Testes from guinea pigs, rabbits, dogs, rats, and hamsters perfused in vitro with maximally stimulating concentrations of ovine LH released 9.76 ± 2.05, 12.80 ± 3.15, 28.94 ± 3.01, 3.18 ± 0.41, and 0.70 ± 0.12 μg testosterone (T)/h, respectively. Adjusting for differences in testicular weight did not eliminate significant (P < 0.01) species variation in testicular capacity for T secretion in response to ovine LH. Similarly, correction for Leydig cell mass, as determined by morphometric analysis, still left significant (P < 0.01) differences in the testosterone secretion rates in response to ovine LH for guinea pigs (262.5 ± 38.6 μg T/g Leydig cell), rabbits (205.5 ± 50.7 μg T/g Leydig cell), dogs (116.4 ± 14.8 jug T/g Leydig cell), rats (83.55 ± 21.80 μg T/g Leydig cell), and hamsters (18.24 ± 3.55 μg T/g Leydig cell). The data suggest that significant between-species variation of T production in response to ovine LH is not due to quantitative differences in the mass of Leydig cells.
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