Social Modulation of Circulating Hormone Levels in the Male

Abstract

SYNOPSIS. In many species, social interactions rapidly modulate circulating hormone levels in the male. Sexual interaction or mere exposure to a conspecific female results in rapid, transient elevation of both plasma luteinizing hormone and testosterone concentrations in a variety of species. In contrast, aggressive interactions result in decreased plasma gonadotropin and testosterone levels and increased levels of adrenal corticoids. In general, these changes are more profound and of longer duration than those accompanying sexual interactions, particularly among subordinate males. These fluctuations in circulating hormone levels appear to be related to an individual's behavioral responsivity. For example, plasma concentrations of luteinizing hormone during a social encounter are positively correlated with the degree of sexual arousal shown by a male during the interaction. Similar correlations have been found between plasma androgen or corticoid levels and patterns of behavior shown by males during both sexual and aggressive interactions. The causal relationship between such rapid hormone fluctuations and behavior remains unclear. Are fluctuating hormone levels causing differences in behavior or aredifferent patterns of behavior causing differences in plasma hormone levels between males? Or is the correlation between these two variables caused by their relationship to another unidentified factor? There are some data favoring the first possibility. Increasing the magnitude of socially induced hormone fluctuations during an aggressive encounter or preventingsuch fluctuations entirely significantly alters an animal's behavior. These data suggest that the endocrine system may play a more important role in an individual's minute-to-minute response to critical social stimuli than was previously realized.