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Histomorphology, oLH and hCG receptors, and testosterone secretion in vitro in Rambouillet rams from lines in which females had been selected for low or high reproductive rate

The objective of this study was to determine whether gross or histomorphological components of the testes, capacity and dissociation constants (K_d) of testicular oLH and hCG receptors, and gonadotrophin-stimulated testosterone secretion in vitro differed among Rambouillet rams from lines selected for low or high female reproductive rate and from rams of a random-bred control line. Lines had been selected for approximately 20 years. Data were collected from 22-month-old rams during the late breeding season. Rams among lines did not differ (P > 0.05) in gross testicular characteristics or most histomorphological characteristics. However, the percentage volume of interstitial vascular tissue was greater (P < 0.05) for rams from lines selected for low female reproductive rate than for rams from lines selected for high female reproductive rate. Receptor sites per Leydig cell and binding capacities of oLH and hCG receptors per testis, per gram of parenchyma, and per milligram of membrane protein did not differ (P > 0.05) among lines. The K_d values for oLH and hCG receptors did not differ (P > 0.05) among lines; however, receptor sites per Leydig cell, capacities of testicular parenchyma to bind gonadotrophin and K_d values were higher (P < 0.05) for oLH than for hCG receptors. Total oLH- and hCG-stimulated testosterone secretion in vitro did not differ (P < 0.05) among lines. In conclusion, selection for or against reproductive rate in Rambouillet ewes has not altered gross or most histomorphometric characteristics of the testes of male offspring, with the exception that selection against reproductive rate increased the proportion of testicular volume occupied by vascular tissue within the interstitium. Furthermore, selection has not altered total oLH- and hCG-stimulated testosterone secretion in vitro or the affinity and capacity of oLH and hCG receptors of the testes of male offspring.