ABSTRACT
The role of plasma lipoproteins in supplying cholesterol for progesterone biosynthesis by human corpus luteum tissue in culture was investigated. Progesterone secretion by tissue fragments maintained in organ culture reached a maximum rate by the third day and subsequently declined. Maximal secretion of progesterone was dependent on the presence of both low density lipoprotein (LDL) and hCG in the culture medium, whereas high density lipoprotein (HDL) was ineffective in supporting progesterone 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. It is concluded that LDL, but not HDL, is the major source of cholesterol used by the human corpus luteum for progesterone biosynthesis.
Subject(s)
Corpus Luteum/metabolism , Lipoproteins, LDL/pharmacology , Progesterone/biosynthesis , Adult , Cholesterol/analysis , Cholesterol Esters/analysis , Chorionic Gonadotropin/metabolism , Female , Humans , Hydroxymethylglutaryl CoA Reductases/metabolism , Lipoproteins, HDL/pharmacology , Lipoproteins, LDL/metabolism , Middle Aged , Organ Culture TechniquesABSTRACT
Human corpus luteum tissue, maintained in organ culture, is dependent upon low-density lipoprotein (LDL) as a source of cholesterol for maximal progesterone secretion whereas high-density lipoprotein (HDL) does not support progesterone biosynthesis by human corpus luteum tissue. In the present investigation, follicular fluid of human ovaries was found to contain little or no LDL or very low-density lipoprotein. The concentration of HDL in follicular fluid approached that found in plasma. We suggest that one reason that granulosa cells of the preovulatory follicle produce limited quantities of progesterone is because of the absence of LDL-cholesterol in follicular fluid. Following ovulation, vascularization of the corpus luteum provides a means by which LDL is available to the luteinized granulosa cells and thence progesterone biosynthesis can commence.
