Graduate Thesis Or Dissertation
 

Plasma membrane composition and luteinizing hormone receptors of ovine corpora lutea during early pregnancy

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  • The lipid composition of plasma membranes of corpora lutea was examined to determine whether changes in this organelle occur during regression and early pregnancy in the ewe. Forty ewes were assigned to be necropsied on days 13 or 15 of the estrous cycle (D13-NP and D15-NP) or pregnancy (D13-P and D15-P). Purification of luteal membranes on discontinuous sucrose gradients yielded two fractions that exhibited the greatest enrichment of 5'-nucleotidase activity over that of the homogenate, and the lowest contamination by endoplasmic reticulum and mitochondrial membranes. Predominant phospholipids identified in membranes obtained from all groups were phosphatidylcholine (PC, 48.9±0.6% of total phospholipid), phosphatidylethanolamine (PE, 33.3±0.4%), sphingomyelin (SPH, 9.7±0.3%), phosphatidylserine (PS, 3.5±0.2%) and phosphatidylinositol (PI 4.0±0.5%). No changes were observed in the μg phospholipid/mg membrane protein for any luteal phospholipid and in the free cholesterol to phospholipid ratio on days 13 and 15 of the estrous cycle or pregnancy. No significant changes in the relative percentages of the major fatty acids present in PC (16:0, 18:1), PE (18:0, 18:1, 20:4) or PS (18:0, 18:1, 22:4) nor in the ratios of unsaturated (U) to saturated (S) fatty acids in these phospholipids were observed. The profile of the major fatty acids present in PI revealed a decrease in 18:0 in D15-NP, an increase in 20:4 in D15-P and an increase in 22:4 in luteal membranes of both D13- and D15-NP ewes relative to levels of these fatty acids in PI of corresponding NP or P ewes. Specific binding of [¹²⁵I]liodo-hCG to luteal plasma membranes from NP and P ewes on days 13 and 15 (6/group) revealed similar affinities and concentrations of unoccupied LH receptors. These results indicate that major changes in the gross composition of luteal plasma membrane lipids and LH receptor binding are not asociated with corpus luteum maintenance during the time of maternal recognition of pregnancy in the ewe. However, changes in phospholipid unsaturated fatty acids of 20 or more carbon atoms may be indicative of continued luteal function during early pregnancy in the ewe.
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