[Approximately hourly rhythm of 3',5'-cAMP in rat parotid gland slices]

3',5'-CAMP concentration in rat parotid gland slices indubated in vitro for 12-14 hours was measured by radioimmunoassay. Clices for determination of cyclic nucleotide concentrations were taken at 10-minute intervals over a period of 2 hours. All slices used in a specific experiment originated from a single gland. Rhythmic changes in 3',5'-cAMP concentration in the rat parotid gland were found. The period of these changes (20-50 min) was similar to that of fluctuations in other parameters, such as dry weight, the rate of protein synthesis and ornithine decarboxylase activity, described for the same system elsewhere.