Increased levels of VIP (vasoactive intestinal polypeptide)‐like immunoreactivity in peripheral venous blood of dogs following injections of apomorphine and bromocriptine. Do dopaminergic agents induce gastric relaxation and hypotension by a release of endogenous VIP?

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Abstract
Injections of the dopaminergic agonist apomorphine give rise to multiple effects in the gastrointestinal tract such as vomiting (Borison & Wang 1953), relaxation of the stomach (Valenzuela 1976, Lefebvre, Willems & Bogaert 1981), vasodilation in the splanchnic region (Goldberg 1972) as well as a release of gastrin, insulin and somatostatin (Uvnäs‐Wallensten, Lundberg & Efendic 1978, Uvnäs‐Wallensten & Goiny 1981). Some of the effects exerted by dopaminergic agents on the gastrointestinal tract are mimicked by injections of the peptide VIP (vasoactive intestinal polypeptide). VIP occurs in neurons in the gastrointestinal tract (Larsson et al. 1976) and VIP, like the dopaminomimetics, relaxes the stomach and dilates blood vessels in the gastrointestinal tract (Eklund et al. 1979).