The American journal of physiology
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Potentiated adrenal responses to the second of two identical hemorrhages spaced 24 h apart are seen in the pentobarbital sodium-anesthetized dog. Although pentobarbital effectively reduces environmental influences, barbiturates affect hemodynamic and hormonal responses and preclude normal daily feeding and activity patterns. To determine the role of anesthesia in these earlier results, we prepared awake trained dogs with chronic adrenal venous catheters. ⋯ No differences were detected in the hemodynamic response to bleeding on the 2 days. Whereas potentiation was seen in epinephrine and norepinephrine responses to a second 10% hemorrhage in anesthetized dogs, larger hemorrhage was needed to elicit this effect in awake dogs. Thus potential adrenal medullary responses to repeated hemorrhage occur in both awake and pentobarbital-anesthetized dogs, but important differences in the threshold and manifestation of this effect are seen.
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The effect of repetitive periods of coronary occlusion on myocardial adenine nucleotides, lactate, and infarct size was studied. In one series of dogs, the circumflex artery was occluded for one, two, or four 10-min episodes, each separated by 20 min of reperfusion. Hearts were excised and sampled for metabolic assays after one or more periods of ischemia before or after reperfusion. ⋯ Necrosis was observed in only one of six dogs and, in this dog, was only 1.5% of the anatomic area at risk. Thus intermittent reperfusion prevents cumulative metabolic deficits and myocardial ischemic cell death, perhaps by restoring the capacity for high-energy phosphate (HEP) production and/or washing out deleterious catabolites. A first episode of ischemia also slows HEP utilization in subsequent episodes.