Plasma Lipoprotein Regulation of Progesterone Biosynthesis by Human Corpus Luteum Tissue in Organ Culture*

Abstract

The role of plasma lipoproteins in supplying cholesterol for progesterone [P4] biosynthesis by human corpus luteum tissue in culture was investigated. P4 secretion by tissue fragments maintained in organ culture reached a maximum rate by the 3rd day and subsequently declined. Maximal secretion of P4 was dependent on the presence of both low density lipoprotein (LDL) and hCG [human chorionic gonadotropin] in the culture medium; high density lipoprotein (HDL) was ineffective in supporting P4 biosynthesis. Human corpus luteum tissue degraded [125I]iodo-LDL by a mechanism which was saturable, and degradation of [125I]iodo-LDL was stimulated by hCG. Although 3-hydroxy-3-methylglutaryl coenzyme A reductase activity was present in microsomes prepared from fresh human corpus luteum tissue, the activity of this enzyme in microsomes prepared from tissue maintained in culture for 3 days was virtually undetectable. Fresh human corpus luteum tissue contained 3 times more unesterified cholesterol than esterified cholesterol. LDL, but not HDL, is the major source of cholesterol used by the human corpus luteum for P4 biosynthesis.