MODULATION OF CHOLESTERYL ESTER HYDROLASE MESSENGER-RIBONUCLEIC-ACID LEVELS, PROTEIN-LEVELS, AND ACTIVITY IN THE RAT CORPUS-LUTEUM

Previous studies have shown that the induction of functional luteolysis (loss of progesterone production) with either prostaglandin F-2 alpha (PGF(2 alpha)) treatment or hypophysectomy (APX) diminished neutral cholesteryl ester hydrolase (CEH) activity in the corpus luteum (CL) and that prolactin (PRL) replacement of APX animals prevented luteolysis and maintained CEH activity at control levels, More recent studies have shown that CEH is the same protein as hormone-sensitive lipase (HSL) and that CEH/HSL activity may be regulated by phosphorylation. However, the possibility that CEH/HSL activity may be under transcriptional and/or translation control has not been excluded. Therefore, in the present study we examined whether PGF(2 alpha) treatment, APX, or inhibition of PRL secretion by bromocryptine (BrC) treatment modulated CEH/HSL mRNA and/or protein levels in a coordinate fashion with CEH activity, Furthermore, we examined whether CEH/HSL mRNA and/or protein levels changed after luteinization of the ovary and after natural functional regression, PGF(2 alpha) treatment and APX significantly reduced CEH activity; and PGF(2 alpha) treatment, APX, and BrC treatment significantly reduced CEH/HSL protein and mRNA levels. PRL replacement after APX substantially blocked the reductions in CEH activity, CEH/HSL protein, and CEH/HSL mRNA levels, PRL replacement during BrC treatment significantly inhibited the reductions in CEH/HSL protein and mRNA levels. CEH/HSL mRNA levels increased twofold after luteinization. Whereas CEH/HSL mRNA levels remained elevated after natural luteal regression, CEH/HSL protein significantly decreased. In summary, the luteolytic actions of PGF(2 alpha), APX, and BrC resulted in coordinate reductions in luteal CEH activity, protein levels, and mRNA levels; PRL replacement significantly reversed the luteolytic effects of APX and BrC; natural luteal regression resulted in a reduction in CEH/HSL protein without a concomitant reduction in CEH/HSL mRNA. These results suggest that ovarian CEH activity is controlled at the level of both transcription and translation, and that PRL is important for continued CEH/HSL mRNA transcription in the CL.