MODULATION OF OVARIAN CYTOCHROME-P450 17-ALPHA-HYDROXYLASE AND CYTOCHROME AROMATASE MESSENGER-RIBONUCLEIC-ACID BY PROLACTIN IN THE DOMESTICTURKEY

The effect of exogenous ovine prolactin (oPRL) on preovulatory follicl e P450 17 alpha-hydroxylase (C17) and aromatase (ARO) mRNA abundance w as investigated in turkeys. Ovine PRL (124 IU/hen per day) was injecte d i.m. into four sets (n = 8) of laying turkeys for 2, 4, 8, or 14 day s. Vehicle was injected into control hens for 8 days (n = 8). Blood sa mples were collected and serum was assayed for LH, progesterone (P), t estosterone (T), and estradiol (E). Theca layers from the largest (F-1 ) and the third (F-3), fifth (F-5), and seventh (F-7) largest preovula tory follicles and from small white follicles (SWF) were examined for C17 and ARO mRNA contents. The number of atretic follicles increased f rom 0 (vehicle-injected controls) to 9 (14-day-oPRL-injected hens). Se rum 8, T, and LH levels decreased, while P levels remained unchanged. There was a transient increase in theca C17 mRNA abundance of 2- and 4 -day-oPRL-treated hen follicles. Cytochrome P450 ARO mRNA levels were reduced in SWF and F-7 in response to oPRL. Thecal C17 and ARO mRNA co ntent was reduced during follicular maturation in laying hens. ARO mRN A was not detectable in granulosa cells. The progressive decline in C1 7 and ARO mRNA content associated with follicular maturation as well a s the absence of ARO mRNA in granulosa cells is consistent with the se cretory activity of P, T, and E in preovulatory follicles. These findi ngs suggest that reduced circulating E may be a consequence of suppres sed ARO gene expression whereas the oPRL suppression of T secretion ma y not be coupled to C17 gene expression.