Effects of sex hormones on rabbit gallbladder prostaglandin biosynthesis

The influence of sex hormones on female and male rabbit gallbladder prostaglandin biosynthesis was examined by radiochromatographic analysis of microsomal membrane fractions. Normal male rabbit total cyclooxygenase activity was modest, producing small amounts of PGE2, PGF2 alpha and 6-keto-PGF1 alpha (breakdown product of PGI2). The normal female gallbladder (GB) microsomes demonstrated an increase in total cyclooxygenase activity when compared to the normal male rabbit gallbladder microsomes. The major prostaglandin (PG) products produced were 6-keto-PGF1 alpha, PGE2 (fivefold higher activity than the male), and PGF2 alpha. The effect of exogenous sex hormones was studied by comparing GB PG biosynthesis in male rabbits treated with exogenous estrogen (50 micrograms/kg sub Q X 5 days) and female rabbits treated with exogenous testosterone (2.5 mg/kg sub Q X 5 days). Exogenous estrogen significantly increased total cyclooxygenase activity in the male rabbit GB microsomes with a significant increase in 6-keto-PGF1 alpha production when compared to the normal male. Exogenous testosterone significantly decreased female rabbit GB total cyclooxygenase activity with a significant decrease in PGE2 biosynthesis and a substantial lowering in 6-keto-PGF1 alpha production. These data suggest that the major sex hormones, estrogen and testosterone, have potent but opposite effects on rabbit GB PG biosynthesis. Both sex hormones may contribute to the sex differences found in our original studies in rabbit GB biosynthesis.