Substance P mechanisms in the regulation of striated muscle microcirculation.

The effects of substance P (SP) on microvessels in the cremaster of sodium pentobarbital-anesthetized male, Sprague-Dawley rats were investigated using closed-circuit television microscopy. Topically added SP (bath concentrations of 10(-13) to 10(-8) M) caused significant dilation of small arterioles. SP vasodilation was sensitive to pretreatment of the muscle tissue with SP analogues, [D-Arg1, D-Pro2, D-Trp7,9, Leu11]-substance P (APTL-SP) and [D-Pro2, D-Trp7,9]-substance P (PT-SP). Attenuation of the responses by pyrilamine suggests that part of the SP-induced dilation involves the release of histamine. The vasodilation was abolished by hydroquinone, suggesting an intermediate role for endothelium-derived relaxing factor in the response to SP.