Desensitization to substance P-induced vasodilation in vitro is not shared by endogenous tachykinin neurokinin A

Two mammalian tachykinins, substance P (SP) and neurokinin A (NKA), were measured by radioimmunoassay in canine cephalic blood vessels and tested for their vasoactivity in vitro. Levels of immunoreactive SP were approximately 2-3 times greater than those of immunoreactive NKA in common carotid, basilar, and middle cerebral arteries. Both endogenous tachykinins relaxed precontracted segments of common carotid and basilar arteries in a dose-dependent manner with an EC50 of 8.9 X 10(-11) M and 7 X 10(-10) M, respectively, when added cumulatively. Relaxation was endothelial dependent for both substances and not blocked or enhanced by pretreatment with indomethacin, propranolol, lithium chloride, or atropine. Neither SP nor NKA released 3H-inositol phosphates from phospholipid membranes of canine carotid segments after preincubation with 3H-inositol. SP but not NKA or the C-terminal fragments SP(4-11) caused desensitization to subsequent additions of itself but not to the relaxation induced by sodium nitroprusside, calcitonin gene-related peptide, or bradykinin. These studies demonstrate that at least 2 peptides derived from beta-preprotachykinin are contained within cephalic blood vessels and that these products share similar vasoactive properties but differ in their ability to desensitize vascular tachykinin receptors.