Rat gastric acid secretion studies with histamine and synthetic gastrin-like pentapeptide.

1. Gastric acid secretion was measured in the urethane anaesthetized rat whilst maintaining a recirculated gastric perfusion fluid at pH 4.2. The latent period of onset of secretion following single intravenous doses of histamine and pentapeptide in combination was significantly shorter than that following either stimulant alone.3. When administered over a period of 2 hr the maximal steady rate of secretion in response to pentapeptide was 75% of that to histamine.4. Acid stimulatory effects were additive both when the drugs were given concurrently over a 2 hr period and when one was administered after a maximal response had been obtained to the other.5. Although there is some evidence to indicate that histamine and pentapeptide might be initiating acid secretion by different mechanisms it is suggested that they may not be acting with total independence.