Attenuation of Gastric Sham Feeding Response during Reflex Sympathetic Activation in Man

Abstract

In six human volunteers we studied the effects of hypovolemia on the secretory activity of the gastric mucosa. The secretion of acid and HCO₃ from the stomach was calculated from continuous measurements of pH and Pco₂ in gastric effluent. Gastric secretion was stimulated by sham feeding (SF), and cardiac filling pressure was decreased by pooling blood in the lower extremities (lower body negative pressure (LBNP)). LBNP at -20 mmHg had no significant effects on systemic arterial pressure or heart rate but increased plasma norepinephrine concentration by 48 ± 6% (p < 0.001). Both the acid and the alkaline responses to SF were significantly attenuated during LBNP (-38 ± 8%, p < 0.01, and -55 ± 14%, p < 0.05, respectively). Analysis of the relationship between acid and HCO₃ secretion in individual experiments suggested a relatively more pronounced inhibition of HCO₃ secretion. The results imply that a decreased responsiveness of the gastric mucosa may be one component of the cardiovascular reflex adaptation to hypovolemia. A downregulation of active secretion will lead to smaller metabolic demands from the secreting cells and may thereby help to maintain a vasoconstriction in the gastric mucosa.

Key Words:

• Acid secretion
• cardiopulmonary receptors
• gastric mucosa
• HCO₃ secretion
• norepinephrine
• sympathetic nerves