Changes in patterns of feeding activity, parotid secretory enzymes and plasma corticosterone in developing rats.

The diet and feeding patterns of developing rats were determined from feed bin weight losses and analysis of stomach contents (details in a previous report). Parotid gland development in the same rats was assessed from the specific activities of the secretory enzymes alpha-amylase, RNase and DNase, with particular attention to the occurrence of circadian variations. The results indicate that during the first week post partum, rats suckle much more by day than by night but have no circadian cycles in their parotid glands. Between 10 and 20 days, there were no consistent cycles either in feeding activity or in parotid enzymes. The progressive change from milk to stock diet between 14 and 30 days appears to promote the maturation of the parotid gland. The halfway point in the dietary change at 21 days coincides with the onset of inversely related circadian cycles in feeding and the parotid enzymes. Premature weaning at 21 days accentuates both cycles and accelerates parotid maturation. The findings indicate that the physical consistency of the diet has an imporant regulatory role in the developmental patterns of feeding activity and parotid glands of rats, but they also hint that other dietary qualities may be involved. Chronologic fluctuations in plasma corticosterone suggest an intricate relationship among this hormone, feeding behavior, and parotid glands in developing rats.