DIFFERENTIAL-EFFECTS OF CHOLINERGIC AND ADRENERGIC AGENTS OF P-R AND R-R INTERVALS IN RAT ECG

In the present study the effect of cholinergic stimulation or blockade and adrenergic stimulation or blockade was telemetrically measured on ECG patterns, such as the P-R and R-R interval, in 6 freely moving ra ts. Subcutaneous administration of the muscarinic cholinergic agonist pilocarpine (20 mg/kg body weight) decreased heart rate. A significant increase in P-R and R-R interval was found. Blockade of the adrenergi c system with subcutaneous administered timolol (1 mg/kg body weight), a beta(1),beta(2)-adrenergic antagonist, decreased heart rate as well , A significant increase in R-R interval and a slight but not signific ant increase in P-R interval was found. Subcutaneous administration of the beta(1),beta(2)-adrenergic agonist isoprenaline (4 mg/kg body wei ght) increased heart rate. A significant decrease in P-R and R-R inter val was found, Blockade of the parasympathetic outflow by the subcutan eous administration of the muscarinic cholinergic antagonist atropine methylnitrate (0.5 mg/kg body weight), increased heart rate and decrea sed R-R interval. From these experiments it is concluded that ECG anal ysis in freely moving rats can be used to determine the activity of th e autonomic nervous system.