression of gonadal function was demonstrated in a population of primates living in their natural habitat. Glucocorticoid actions mostly at the testes were implicated as possible underlying endocrine mechanisms for such regulation.