Difference in sensitivity of parotid glands brought about by disuse and overuse.

The sensitivity to methacholine of the parotid glands in rats maintained on a liquid diet (aiming at sensitization) for a period of 2 weeks or 3-4 weeks was compared with that of the parotid glands in rats on a pelleted bulk diet (aiming at desensitization). In the rats on the liquid diet, it was found that the dose needed to evoke a just perceptible secretion of saliva was smaller, that the secretion started earlier and continued over a longer time period, and further that the amount of saliva secreted expressed per gland weight in response to submaximal doses of the sialogogue drug was bigger when compared with the rats on the pelleted bulk diet. These findings are interpreted as signs of a higher degree of sensitivity of the glands in the rats on the liquid diet than of those in the rats on the pelleted bulk diet.