Norepinephrine-mediated hypoxic stimulation of embryonic red cell carbonic anhydrase and 2,3-DPG synthesis

Abstract

Hypoxia is the stimulus for activation of red cell carbonic anhydrase II (CAII) and 2,3-diphosphoglycerate (2,3-DPG) synthesis of chick red blood cells during late embryonic development. We have tested whether plasma catecholamines are involved as hormonal mediators, because hypoxia is a well-known stimulus for catecholamine release in mammalian fetuses. Plasma catecholamines were measured in 8- to 16-day-old chick embryos. Plasma levels of norepinephrine (NE) were initially low, but its concentration increased rapidly from 2.7 nM (day 12) to 13.4 nM at day 13 and 25.5 nM at day 16. Epinephrine (E) was not detectable before day 13. Short-term hypoxic exposure of day 11 embryos (1-h incubation at 13.5% O2) increased plasma NE concentration fivefold compared with the controls but had no effect on E. During 15-h in vitro incubation of red blood cells from day 11, addition of 1 microM NE to the incubation medium increased the red cell 2,3-DPG concentration nearly threefold and CAII activity sixfold compared with the control. The CAII activity and 2,3-DPG concentration were also increased when cells were incubated with plasma from late chick embryos. The activation was induced by beta-adrenergic stimulation of adenylyl cyclase. Atenolol and propranolol blocked the effects of NE and embryonic chick plasma. Analysis of de novo protein synthesis ([35S]methionine incorporation) demonstrated that catecholamines stimulate the synthesis of several proteins besides CAII. The results indicate that developmental changes of plasma NE concentration are instrumental in the adenosine 3',5'-cyclic monophosphate-dependent activation of CAII and 2,3-DPG synthesis of red blood cells from late chick embryos.