Related Experiment Videos
Altered alpha 1-adrenoceptor subtypes mediated cardiac function after treatment of propranolol to rats
1Department of Pharmacology, Chinese Academy of Medical Sciences, Beijing, China.
Aim:
To study inotropic and chronotropic effects mediated by alpha 1A- and alpha 1B-adrenoceptors after 5-d propranolol (Pro) treatment.
Methods:
The positive inotropic and chronotropic effects mediated by alpha 1A and alpha 1B subtypes were determined on isolated left ventricular papillary muscles and right atrium in Pro- and NaCl-treated rats.
Results:
The basic contractility of papillary muscles induced by phenylephrine (Phe) was 90 +/- 18 mg in Pro-treated rats and 53 +/- 17 mg in control group (P < 0.05). The increment on force of contraction was 20 +/- 12 mg in Pro-pretreated rats and 5 +/- 5 mg in NaCl-treated rats (P < 0.05). After preincubated with chloroethylclonidine, the increment on force of contraction was reduced in Pro-treated rats, but was not much changed in control group. Phe in presence of 5-methylurapidil induced positive inotropic effect with 13 +/- 5 mg in Pro-treated group, but not in NaCl-treated rats. Under the normal and the inhibited cardiac state, the maximal increment in beat rate mediated by alpha 1B showed no difference between the Pro-treated and NaCl-treated rats.
Conclusion:
After chronic treatment of Pro, alpha 1-adrenoceptor-mediated positive inotropic effect in rat heart was improved, which was mainly induced by stimulation of alpha 1B when beta-adrenoceptors were blocked.