A possible origin of circulating gastrin component IV in cats.

1. Blood circulating in the cat is known to contain relatively large concentrations of gastrin components corresponding to Rehfeld's Components III and IV, whereas human blood has mostly Components II and III. 2. Synthetic cat gastrin 17NS was continuously injected into chloralose anaesthetized cats and at 1, 10 and 40 min after the start of injection there were significantly greater concentrations of immunoreactive gastrin Component IV than Component III in arterial blood (P less than 0.025 in each case). These concentrations were also greater than the total arterial gastrin concentration in the basal state. 3. Cat blood with EDTA incubated at 37 degrees C with synthetic cat and natural porcine gastrins 17NS produced Component IV. Hunan blood with EDTA incubated in a similar way with natural and synthetic human gastrins 17NS did not produce any detectable Component IV. Cat blood incubated with natural porcine and synthetic cat gastrin 17NS at 0 degrees C did not produce any Component IV. 4. We conclude that there may be an enzyme or enzymes in cat blood which cause the conversion of gastrin 17NS to Component IV.