Luteal progesterone synthesis and high-density lipoprotein. Evidence implicating a pronase-sensitive HDL-binding site in the mechanism by which HDL supports luteal progesterone synthesis.
We have shown previously that corpus luteum cells isolated from the superovulated ovaries of rats treated with 4-amino-pyrazolo[3,4-d]pyrimidine constitute a suitable experimental system by which to investigate the mechanism in which plasma high-density lipoprotein (HDL) plays a role in luteal cellular progesterone synthesis. In the present study, the rate of luteal cellular progesterone synthesis was shown to be stimulated by 125I-labelled HDL up to about 70% of the rate achieved in the presence of native HDL. The concentration of HDL needed for half-maximal stimulation of progesterone synthesis in the presence of lutropin was not significantly different irrespective of whether radioiodinated HDL or unlabelled HDL was used. Experimental conditions for studying the binding of 125I-labelled HDL to isolated luteal cells have been defined and cellular binding affinity and binding capacity have been measured. Exposure of the luteal cells to pronase virtually abolished their capacity to bind 125I-HDL and made them unable to respond to added HDL by increasing their rate of progesterone synthesis in the presence of lutropin. Control experiments showed this effect of pronase on cellular progesterone synthesis not to be due to destruction of cellular lutropin receptors, nor to general cellular damage. This evidence supports the view that luteal cellular binding of HDL is part of the mechanism by which HDL acts in luteal progesterone synthesis. Cellular binding capacity and affinity for 125I-labelled HDL were the same irrespective of whether or not lutropin was present during incubation. Furthermore, the binding capacity and affinity of cells from the ovaries of rats not treated with 4-amino-pyrazolo[3,4-d]pyrimidine were the same as in luteal cells isolated from rats that had been treated.
Aitken
J W
JW
Department of Biochemistry, University of Dundee, Scotland.
Booth
R
R
Stansfield
D A
DA
D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D008076:Cholesterol, HDL / Q000378:metabolism*; D003338:Corpus Luteum / Q000378:metabolism*; D005260:Female; D066298:In Vitro Techniques; D008075:Lipoproteins, HDL / Q000378:metabolism*; D007986:Luteinizing Hormone / Q000494:pharmacology; D011374:Progesterone / Q000096:biosynthesis*; D011402:Pronase; D051381:Rats
D008076:Cholesterol, HDL; D008075:Lipoproteins, HDL; C004420:4-aminopyrazolo(3,4-d)pyrimidine; D011374:Progesterone; D007986:Luteinizing Hormone; D011402:Pronase; D000225:Adenine