PDGF‐receptor protein tyrosine kinase activity in carotid artery is enhanced by injury and inhibited in vivo by tyrphostin RG 13291

Tyrphostins (TKI) are synthetic low molecular weight compounds which inhibit in vitro platelet‐derived growth factor (PDGF) mitogenesis by blocking PDGF receptor protein tyrosine kinase activity (PDGF R‐PTK). To determine whether TKIs act by this mechanism in vivo, a rat model of vascular injury was used. Rat carotid arteries were injured by implantation of a tygon cuff machined so that 1 mm of each end touched the artery. PDGF R‐PTK was measured ex vivo by incubation of the excised denuded artery with porcine PDGF followed by homogenization and Western blotting with antiphosphotyrosine/antiPDGF‐R antisera. In arteries from control rats, PDGF produced a maximal 2‐fold increase in R‐PTK at 120 ng/ml. In cuffed arteries, PDGF stimulated R‐PTK in a dose‐related manner after one day of injury; R‐PTK remained elevated for 4–5 days post injury (6‐fold increase in R‐PTK activity at 180 ng/ml). A similar response to PDGF was also evident in contralateral uncuffed arteries. Intraperitoneal injection (+ 2 h) of TKI RG 13291 inhibited PDGF R‐PTK of cuffed artery with an IC50 value of ∽ 2 mg/kg and of the uncuffed artery with IC50 value of ∽ 30 mg/kg. It is concluded that TKIs are potential in vivo inhibitors of injury‐induced PDGF R‐PTK activity and may be useful as inhibitors of PDGF‐dependent effects such as proliferation.