Involvement of apoptosis in the induction of germ cell degeneration in adult rats after gonadotropin-releasing hormone antagonist treatment.

In adult mammals, including man, germ cell death is conspicuous during spermatogenesis and plays a pivotal role in sperm output. The possible mechanism(s) underlying this phenomenon remains, however, poorly understood. Apoptosis is a programmed physiological process by which cells die either spontaneously or in response to changes in the levels of specific physiological stimuli. Previously, we reported that early deprivation of gonadotropin and testosterone by GnRH antagonist (GnRH-A) treatment is followed by a stage-specific degeneration of germ cells in the testis. In this study, we examined the possible involvement of apoptosis in the induction of germ cell degeneration. Adult male rats were given a daily injection of Nal-Glu GnRH-A (1 mg/kg BW) for 0 (control), 2, or 5 days. The onset of germ cell degeneration was assessed by high resolution light microscopy as well as by a germ cell degeneration assay. The occurrence of apoptosis was characterized by 1) detection of internucleosomal DNA fragmentation after agarose gel electrophoresis, and 2) direct immunoperoxidase detection of digoxigenin-labeled genomic DNA in specific cell types. The earliest morphological signs of germ cell degeneration involving preleptotene and pachytene spermatocytes, step 7 spermatids (at stage VII), and step 19 spermatids (at both stages VII and VIII) were detected 5 days after the commencement of GnRH-A treatment. The onset of germ cell degeneration was further accompanied by a significant increase in the degree of low mol wt DNA fragmentation. In situ detection of apoptosis within this time frame fully corroborates the observed stage-related degeneration of specific germ cells. These results suggest that apoptosis provides the basic mechanism by which germ cells die in the testis in response to a lack of hormonal stimulation.