Plasma testosterone levels and sexual performance of young obese male Zucker rats

The sexual behavior of obese male Zucker rats was studied at the age of 7, 8, 9, 10, 11, 14, and 16 weeks. Between 12–14 weeks of age, obese rats were treated with 400 μg testosterone propionate daily. Plasma testosterone levels were determined at the age of 10, 14, 16, and 20 weeks. Compared to lean rats, the sexual performance of the obese rats was abnormal at all ages. Plasma testosterone levels of obese rats were significantly lower at the age of 20 weeks but not at the age of 10 and 16 weeks, compared to those of their lean littermates. At the age of 14 weeks, after 2 weeks of testosterone treatment, plasma testosterone concentration rose to levels significantly higher than those of their lean littermates. However, there was no improvement in their sexual behavior following this period of hormone treatment. This study strongly suggests that obese male Zucker rats have abnormal reproductive function at all ages and that testosterone deficiency is not a primary cause of this abnormality.