The influence of luteinizing hormone on the Leydig cells of cryptorchid rat testes.

The influence of circulating LH levels on Leydig cells from cryptorchid adult rats was examined after ablation of the pituitary. After 2 weeks cryptorchidism, serum FSH and LH levels rose 2-fold while serum testosterone (T) remained unchanged. Leydig cells were hypertrophied and showed an increased response to in vitro hCG stimulation. Two weeks after hypophysectomy (hypox), serum hormone levels (LH, FSH and T), Leydig cell size, cytoplasm, organelle content and in vitro T production were all dramatically reduced. However, when hypophysectomy was combined with cryptorchidism (hypox/crypt), there was an increase in Leydig cell size, compared to hypophysectomy alone, in the presence of very low levels of serum FSH, LH and T. Compared to the hypophysectomised state, the mitochondria were larger and the cytoplasm contained more smooth endoplasmic reticulum. The response of the hypox/crypt testes to in vitro hCG stimulation, though significantly less than the cryptorchid testes, was significantly greater than the hypox testes. These results demonstrate that the changes observed in the Leydig cell after cryptorchidism can occur in the absence of peripheral pituitary hormones and are consistent with the hypothesis that a local feedback loop exists within the testis.