In the present study, functional Sertoli cells were identified by immunostaining for MIS. In samples dated as 4964 days of gestation, the degree to which the MIS-positive cells were organized into ‘‘cords’’ varied considerably between samples. In all cases, the cords were not as distinct as those seen in the tissue obtained during the second trimester This is consistent with previously published studies, which reported the production of functional MIS in testes obtained at 7-8 wk of gestation. Our findings also agree with reports that cord formation takes place gradually over the period of 6-8 wk of gestation.
Steroidogen-ically active Leydig cells and AR-positive peritubular cells were easily identifiable in the testes from the second trimester but were not detected in first-trimester samples. Sii-teri and Wilson, who examined the ability of human fetal testes to convert pregnenolone into testosterone, did not detect enzymatic activity before approximately 8 wk of gestation and noted that the peak of testosterone formation per whole organ occurred at 17-21 wk. Murray et al. also noted an increase in the number of immunopositive Leydig cells in testes from 14 to 18 wk of gestation and detected AR-immunopositive peritubular cells in the same set of samples.