This study focuses on the histomorphologic damage produced by an acute elongation process, as well as on quantifying the alterations in arterial contractility following the application of this technique. Light microscopy and scanning electron microscopy studies were prepared from expanded and non-expanded pig superficial femoral arteries (SFA) harvested immediately following expansion, and again at 24- and 72-hr intervals. Histologically, the expanded vessels showed minor, patchy, endothelial slough, but not fragmentation of the internal or external elastic lamina. At 24 hr, the endothelium showed reactive changes, but no evidence of smooth-muscle necrosis of the tunica media was observed. At 72 hr, healing of the endothelium was evident by SEM. Similar specimens, also from the SFA, were harvested and placed in organ chambers immediately following expansion and 24 hr later, to measure contractility when exposed to alpha-adrenergic agonists. The vessels were exposed to the contractile agonists, phenylephrine and 5-hydroxytryptamine, which evoked similar concentration-dependent increases in tension in both the expanded group and the controls. From these observations, the authors conclude that acute intraoperative elongation of arteries results in only minor endothelial damage, without affecting the inherent contractility of the vessel wall.
Summary: The present study investigated whether or not thrombin may affect the induction of nitric oxide (NO) synthase caused by interleukin-1β in cultured smooth muscle cells (SMCs) from the rat aorta. The release of nitrite, an oxidation product of NO, from interleukin-1β-activated SMCs was inhibited by thrombin. The inhibitory effect of thrombin was prevented by hirudin, a thrombin inhibitor, and required the presence of thrombin during the induction period. Under bioassay conditions, the perfusate from interleukin-1β-activated SMCs relaxed endothelium-denuded rat aortic rings precontracted with phenylephrine. The perfusate from untreated SMCs or cells exposed to thrombin alone or to interleukin-1β in combination with thrombin relaxed only minimally the detector blood vessel. These observations demonstrate that thrombin inhibits the production of NO by the inducible NO synthase in cultured vascular SMCs.
The effects of bradykinin, adenosine diphosphate, calcium ionophore A23187 and nitric oxide on the production of adenosine 3′:5′‐cyclic monophosphate (cyclic AMP) and guanosine 3′:5′‐cyclic monophosphate (cyclic GMP) were investigated in cultured aortic endothelial cells of the pig. Bradykinin (10 −7 m ), adenosine diphosphate (3 × 10 −5 m ), nitric oxide (2 × 10 −6 m ) and A23187 (10 −6 m ) stimulated the production of cyclic GMP. This stimulation reached a maximum within 1 min and declined rapidly with the first three agonists whereas that induced by A23187 was long‐lasting. These concentrations of bradykinin, A23187 and nitric oxide had no effect on cyclic AMP production. However, adenosine diphosphate (3 × 10 −5 m ) slightly but significantly enhanced its production by about 1.7 fold. The basal content of cyclic GMP in endothelial cells was significantly reduced by haemoglobin (10 −5 m , a scavenger of endothelium‐derived relaxing factor(s) and methylene blue (10 −5 m , an inhibitor of the activation of soluble guanylate cyclase) and was significantly enhanced by superoxide dismutase (500 u ml −1 , a scavenger of superoxide anions). The basal content of cyclic GMP was not affected by N G ‐monomethyl‐ l ‐arginine (10 −5 m , a specific inhibitor of the formation of nitric oxide from l ‐arginine) and was slightly but significantly increased by its d ‐enantiomer, N G ‐monomethyl‐ d ‐arginine. The production of cyclic GMP stimulated by bradykinin, adenosine diphosphate, A23187 and nitric oxide was inhibited by haemoglobin (10 −5 m ) and methylene blue (10 −5 m ) but was unaffected by superoxide dismutase (500 u ml −1 ). The production of cyclic GMP stimulated by bradykinin, adenosine diphosphate or A23187, but not that stimulated by nitric oxide, was significantly reduced by N G ‐monomethyl‐ l ‐arginine (10 −5 m ). The production of cyclic GMP evoked by nitric oxide, but not that induced by the other three agents, was enhanced significantly by N G ‐monomethyl‐ d ‐arginine by about 1.5 fold. These data indicate that the endothelium‐dependent vasodilators bradykinin, adenosine diphosphate and A23187 activate the production of cyclic GMP in endothelial cells via the synthesis of nitric oxide, which in turn stimulates the soluble guanylate cyclase.
Experiments were designed to determine whether the ω3-unsaturated fatty acid eicosapentaenoic acid affects the production of nitric oxide evoked by interleukin-lβ in cultured vascular smooth muscle cells. Incubation of cultured rat or human aortic smooth muscle cells with interleukin-1β evoked a time- and concentration-dependent release of nitrite, an oxidation product of nitric oxide. The exposure of cells to interleukin-1β in combination with eicosapentaenoic acid caused a significantly larger production of nitrite than that evoked by the cytokine alone. The potentiation by eicosapentaenoic acid was concentration-dependent. The production of nitrite evoked by equieffective concentrations of interleukin-1β in the presence and absence of eicosapentaenoic acid were inhibited to a similar extent by nitro L-arginine (an inhibitor of nitric oxide synthase), transforming growth factor β1 platelet-derived growth factorAB and thrombin. The addition of interleukin-1β -activated smooth muscle cells to suspensions of washed and indomethacin-treated platelets inhibited the aggregation caused by thrombin. The inhibitory effect was enhanced when the smooth muscle cells were exposed to the cytokine in the presence of eicosapentaenoic acid prior to the experiment. Smooth muscle cells exposed to interleukin-1β and eicosapentaenoic acid did not affect platelet aggregation in the presence of oxyhemoglobin or methylene blue. Untreated cells or cells exposed to the fatty acid alone did not have such effects. These observations suggest that eicosapentaenoic acid potentiates the production of nitric oxide evoked by interleukin-1β in vascular smooth muscle.
Summary: The effect of l-arginine [the substrate for the formation of nitric oxide (NO) in endothelial cells] on the reactivity of isolated vascular preparations was studied. Rings of rat aorta, with or without endothelium, were suspended in organ chambers for the measurement of isometric force. After various incubation periods in physiological salt solution (37°C, 95% O2 and 5% CO2), they were contracted with phenylephrine (10-6M) before the addition of cumulative concentrations of l-arginine. l-Arginine evoked only minor changes in tension in preparations incubated for 0.5 h. However, when the incubation period was longer than 2 h, the amino acid evoked concentration- and time-dependent relaxations in preparations both with and without endothelium. The relaxations evoked by l-arginine were impaired by nitro-l-arginine and methylene blue. Other basic cationic amino acids (d-arginine, l-homoarginine, l-citrulline, l-lysine, and l-ornithine) evoked only small or no relaxations in both types of preparations. These observations demonstrate that l-arginine stereoselectively and specifically relaxes the rat aorta whether or not it contains the endothelium; this response depends on the duration of the prior incubation of the rings in physiological salt solution. The relaxations are impaired by inhibitors of both the formation and the action of NO, demonstrating that the endothelial cells and the vascular smooth muscle of the rat aorta possess an l-arginine-NO pathway(s) associated with relaxation.
