CHANGES IN EQUINE ENDOMETRIAL RETINOL-BINDING PROTEIN RNA DURING THE ESTROUS-CYCLE AND EARLY-PREGNANCY AND WITH EXOGENOUS STEROIDS

A cDNA library was constructed from poly(A) RNA obtained from Day 14 n onbred equine endometrium. A cDNA probe for porcine retinol-binding pr otein (RBP) was used to screen the library, and a complete cDNA sequen ce (1133 bp, excluding the poly(A) tail) was obtained. Endometrial bio psies were obtained from cycling, nonbred mares at Days 0, 1, 4, 8, 10 , 11, 13, and 15 and from pregnant mares at Days 11, 13, 15, and 17 af ter ovulation (n = 2 mates each day). Endometrial biopsies were also t aken from 18 noncycling anestrous mares after the following treatments : C (vehicle control for 1 day, n = 3), E (estradiol-17 valerate, 5 mg /day for 6 days, n = 3), P (progesterone, 250 mg/day for 6 days, n = 4 ), ESP (E for 6 days followed by P for 6 days, n = 4), and ELF (E for 6 days followed by P for 12 days, n = 4). Northern blot analyses were performed on total RNA (30 mu g) using cDNA probes to equine (e) RBP a nd human glyceraldehyde-3 phosphate dehydrogenase (G3PDH). The RBP RNA levels (normalized to G3PDH) from nonbred mares were low during early diestrus and increased after Day 10, and RBP RNA levels from pregnant mares were similar to those of nonbred mares for corresponding days. E tended to decrease endometrial RBP RNA; and P, ESP, and ELF increase d it compared to C. There were no significant differences among P, ESP , and ELF RBP RNA levels. These results demonstrate that equine endome trial RBP RNA increases from early to late diestrus, that levels are s imilar between nonbred and pregnant mares, and that levels are under s teroid regulation.