Action of dopamine on the exocrine pancreatic secretion of the intact dog.

The effects of dopamine and domperidone, a dopamine antagonist, have been studied on the exocrine secretion of the dog pancreas. The purpose of this study was to see if dopamine acted on enzyme secretion and if its action was merely 'pharmacological' or had a physiological role. Conscious Beagle dogs, fitted with Thomas cannulae were studied following infusions of dopamine 125-1000 micrograms kg-1 h-1. During dopamine infusion, a secretory peak lasting 10 min was observed. This was followed by a stable plateau which was approximately 1/3 of the peak. The pattern of water, bicarbonate and protein secretion was similar. The maximum effect was obtained with 500 micrograms kg-1 h-1 dopamine. The stimulatory action of dopamine was blocked by domperidone, without any detected effect on the central nervous system, but not by propranolol or phenoxybenzamine. Domperidone 10 micrograms kg-1 almost completely suppressed the secretory response to the maximally effective dose of dopamine. This inhibition was not competitive. Atropine decreased the secretory response to dopamine. The protein response was not observed when dopamine was infused against a background infusion of secretin. This suggests that the effect of dopamine on protein secretion could be due to a wash-out phenomenon. The maximally effective dose of domperidone, 10 micrograms kg-1, did not modify the pancreatic response to a solid meal. Thus, in the non-anaesthetized dog, the effect of dopamine on water and bicarbonate secretion has been confirmed. It is concluded that dopamine had no detectable action on protein secretion and that the physiological role of dopamine with respect to pancreatic secretion is still questionable.