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Abstract
The properties (association and dissociation rates, affinity and specificity) of GnRH receptors in the rat pituitary and the Leydig cells are very similar. In addition, in vivo administration for 5 or 11 days of 10 μg of GnRH to adult rats resulted in an increase (p< 0.01) in both Leydig cell and pituitary GnRH receptors. In contrast, the same treatment caused a significant decrease (p< 0.01) of Leydig cell LH receptor number. Furthermore, testosterone propionate (500 μg/day), which had no effect on Leydig cell LH receptors, caused a significant increase (p< 0.01) of testicular GnRH receptors but a decrease (p< 0.01) of pituitary GnRH receptors. Estradiol 17β valerate (5 μg/day) reduced (p< 0.01) both testicular (5 days) and pituitary (5 and 11 days) GnRH receptors. Such treatment for 5 days also decreased (p< 0.05) the Leydig cell LH receptors. No effect of dexamethasone and 17-hydroxyprogesterone was seen after 5 or 11 days of treatment.
Thus, although pituitary and Leydig cell receptors appear similar, their regulation by exogenous hormone treatments is different. Furthermore, the regulation of Leydig cell GnRH and LH receptors also appears very different, suggesting different roles of the receptors in the control of the Leydig cell function.