HORMONAL-CONTROL OF APOPTOTIC CELL-DEATH IN THE TESTIS - GONADOTROPINS AND ANDROGENS AS TESTICULAR CELL-SURVIVAL FACTORS

Although the requirement for pituitary gonadotropins during testicular cell differentiation is well documented, the possible role of FSH and LH in regulating testicular cell survival has not been studied. Using a quantitative autoradiographic method for the detection of internucl eosomal DNA fragmentation, a hallmark feature of apoptosis, the hormon al control of apoptotic cell death was studied in testicular cells col lected from immature rats after hypophysectomy. After surgery, animals were treated with daily injections of 20 IU long-acting FSH agonist ( FSH-CTP) or 50 IU human CG (hCG) for 2 days. Hypophysectomy decreased testis weight by 25%, but treatment with FSH-CTP or hCG prevented the effect of hypophysectomy. Testes of intact animals contained predomina ntly high-mol wt DNA, whereas hypophysectomy increased DNA cleavage in to low-mol wt (<15 kilobases) ladders characteristic of apoptosis. In contrast, treatment with FSH-CTP or hCG inhibited hypophysectomy-induc ed apoptotic DNA cleavage by 84% and 51%, respectively. Hypophysectomy -induced DNA fragmentation was found in both interstitial cells and se miniferous tubules. Similar to whole testis, treatment with FSH-CTP su ppressed hypophysectomy-induced apoptosis by over 90% in seminiferous tubules and interstitial cells. In contrast, hCG treatment was less ef fective in preventing hypophysectomy-induced DNA cleavage (46% suppres sion in tubules and 77% suppression in interstitial cells). Furthermor e, testosterone replacement also suppressed hypophysectomy-induced DNA fragmentation by 75% in the whole testis tissue, 64% in tubules, and 55% in interstitial cells. To further study the role of gonadotropins, intact animals were treated with a potent GnRH antagonist (Azaline B, 10 mug/day) to decrease serum gonadotropin levels. This treatment inc reased testicular DNA fragmentation to levels comparable to those indu ced by hypophysectomy, suggesting that gonadotropins are the primary p ituitary factors regulating testicular cell survival. These data indic ate that, in addition to their well known role in stimulating testicul ar cell differentiation and growth, both FSH and LH/hCG are essential for preventing testicular cell death in both seminiferous tubules and interstitial cells. Furthermore, the suppressive effect of LH/hCG on a poptotic cell death in the seminiferous epithelium may be partially me diated by androgens. Future use of the present autoradiographic method to study hormonal regulation of testicular apoptosis should provide n ew insight on testis physiology and pathophysiology.