Influence of oral and gastric NaCl preloads on NaCl intake and gastric emptying of sodium-deficient rats

Evidence is mixed as to whether oral metering contributes to the satiation of NaCl intake. To examine this in detail, we measured NaCl intake of sodium-deficient rats given preloads of NaCl that were sham ingested, normally ingested, or intubated into the stomach. Intake of 500 mM NaCl was reduced by prior ingestion, but not by sham ingestion, of an NaCl preload. NaCl intubation reduced NaCl intake if the test began 15 min, but not 60 min, after the preload. Gastric emptying of NaCl was initially more rapid after intubated than after ingested NaCl. Plasma aldosterone concentrations dropped more rapidly after ingested than after intubated NaCl and also dropped after sham ingestion of NaCl, raising the possibility of a cephalic-phase influence on aldosterone levels. These findings suggest that oral factors do not directly control the amount of NaCl consumed by sodium-deprived rats. Differences between the physiological effects of voluntary ingestion and intubation may be responsible for the results of several early studies purported as evidence for oral metering of sodium consumption.