Figure 8.

Effect of desloratadine (DL), 4-DAMP, or methoctramine on oxotremorine-induced decrease of heart rate (HR) in the pithed rat. Isoflurane-anesthetized animals (n = 6) were pithed after insertion of femoral and carotid arterial catheters. The femoral catheter was inserted approximately four centimeters into the femoral artery to enable recording of heart rate. Anesthesia was then discontinued. Following administration of atenolol (1.0 mg/kg, i.v.), oxotremorine was administered in random (n = 3) and ascending (n = 3) order of doses. The third generation antihistamine, DL (1.0 mg/kg, i.v.), the muscarinic M₃ receptor antagonist, 4-DAMP (1.0 mg/kg, i.v.), or the muscarinic M₂ receptor antagonist, methoctramine (0.5 mg/kg, i.v.), was then administered and the oxotremorine doses were repeated. No statistically significant differences were found between animals in which oxotremorine was given in random vs. ascending order of doses and both sets of data were pooled. Data are representative of the maximal percent fall in heart rate compared to control following the administration of each dose of oxotremorine. The highest dose tested for oxotremorine (0.04 mg/kg, i.v.) could not be given prior to treatment with 4-DAMP. Statistical analysis was done using the paired t-test with P < 0.05 denoting a statistically significant difference versus control as indicated by an asterisk.