Effects of Luteinizing Hormone on Progestin Biosynthesis in the Luteinized Rat Ovary

Abstract

A rapid 2-dimensional thinlayer chromatographic procedure has been described for the isolation and quantitative measurement of progesterone. The regulation of progesterone synthesis in lutein tissue obtained from rats pretreated by the PMS: HCG method of Parlow has been investigated. Addition of LH to the media in which ovarian slices were incubated produced highly significant (p l4C remained unchanged or was decreased by the action of LH in the medium. Similar effects were produced by LH administered intravenously to ovary donors 30 min before excision of ovaries. A reversal of these effects of LH occurred when an hour or more elapsed between initiation of the in vivo LH treatment and ovarian excision, regardless of the mode of administration of LH in vivo. Progesterone synthesis, measured chemically, was decreased considerably below the control level, whereas its specific activity was greatly increased. These observations suggest that LH acts initially by increasing the conversion of some preformed precursor to progesterone. After its continued action in vivo for an hour or more, the tissue stores of this precursor are depleted to such an extent that elevated progesterone synthesis can no longer occur when the ovary is excised. The reduced size of the precursor pool, combined with a compensatory increase in rate of precursor synthesis, may explain the increased acetate-UC incorporation into progesterone synthesized under these conditions. The stimulation of glycolysis by LH in vivo reported previously seems to be associated with this compensatory increase in precursor synthesis rather than with the initial action of LH. Specific activity of cholesterol synthesized from acetate-1-^l4C was considerably less than that of progesterone synthesized under all experimental conditions tested, indicating that the entire cholesterol pool was not being drawn upon for progesterone synthesis. Further evidence of this was provided by the virtual failure of incorporation into progesterone of cholesterol-4-^l4C added to the incubation medium, even though some penetration within the tissue took place. No stimulation by LH of cholesterol-4-^l4C incorporation into progesterone was observed even under conditions in which acetate-l-^l4C incorporation was stimulated 100-fold. (Endocrinology75: 488, 1964)