Abstract
The objective of the present study was to determine if postpubertal boars (12–13 months of age; 156 ± 8 kg) with large testes had altered hypothalamic control of secretion of luteinizing hormone (LH). Seven boars with the highest estimated 150 d, paired testis weights from a line selected for large testes (769 ± 60 g = mean weight of excised testes) and 8 boars from a control group (control, 544 ± 20 g) were tethered in stalls and fitted with indwelling jugular catheters. Males were bled when they were intact, 14 days after castration and during administration of sodium pentobarbital anesthetic (subsequent to castration) to block secretion of endogenous LH-releasing hormone (LHRH). Blood samples were collected at 12-min intervals for 6 hr before and 1 hr after intravenous injection of LHRH in intact and castrated males. During anesthesia, LHRH was administered 4 times at 1-hr intervals and blood samples were collected every 6 min. All samples were analyzed for concentrations of LH and pooled samples were analyzed for concentrations of 17-β estradiol (E 2) and testosterone (T). In intact and castrated males, mean concentrations of LH, frequency and amplitude of pulses of LH, and concentrations of E 2 and T were not different between boars of the two groups (P>.10). Response to exogenous LHRH was less (P<.05) in intact males with large testes than in corresponding males from the control group (P<.05). Fourteen days after castration, males that had larger testes before castration had less of a response to LHRH than males from the control group (P<.05). In anesthetized males, response to initial injection of LHRH tended (P<.09) to be less in males with larger testes, while responses to the 3 subsequent injections of LHRH were not significantly different between males of the two groups. It is concluded hypothalamic control of hypophyseal secretion of LH in postpubertal boars with larger testes may be different from that of boars with smaller testes since the response of the anterior pituitary to exogenous LHRH in boars with larger testes was less than that of boars with smaller testes.
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