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Changes in Patterns of Feeding Activity, Parotid Secretory Enzymes and Plasma Corticosterone in Developing Rats^{1, 2,}

Division of Oral Biology, School of Dentistry, University of Minnesota, Minneapolis, Minnesota 55455, and School of Dental Medicine, State University of New York at Stony Brook, Stony Brook, N.Y. 11790

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 -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 important 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.

KEY WORDS: • weaning • circadian rhythms • corticosterone • parotid development

¹ This investigation was supported in part by Research Grants DE-102 and DE-03330 from the National Institute of Dental Research, and by a grant-in-aid of research from the Graduate School of the University of Minnesota. Statistical analysis was aided by National Institutes of Health Grant RR-276 to the University of Minnesota Health Computer Science Facility. Dr. Redman was the recipient of Public Health Service Research Career Development award DE-40019 from the National Institute of Dental Research.

² A preliminary report of this investigation was presented at the 54th general session of the International Association for Dental Research. Miaml Beach. Florida, March, 1976, and an abstract published in J. Dent. Res. 55, (Special Issue), B230.

³ Present address: Veterans Administration Hospital. Room A940. Building 1, 1055 Clermont Street, Denver, Colorado 80220.

Manuscript received 17 February 1976.