Effect of co‐dergocrine in the autoperfused superior mesenteric vascular bed of the rat

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Abstract
1 The influence of local administration of co-dergocrine in the in situ, constant flow autoperfused, superior mesenteric vascular bed of the rat was investigated. 2 Local infusion of co-dergocrine (0.1-mu-g kg-1 min-1) reduced the pressor response to electrical stimulation of the periarterial sympathetic nerves for the whole frequency range studied during cumulative frequency-response curves (1-8 Hz). 3 Co-dergocrine (0.01, 0.03, 0.1-mu-g kg-1 min-1) dose-dependently inhibited the pressor response to electrical stimulation at 4 Hz; increases in perfusion pressure produced by locally administered noradrenaline were inhibited to the same degree. 4 Pressor responses induced by locally administered phenylephrine were also inhibited by co-dergocrine (0.1-mu-g kg-1 min-1) while those produced by local injection of angiotensin II were not. 5 Local administration of the DA1-/DA2-receptor antagonist haloperidol (1-mu-g kg-1), the DA2-receptor antagonist domperidone (10-mu-g kg-1) and the alpha-2-adrenoceptor antagonist rauwolscine (100-mu-g kg-1) partially prevented the influence of co-dergocrine on the electrically induced response. 6 The results show that the effect of co-dergocrine in the rat superior mesenteric vascular bed cannot simply be ascribed to interaction with the presynaptic inhibitory DA2-receptors on the noradrenergic nerve endings; it also has an antagonistic action at the postsynaptic alpha-1-adrenoceptors and an agonist action at the presynaptic alpha-2-adrenoceptors