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Changes in rat testicular adenylate cyclase activities and gonadotrophin binding during unilateral experimental cryptorchidism

Summary. Unilaterally cryptorchid rats were examined at 3, 8, 15, 22 and 28 days after operation. There was a selective decrease in the adenylate cyclase (ATP pyrophosphate–lyase (cyclizing), EC 4.6.1.1 [EC] ) responses to gonadotrophin stimulation in the abdominal testis. This was associated with a parallel decrease in specific FSH and LH binding. There was no reduction in the response of testicular adenylate cyclases to prostaglandin (PG) E-1 or fluoride stimulation, indicating that both the GTP binding protein (N-component) and the catalytic subunit of the adenylate cyclase complexes were intact.

The reduction in FSH-responsive adenylate cyclase activity in the abdominal testis was not due to a change in the K_m for adenylate cyclase activation, but was due to a reduction in maximal velocities.

Unilateral cryptorchidism was also associated with a rapid decline in soluble Mn²⁺-dependent adenylate cyclase activity in germ cells (spermatids). By 3 days after operation there was an 82% decrease in germ cell adenylate cyclase activity. The loss of soluble Mn²⁺-dependent adenylate cyclase activity was associated with a parallel decrease in Sertoli cell secretion of androgen binding protein, indicating that Sertoli cell factors may be important for the maintenance of germ cell adenylate cyclase activity. The desensitization of the gonadotrophin–responsive adenylate cyclases and the loss of gonadotrophin receptors in Leydig and Sertoli cells were not due to changes in plasma gonadotrophin values because LH concentrations were within normal limits and plasma FSH was only marginally elevated in the cryptorchid rats.

No significant alterations of any of these parameters were seen in the scrotal testis of unilaterally cryptorchid rats when compared to values for intact controls.