Circulating triacylglycerols, lipoproteins, and tissue lipoprotein lipase activities in rat mothers and offspring during the perinatal period : effect of postmaturity .

Abstract

Mammary gland and adipose tissue lipoprotein lipase activities have been implicated in the changes of circulating triacylglycerol levels which occur in the mother at late gestation. In the newborn the temporal accumulation of triacylglycerols in the liver coincides with the appearance of a lipoprotein lipase peak. The relationships of these changes with the rise in circulating prolactin in the mother before parturition and the extrauterine nutritional status in the offspring were studied in a postmaturity model produced in the rat by subcutaneous injection of 7 mg progesterone/ day to pregnant animals from the 20th day of gestation. Pregnant controls received the medium. Parturition occurred at day 21.5 of gestation in pregnant controls while it did not occur before the 23rd day in those receiving progesterone. At the 20th day of gestation. plasma triacylglycerol concentrations and all lipoprotein fractions (especially VLDL) were much higher in mothers not receiving progesterone than in age-matched virgins. and these differences disappeared at the 21st day of gestation. Lipoprotein lipase activity was maintained low in control mothers' adipose tissue until the 23rd postfecundation day while it greatly increased in mammary gland from parturition time. In progesterone treated mothers, both triacylglycerol and lipoprotein fractions (especially VLDL) in plasma were maintained elevated until the 23rd postfecundation day and adipose tissue and mammary gland lipoprotein lipase activities were maintained low until this time. Circulating prolactin levels increased around parturition in control mothers while they did not change in the progesterone treated mothers at any of the times studied. In offspring from control mothers. plasma triacylglycerols were low and their most abundant circulating lipoprotein fraction appeared to be LDL. In contrast to mother's liver, in offspring liver a marked lipase activity with all the inhibitory char&cteristics of lipoprotein lipase in the presence of both NaCl and protamine sulfate appeared around birth. coinciding with a sharp increase in liver triacylglycerol concentration and plasma ketone body levels. In postmature fetuses. liver lipoprotein lipase activity and triacylglycerol content decreased from the 20th to the 23rd postfecundation day while levels of both acetoacetate and beta-hydroxybutyrate rose in blood. Results indicate that increased mammary gland lipoprotein lipase in the mother may play a role in the decline of hypertriglycerolemia before parturition and that the initial change is driven by the rise in circulating prolactin at that time. On the contrary, the reduction in adipose tissue lipoprotein lipase activity in late gestation is not associated with the increase in circulating prolactin levels. We sp~cuiat.e that in offspring from control mothers. the high fat content of the mother's milk produces a substrate induction mechanisrn on Hver lipoprotein lipase converting the liver of the newiJcrn into a temporary lipid storage organ. Consumption of endogenous resources and maintenance of maternal ketone bodies transfer throl!gh the placenta ensure development of postmature fetus.