Hemodynamic effects of norepinephrine and isoprenaline in various regions of the canine splanchnic area

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Abstract
Responses to norepinephrine (NE) and isoprenaline (ISO) (1–1024 ng/kg i.v.) were assessed by electromagnetic flowmetry on 18 arteries of the splanchnic region in anesthetized dogs. Measurements were judged according to the 2 criteria: 1. direction of effect; 2. sensitivity of vascular areas to catecholamines, expressed as D50 (i.e. the calculated dose inducing 50% of the maximum effect). NE decreased flow in all arteries (40–80%), but caused additionally an increase in the celiac, splenic and splenic artery proper. Thus changes in the spleen are responsible for the increase with NE. Flow reduction in the pancreatic branch of the cranial mesenteric artery was small. All flow reductions induced by NE had a similar D50 (about 30 ng/kg), except that in the hepatic artery (100 ng/kg). ISO increased all flows except that to the pancreas. Increase in the left gastric artery was higher (316%) than all other flow increases (62–168%). Activity of ISO is greatly different in the various vascular beds. D50 of flow to antrum and spleen were the lowest (4 ng/kg). Sensitivity decreases from cranial (D50 about 16 ng/kg) to caudal end (D50 about 70 ng/kg) of the gut. This gradual decrease is compared with functional and anatomical gradients reported in the literature. The varying response to ISO suggests presence of different vascular β-adrenergic receptors. The generally accepted distinction in cardiac β1-receptors and peripheral β2-receptors should be refined at least for β2-adrenergic vascular receptors.