THE EFFECT OF DISTENSION OF THE STOMACH ON PLASMA-RENIN ACTIVITY IN THE ANESTHETIZED PIG

It has recently been shown that distension of the stomach in anestheti zed pigs causes reflex hemodynamic responses through efferent sympathe tic mechanisms. The present study was undertaken to investigate whethe r these mechanisms include activation of the renin-angiotensin system. In twelve anesthetized pigs, intragastric balloons were distended for periods of 30 minutes by 0.81 of warm Ringer solution (mean gastric t ransmural pressure of about 12 mmHg). Changes in arterial blood pressu re and heart rate were respectively prevented by a pressurized reservo ir connected to the left femoral artery and by atrial pacing. Plasma r enin activity was measured during the last minute of distension by rad ioimmunoassay of angiotensin I. In each of the twelve pigs distension of the stomach caused an increase in plasma renin activity. In five pi gs, this response was graded with step increments of the distension. T he increase in plasma renin activity to gastric distension was abolish ed by bilateral subdiaphragmatic vagotomy (six pigs) and by bilateral section of the renal nerves (six pigs). The present study showed that innocuous distension of the stomach in the anesthetized pig reflexly i ncreased plasma renin activity. The afferent limb of the reflex was in the vagal nerves and the efferent limb involved renal nerves.