Decreased Leydig cell responsiveness in the testicular feminized male rat

The Stanley-Gumbreck pseudohermaphrodite or testicular feminized male (tfm) rat exhibits a decreased Leydig cell sensitivity to human CG (hCG) measured by androgen and cyclic-3',5',-adenosine monophosphate production in vitro. These changes were associated with an 80% reduction in the number of LH receptors in the tfm testis, when compared on the basis of equivalent amounts of testis particle protein or per 10(6) isolated Leydig cells. Androstenedione and not testosterone is the major androgen secreted by the tfm Leydig cell and androstenedione secretion is, therefore, a more appropriate end point than testosterone secretion for Leydig cell function in tfm animals. A dose of hCG (3 ng/2 ml) which elicited a near maximal response in androgen production from the decapsulated testes and Leydig cell suspensions of normals rats, did not significantly stimulate androgen production from Leydig cells of the tfm animals. A much higher dose of hCG (200 ng/2 ml) gave a response from the tfm Leydig cells which was comparable to that obtained with 3 ng from Leydig cells of normal littermates. This indicates that the small number of LH receptors on the tfm Leydig cell membrane are functional and that the reduction in receptor number results in a decrease in the sensitivity of response to LH rather than a reduction in the maximum steroid response.