Regulation of Mammary and Adipose Tissue Lipoprotein Lipase and Blood Triacylglycerol in Rats during Late Pregnancy

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Abstract
The effects of several prostaglandins on lipoprotein lipase activity of mammary gland and adipose tissue and serum triacylglycerol were studied during late pregnancy in rats. Prostaglandins were injected twice daily for 2 days before and once on the day of analysis. In rats pregnant 20 days, prostaglandin F2α (PGF2α) increased the activity of lipoprotein lipase in mammary gland fourfold, reduced the activity in adipose tissue about 60%, and decreased serum concentration of triacylglycerol 50%. PGF2α also reduced serum concentration of progesterone 90% and increased that of prolactin fivefold, but had no effect on serum concentrations of either immuno-reactive insulin or 17β-estradiol. Injections of 13,14-dihydro-15-keto PGF2α, a metabolite of PGF2α, had similar effects in rats pregnant 20 days, whereas prostaglandins E1 and E2 did not. In rats pregnant 16 days, PGF2α did not affect lipoprotein lipase activity in the tissues or the concentration of triacylglycerol and prolactin in serum, although it decreased serum progesterone 80%. 2-Br-α-ergocryptine prevented the increase in serum prolactin in response to PGF2α, but did not alter the effect of PGF2α on lipoprotein lipase activity or serum triacylglycerol. Progesterone completely blocked the effects of PGF2α on lipoprotein lipase activity and serum triacylglycerol and prolactin concentrations. These findings indicate that the changes in lipoprotein lipase activity and serum triacylglycerol in PGF2α-treated rats are probably related to the inhibitory action of PGF2α on progesterone secretion. They also suggest that endogenous F prostaglandins may play a role in the regulation of lipoprotein lipase activity in mammary gland and adipose tissue near parturition.