| Summary: | Many of the early studies which attempt to relate hormones to 'aggression' have methodological problems. Consequently, one thousand, six hundred and twenty-seven male mice rendered aggressive by breeding experience were used in a series of studies to assess the abilities of sex steroids to maintain post-castrational aggressiveness. A range of relatively low doses of oil-based intra-muscular injections of androstenedione; testosterone; 19-hydroxytestosterone; 5a dihydrotestosterone; 50 dihydrotestosterone; androsterone; 5a 19-hydroxydihydrotestosterone; oestradiol benzoate; oestradiol-l70; oestrone; oestriol; diethyl stilboestrol and 2a, 7a dimethyl androst-5-en-30, 170-diol were assessed for both behavioural and somatic actions. The results indicate that: (i) Steroidal and non-steroidal oestrogens are more behaviourally potent (on weight injected basis) than any other investigated compounds. This suggests that possession of an aromatized 'A' ring augments potency with respect to fighting behaviour. (ii) Aromatizable androgens are behaviourally and somatically potent whereas nonaromatizable (5a-reduced) compounds generally have low behavioural and high somatic potencies. However, 5mDHT does maintain behaviour so one cannot argue that 5a reduction abolishes the ability to maintain aggressive motivation. 5aDHT may, however, be an unusual compound. (iii) 19-hydroxylation seems to reduce both behavioural and somatic potencies. Subsequently, the abilities of a variety of anti-androgens, anti-oestrogens, aromatase inhibitors and progesterone to suppress androgen or oestrogen maintained fighting were investigated. The most striking finding here was that the anti-aromatase blocked testosterone but not oestrogen-maintained fighting. The results provide strong support for the suggestion that aromatization of androgens to oestrogenic metabolites has a potent effect on their ability to maintain fighting. It is not certain, however, whether this conversion is obligatory. The results do, however, strongly indicate the need to consider the effects of possible metabolic conversions of applied steroid treatments when assessing the effects of hormones in both animal behavioural and clinical studies.
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