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Cholesterol Esterase Stimulation by Luteinizing Hormone in Luteinized Rat Ovaries

Endocrinology Research Laboratories, Harvard School of Dental Medicine, and Department of Anatomy,Harvard Medical School, Boston, Massachusetts 02115, and Departments of Physiology and of Obstetrics and Gynecology, University of Western Ontario London, Ontario, Canada

Abstract

Cholesterol esterase activity was measured in luteinized ovarian tissue from immature superovulated rats. Enzyme activity was determined from the rate of appearance of lmitic acid-l-14C, hydrolyzed from a cholesteryl pa lmitate-l-¹⁴C substrate during 30 min of incubation at 37 C. Direct proportionality of incubation time with hydrolysis and enzyme concentration with reaction velocity was established for the enzyme assay system. Esterase activity was present in all subcellular fractions but most enzyme activity was found in the 100,000 xg defatted supernatant fraction. LH 10 ng), administered iv 1 hr before sacrifice, resulted in a highly significant (p <.001) increase esterase activity over saline-injected controls. suspension of 1500 xg pellet from homogenized luteal tissue was incubated in the presence of ATP (1.7x10^-3M), theophylline (10^-3M) and LH or saline; the supernatant fractions from these incubations when added to the usual 100,000 xg supernatant fraction produced no differences in esterase activity. Addition of cyclic 3',5'-AMP (0.5x10^-4M) and/or theophylline (10^-3M) with the 100,000 xg supernatant fraction was found to have no effect on cholesterol esterase activity. The present findings suggest that the depletion of sterol esters observed after LH treatment may arise from stimulation of cholesterol esterase activity, thereby enhancing the intracellular transfer of stored (esterified) cholesterol into the mitochondria, for conversion to pregnenolone. The mechanism of this stimulation appears not to be mediated directly via cyclic 3',5'-AMP.(Endocrinology 85: 474, 1969)

Footnotes

Supported by USPHS Grants HD02503 and AM00292.

¹ Medical Research Council Fellow Canadian 100-2B-79).

² USPHS Research Career Development Awardee (1-K3-HD-19448). Present address: Depts. Obstetrics and Gynecology and of Physiology, University of Western Ontario, London, Ontario, Canada.

Received December 4, 1968.

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