Leydig Cell Function in Rats Chronically Deprived of Normal Gonadotrophic Stimulation: The Effect of Treatment with hCG

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Abstract
Leydig cell function was assessed in adult rats 11 months after active immunization against LH‐RH. Immunized rats were divided into 2 groups according to whether the serum levels of LH and FSH were always undetectable (Group A) or were detectable at some time during the 11 months (Group B). Compared with controls, testicular weight was reduced by 84% (Group A) and 78% (Group B), but the number of Leydig cells per unit area of testis was increased by a factor of 7. Despite the latter change, the binding of 125I‐hCG per 20 mg testicular homogenate was 40% lower in immunized than in control rats. The serum level of testosterone in immunized rats was ≤ 0.1 ng/ml whilst levels ranged from 0.7 to 2.9 ng/ml in controls. In the same rats the testicular production of testosterone in vitro, both basally and after incubation with hCG or dibutryl cyclic AMP, was reduced by over 90% in immunized animals, although this impairment was more severe in Group A than in Group B animals.Leydig cell function was also assessed at 48 h after a single injection of 100 IU hCG. This treatment reduced the testicular binding of 125I‐hCG by over 89% in controls as well as both groups of immunized rats and caused a 3‐ to 4‐fold increase in the serum levels of testosterone in all animals. Following injection of hCG, the basal production of testosterone by the testis in vitro was doubled in controls whereas this increase was over 50‐fold in Group A immunized rats. In the latter, the maximum steroidogenic response of the testis in vitro was more than trebled by prior injection of hCG whilst this treatment caused a 30% reduction in the maximum response of testes from controls.

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