THE TEMPORAL SEQUENCE OF G-PROTEIN EXPRESSION IN INTIMAL HYPERPLASIA

The universal response of a blood vessel to intimal injury is the deve lopment of intimal hyperplasia, The etiology of this lesion is not ful ly understood but is assumed to involve stimulation of receptors on sm ooth muscle cells with their subsequent proliferation. Many receptor-m ediated processes are coupled to G-proteins but little information exi sts regarding the expression of G-proteins during the development of i ntimal hyperplasia. This study examines the kinetics of G-protein expr ession in experimental vein grafts. Male New Zealand White rabbits had a right carotid interposition bypass graft using the ipsilateral exte rnal jugular vein. These were harvested on days 1, 3, 5, 7, 14, and 28 postoperatively for histology (n = 3) for in vitro isometric tension studies of potassium chloride, serotonin, bradykinin, and histamine (n = 3), or for Western blot analysis (n = 3) of the G-protein subunits (alpha(i1), alpha(i2), alpha(i3), alpha(s) and beta), The results show that expression of alpha(i3) developed de novo, was detectable by day 1, and continued to increase through day 7, paralleling the developme nt of intimal hyperplasia. The expression of alpha(s) (52 kDa) increas ed significantly by day 1 and also continued to increase until day 7. In contrast, expression for alpha(i2), alpha(s) (45 kDa) and beta subu nits increased at a much slower rate from 1 to 7 days and remained con stant thereafter. No alpha(i1) was detected. The contractile response to potassium chloride was significantly reduced (36% of the response i n the jugular vein) over the first 7 days and increased to 196% of the jugular vein response at 14 and 28 days. There was minimal response t o serotonin, bradykinin, and histamine over the first 7 days. Contract ile responses to serotonin increased while those to bradykinin and his tamine decreased from 7 to 28 days. This study demonstrates that there are specific changes in alpha(i) and alpha(s) subunits within 24 hr o f grafting and that increases in all G-proteins occur in a time depend ent manner up to 7 days postoperatively. Microscopic development of in timal hyperplasia occurs from days 3 to 5 and increases rapidly betwee n 7 and 14 days. Changes in the expression of G-proteins in the vein g rafts, particularly the alpha(i3) subunit, parallel this formation of intimal hyperplasia. These alterations in G-protein expression do not appear to correlate with G-protein-mediated, contractile responses in the vein grafts. (C) 1996 Academic Press, Inc.