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Effect of Lipoproteins and Luteinizing Hormone on Progesterone Production by Large and Small Luteal Cells throughout the Porcine Estrous Cycle¹

University of Manitoba² Winnipeg, Manitoba, Canada R3T 2N2

Abstract

Large and small cells were isolated from porcine corpora lutea (CL) on d 10, 15 or 18 of the estrous cycle. They were incubated 13 to 16 h in cholesterol- and serum-free media and then supplied with 0, 10, 50 or 100 µg of either porcine low density lipoprotein (LDL) or porcine high density lipoprotein (HDL). Each dose was supplemented with 0, 10, 50 or 100 ng of porcine LH. Media progesterone (P4) content was assessed immediately before and 2 and 24 h after addition of lipoproteins and LH. Production of P4 by large cells always exceeded that of small cells. Day 10 large cells were stimulated by LDL, unaffected by LH, and either inhibited or unaffected by HDL. No treatment affected d 10 small cells. Day 15 large cells and small cells were stimulated by both lipoproteins (LDL>HDL). The large cells were stimulated to a small extent by LH at 2 h (P<.05). Large cells could be isolated from only two of five preparations of d 18 CL. Day 18 small cells produced a small quantity of P4 in a response which qualitatively resembled that of d 15 small cells. Cell type, cycle stage and lipoprotein (particularly LDL) were the major effectors of P4 production. The minimal response to LH supports the theory of autonomy of the porcine CL with respect to P4 production. Days 10 and 15 bracket the period of commitment to luteolysis, and the nature of P4 production by each cell type changed over that period. However, responsiveness to lipoproteins and LH, and cell presence over the cycle, hint that large cells may be more closely correlated than small cells with porcine luteal function.

¹ The author thanks Ms. L. Mollison and Mr. A. Canvin for expert technical assistance, Dr. N. E. Stanger for surgical expertise and Dr. G. H. Crow and Ms. M. Sheridan for statistical analyses. The pLH was generously supplied by the National Institutes of Health, Baltimore, MD. Progesterone antiserum was provided by Dr. N. C. Rawlings, Univ. of Saskatchewan. This research was supported by an operating grant from the Nat. Sci. and Eng. Res. Council of Canada.

² Dept. of Anim. Sci.