Prostaglandin F(2α) receptor concentrations in corpora lutea of cycling, pregnant, and pseudopregnant pigs

Abstract

The objective of this study was to measure and compare the concentrations of PGF(2α) receptors on luteal cells taken from cycling, pregnant, and pseudopregnant pigs. Corpora lutea were removed surgically from cycling, pregnant, and pseudopregnant (induced with 5 mg estradiol valerate/day i.m. beginning on Day 11) pigs on Day 12, 13, and 14 (postestrus) and were subjected to collagenase dissociation. Dissociated luteal cells (~100 000 large viable cells per tube) were assayed for specific PGF(2α) binding by Scatchard analysis, using [3H]PGF(2α) and varying doses (0-5 μM) of unlabeled PGF(2α). Luteal cells from all three types of pigs were shown to possess two specific PGF(2α) binding sites (high affinity, K(d) = 9-47 nM; low affinity, K(d) = 243-1359 nM). The concentrations of the high-affinity PGF(2α) binding site (PGF(2α) 'receptor') on Days 12 and 13 were not significantly different (NS) between cycling (1.7 and 1.1 x 106 receptors per large luteal cell, respectively), pregnant (1.3 and 1.2 x 106), and pseudopregnant (1.1 and 0.8 x 106) pigs. However, on Day 14, luteal PGF(2α) receptor concentrations were significantly higher (p < 0.05) in cycling (4.2 x 106) compared with pregnant (1.3 x 106) and pseudopregnant (1.4 x 106) pigs. We speculate that reduced luteal PGF(2α) receptor concentrations on Day 14 in pregnant and pseudopregnant compared with cycling pigs may lead to decreased luteal sensitivity to PGF(2α) in these animals, and that this mechanism may play a role in the maternal recognition of pregnancy in this species.