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

The cardiovascular effect of isoproterenol pretreatment (ISO) mimicking short duration sympathetic hyperactivity was studied in conscious adult male albino rats. Cardiac hypertrophy of right and left ventricles was observed after pretreatment 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 micrograms/kg, iv) was slightly but consistently larger in the ISO group than in the control group (in mmHg, Control = 109 +/- 3.5; NOR 1 = 114 +/- 3.3; NOR 10 = 116 +/- 4; NOR 100 = 127 +/- 5.6 and NOR 1000 = 152 +/- 7.3 for saline-treated rats and, Control = 106 +/- 5.1; NOR 1 = 112 +/- 5.1; NOR 10 = 118 +/- 5.3; NOR 100 = 134 +/- 4.9 and NOR 1000 = 162 +/- 7.5 for ISO groups). An increased reflex bradycardia was also observed in response to increasing doses of noradrenaline (in bpm, Control = 323 +/- 5.6; NOR 1 = 313 +/- 6.8; NOR 10 = 309 +/- 8.6; NOR 100 = 293 +/- 7.5 and NOR 1000 = 284 +/- 5.3 for saline-treated rats and Control = 316 +/- 4.3; NOR 1 = 294 +/- 4.3; NOR 10 = 289 +/- 3.4; NOR 100 = 267 +/- 4 and NOR 1000 = 251 +/- 2.6 for ISO groups; ANOVa, P < 0.01). There were no significant differences in autonomic tone to the heart between control and isoproterenol-pretreated animals. The present results indicate that isoproterenol treatment induces significant in vivo cardiovascular modifications.