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 sodiu m-deficient rats given preloads of NaCl that were sham ingested, normally i ngested, or intubated into the stomach. Intake of 500 mM NaCl was reduced b y prior ingestion, but not by sham ingestion, of an NaCl preload. NaCl intu bation 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 intuba ted than after ingested NaCl. Plasma aldosterone concentrations dropped mor e rapidly after ingested than after intubated NaCl and also dropped after s ham ingestion of NaCl, raising the possibility of a cephalic-phase influenc e on aldosterone levels. These findings suggest that oral factors do not di rectly control the amount of NaCl consumed by sodium-deprived rats. Differe nces between the physiological effects of voluntary ingestion and intubatio n may be responsible for the results of several early studies purported as evidence for oral metering of sodium consumption.