Stress-Induced Elevation of Testosterone Concentrations in High Ranking Baboons: Role of Catecholamines*

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Abstract
In an ongoing study of wild olive baboons living in a protected reserve in Kenya, the response of the testicular axis to the acute stress of rapid capture and immobilization was studied. The stress suppressed LH and testosterone (T) concentrations; previous work showed this to be due to stress-induced release of opiates and glucocorticoids, acting to inhibit LH release and testicular sensitivity to LH, respectively. There was considerable individual variation in this phenomenon, which was related to the social status of individual males. High ranking males (by reproductive criteria) were less vulnerable to the suppressive effects of stress on T concentrations, and, in fact, showed transient increases in T concentrations during the first poststress hour. T concentrations in subordinates, in contrast, declined promptly and continuously. This difference in T profiles occurred despite similar suppressions of LH concentrations in both groups, suggesting a peripheral mechanism for the transient elevation of T concentrations in high ranking males. Part of this distinctive pattern had been shown to be due to the lesser sensitivity of the testes of high ranking males to the suppressive effects of glucocorticoids. The present report suggests an additional mechanism accounting for this rank-related difference. Administration of chlorisondamine, a sympathetic ganglionic blocker which attenuates stress-induced release of epinephrine and norepinephrine, failed to alter any aspect of LH or T profiles in low ranking males or LH profiles in high ranking males. However, it completely eliminated the transient rise in T concentrations in these males. This suggests that sympathetic catecholamines, released during stress and acting peripherally, directly, or permissively lead to increased T concentrations. This could be via increased blood flow through the testes and/or through direct stimulation of T release by catecholamines. The limitation of this sympathetic regulation of the testes to high ranking males suggests either enhanced sympathetic tone during stress in these animals (relative to subordinates) or enhanced target tissue sensitivity to catecholamines.