Effect of intraperitoneal and intragastric loading with water and isosmotic solutions of saline and glucose on water intake of dehydrated rats

Abstract

Female rats, dehydrated with food available for 24 hr, lost 6 to 8% of body weight. When allowed access to water, 40 to 60% of the weight deficit was replaced within the first hr. Either intraperitoneal (IP) or intragastric (IG) water loads (3% of body weight) administered just prior to return of water inhibited water intake of dehydrated rats nearly completely during the first hr of access to water. In contrast, similar loads of isotonic saline were much less effective. Even when 0.5 and 1.0 hr elapsed between IP loading (3% of body weight) with isotonic saline and access to water, water intake was not significantly different from that of untreated, dehydrated controls. In contrast, a similar IP load of water at these times completely inhibited water intake. Because of the contrasting effects of similar loads of water and isotonic saline on water intake of dehydrated rats, additional studies were carried out with an isosmotic solution of glucose (5%). IG administration (3% of body weight) of glucose inhibited water intake of dehydrated rats. IP administration (3% of body weight) attenuated the drinking response but did not reduce it to the level observed in dehydrated rats given an IP water load. When isosmotic glucose was administered at 0.5, 1.0, and 2.0 hr prior to allowing access to water, water intake was reduced significantly below that of dehydrated controls and to the same extent regardless of time of administration of the glucose load. This suggests that inhibition of water intake in dehydrated rats can result from either IG or IP loading and is a function of the type of loading solution rather than the extent of stretch of the gastrointestinal tract or peritoneal cavity. These results also suggest that those loading solutions which draw solutes from extracellular fluid into the peritoneal cavity or gastrointestinal tract inhibit water intake of dehydrated rats. Isotonic saline solutions, which fail to do this, are relatively ineffective in reducing water intake of dehydrated rats. In support of this hypothesis, the effectiveness of similar volumes of saline loading solutions in reducing water intake appeared to increase with decreasing concentrations.