EFFECTS OF HYPOXIA AND HYPERCAPNIA ON WHOLE-BODY RELEASE AND CLEARANCE OF CHOLINE

We have recently demonstrated an increase in arterial blood choline (C h) concentration in normocapnic hypoxia and apnea. This could be due t o enhanced release of free Ch from tissues, to decreased Ch clearance, or both. The present investigation was undertaken to determine the in dividual contributions of these processes to the whole body balance of Ch, using an intravenous infusion of tracer quantities of [H-2(4)]Ch to assess the bidirectional flux between the central pool and peripher al pools. Rats were subjected to normocapnic hypoxia or hypercapnia; r elease and clearance of Ch were calculated using a simple model. Hypox ia caused an increase in Ch production and a decrease in Ch clearance. At severe levels of hypoxia, Ch clearance was essentially zero. Hypox ia was attended by progressive acidosis that was related to the magnit ude of the hypoxic challenge. To determine the possible effects of aci dosis per se on the variables measured, respiratory acidosis with norm oxia was provoked by controlled administration of CO2. Under these con ditions, parallel decreases in Ch production and Ch clearance were obs erved.