Release of VIP-like immunoreactivity in response to dopamine agonists, insulin hypoglycemia and feeding in conscious dogs.
VIP levels were measured by radioimmunoassay in peripheral venous blood of conscious dogs. Bolus injections of the dopamine agonists apomorphine, 0.05 mg/kg, and bromocriptine, 0.2 mg/kg, were found to increase VIP levels from approximately 5 pmol/l to 150 pmol/l. The release responses were abolished by pretreatment with dopamine antagonists (haloperidol 0.1 mg/kg or halopemid 0.1 mg/kg) and by hexamethonium (1 mg/kg) a blocker of ganglionic transmission. Vagotomy did not inhibit the dopamine agonist induced output of VIP. Vagal activation by means of feeding or insulin hypoglycemia caused only minor rises of VIP levels (5-10 pmol/l). It is concluded that dopamine agonists stimulate the release of VIP from populations of neurons other than those affected by vagal and sympathetic activation. Possible sites of action for the VIP releasing effect exerted by dopamine agonists are discussed. Furthermore, it is suggested that some of the peripheral effects exerted by dopaminergic drugs are exerted via a previous release of VIP.
D000818:Animals; D001058:Apomorphine / Q000494:pharmacology*; D001971:Bromocriptine / Q000494:pharmacology; D003243:Consciousness / Q000502:physiology; D004285:Dogs; D004298:Dopamine / Q000502:physiology*; D004435:Eating; D006220:Haloperidol / Q000494:pharmacology*; D018738:Hexamethonium; D006584:Hexamethonium Compounds / Q000494:pharmacology*; D007003:Hypoglycemia / Q000503:physiopathology*; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D011863:Radioimmunoassay; D014660:Vasoactive Intestinal Peptide / Q000097:blood / Q000378:metabolism*
D006584:Hexamethonium Compounds; D007328:Insulin; D014660:Vasoactive Intestinal Peptide; D001971:Bromocriptine; D018738:Hexamethonium; D006220:Haloperidol; D001058:Apomorphine; D004298:Dopamine