Abstract

The effects of short-term, 7-day, treatment with synthetic 15-leucine human gastrin I, pentagastrin or sulfated cholecystokinin-8 on the activity of histamine (HA)-stimulated adenylate cyclase in membranes isolated from guinea pig gastric mucosa and H2-receptor-mediated contractions of isolated ilea were evaluated. Treatment with each of the peptides produced a decrease in the maximal rate of HA-stimulated adenylate cyclase. The decreases in the maximal rate occurred without any effect on the potency of HA or any effect on basal rates of activity. In animals treated with pentagastrin, but not with cholecystokinin octapeptide sulfate, the contractile activity of dimaprit, a selective H2-agonist, was decreased. In animals treated with pentagastrin, the contractile actions of pentagastrin on isolated ileal preparations were increased. A 7-day treatment with the H2-antagonist, tiotidine, did not alter the potency of or the maximal response for HA-stimulated adenylate cyclase activity. Co-treatment with tiotidine prevented the effects of pentagastrin on gastric mucosal HA-stimulated adenylate cyclase. Treatment with pentagastrin did not alter the sensitivity of the gastric mucosal H2-receptor to inhibition by tiotidine. The effects of treatment with gastrin on NaF-stimulated adenylate cyclase activity also were determined. Treatment with gastrin did not alter the actions of NaF, suggesting that the coupling between the Gs subunit and the catalytic subunit of adenylate cyclase was not altered.(ABSTRACT TRUNCATED AT 250 WORDS)