HORMONAL INFLUENCE ON LIPID-PROTEIN INTERACTIONS IN BIOLOGICAL-MEMBRANES - LACTATION EFFECTS ON ALKALINE-PHOSPHATASE ACTIVITY AND INTESTINAL BRUSH-BORDER MEMBRANE-PROPERTIES IN RAT

It is known that prolactin modifies the fluidity of different biologic al membranes in rats and that the activity of intestinal alkaline phos phatase varies directly with the fluidity of the membranes in which it is found. Our objective was to study the intestinal alkaline phosphat ase (IAP) activity, lipid composition and fluidity of the proximal sma ll intestine brush border membranes under the influence of physiologic al high levels of prolactin, in rats with 15 days of lactating (Dams 1 5 days) compared with control virgin rats. The phenomenon was corrobor ated in dams from which the suckling pups had been withdrawn on the te nth day of lactation (Dams 10 days). The results showed a decrease on the IAP activity in dams in lactation with relation to control virgin and dams with withdrawal of pups. We found decreases in total phosphol ipids contents and fluidity and an increase in the microviscosity lipi d membrane in dams with 15 days of lactating compared to virgins. In t he same groups there were no differences in total lipids content and n o modifications were observed in the quantity of total cholesterol and proteins. These results suggest that the changes produced by lactatio n could be one of the causes of alteration of brush border membranes p roperties by modifying the lipid-protein interactions and the alkaline phosphatase activity in the proximal small intestine.