Effects of heat acclimation on the secretory products of the submaxillary gland of the rat. An ultrastructural and biochemical study.

Secretory granule area and glycoprotein concentration of the saliva in the submaxillary gland of rats were measured during various stages of acclimation to heat at 34 +/- 1 degrees C. Granule size decreased by 18% during the first five days of heat acclimation (0.025 less than p less than 0.05) after which period it increased to reach 118% of the control levels after 28 days (p less than 0.05). Glycoprotein concentration in the saliva of stimulated glands rose above control levels, reaching a maximum between the 2nd and 5th day of acclimation (p less than 0.05). It was concluded that the initial decrease in granule size reflects a decrease in glycoprotein content following an increase in salivary flow known to occur at high ambient temperatures. The subsequent increase in granule size is considered an adaptation of the gland to continuous stimulation. The rise in salivary glycoprotein concentration suggests increased efficiency of the secretory mechanism.