Hormonas

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HORMONES AND SPORT Behavioural effects of androgen in men and women
K Christiansen
Institute of Human Biology, University of Hamburg, Martin-Luther-King-Platz 3, D-20146 Hamburg, Germany (Requests for offprints should be addressed to K Christiansen; Email: kchristiansen@public.uni-hamburg.de)

Introduction Since the early 1970s psychoendocrinological research on sexually dimorphicbehaviour has focused on testosterone, qualitatively the most potent androgen in males (Rommerts 1998), which is also present in females at approximately one-tenth of the male serum concentration (Longcope 1986). Testosterone does not cause behavioural changes per se; it can only alter the probability that particular behaviour will occur in the presence of a particular stimulus. Sex hormones caninfluence regions of the central nervous system (CNS) which contain hormone receptors. This interaction of a hormone with its receptor begins a series of cellular events that lead to a genomic response wherein the hormone acts directly or indirectly to activate genes that regulate protein synthesis (e.g. Chalepakis et al. 1990, Genazzani et al. 1992, McEwen 1992, Bixo et al. 1995). Two decisive phases havebeen identified in the effects of testosterone on brain structures and consequently on behaviour. During fetal and neonatal life, relatively high concentrations of testosterone are thought to influence brain development by organizing the undifferentiated brain in a sex-specific manner. It has been shown, from studies primarily of rodents, but also of primates and other mammals, that the hypothalamus,the hippocampus, the preoptic-septal region and the limbic system are important target areas for sex steroid action (e.g. Hutchinson 1991, McEwen 1992, Collaer & Hines 1995). These brain structures and hence the corresponding behavioural repertoires are then thought to be activated at the beginning of puberty when the production of sex hormones increases (Schulkin 1993). In humans, however,hormonal influences on behaviour are much less potent than in animals. Differences in behaviour are considered to result mainly from a combination of intrapsychic, social and cultural factors. General methodological issues Hormonal influences on human behaviour are difficult to prove as pertinent research has to rely predominantly on

correlational studies of endogenous hormone levels and behaviour whichcannot ascertain hormonal influences. Some knowledge derives from clinical studies on individuals who have been exposed to atypical levels of hormones during some developmental period of their lives, so-called ‘experiments of nature’. Only on very few occasions can scientists ethically manipulate hormone levels in humans in order to examine subsequent effects on brain and behaviour. But even fromthese studies on hormone substitution one cannot always draw firm conclusions regarding a particular hormonal– behavioural relationship. From double-blind, placebocontrolled studies it may be possible to conclude that a particular hormone is the metabolic agent associated with behaviour. However, such studies are rare exceptions in human behavioural endocrinology. When interpretingpsychoendocrinological findings, these caveats should be borne in mind. The interaction between sex hormones and behaviour is complex. If the relationship is to be investigated, endogenous and genetic factors influencing the gonadal system, e.g. pulsatile patterns, circadian variations, circannual rhythms, age-related changes and body constitution have to be considered in the study design (Christiansen 1999).Moreover, a person’s androgen level and his or her behaviour are mutually dependent; sex hormones can affect behaviour, and behaviour can alter sex hormone levels. Behaviour influencing androgen levels, especially testosterone, has been reported for sexual behaviour, alcohol consumption, nutrition, physical exercise and psychic and psychosomatic stress. The general concept that behaviour can feed back...