Prevention by selenium supplementation of cyclosporin-A-induced vascular toxicity.

OBJECTIVE: The aim was to determine whether selenium supplementation, an important component of glutathione peroxidase, might attenuate cyclosporin (Cx)-induced vascular toxicity. METHODS: Four groups of rats were treated in parallel: the first group was supplemented with selenium (sodium selenite, 0.5 mg.kg-1) orally (p.o.) for 5 weeks and the same dose of selenium plus Cx 20 mg.kg-1 (i.m.) during the 6th week; group 2 received Cx only (20 mg.kg-1 i.m. for 1 week); group 3 was supplemented with selenium (0.5 mg.kg-1 p.o., for 6 weeks) and group 4 served as control. Thoracic aortas isolated from these various groups were studied in organ baths. RESULTS: In comparison with the control group, selenium supplementation did not modify acetylcholine (Ach)- and nitroprusside-induced relaxations. In group 2, endothelium-dependent relaxations (Ach) were markedly impaired and endothelium-independent relaxations (nitroprusside) were shifted to the right; with selenium supplementation (group 1), the responses to Ach were partially restored whereas the rightward shift of the concentration-response curves to nitroprusside persisted. Incubation with superoxide dismutase (SOD, 150 IU.ml-1) or selenium (1 microgram.ml-1) (but not with selenium plus an inhibitor of the glutathione redox cycle) improved the relaxations to Ach in group 2. CONCLUSIONS: The vascular toxicity of Cx seems related to generation of oxygen-derived radicals promoting EDRF destruction and is attenuated by selenium supplementation.

Effect of dietary supplementation with fish oil on cyclosporine A-induced vascular toxicity.

We wished to determine whether dietary supplementation with fish oil prevents the vascular toxicity of cyclosporine (Cx). In a first set of experiments, we assessed the endothelial function of aortas isolated from rats supplemented for 6 weeks with fish oil (FO), administered by gavage, and providing 150 mg/kg/day of eicosapentaenoic acid and 100 mg/kg/day of docosahexaenoic acid. FO treatment altered neither acetylcholine- and histamine-induced relaxations, nor serotonin-induced contractions (NS vs. control group). Thereafter, three groups of rats were treated in parallel. Group 1 received FO supplementation (by gavage) for 6 weeks, and Cx (10 mg/kg/day po) was added during the last 2 weeks, group 2 received Cx only (10 mg/kg/day po) for 2 weeks, and group 3 served as a control. Both acetylcholine-and histamine-induced relaxations were reduced in group 2 compared with the control group, as indicated by the area under the curve (AUC), which was significantly higher: 296 +/- 17 vs. 138 +/- 32, and 392 +/- 38 vs. 318 +/- 25 for acetylcholine and histamine, respectively. In group 1, AUC for acetylcholine remained significantly different from the control (241 +/- 31 vs. 138 +/- 32), whereas AUC for histamine was 367 +/- 28 (NS vs. control). The serotonin-induced contractions were also enhanced in group 2 compared with those of the control group, and this alteration was not attenuated in group 1. After mechanical removal of the endothelium, the increased responsiveness to serotonin persisted in groups 1 and 2, suggesting this functional alteration to be located in the smooth muscle cells. Thus, in the rat the attenuation of Cx-induced vascular toxicity by fish oil supplementation is only partial, that is, it involves a slight improvement in endothelial function, but with persistence of functional changes in smooth muscle.

Coronary vasomotor responses in cyclosporine-treated piglets.

Chronic treatment with cyclosporine A (Cx) seems to produce a decreased ability of the endothelium to secrete nitric oxide. However, its effect on the coronary arterial system remains controversial. Therefore, coronary arteries isolated from piglets treated by intramuscular injections of Cx (10 mg/kg/day, IM, for 22 days) were studied in organ baths and compared with those isolated from control animals (IM injections of the Cx solvent). Depolarization-induced contractions (KCl 120 mM) were similar in both groups, whereas the acetylcholine-induced contractions (percent of 120 mM KCl) were enhanced: The area under the curve (AUC) was 245 +/- 51 in the Cx group versus 110 +/- 15 in the control group (p < 0.05). Removal of the endothelium did not significantly modify the acetylcholine-induced contractions in both groups and, therefore, did not attenuate the enhanced responsiveness to acetylcholine in the Cx group. On unrubbed rings contracted with prostaglandin F2 alpha, the endothelium-dependent relaxations from serotonin (in the presence of 1 microM ketanserin) were reduced: The AUC was 479 +/- 24 in the Cx group versus 385 +/- 22 in the control group (p < 0.02). Larger AUC values were also found for bradykinin and substance P in the Cx group: 158 +/- 18 versus 55 +/- 17 (in the control group, p < 0.01) and 198 +/- 8 versus 145 +/- 12 (p < 0.01), respectively. Nevertheless, no alteration in calcium ionophore-induced relaxations was observed: The AUC was 217 +/- 10 in the Cx group and 224 +/- 18 in the control group (NS). Indomethacin incubation (10 microM) did not prevent the impairment in endothelium-dependent relaxations and did not attenuate the cyclosporine-induced augmentation of acetylcholine-induced contractions. Thus, chronic administration of cyclosporine to piglets impairs the coronary endothelial function and produces functional changes in smooth muscle cells. These alterations may play a role in the occurrence of cardiac graft vasculopathy.

Chronic angiotensin-converting enzyme inhibition and endothelial function of rat aorta.

To determine whether chronic angiotensin-converting enzyme (ACE) inhibition produces functional changes in the aorta normotensive rats, four groups of rats were studied in parallel for 6 weeks. Group 1 orally received ramipril and beta 2-kinin antagonist HOE140 500 micrograms/kg per day s.c. by injection for the remaining 2 weeks; group 3, hydralazine 100 mg/kg per day PO for 6 weeks; group 4 (control), subcutaneous injections of saline solution during the last 2 of 6 weeks. In aorta isolated from group 1 the relaxations induced by bradykinin, acetylcholine, and histamine were significantly potentiated compared with those of group 4. In group 3, despite a decrease in systolic blood pressure similar to that induced by ramipril treatment, the responses to these three endothelium-dependent vasodilators were not different from those of group 4. In group 2, bradykinin-induced relaxations were completely abolished whereas acetylcholine-induced and histamine-induced relaxations were to those of group 4. The inhibitory effect of the endothelium on serotonin-induced contractions was significantly increased in preparations of group 1 compared with those of groups 2 through 4. Indirect measurements of nitric oxide formation such as contractions evoked by NG-monomethyl-L-arginine (L-NMMA) and aortic cGMP content were also significantly enhanced in preparations from group 1 compared with those of groups 2 through 4. Moreover, because the relaxations to nitroglycerin and nitroprusside were similar in groups 1, 2, and 4 an alteration of the guanylate cyclase activity by ramipril treatment is quite unlikely. Thus long-term treatment with ramipril potentiates the endothelium-dependent responses in the rat aorta by enhancing nitric oxide availability.

Attenuation of cyclosporine A-induced vascular toxicity by ramipril.

We wished to determine whether chronic inhibition of angiotensin-converting enzyme (ACE) prevents the vascular toxicity of cyclosporine A (Cx). In aortas isolated from rats treated with ramipril [10 mg/kg/day orally (p.o.) for 4 weeks], the endothelium-dependent relaxations to acetylcholine (ACh) were potentiated (the area under the curve (AUC) decreased from 154 +/- 35 to 63 +/- 12, p < 0.05), but contractions induced by phenylephrine (PE) and angiotensin II (AII) were not affected. Therefore, we studied three groups of rats in parallel. Group 1 received ramipril 10 mg/kg/day p.o. for 4 weeks and ramipril 10 mg/kg/day p.o. plus Cx 20 mg/kg/day intramuscularly, in fifth week; group 2 received Cx only (20 mg/kg/day i.m. for 1 week), and group 3 served as control. In group 2, ACh-induced relaxations were reduced as compared with those of the control group (AUC increased from 141 +/- 34 to 240 +/- 32, p < 0.05), whereas in group 1, AUC was not significantly different from that of group 3 (195 +/- 28 vs. 141 +/- 34). In group 2, PE- and AII-induced contractions were enhanced; AUC values for PE and AII were 495 +/- 45 versus 348 +/-38 in group 3 and 424 +/- 28 versus 314 +/- 17 in group 3, respectively (p < 0.05). In group 1, AUCs for PE and AII were not significantly different from those of group 3. After mechanical removal of the endothelium, the increased responsiveness to PE and AII persisted in group 2 whereas AUC values in group 1 were not different from those of group 3.(ABSTRACT TRUNCATED AT 250 WORDS)

Nitrate tolerance and aging in isolated rat aorta.

The purpose of this study was to determine whether there are age-related changes in the extent of in vitro-induced nitrate tolerance. Nitroglycerin pre-exposure (10 microM for 30 min) provoked a significant shift to the right of the dose-response curve to nitroglycerin in aortae isolated from rats of 8 weeks, 12 and 18 months. However, this shift to the right was significantly larger at 18 months, both when KCl or phenylephrine were used as contractile agents. On the contrary, nitroglycerin pre-exposure did not significantly alter the dose-dependent relaxation to Sin-1 (3-morpholinosydnonimine, the active metabolite of molsidomine) at 8 weeks, 12 and 18 months. These data indicate that the extent of the in vitro-induced nitrate tolerance is larger when aortae are isolated from senescent rats. This increase in tolerance does not appear to involve desensitization of guanylate cyclase.