SIGNIFICANCE OF APOPTOSIS IN THE TEMPORAL AND STAGE-SPECIFIC LOSS OF GERM-CELLS IN THE ADULT-RAT AFTER GONADOTROPIN DEPRIVATION

The major objectives of the present study were to document the tempora l and stage-specific acceleration of germ cell apoptosis in adult rats after selective suppression of pituitary gonadotropins by GnRH antago nist (GnRH-A) treatment, and to examine the possibility that apoptosis is the sole mechanism of germ cell death in response to hormonal depr ivation. Groups of adult male rats were given a daily injection of a v ehicle for 14 days or GnRH-A (1.25 mg/kg BW) for 2, 5, 7, and 14 days. Analysis of testicular apoptotic DNA fragmentation revealed a detecta ble increase at Day 5 and a maximal increase at 14 days after treatmen t. In situ analysis of germ cell apoptosis fully corroborated the obse rved increase in the degree of DNA fragmentation with time and also re vealed a stage-related activation of apoptosis of specific germ cells. A low incidence (0.06-0.09) of germ cell apoptosis (expressed as numb ers per Sertoli cell) was detectable at stages I, IX-XI, and XII-XIV i n control rats. Mean incidence of apoptotic germ cells specifically at stages VII-VIII increased significantly (0.40 +/- 0.06) by Day 5 and increased another 2.2-fold (over the 5-day treatment values) on Day 7 after GnRH-A treatment as compared to values in controls, where no apo ptosis was detected. Significantly increased incidence of apoptosis at stages IX-XI (0.37 +/- 0.05) over control values (0.07 +/- 0.01) was noted by Day 7. Within the study paradigm, the highest number of dying cells occurred by Day 14, at which time a modest but significant (p < 0.05) increase in the incidence of apoptosis was also noted at stages I, II-IV, V-VI, and XII-XIV in comparison with control values. Stages VII-VIII and IX-XI still exhibited the higher number of cells undergo ing apoptosis (0.97 +/- 0.22, and 1.03 +/- 0.22, respectively). Compar ison between rates of apoptosis and cell degeneration measured at stag es VII-VIII demonstrated an intimate association (r = 0.94; p < 0.001) between apoptosis and germ cell loss, strongly supporting the concept that germ cell death (at these stages) after removal of hormonal supp ort in the adult rat occurs almost exclusively via apoptosis.