THE METABOLISM OF HUMAN PLACENTA IN VITRO

Abstract

The placenta is an organ of unusual interest, for in a short period of time it undergoes rapid development, attains full functional maturity, and then exhibits a partial regression.This tendency of the placenta toward "senescence" at term was first described from gross and microscopic observation (1).Decreases in the rates of oxygen consumption and of anaerobic glycolysis as gestation proceeds were reported previously (2-5).Other changes in the chemical composition and activity of the placenta during pregnancy are reported in the present paper. Materials and MethodsTerm placentas were obtained directly from the delivery room and were used within 5 minutes of delivery.Earlier placentas were obtained at cesarean sections performed either for delivery or for therapeutic interruption of pregnancy and were used within 5 minutes of their removal from the patient's body.Placental slices about 0.5 mm.thick, weighing about 200 mg., were prepared either with a Stadie-Riggs microtome or with iridectomy scissors and were incubated in Warburg vessels at 37" in an oxygen atmosphere.Care was taken in preparing the slices to avoid areas of necrosis.The composition of the incubation medium, expressed in millimoles per liter, was as follows: K+ 50, Na+ 80, Mg++ 10, phosphate 40, Cl-100, pyruvate 10, and glucose 11.1, except where specifically stated otherwise.The initial pH of the medium was 6.8 and the pH after incubation was 6.8 f 0.1 (determined by glass electrode).Other slices of the placenta were used for determination of initial glycogen content and of wet weight-dry weight ratios.After a 2 hour incubation the slices were removed, weighed, and amalyzed for glycogen.Aliquots of the incubation medium were analyzed for glucose (6), pyruvate (7), and lactate (8).In those experiments in which CY4labeled substrates were used, the respiratory COZ was recovered from the center well alkali, converted to BaC03, and counted with a windowless, proportional flow couilter (9).Glucose was isolated from ot,her aliquots