Preavoidance hypercapnia and decreased hematocrit in micropigs.

Previous studies found that regular confinement of dogs in an experimental environment preceding onset of an avoidance task was associated with increases in blood pressure and decreases in heart rate and respiration rate that were not prevented by adrenergic antagonists. The present study investigated a) whether divergent changes in blood pressure and heart rate also occur in micropigs preceding onset of an avoidance task, and b) the nature of changes in blood gases, plasma pH, plasma bicarbonate, hematocrit, and plasma electrolytes observed under these conditions. Blood pressure increased and heart rate decreased during 2-h preavoidance periods, whereas both blood pressure and heart rate were elevated during 20-min avoidance periods. During preavoidance periods, pO2, plasma pH, and plasma potassium pCO2 were decreased below home kennel levels during early preavoidance, whereas pCO2 and plasma bicarbonate were persistently increased and hematocrit was persistently decreased for the duration of the preavoidance periods. Each of these changes was reversed during the avoidance sessions. These findings suggest that behaviorally induced hypercapnia might participate in blood pressure regulation via increased renal sodium/hydrogen exchange and renal sodium retention.