Cryptorchidism and the pituitary--testicular axis in bulls.

In calves made cryptorchid at birth, serum LH concentrations were elevated (P less than 0.01) over those of intact controls by 7 weeks of age; a difference which persisted until after puberty. When intact and cryptorchid bulls were given LH-RH, i.v., at approximately 18 months of age, cryptorchid bulls were more responsive. Serum LH concentrations (mean +/- s.e.m.) after 250, 1000 and 4000 ng LH-RH were 0.2 +/- 0.03, 1.2 +/- 0.3 and 12.1 +/- 2.0 ng/ml for intact bulls and 1.0 +/- 0.6, 5.1 +/- 0.8 and 19.6 +/- 2.1 ng/ml for cryptorchid bulls. Testes from cryptorchid bulls weighed less (P less than 0.01) than testes from intact bulls (68 +/- 6 and 655 +/- 36 g) at 24 months of age. Ability to secrete testosterone in vitro was determined by incubating minced pieces of testes at 36 degrees C for 3 h in Krebs-Ringer-bicarbonate buffer (pH 7.2) containing 1 mg glucose/ml and 100 mi.u. hCG/ml. Cryptorchid testes secreted slightly more testosterone than scrotal testes on a unit weight basis, but when expressed on a paired testis weight basis, testosterone secretion by cryptorchid testes was less (8 +/- 2 and 60 +/- 10 mg, P less than 0.01). Autoradiographic localization techniques were used to show the existence of LH/hCG binding sites in cryptorchid testes. These studies suggest that cryptorchid bull testes have a reduced capacity to secrete testosterone and the near-normal serum testosterone concentrations are maintained in the presence of increased serum gonadotrophins.