GASTRIC-ACID SECRETION IN THE CHICKEN - EFFECT OF HISTAMINE H(2) ANTAGONISTS AND H+/K+-ATPASE INHIBITORS ON GASTROINTESTINAL PH AND OF SEXUAL MATURITY CALCIUM-CARBONATE LEVEL AND PARTICLE-SIZE ON PROVENTRICULAR H+/K+ ATPASE ACTIVITY

1. Cimetidine was more potent 4 hr after a single injection of 25 or 100 mg/kg body wt in increasing gastric pH than other H-2 receptor antagonists, ranitidine and famotidine but was less efficient than H+/K+-ATPase inhibitors. Omeprazole rose proventricular and gizzard pH at a lower dose than SCH 28080 and Ro 18-5364 (30, 50 and 200 mg/kg body wt, respectively). 2. Proventricular and gizzard pH values were maximal 1 and 4 hr after a single injection of 7.5 mumol/kg body wt omeprazole. Inhibition of acid secretion was maintained for 24 hr after an injection of 100 mumol/kg. 3. H+/K+-ATPase activity in vitro was 10 mumol P(i)hr/mg protein in the microsomal fractions of the proventriculus. It was doubled by nigericine and inhibited by SCH 28080. However, western blots by high specific H+/K+-ATPase monoclonal antibody 95-A3 and 95-111 recognized a 42 kDa band but hardly exhibited the specific 95 kDa band recognition. 4. Chickens and immature pullets showed a higher H+/K+-ATPase activity than laying hens. Calcium level of the diet did not affect the enzyme activity but coarse particles of calcium fed to pullets or laying hens enhanced the H+/K+-ATPase activity when compared with ground particles.