Ovine prostaglandin F 2α receptor

Expression of the receptor for prostaglandin F 2α (PGF 2α ) is decreased in the ovine corpus luteum during regression and increased in early pregnancy. This study was designed to evaluate the influence of progesterone and/or 17β-estradiol (E 2 ) on this regulation. Circulating progesterone (functional regression) and luteal PGF receptor mRNA decreased ( p <0.05) within 8 h of PGF 2α -induced luteal regression in midluteal phase (day 10; d 10) ewes; however, internucleosomal DNA fragmentation (structural regression) was not yet increased. Additionally, luteal PGF receptor mRNA and circulating progesterone were greater ( p <0.05) in pregnant than in nonpregnant ewes on d 14, but not on d 12. Twelve hours following injection of d 10 ewes with E 2 , steady-state levels of mRNA for PGF receptor were decreased ( p <0.05), although circulating progesterone and DNA laddering were unchanged. Conversely, luteal mRNA for PGF receptor was increased ( p <0.05) by E 2 treatment in hysterectomized ewes. These results provide evidence that (1) luteal PGF receptor expression parallels circulating progesterone levels during functional regression and in early pregnancy, but (2) expression of PGF receptor can be dissociated from alterations in circulating progesterone by injection with E 2 . Additionally, decreased PGF receptor expression initiated by E 2 is uterine-dependent, whereas the direct luteal effect (hysterectomized ewes) of E 2 is a stimulation of PGF receptor expression. These results collectively support the belief that the apparent downregulation of PGF receptor during luteal regression is associated with uterine-derived PGF 2α and its intracellular effects rather than with alterations in ovarian steroid production.