RECEPTORS FOR PROSTAGLANDINS-F2-ALPHA AND E2 IN OVINE CORPORA-LUTEA DURING MATERNAL RECOGNITION OF PREGNANCY

Plasma membrane receptors for prostaglandins (PG) F2alpha and E2 were quantified in ovine corpora lutea obtained from nonpregnant and pregnant ewes on Days 10, 13, and 15 post-estrus, and from additional ewes on Days 25 and 40 of pregnancy. Regardless of reproductive status or day post-estrus, concentrations of luteal receptors for PGF2alpha were 7- to 10-fold greater than those for PGE2. In pregnant ewes the concentration of receptors for PGF, was highest on Day 10 (35.4 +/- 2.8 fmol/mg) and lowest on Day 25 (22.3 +/- 2.5 fmol/mg). A difference in the concentration of luteal receptors for PGF2alpha between pregnant and nonpregnant ewes was apparent only on Day 15 post-estrus, at which time the concentration of receptors for PGF2alpha was higher in pregnant ewes than in nonpregnant ewes (27.1 +/- 2.7 vs. 17.7 +/- 2.7 fmol/mg). Concentrations of receptors for PGE2 in pregnant ewes were similar (p > 0.05; 2.8 +/- 0.3 to 3.7 +/- 0.2 fmol/mg) between Days 13 and 40 but were higher (p < 0.05) than in corpora lutea obtained from nonpregnant ewes on Days 10 (5.0 +/- 0.4 vs. 4.1 +/- 0.2 fmol/mg) and 15 (3.7 +/- 0.2 vs. 2.0 +/- 0.4 fmol/mg) post-estrus. Although concentrations of receptors for both PGF2alpha and PGE, were lowest in corpora lutea obtained from nonpregnant ewes on Day 15, this was not due to luteal regression since the weights and concentrations of progesterone in corpora lutea on Day 15 were not lower than those for corpora lutea obtained on Days 10 and 13. Since it is established that the corpus luteum of pregnancy is not resistant to the luteolytic actions of PGF2alpha until Day 13, it appears that decreased sensitivity of the corpus luteum to PGF2alpha during maternal recognition of pregnancy is not due to a reduction in the concentration of receptors for PGF2alpha, or an increase in the concentration of receptors for PGE2.