ag-213 and Hypertension

The mechanisms of vascular structural alterations in hypertension were studied in cultured adventitial fibroblasts isolated from aortas of spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. Basic fibroblast growth factor (bFGF)-, epidermal growth factor (EGF)-, or platelet-derived growth factor (PDGF)-induced DNA synthesis and phospholipase C activity were estimated by determining 3H-thymidine incorporation and 3H-inositol phosphate production, respectively. The role of protein tyrosine kinases was assessed by stimulating the cells in the presence of tyrphostin, a protein tyrosine kinase inhibitor. Both the mitogenic potency of bFGF, EGF, and PDGF and the phospholipase C activity elicited by these factors were increased markedly in SHR (v WKY) fibroblasts. SHR fibroblasts were significantly less sensitive to tyrphostin inhibition of bFGF-induced 3H-thymidine incorporation than WKY fibroblasts, whereas when the cells were stimulated with EGF, PDGF, or 5% serum, SHR and WKY fibroblasts were equally sensitive to tyrphostin inhibition. At doses that abolished bFGF-induced 3H-thymidine incorporation, tyrphostin did not affect bFGF-induced 3H-inositol phosphate production. These results indicate that in aortic fibroblasts phospholipase C activation is not sufficient for bFGF-induced DNA synthesis. They suggest that tyrosine kinase activation is a necessary step in the transduction of bFGF mitogenic signal and plays an important role in the enhanced DNA synthesis exhibited by SHR (v WKY) cells. Therefore, one may envisage that bFGF contributes, through paracrine/autocrine mechanisms, to the vascular smooth muscle hyperplasia/hypertrophy in SHR.

Topics: Animals; Aorta; Arteries; Catechols; DNA; Epidermal Growth Factor; Fibroblast Growth Factor 2; Fibroblasts; Hypertension; Male; Nitriles; Platelet-Derived Growth Factor; Protein-Tyrosine Kinases; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Signal Transduction; Thymidine; Type C Phospholipases; Tyrphostins

The role of protein tyrosine kinases (PTKs) in vascular smooth muscle (VSM) contraction was examined in spontaneously hypertensive rats (SHRs). Aorta from SHRs was hyperresponsive to PTK-mediated contraction relative to normotensive Wistar-Kyoto rats (WKYs). Aorta from SHR was also hyporesponsive to vasorelaxation by tyrphostin, a selective inhibitor of PTKs. Further, we found alterations in PTK activity in aorta from SHRs. PDGF stimulated PTK activity to a greater extent in the SHR. Tyrphostin inhibited PDGF-induced PTK stimulation in both strains, however, activity returned to basal levels in the WKY only. The results suggest that PTKs may be involved in VSM contraction and in the development of hypertension.

Topics: Animals; Aorta, Thoracic; Catechols; Drug Interactions; Hypertension; Isometric Contraction; Male; Muscle Contraction; Muscle Relaxation; Muscle, Smooth, Vascular; Nitriles; Platelet-Derived Growth Factor; Protein-Tyrosine Kinases; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Sensitivity and Specificity; Tyrphostins

The effect of protein tyrosine kinase (PTK) inhibition on spontaneously hypertensive rat vascular smooth muscle contraction was examined in this study. By using isolated aortic strips, it was found that platelet-derived growth factor (PDGF) (0.1-1 nM), an activator of PTKs, elicited contraction with an EC50 of 0.25 +/- 0.08 nM. Treatment with tyrphostin (0.02-200 microM), a selective inhibitor of PTKs, caused a significant rightward shift of the concentration-response curves (P < .05). The IC50 for tyrphostin in the spontaneously hypertensive rat was calculated to be 9.5 +/- 4.2 microM. Tyrphostin also inhibited contractile activity in normotensive control Wistar-Kyoto rat aorta with an IC50 of 0.24 +/- 0.09 microM. Tyrphostin inhibited PDGF-induced contraction over a range of calcium concentrations, suggesting that it may oppose contraction through inhibition of calcium influx via PDGF-induced receptor-operated channel. However, KCl-mediated voltage-operated calcium channels were largely unaffected by tyrphostin, because it was unable to relax aortae which had been partially depolarized. Tyrphostin also had no significant antagonistic effect on contraction induced by phenylephrine or phorbol-12,13-dibutyrate. For both of these agents, contraction is mediated through activation of protein kinase C, which further alludes to the specificity of tyrphostin for PTKs. Treatment with 1 nM PDGF caused a significant stimulation of particulate/membrane PTK activity in the aorta. Tyrphostin attenuated PDGF-induced PTK activity in a concentration-dependent manner. The data suggest that PTKs may play a role in vascular smooth muscle contraction and that specific inhibition of PTK activity results in vasorelaxation. Furthermore, the results suggest that vasoconstriction and vascular smooth muscle cell proliferation may share common biochemical signalling pathways.

Topics: Animals; Aorta, Thoracic; Catechols; Drug Synergism; Hypertension; In Vitro Techniques; Isometric Contraction; Kinetics; Male; Muscle Contraction; Muscle, Smooth, Vascular; Nitriles; Phenylephrine; Phorbol 12,13-Dibutyrate; Platelet-Derived Growth Factor; Protein-Tyrosine Kinases; Rats; Rats, Inbred SHR; Rats, Inbred WKY; Tyrphostins