CONCENTRATION OF MESSENGER-RNA ENCODING 3-BETA-HYDROXYSTEROID DEHYDROGENASE DELTA(5),DELTA(4) ISOMERASE (3-BETA-HSD) AND 3-BETA-HSD ENZYME-ACTIVITY FOLLOWING TREATMENT OF EWES WITH PROSTAGLANDIN-F2-ALPHA

The objectives of these experiments were (1) to determine if prostagla ndin F-2 alpha (PGF(2 alpha)) decreased mRNA encoding 3 beta-hydroxyst eroid dehydrogenase/d(5),Delta(4) isomerase (3 beta-HSD) specifically in large steroidogenic luteal cells, which contain the high affinity r eceptors for PGF(2 alpha); and (2) to determine if the decreased conce ntration of mRNA encoding 3 beta-HSD following administration of PGF(2 alpha) was associated with a decrease in 3 beta-HSD enzyme activity, Ewes on days 11 or 12 of the estrous cycle were administered PGF(2 alp ha) (25 mg iv followed by 10 mg im 2 h later) and corpora lutea collec ted 4, 12, 24, or 48 h later (n = 4-5/time). Corpora lutea were also c ollected from non-injected (n = 4) or saline-injected (n = 4) control ewes. Administration of PGF(2) decreased (P< 0.05) steady-state concen trations of mRNA encoding 3 beta-HSD to 35, 15, 9, and 5 percent of th e concentrations in the control group at 4, 12, 24, and 48 h, respecti vely. Concentrations of mRNA encoding 3 beta-HSD in large luteal cells were decreased to 43% of controls 4 h following injection, which was similar to the decrease seen in steady-state concentrations of this mR NA in total luteal mRNA (35%), However, 3 beta-HSD enzyme activity was not significantly decreased by 48 h after PGF(2 alpha) injection. Thu s, the dramatic decreased in mRNA encoding 3 beta-HSD was not associat ed with an immediate decrease in 3 beta-HSD enzyme activity and, there fore, does not appear to be responsible for the acute decrease in secr etion of progesterone from ovine luteal tissue during PGF(2 alpha)-ind uced luteolysis.