Rate of the myogenic response increases with the constriction level in rabbit femoral arteries.

The myogenic response forms an important aspect of blood flow regulation and is usually quantified by the steady-state relation between pressure and diameter. The aim of the present study is to analyze the dynamics of the myogenic response. In six isolated rabbit femoral arteries, the time course of the active part of the diameter response to a pressure step from 95 to 110 cm H2O (from 9.5 to 11 kPa), at two levels of norepinephrine (NE)-induced constriction, was fitted to a monoexponential curve to obtain the time constant. The NE concentrations used in the superfusion solution were between 0.8 and 1.5 microM for high constriction and between 0.2 and 0.6 microM for low constriction. Acetylcholine (1 microM in perfusion) was used to check endothelial function. The respective median values of the time constants with and without endothelium, are 13.2 and 15.5 sec (NS) for the high level of constriction and 49.5 and 58.5 sec (NS) for the low constriction level. Time constants at the two constriction levels were significantly different (p = 0.002). In seven separate experiments using 40 mM KCl, in the superfusion fluid, to constrict femoral arteries to the same level as during the high level of NE constriction, it was found that the amplitude of the myogenic response was much smaller, compared with the norepinephrine experiments, and the time constant was significantly longer (median: 80.8 sec). We conclude that the dynamics of the myogenic response in the rabbit femoral artery is independent of the endothelium, but is dependent on the constriction level and type of constricting agent.