Theca cell cytochrome P450 17-hydroxylase and aromatase messenger ribonucleic acid abundance and serum steroid levels during follicular atresia associated with incubation behavior in the domestic turkey hen.

This study was designed to examine changes in cytochrome P450 17 alpha-hydroxylase (C17) and aromatase (ARO) mRNA contents in the theca layer of preovulatory follicles (POF) as turkey hens transit from egg laying to incubation. Hens were grouped into the following categories: 1) laying hens--laid one egg per day and nested 1-2 times per day; 2) transitional hens--laid one egg per day and nested > 4 times per day; and 3) Day 1, Day 3, and Day 5 incubating hens--laid no eggs for 2, 4, or 6 days, respectively, and nested > 4 times per day. Small white follicles (SWF) and the theca layer from the largest (F1) and the third (F3), fifth (F5), and seventh (F7) largest POF were dispersed and challenged with testosterone (T) for 5 h. Relative levels of C17 and ARO mRNA were examined from the theca layers of F1, F3, F5, F7, and SWF. The number of atretic follicles increased from 0 (layers) to 8 (Day 5 incubating hens). Serum LH, progesterone (P), and estradiol (E), but not T, declined on Day 1 of incubation. Basal levels of P, T, and E from theca and SWF cells declined in incubating hens. Both basal and T-stimulated theca and SWF production of E decreased in incubating hens. C17 and ARO mRNA declined in SWF, F7, and F5 during follicular atresia. It is suggested that reduced gene expression of ovarian steroidogenic enzymes may be a partial determinant of reduced circulating sex steroid levels in incubating hens.(ABSTRACT TRUNCATED AT 250 WORDS)