Cardiac muscarinic receptors density and R-R interval duration in normal (N) and vagal hyperreactive (H) rabbits.

The severity of vagal pauses was evaluated in conscious animals by measuring the duration of R-R interval on the ECG recording after challenge with PNE 500 µg kg−1 following the procedure described in Material and Methods. Total, M2 and M3 muscarinic receptors densities (Bmax) in hearts from normal (N) and vagal hyperreactive (H) rabbits were obtained from Scatchard analysis of the saturation data using [3H]NMS (total), [3H]AF-DX 384 (M2) and [3H]4-DAMP (M3) as radioligands. Binding conditions were as described in Material and Methods. Values are means (SD) of n independent experiments. P: H versus N within each group.