Determination of cytosolic androgen receptors in the hypothalamus of the boar

Twenty-one crossbread boars (of Landrace x Duroc and Landrace x Duroc X Yorkshire breeding) were used to determine the presence of androgen receptors in the hypothalamus of the boar. These animals, at 47-58 days of age, had been randomly allotted in equal numbers to one of three diet treatments containing either 50, 150, or 300 ppb selenium. Libido of each boar was routinely scored upon exposure to ovariectomized-estrogenized gilts beginning at five months of age. The boars were slaughtered at nine months of age and the brain removed for subsequent excision of the hypothalamus. The hypothalamus was then sectioned into anterior, medial and posterior sections. A blood sample was also taken at the time of slaughter for later analysis of plasma testosterone concentration. Using a charcoal adsorption assay, androgen receptors were found to be distributed throughout the hypothalamus. Although section of the hypothalamus had no significant effect(P>.10) on the amount of testosterone or 5α-dihydrotestosterone binding, testosterone appeared to accumulate more in the medial hypothalamus with more 5α-dihydrotestosterone binding in the posterior hypothalamus. The protein receptor seemed to be more specific for 5α-dihydrotestosterone than for testosterone, especially in the medial and posterior sections. A significant difference (P<.05) in protein concentration between the medial hypothalamus (24.33 ± 1.26 ug/mg of tissue) and the posterior hypothalamus (20.44 ± 1.26 ug/mg of tissue) was detected. Plasma testosterone level was related to both 5α-dihydrotestosterone binding (r = .41, P<.10) and protein (r = .52, P<.G5) concentration in the medial section, suggesting that metabolic conversion of testosterone to 5α-dihydrotestosterone is needed for controlling gonadotropin release. An inverse relationship (r= -.45), which approached significance (P<.10), was observed between testosterone binding in the medial hypothalamus and libido, while no relationship was detected between libido and 5α-dihydrotestosterone binding. Selenium diet treatment had no effect (P>.10) on androgen binding, protein concentration, plasma testosterone levels, or libido. These findings suggest that a cytoplasmic receptor for androgens exists in the hypothalamus of the boar which may play an important role in regulating reproductive function.