A RELATIONSHIP BETWEEN PLASMA CONCENTRATIONS OF TESTOSTERONE AND CORTICOSTEROIDS DURING SEXUAL AND AGGRESSIVE BEHAVIOUR IN THE BOAR

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Abstract
SUMMARY: Copulation with an oestrous sow or exposure to an aggressive boar resulted in a sharp rise in the concentration of corticosteroids in the plasma of boars, and subsequently, an immediate increase in the concentration of testosterone. Placing a test boar in close proximity to an oestrous sow for a period of 10 h caused three peaks in the concentration of corticosteroids in the plasma, each of which preceded a peak testosterone concentration. An inhibitor of 11 β-hydroxylation, metyrapone, was administered intravenously to limit corticosteroid production. One injection of 5 mg metyrapone/kg body weight or three injections of 4 mg metyrapone/kg body weight did not interfere with the response of the testes to stimulation by luteinizing hormone or human chorionic gonadotrophin. Peak values in the concentrations of corticosteroids and testosterone in the plasma after injection of adrenocorticotrophic hormone were limited to approximately one half when metyrapone was given. Similarly, metyrapone treatment reduced the response, in terms of plasma steroid levels, when test boars were exposed to an oestrous sow or an aggressive boar. The results show that an increase in the concentration of testosterone in the plasma during sexual or aggressive behaviour in the boar is highly correlated with an increase in the concentration of corticosteroids.