Cardiovascular effects on conscious rats of pretreatment with isoproterenol for 3 days

The cardiovascular effect of of isoproterenol pretreatment (ISO) mimicking short duration sympathetic hyperacitivity was studied in conscious adult male albino rats. Cardiac hypertrophy of right and left ventricles was observed after pretreatmewnt with isoproterenol for 3 days (0.1 mg/kg, 3 times a day). when compared to saline-treated rats. The pressor response to noradrenaline (NOR, 1 to 1000 ug/kg, iv) was slightly but consistently larger in the ISO group than in the control group (in mm Hg, Control = 109 ñ 3.5; NOR 1 = 114 ñ 3.3; NOR 10=116 ñ 4: NOR 100 = 127 ñ 5.6 and NOR 1000 = 152 ñ 7.3 for saline-treated rats and, Control = 106 ñ 5.1; NOR 1 = 112 ñ 5.1; NOR 10 = 118 ñ 5.3; NOR 100 = 134 ñ 4.9 and NOR 1000 = 162 ñ 7.5 for ISO groups). An increased reflex bradycardia was also observed in response to increasing doses of noradrenaline (in bpm, Control = 323 ñ 5.6; NOR 1 = 313 ñ 6.8; NOR 10 = 309 ñ 8.6; NOR 100 = 293 ñ 7.5 and NOR 1000 = 284 ñ 5.3 for saline-treated rats and Control = 316 ñ 4.3; NOR 10 = 289 ñ 3.4; NOR 100 = 267 ñ 4 and nor 1000 = 251 ñ 2.6 for ISO groups; ANOVA, P<0.01). There were no significant differences autonomic tone to the heart between control and isoproterenol-pretreated animals. The present results indicate that isoproterenol treatment induces significant in vivo cardiovascular modifications

Activation of the langendorff perfused rat heart under depolarizing conditions

Myocardial activation under depolarized conditions was studied in spontaneoustly beating Langendorff perfused hearts from albino rats. Depolarization was obtained incrasing external potassium concentration in steps (5.4, 7.4, 10, 10.5, 11, 11.5 mM) in the perfusisng solution. Left ventricular isovolumic systolic pressure and coronary flow did not change as external potassium increased, but the atrial and ventricular beat rates decreased, the latter showing a larger decline. In the electrocardiogram, the P-R interval increased as a function of external potassium and the amplitude of the ORS complex diminished as its duration invreased. The mamjority of perfused hearts stopped punping when external potassium was raised to 11.5 mM