Sapolsky RM, Share LJ. Rank-related differences in cardiovascular function among wild baboons: role of sensitivity to Glucocorticoids. American Journal of Primatology. 1994; 32: 261-75

Wild baboons of known dominance were challenged with epinephrine [adrenaline] when anesthetized, and the more dominant males had the quickest and largest rise in blood pressure, and the pulse, and the most rapid recovery. Using selective (alpha and beta agonists), separately, the same rank related difference was seen. Anesthesia is a significant cause of glucocorticoid secretion, which augment the action of the hormones used, so when the secretion of glucocorticoids was pharmacologically blocked, the rank related differences among the baboons were not observed. This adds indirect evidence to the differences in response to cardiovascular stress arising from different sensitivity to the cardiovascular actions of glucocorticoids which are secreted during stress. 

Abstract

In a population of wild baboons living in East Africa, we have observed endocrine differences among individuals as a function of dominance rank. Among these differences, we previously observed indirect evidence for dominant males being more responsive to sympathetic catecholamines than were subordinate males. The present report tests this explicitly. Male baboons of known rank were anesthetized, and sympathetic and parasympathetic activity was pharmacologically inhibited. In experiment I, males were challenged with epinephrine; over a wide dose range, dominant males had the largest and fastest rises in systolic pressure, the greatest peak systolic pressure, and the most rapid recovery from the epinephrine challenge. Similar rank-related differences in heart rate, response to epinephrine also occurred. Experiment II showed that this phenomenon probably reflects rank-related differences at both the heart and vasculature. As evidence, the same rank differences in systolic blood pressure responsiveness occurred when males were challenged with the alpha receptor agonist phenylephrine (which predominantly constricts systemic veins and arterioles), while the same rank differences in heart rate responses occurred following stimulation with the beta receptor agonist isoproterenol (which selectively works at the heart).

Male baboons of known rank were anesthetized, and sympathetic and parasympathetic activity was pharmacologically inhibited. In experiment I, males were challenged with epinephrine; over a wide dose range, dominant males had the largest and fastest rises in systolic pressure, the greatest peak systolic pressure, and the most rapid recovery from the epinephrine challenge. Similar rank-related differences in heart rate, response to epinephrine also occurred. Experiment II showed that this phenomenon probably reflects rank-related differences at both the heart and vasculature. As evidence, the same rank differences in systolic blood pressure responsiveness occurred when males were challenged with the alpha receptor agonist phenylephrine (which predominantly constricts systemic veins and arterioles), while the same rank differences in heart rate responses occurred following stimulation with the beta receptor agonist isoproterenol (which selectively works at the heart).

These data were obtained from animals stressed by anesthetization, known to cause considerable glucocorticoid secretion in this population. Such steroids are well known for their capacity to augment catecholamine action. In experiment III, we blocked endogenous glucocorticoid secretion with the steroidogenesis inhibitor metyrapone, and repeated the epinephrine challenge. Under these conditions, the rank differences in epinephrine responsiveness were eliminated. Thus, dominant males are not such much preferentially sensitive to catecholamine action, as much as to the potentiating effects of glucocorticoids upon such action. In agreement, we have observed previously that dominant males are also more sensitive to glucocorticoid negative feedback regulation.

Collectively, these data suggest that dominant males have cardiovasuclar stress-responses which are larger, faster, and recover more rapidly than do subordinates; moreover, these differences arise from differing sensitivity to the cardiovascular actions of glucocorticoids.

Keywords

• cortisol
• glucocorticoids
• hierarchy
• social stratification
• stress