RELAXIN IN PERIPHERAL PLASMA OF BOARS DURING DEVELOPMENT, COPULATION,AFTER ADMINISTRATION OF HCG AND AFTER CASTRATION

Seventy-two Yorkshire boars were used in five experiments to evaluate the temporal changes in relaxin concentrations in peripheral blood pla sma during prepubertal development, copulation, after castration and a fter treatment with hCG. High concentrations of relaxin (484+/-27 pg m l(-1)) were detected at II weeks of age but there was no positive corr elation with testicular development. Relaxin concentrations fluctuated in mature boars but the results do not suggest a diurnal rhythm, alth ough there is the possibility of pulsatile secretion. A decrease (P<0. 05) in circulating relaxin was observed before and immediately after c opulation. Castration of boars at 90, 115, 160 and 200 days of age did not significantly decrease relaxin concentrations within 48 h. Admini stration of hCG significantly depressed relaxin secretion at 90 days o f age but not at 160 days of age. These studies suggest a non-gonadal source of boar relaxin that is not correlated with testicular growth o r testosterone concentrations, is modulated by copulation and by hCG b ut only at specific stages of development.