TY - JOUR
T1 - Paradoxical inotropic effects of clonidine and labetalol in the conscious rabbit
AU - McRitchie, R. J.
AU - Chalmers, J. P.
PY - 1981/7
Y1 - 1981/7
N2 - Both clonidine and labetalol when given by bolus intravenous injection into conscious rabbits produce an initial rise in left ventricular pressure associated with a decrease in myocardial contractility as assessed by left ventricular dP/dt. While clonidine also produces a marked bradycardiac effect, labetalol causes no change in heart rate. Acute β-adrenoceptor blockade with propranolol, 1 mg/kg, i.v., does not significantly modify the response produced by either clonidine or labetalol. Following cardiac cholinergic blockade with scopolamine methylbromide, 50 μg/kg, the negative inotropic effect produced by clonidine is abolished and is replaced by a positive inotropic effect, while the negative inotropic response produced by labetalol is attenuated. Following cardiac autonomic blockade with propranolol and scopolamine methyl-bromide, both clonidine and labetalol produce a positive inotropic response. These positive inotropic responses may be due to the partial α-adrenoceptor-agonist properties which both drugs possess and which could be unmasked by cardiac autonomic blockade.
AB - Both clonidine and labetalol when given by bolus intravenous injection into conscious rabbits produce an initial rise in left ventricular pressure associated with a decrease in myocardial contractility as assessed by left ventricular dP/dt. While clonidine also produces a marked bradycardiac effect, labetalol causes no change in heart rate. Acute β-adrenoceptor blockade with propranolol, 1 mg/kg, i.v., does not significantly modify the response produced by either clonidine or labetalol. Following cardiac cholinergic blockade with scopolamine methylbromide, 50 μg/kg, the negative inotropic effect produced by clonidine is abolished and is replaced by a positive inotropic effect, while the negative inotropic response produced by labetalol is attenuated. Following cardiac autonomic blockade with propranolol and scopolamine methyl-bromide, both clonidine and labetalol produce a positive inotropic response. These positive inotropic responses may be due to the partial α-adrenoceptor-agonist properties which both drugs possess and which could be unmasked by cardiac autonomic blockade.
KW - Cardiac autonomic blockade
KW - Clonidine
KW - Inotropic effect
KW - Labetalol
UR - http://www.scopus.com/inward/record.url?scp=0019489874&partnerID=8YFLogxK
U2 - 10.1097/00005344-198107000-00015
DO - 10.1097/00005344-198107000-00015
M3 - Article
C2 - 6167811
AN - SCOPUS:0019489874
SN - 0160-2446
VL - 3
SP - 818
EP - 827
JO - Journal of Cardiovascular Pharmacology
JF - Journal of Cardiovascular Pharmacology
IS - 4
ER -