Observations on the role of salivary secretions in the regulation of food and fluid intake in the white rat.

Abstract

Observations on the food and water intake, specific hunger, and taste preference behavior of rats made desalivate by ligation of the principal salivary ducts are described. Desalivate rats drink excessive amounts of water when feeding on a dry diet, which is attributed to the use of drinking water as an exogenous saliva to facilitate the swallowing of dry food. The feeding pattern of desalivate rats is strikingly similar to that seen in animals recovered from lateral hypothalamic lesions, suggesting that these lesions disrupt normal salivary secretions. Changes in the preference behavior for sodium chloride solutions, quinine rejection thresholds, and the sucrose preference of pancreatectomized and adrenalectomized rats following desalivation strongly suggest that alterations in salivary composition may alter the peripheral taste receptor response and thereby the volume intake of substances which normally stimulate the receptors in the course of ingestion.The role of salivary secretions in the regulation of food and fluid intake has been considered almost exclusively in connection with Cannon's theory of thirst, which maintained that thirst was synonymous with a dryness of the oral cavity normally resulting from a reduced salivary flow (Cannon, 1918). This xerostomic, or dry mouth, view of thirst has been espoused more recently by Gregerson and Cizek (1961) who, after reviewing the several factors giving rise to an increased water intake, conclude that, "The common factor ... in all forms of thirst examined appears to be a reduction in salivary flow [p. 325]."The "dry mouth" theory, however, has received anything but unqualified experimental support (for review, see Wolf, 1958). Despite a sizable literature on xerostomia and water intake, only a few studies have dealt with desalivate animals. Bidder and Schmidt (1852) found an enhanced water intake in desalivate dogs, and Gre-

Acute and chronic desalivation and isotonic saline preference in rats

“…Although the finding that desalivated rats show greater saline preference than the controls validates Vance's (1965) previous observations to this effect, we also found that the group differences disappear after a number of test sessions. It is impossible to ascertain whether the disappearance of group differences was due to successive exposure to the twobottle situation or to the possibility that postoperative effects may be minimized after a certain period after the operation.…”

“…We feel that it is necessary to validate Vance's (1965) results under conditions more' amenable to statistical analysis. The present experiment was designed to compare the isotonic saline intake of desalivated and sham-operated rats over a number of days once the operation was completed.…”

“…Experiment 2 dealth with BD IX agouti Norway rats which were tested for 10 consecutive days 140 days after the operation. The results of both experiments indicated that desalivated rats show greater saline preference than control rats during most of the initial 10 test sessions.In an extensive monograph on the effects of desalivation on the rat's food and water intake, Vance (1965) concluded that the presence or absence of saliva is very important in regulating the amount of NaCI a rat will ingest. This conclusion was drawn from the results of an experiment comparing sodium preference among the desalivates.…”

“…In an extensive monograph on the effects of desalivation on the rat's food and water intake, Vance (1965) concluded that the presence or absence of saliva is very important in regulating the amount of NaCI a rat will ingest. This conclusion was drawn from the results of an experiment comparing sodium preference among the desalivates.…”

The effects of vagotomy on the water intake of the white rat

“…Desalivation in rats, on the other hand, does lead to an excessive water intake when the animals are feeding on a dry diet (Epstein et al, 1964;Vance, 1965). In this case, the increased "thirst" is associated with an exaggerated prandial drinking, the animals using large amounts of drinking water to facilitate the swallowing of dry food.…”