Enhanced norepinephrine sensitivity in renal arteries at elevated transmural pressure.

The electrical and mechanical responses of vascular smooth muscle to norepinephrine were compared at three different levels of transmural pressure (60, 100, and 140 mmHg) in cannulated small arteries that were isolated from dog kidneys. Elevation of transmural pressure caused depolarization of the vascular smooth muscle and a significant increase in vessel sensitivity to norepinephrine. Norepinephrine produced less depolarization as transmural pressure was elevated. Comparison of the relationship between transmembrane potential and norepinephrine concentration at these different transmural pressures suggests that membrane depolarization contributes to, but is not the sole explanation of, the increased norepinephrine sensitivity at higher transmural pressures. The results of this study suggest that transmural pressure in a blood vessel may be an important determinant of its sensitivity to vasoactive agonists.