Morphological assessment of the effect of growth hormone on preantral follicles from 11-day-old mice in an in vitro culture system

The present study was carried out to verify that the cells attached to the outside of the basement membrane of mechanically isolated follicles are the ca cells and to evaluate the effect of growth hormone (GH) on these cells. Preantral follicles, 100-140 mu m in diameter, were mechanically isolated f rom 11-day-old BDF1 hybrid immature mice, divided randomly into two groups, and cultured in vitro. One group was treated with 0.1% collagenase immedia tely after mechanical isolation in an attempt to remove theca cells attache d to the outside of the basement membrane. The other group was untreated. M orphological examination revealed that 86.1% of mechanically isolated folli cles before collagenase treatment had at least one theca cell around the ba sement membrane on the single section. However, after collagenase treatment no theca cells remained on the basement membrane of the follicles, Androst enedione secretion as a result of stimulation by 100 ng/ml hCG was signific antly higher in the culture medium of the follicles with theca cells than i n those of collagenase-pretreated follicles (p < 0.0001), indicating that t he cells attached to the outside of the basement membrane were actually fun ctional theca cells, not interstitial cells. To elucidate the effect of GH on theca cells, preantral follicles cultured in the presence of 1.0 mIU/ml GN were morphologically examined. Preantral follicles mechanically isolated from immature mice showed significant proliferation of not only granulosa cells hut also theca cells in the presence of GR. In particular, theca cell s, which remained dotted on the basement membrane in a small number just af ter isolation, proliferated and finally formed complete layers after the cu lture with GH. This is the first report that GH induced the proliferation o f theca cells to form morphologically complete layers around the preantral follicle from 11-day-old mice. (C) 2000 Academic Press.