203 Estrogen Synthesis by Immature Rat Sertoli Cells In Vitro CARLOS A. SUAREZ-QUIAN, MARTIN DYM, ANASTASIA MAKRIS, JOANNE BRUMBAUGH, KENNETH J. RYAN, AND JACOB A. CANICK Past research has implicated both the Leydig and Sertoli cells as sources of testicular estrogens. To study this issue further, we investigated the ability of Sertoli cells isolated from the testes of immature (10-day-old) rats to synthesize estrogens in response to FSH in vitro. The aromatase activity of Sertoli cells was examined by comparing simultaneously two different methods: 1. the conversion of 19-(6,7-3H)-hydroxyandrostenedione to (3H)estrone and (3H)estradiol, measured by silica gel thin layer chromatography; and 2. the conversion of unlabeled 19-hydroxyandrostenedione to total estrogen (El + E2), measured by RIA. Sertoli cells, cultured in the presence of substrate, ex- hibited aromatase activity in response to FSH. Values obtained for total estrogen synthesis, measured by di- rect tracer methodology, at FSH dosages of 0.5 &g/ml and 1.0 &g/ml, during a 24-hour period of incubation, were 620 pg/mg and 580 pg/mg, respectively; and after a 48-hour incubation, values obtained were 570 pg/ml and 560 pg/mg, respectively. When measured by RIA, simi- lar results were obtained for estrogen synthesis at iden- tical FSH dosages and times of incubation. A dose re- sponse of FSH-stimulated aromatization was also obtained by RIA. Neither control nor LH-treated cells, however, in the presence of substrate, produced detect- able levels of labeled or immunoassayable estrogens. Aromatase activity was also studied in the presence of a cold estrogen trap and measured by direct tracer meth- odology. In this case, estrogen synthesis was more than doubled. These data may suggest the further metabo- lism of estrogen by Sertoli cells. Finally, our results are discussed with respect to the role of the immature Ser- toli cell in the synthesis of testicular estrogens. Key words: Sertoli cells, estrogen synthesis, aromatase, immature testis. Drs. Suarez-Quian and Dym’s present address: Georgetown Medical School-School of Dentistry, Department of Anatomy, 3900 Reservoir Rd. N.W., Washington, D.C. 20007. Supported by grant no. 7R01 HD16260-01. Reprint requests: C. A. Suarez-Quian, Georgetown Medical School-School of Dentistry, Department of Anatomy, 3900 Reservoir Rd, N.W., Washington, D.C. 20007. Submitted for publication June 11, 1982; revised version re- ceived September 21, 1982; accepted for publication September 21, 1982. From the Departments of Anatomy and Obstetrics and Gynecology, Laboratory of Human Reproduction and Reproductive Biology, Harvard Medical School, Boston, Massachusetts Ever since Zondek (1934) first noted estrogen- like activity in stallion testes, the testicular cell type responsible for aromatization has been de- bated. Indirect methods of observation used in the past have implicated both the Leydig and Sertoli cells as likely candidates for estrogen synthesis. For example, feminization of men was observed in cases wherein testicular tumors were believed to have originated from either Leydig or Sertoli cells (Hunt and Budd, 1939; Huggins and Moulder, 1945; Teilum, 1949). Experimental evidence supports the Leydig cell as the major site of testicular aromatization. Ad- ministration of hCG in men caused an increase in both testosterone and estrogen (Leach et al, 1956). The production of estrogen per mg protein in men was greater in whole testes than in isolated seminiferous tubules (Payne et al, 1976). More re- cently, it has been shown that aromatase activity in immature (Canick et al, 1979) and mature (Val- ladares and Payne, 1979) rat testes can be stimu- lated by hCG but not by FSH. The case for Sertoli cells as the source of testicu- lar estrogens gained much support when 17f3-es- tradiol was found to increase in isolated seminif- erous tubules of the mature rat but not in intersti- tial tissue (dejong et al, 1974). Moreover, cultured Sertoli cells from immature rats have been shown to produce immunoreactive estrogens, although the identity of estrogens produced could not be established with certainty by the methodology 0196-3635/83/0500/0203/$01.15 © American Society of Andrology (J Androl 1983; 4:203-209)