Psychological and Behavioural Effects of Endogenous Testosterone Levels and Anabolic-Androgenic Steroids Among Males: A Review

by Michael S. Bahrke, Charles E. Yesalis III, and James E. Wright

3. Plasma Testosterone Levels and Aggression

3.1 Testosterone and Aggression in Animals

Numerous studies have shown relationships between testosterone levels, dominance, and aggressive behaviour in various species of animals (Allee et al. 1939; Barfield et al. 1972; Bouissou 1983; Bouissou & Gaudioso 1982; Hamilton 1938; Kurischko & Oettel 1977; Payne & Swanson 1973; Rose et al. 1971; Simon et al. 1985; Steklis et al. 1985; Svare 1983; van de Poll et al. 1981, 1986; Zumpe & Michael 1985) including nonhuman primates (Joslyn 1973; Rejeski et al. 1988a; Steklis et al. 1985; Zumpe & Michael 1985).

It has been argued by some reviewers that primates are less dependent on androgens for the expression of aggression than ungulates or other animals lower in the evolutionary chain (Bouissou 1983). However, Rejeski et al. (1988a) determined that intramuscular injection of testosterone propionate increased the frequency of aggressive behaviour in monkeys. 10 cynomolgus monkeys were assigned to either an experimental (n=5) or a control group (n=5) and given biweekly injections; the experimental group received testosterone propionate 4 mg/kg, and the controls a sham solution. Prior to and upon completion of an 8-week treatment period, behavioural observations (slapping, grabbing, stare threat, chasing, fleeing, etc.) were conducted. Although the administration of testosterone propionate resulted in a significant increase in aggression, more important was the finding that changes in behaviour were mediated by social status; that is, the incidence of both contact and noncontact aggression in dominant monkeys was far greater than the frequency of these behaviours in subordinate monkeys.

Joslyn (1973) has reported that injecting 3 infant female rhesus monkeys with 2mg of testosterone propionate intramuscularly 3 times per week over 8 months increased their aggressive behaviour so much so that they replaced males in top positions of the social hierarchy. Since this behaviour persisted for a year after the last hormone injection, the author suggests either that the male hormone may have directly induced a permanent change in the nervous system or alternatively that the socially dominant behaviour was so well learned during hormone treatment that it became independent of hormonal support.

Indeed, Bernstein et al. (1974) have evaluated in a series of experiments the converse of this relationship, i.e. the influence of multiple environmental and social variable upon circulating testosterone levels in the male rhesus monkey. Factors shown to significantly influence levels of circulating testosterone included among others, alterations in social rank and ‘successful’ and ‘unsuccessful’ agonistic encounters.

In general, these and other studies indicate that the level of testosterone, particularly in the prenatal period, but also during puberty and even in adulthood are important in establishing a biological readiness for normal aggressive behaviour and in facilitating the expression of aggression in ‘appropriate’ social settings in adult animals. They also indicate that both social factors and learning significantly influence the actual expression of aggression in adulthood (Rada et al. 1976a). However, the extent to which exposure to testosterone or other anabolic-androgenic steroid at any phase of the life cycle, and particularly during adulthood, is related to altered moods and feelings in humans, to the expressions of aggression in humans and even other primates, relative to animals lower in the evolutionary chain, is not well known.

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Originally appearing in Sports Medicine 10(5) 303-337. 1990.

Copyright © 1990 by Adis International Limited. All rights reserved. Reprinted by MESO-Rx with permission.  Any duplication of this document by electronic or other means is strictly prohibited.