Regional differences in phorbol 12-myristate 13-acetate stimulation of PDGF production in the normal canine aorta

Objective: Platelet-derived growth factor (PDGF) is a potent smooth muscle cell mitogen implicated in the development of intimal hyperplasia and ather osclerosis. A regional variation in canine aortic production of PDGF (great er in the distal than in the proximal aorta) was demonstrated previously in organ culture. The response of aortic segments in organ culture, as well a s of aortic endothelial cells and smooth muscle cells, to stimulators of PD GF secretion-phorbol 12-myristate 13-acetate (PMA) and thrombin-was assesse d to elucidate whether these regional variations were due to intrinsic diff erences in the abilities of cells to produce PDGF. Methods: Proximal and distal aortic segments were removed from 10 dogs and placed in organ culture, then treated with PMA or thrombin for 72 hours. PD GF in the conditioned media was measured by radioreceptor assay. Results: PDGF production in the distal, unstimulated aorta was 2.5-fold hig her than that in the proximal aorta (P < .05). Treatment of the proximal ao rta with 10 nmol/L and 100 nmol/L PMA increased PDGF production twofold and threefold, respectively, whereas no increase with PIMA treatment was seen in the distal aorta. After thrombin treatment, no increase in PDGF producti on was noted in the proximal aorta and only a minimal increase was noted in the distal aorta. Endothelial cells and smooth muscle cells (n = 6) were c ultured from four aortic segments (ascending thoracic, descending thoracic, abdominal, and infrarenal) and treated with PMA. PDGF production by unstim ulated endothelial cells from the infrarenal aorta was 2.5-fold higher (P < .01) than that from the ascending thoracic aorta. With PMA treatment, PDGF secretion increased in endothelial cells from all segments, the greatest p ercentage increase being observed in the proximal segments. Thrombin also i ncreased PDGF release from endothelial cells, but with no regional variatio n. Unstimulated smooth muscle cells did not exhibit regional variation in P DGF production and did not increase PDGF secretion after treatment with PMA or thrombin. Conclusions: These findings suggest that endothelial cells in the aorta may have a differential capacity to produce PDGF in response to stimulants, re flecting intrinsic differences in endothelial cells from the proximal aorta versus the distal aorta, and this may account in part for the propensity o f the distal aorta to develop atherosclerosis.