Circadian rhythms of serum gastrin and plasma cholecystokinin in rodents.

Fluctuations in serum gastrin and plasma cholecystokinin (CCK) over a 24-hr period were examined in fasted and freely fed adult BALB/c mice and Sprague Dawley rats. Eighty-four mice and 84 rats were caged in groups of (six) each and placed in separate isolation chambers with light from 0600 to 1800 hr (CST) daily (LD 12:12). After standardization for 30 days, one-half of the animals were fasted 24 hr prior to circadian sampling, and the remainder were allowed continuous access to food. Animals were removed and killed by rapid cervical dislocation every 4 hr beginning at 0800 hr for seven time points. Blood was collected and serum gastrin and plasma CCK were measured by specific radioimmunoassays. The data document a circadian bioperiodicity for serum gastrin and plasma CCK. The parameters of the rhythms, evaluated by cosinor rhythmometric methods, are characterized by an acrophase that occurs in the dark period for both fed and fasted rodents and a mesor that is higher in fed than fasted animals. Circadian sampling time and nutritional status appear to be important in studies involving serum levels of gastrin and plasma CCK in rodents.