Serum Testosterone and Gonadotropins in the Genetically Obese Male Zucker Rat*

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Abstract
Serum concentrations of testosterone, LH, and FSH were measured in obese and lean male Zucker rats 1–6 months of age. The serum concentrations of testosterone were lower in the 2-, 3-, and 4-month-old obese rats than in their lean controls. There was no correlation between fertility and serum testosterone concentration in the obese rats. Serum LH and FSH concentrations were normal, as was the response of the obese rats to LHRH stimulation. Testes morphology differed between the obese and the lean rats. Although the Leydig cells of the obese rat testes were hypertrophied, they contained numerous fat droplets and few signs of active hormone synthesis. These data suggest that the obese male Zucker rat has a defect in testicular testosterone production but has a normal pituitary response to hypothalamic stimulation.