INTERDEPENDENCE OF RED CELL HEXOKINASE, INORGANIC PHOSPHORUS(Pi)AND 2, 3-DIPHOSPHOCLYCERATE(2, 3-DPG)IN THE DEVELOPING FETAL LAMB

Abstract

Previous studies have demonstrated that 2, 3-DPG inhibits red cell hexokinase activity in vitro and that the concentration of red cell 2, 3-DPG may be influenced by serum Pi in vivo. Since the developing fetal lamb exhibits wide variation in its red cell 2, 3-DPG content, hexokinase activity and serum Pi were studied in 7 lambs that were followed sequentially from birth until 8 weeks of life. The mean 2, 3-DPG concentration on day 1 of life was 4389±994 mumoles/ml RBC. There was a significant increase(p<0.005) in 2, 3-DPG from day 4 of iife(mean:8249±1754) through days 10-11 (mean:7577±1670). By day 17 of life the mean 2, 3-DPG concentration decreased to 4242±1832 mμmoles/ml RBC, and thereafter fell rapidly; by day 45 of life, 2, 3-DPG was not detected. No measurable 2, 3-DPG was found in 6 adult sheep. Red cell hexokinase activity appeared to be modulated by changes in the 2, 3-DPG content: Hexokinase was 1.18±0.33 units/gm hemoglobin on day 1, fell to 0.94±0.05 by days 10-11, and increased to 1.16±0.13 on day 17. From days 1 through 60 of life, changes in red cell 2, 3-DPG content correlated directly with the serum Pi(r = 0.82; p<0.001). These data demonstrate an in vivo confirmation of inhibition of red cell hexokinase activity by 2, 3-DPG and the regulation of red cell 2, 3-DPG concentration by serum Pi in the developing fetal lamb.