ANDROGEN RECEPTORS IN THE PELVIC DIAPHRAGM MUSCLES OF DOGS WITH AND WITHOUT PERINEAL HERNIA

Levator ani and coccygeus muscle estrogen and androgen receptors were measured in 6, healthy, greater than or equal to 5-year-old, noncastra ted, male Beagles (controls) and in 24 dogs with perineal hernia. Estr ogen and androgen receptor analyses were performed on levator ani and coccygeus muscle specimens obtained from control dogs at the time of c astration; contralateral levator ani and coccygeus muscle specimens we re assayed 2 months after castration. During herniorrhaphy of dogs wit h perineal hernia, levator ani (noncastrated, n = 12; castrated, n = 7 ) and/or coccygeus (noncastrated, n = 5; castrated, n = 4) muscle biop sy specimens were obtained for estrogen and androgen receptor analyses . For estrogen and androgen receptor assays, each muscle biopsy specim en was homogenized in Tris-EDTA-glycerol buffer, and centrifuged at 30 ,000 X g; extracts were used for binding with ligands: [H-3]methyltrie nolone (H-3-R1881) for androgen receptors, and [H-3]estradiol-17 beta for estrogen receptors. Extracts were incubated overnight at 0 to 4 C. Nonspecific binding was estimated, using 100-fold concentration of co ld ligands. Bound and free hormones were separated, using hydroxylapat ite batch assay. Receptor numbers for each tissue were calculated as f emtomoles (fmol) per milligram of protein. Quantified data were compar ed between precastration and postcastration controls, using a paired t -test. One-way ANOVA and Bonferroni post-hoc test were used to compare values for precastration controls, postcastration controls, castrated dogs with perineal hernia, and noncastrated dogs with perineal hernia . Significance was set at P < 0.05. Estrogen receptors were not detect ed. Androgen receptors were characterized by Scatchard analysis (disso ciation constant = 3.16 to 6.6 nM R1881, receptor number = 23 to 175 f mol/mg of protein). Postcastration controls had significantly higher n umbers of androgen receptors in levator ani and coccygeus muscles than did precastration controls. Dogs with perineal hernia (castrated and noncastrated) had lower numbers of androgen receptors than did either control group. The paucity of androgen receptors in pelvic diaphragm m uscles of dogs with perineal hernia, compared with controls, suggests that decreases in quantity of androgen receptors contribute to the eti opathogenesis of perineal hernia in dogs.