Splanchnic organ blood flow during calcitonin gene-related peptide-induced hypotension with or without propranolol in dogs.

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Propranolol has been used to attenuate reflex tachycardia during induced hypotension. The purpose of the current study was to determine whether propranolol can modify splanchnic organ blood flow during calcitonin gene-related peptide (CGRP)-induced hypotension in dogs anesthetized with 1.3% isoflurane in oxygen. After surgical preparation and hemodynamic stabilization, saline as a control, 0.5 mg/kg and 2.0 mg/kg propranolol (n = 10, each) were administered in a bolus injection 20 min before hypotension was induced. Mean arterial pressure was reduced to 60 mm Hg during 60 min of CGRP infusion. Renal blood flow (RBF), hepatic blood flow (HBF), and pancreatic blood flow (PBF) were measured using the hydrogen clearance method. Cardiac index did not change in all three groups, and heart rate in the control group remained unchanged. In the propranolol groups, however, heart rate decreased (P < 0.01). Plasma norepinephrine (NE), but not epinephrine (E), increased (P < 0.05) after propranolol administration. The NE and E increased (P < 0.01) during induced hypotension in all three groups. NE was higher in the 0.5 mg/kg propranolol group than in the control group. RBF in the control group remained unchanged throughout observation. RBF, HBF, and PBF decreased (P < 0.01) after propranolol and remained decreased during and after induced hypotension. The degrees of decreased HBF and PBF in the control group were less than those in the 2.0 mg/kg propranolol group. In conclusion, pretreatment with propranolol decreases splanchnic organ blood flow further during CGRP-induced hypotension, due in part to increased plasma catecholamine concentrations. The reductions in splanchnic organ blood flows during CGRP-induced hypotension with propranolol are due to a reflex augmentation in sympathetic vasoconstrictor tone caused by an increase in plasma catecholamine concentrations. These findings suggest that propranolol may impair splanchnic organ blood flow during CGRP-induced hypotension.