Effects of fasting and refeeding on antral, duodenal, and serum gastrin levels and on colonic thymidine kinase activity in rats.

Antral, duodenal, and serum gastrin levels and colonic thymidine kinase activity were determined in 1- to 4-day-fasted rats and after refeeding of 4-day-fasted rats for 3-24 h. The effect of pentagastrin on colonic thymidine kinase activity was also determined. Total deprivation of food caused a drastic reduction in gastrin concentrations in serum and tissues. After 4 days of fasting, serum gastrin levels in most animals fell below the present detection limit of the assay (10-15 pg/ml), and antral and duodenal gastrin levels decreased to 15 and 50% of the respective initial fed control. After 9 and 24 h of refeeding, gastrin concentration in serum and antrum had increased to about 35% of the initial fed level. On the other hand, refeeding for 3-24 h produced no significant change in duodenal gastrin concentration. Fasting for 1-4 days resulted in a 60-70% reduction in colonic thymidine kinase activity, compared to the initial fed control. Refeeding caused a prompt stimulation in the enzyme activity, which after 6 h was found to be 72% above the 4-day-fasted group. Daily injection of pentagastrin, at doses between 125 and 500 micrograms/kg, during a 4-day fasting period resulted in a significant stimulation in colonic thymidine kinase activity, compared to the saline-treated control. The maximal stimulation of an enzyme activity 90% higher than in the saline control was attained with a pentagastrin dose of 125 micrograms/kg. Higher doses decreased the maximal stimulatory effect of pentagastrin.(ABSTRACT TRUNCATED AT 250 WORDS)