Aging and the trophic effects of cholecystokinin, bombesin and pentagastrin on the rat pancreas.

We examined the effect of age on the trophic response of the pancreas to chronic treatment with cholecystokinin (CCK), bombesin, or pentagastrin. Three age groups (3-, 12-, and 24-months) male F344 rats received saline; CCK-8 (5 ng/kg), bombesin (10 micrograms/kg), or pentagastrin (100 micrograms/kg) by intraperitoneal injection t.i.d. for 2 weeks. Rats were then killed and the pancreases excised, weighed, and assayed for DNA, RNA, protein, and polyamine (putrescine, spermidine, and spermine) concentrations and contents. We found that none of the treatments altered body weight at any age. All three hormones increased pancreas size and cell number in 3-month old rats, but by 12 months, all three had increased only pancreatic RNA content. Pancreatic spermidine concentration was decreased by all three hormone regimens in 3- but not in 12-month old rats, and pancreatic putrescine concentration and content were increased in 12-month old rats receiving all three hormones. There was no change in any parameter following any of the three hormones, tested at 24 months of age. We conclude that, at the dosages tested, the trophic response of pancreas to chronic administration of CCK, bombesin, and pentagastrin, which is normally present in young adult rats, is lost with aging.