Psychological stress activates phosphorylase in the heart of the conscious pig without increasing heart rate and blood pressure.

The present study uses a technique that enables the collection of multiple freeze-biopsy samples from the myocardium of the conscious pig (i.e., through a thoracic window). This technique enables sequential analysis of the metabolic state of the myocardium during different behavioral conditions. The results demonstrate that with daily adaptations to an unfamiliar environment (i.e., stress reduction), the phosphorylase activation ratio (phosphorylase a/total phosphorylase) in the quiescent pig declines steadily from approximately 80% to 30% (r = -0.91, P less than 0.01). This decline occurs with both the mean resting heart rate and left ventricular blood pressure remaining constant. The decline is seen within individual subjects during the whole adaptation sequence as well as between subjects whose samples were taken either early or late in the adaptation series. The dissociation of hemodynamic functional and metabolic activation in the unadapted, psychologically stressed pig may be associated with the occurrence of increased vulnerability of the ischemic heart to ventricular fibrillation, a phenomenon previously observed under the same behavioral conditions.