Effect of autonomic blockers on the heart rate of intact rats and animals with artificial hyperthyroidism.
The effect of various autonomic blockers on the heart rate (from the ECG recording) of intact rats and of animals with experimental hyperthyroidism induced by the administration of dried thyroid was studied. In intact rats, the heart rate fell significantly (by 22%) during the first week after the peroral administration of propranolol (0.05% in food), but trimepranol (0.02%), reserpine (0.001%) and guanethidine (0.1%) had no effect (in a suplementary experment, a small, but statistically significant decrease was also found after trimepranol). In experimental hyperthyroidism, using the same blocker doses, the heart rate fell significantly after propranolol (by 23%), trimepranol (22%), reserpine (16%) and, in a preliminary experiment, guanethidine (19%). On injecting 0.05 mg propranolol intravenously, the maximum drop in the heart rate in intact rats was 22%, while in hyperthyroidism it was hardly more than half this value (at all the intervals from 2 to 30 minutes the decrease was statistically significant). Practolol, in a dose of 0.3 mg i.v., was less effective -- in intact rats the heart rate fell by not more than 12% (at all the intervals from 2 to 30 minutes the decrease was significant), but in hyperthyroidism the drop was slower and statistically non-significant. The results do not furnish an unequivocal answer to the question of the role of adrenergic regulation of the heart rate under physiological conditions and in experimental hyperthyroidism in rats.
D000818:Animals; D006145:Guanethidine / Q000494:pharmacology; D006339:Heart Rate / Q000187:drug effects*; D006980:Hyperthyroidism / Q000503:physiopathology*; D008297:Male; D011217:Practolol / Q000494:pharmacology; D011433:Propranolol / Q000494:pharmacology; D051381:Rats; D012110:Reserpine / Q000494:pharmacology; D013565:Sympatholytics / Q000494:pharmacology*
D013565:Sympatholytics; D012110:Reserpine; D011433:Propranolol; D011217:Practolol; D006145:Guanethidine