ENDOCRINE CORRELATES OF PARTNER PREFERENCE BEHAVIOR IN RAMS

We studied a unique group of rams that would not mate with estrous ewe s during extensive testing for sexual behavior. The same rams courted males in preference to females in 30-min sexual preference tests and w ere classified as male-oriented (n = 6). We compared the following end ocrine profiles: systemic steroid concentrations, the capacity of the testes to biosynthesize 17 alpha-hydroxyprogesterone and testosterone from H-3-progesterone in vitro, and the levels of brain aromatase acti vity (AA) in mate-oriented rams vs, rams that were proven breeders and designated as female-oriented (n = 7). After the last behavioral test , sera were collected, and males in each experimental group were kille d. Brains and testes were obtained for subsequent determinations of AA and measurements of steroidogenic enzyme activity. All dissections an d subsequent assays were performed without knowledge of experimental g roup assignments, Serum concentration of testosterone (T), dihydrotest osterone (DHT), androstenedione, estrone (E(1)), and estradiol-17 beta (E(2)) were determined by RIA. AA was quantified by a (H2O)-H-3 assay validated for neural tissue of the ram. We studied frontal, parietal and cingulate cortex, cerebellum, hippocampus, olfactory bulb, septum, amygdala, infundibulum-median eminence, and preoptic area (POA). Seru m T, E(1), and E(2) concentrations of female-oriented subjects were si gnificantly higher (p < 0.05) than those in male-oriented subjects (SE M: 1559 +/- 228, 46 +/- 2, and 15 +/- 3 pg/mi vs. 874 +/- 196, 40 +/- 2, and 8 +/- 1 pg/ml serum, respectively). DHT and androstenedione con centrations in the systemic circulation did not differ between groups. Likewise, biosynthesis of labeled T and 17 alpha-hydroxyprogesterone from H-3-progesterone by testicular homogenates in vitro was significa ntly higher (p < 0.05) in female-oriented than in male-oriented subjec ts (28.8 +/- 8.1 vs. 12.1 +/- 2.3 mu mol . h(-1). mg protein(-1) for T and 416.9 +/- 100.8 vs. 186.3 +/- 30.7 mu mol . h(-1). mg protein(-1) for 17 alpha-hydroxyprogesterone). The highest level of AA was found in the POA, which was significantly greater in female-oriented than in male-oriented rams (472 +/- 34 vs. 296 +/- 24 fmol (H2O)-H-3 . h(-1). mg protein(-1), p < 0.05). AA in other brain areas did not differ bet ween experimental groups. Our data suggest that the testes of the male -oriented ram have reduced capacity for T production. In other species , T controls in situ estrogen formation not only by providing substrat e for aromatization but also by up-regulating P450(arom) mRNA in the P OA. Because the POA is part of a neural circuitry that mediates male s exual behavior in many species, we hypothesize that the capacity for a romatization influences sexual orientation of these rams.