Gastric oxygen uptake during autoregulatory escape from sympathetic stimulation

To assess the effects of sympathetic stimulation on gastric blood flow and oxygen utilization, the perivascular nerves were stimulated at 2, 4, 6, and 8 Hz in chambered segments of canine gastric corpus perfused at constant pressure. Spectrophotometric arteriovenous oxygen difference and electromagnetic blood flow were recorded continuously. Except at the lowest frequency of stimulation (2 Hz), total blood flow exhibited autoregulatory escape, i.e., blood flow decreased initially but then returned toward control. The fall in total blood flow at the onset of sympathetic stimulation was smaller at 2 Hz than at 4 Hz, but stimulation at 6 and 8 Hz caused no further reductions in total blood flow. However, at all frequencies, total blood flow escaped to the same steady-state value (approximately 17 ml.min-1.100 g-1). Although total blood flow was still less than control (approximately 25 ml.min-1.100 g-1), oxygen extraction increased proportionately so that oxygen consumption was not significantly less than control at any frequency of stimulation. We conclude that autoregulatory escape from sympathetic stimulation is mediated by local mechanisms acting to maintain tissue oxygenation in the stomach.