Diabetes was induced in rats by an injection of streptozotocin (55 mg/kg). Endothelium-dependent relaxations in mesenteric resistance arteries (luminal diameter 210 +/- 20 microns) of control and diabetic rats were compared in myographs. Acetylcholine induced endothelium-dependent relaxations that were mediated by nitric oxide (EDNO). EDNO-mediated relaxations were impaired in diabetic arteries; concentrations of acetylcholine required to produce 50% relaxation (ED50) of activated arteries were 5 nM in control and 13.5 nM in arteries from diabetic rats studied after 6 wk (P < 0.05). The impairment in relaxation worsened with duration of the diabetes; ED50 for acetylcholine increased to 63 and 100 nM in diabetic arteries studied after 16 and 24 wk of diabetes, respectively. NG-nitro-L-arginine produced 5.5- and 16-fold decreases in sensitivity of control and diabetic arteries to acetylcholine. NG-nitro-L-arginine produced at least as much inhibition of acetylcholine relaxations in diabetic arteries, indicating that the impaired relaxation noted in diabetic arteries does not result from decreased production of EDNO. EDNO-mediated relaxations in diabetic arteries were impaired by increased production of endothelium-derived free radicals. Superoxide dismutase, a scavenger of superoxide anion, and dimethylthiourea, a scavenger of hydroxyl radicals, normalized EDNO-mediated relaxations in diabetic arteries. The ED50 values for acetylcholine were 13.5, 5.5, and 4 nM for untreated and SOD- and DMTU-treated diabetic arteries, respectively (P < 0.05 for treated vs. untreated arteries). Superoxide anion and hydroxyl radicals appear to block EDNO-mediated relaxation by inactivating EDNO.(ABSTRACT TRUNCATED AT 250 WORDS)

Vasoconstriction and hypertension are major side effects of cyclosporine therapy. The mechanism or mechanisms responsible for the vascular effects of cyclosporine are unclear. The vascular effects of cyclosporine may arise as a consequence of endothelial dysfunction induced by the agent. To test this possibility, we compared in vessels prepared in myographs endothelium-mediated relaxations of mesenteric resistance arteries of Wistar-Kyoto rats treated for 21 to 28 days with subcutaneous injections of cyclosporine (25 mg/kg per day) or vehicle. Endothelium-dependent relaxations in response to acetylcholine were impaired in arteries from cyclosporine-treated rats; the concentrations of acetylcholine required to produce 50% relaxation of norepinephrine activation (pD 2 ) were 31.6±0.1 versus 5±0.1 nmol/L in control arteries (P<.05). Nitro-L-arginine produced comparable 10-fold decreases in sensitivity to acetylcholine in arteries from both rat groups, indicating that the relaxations were mediated by endothelium-derived nitric oxide. Acetylcholine-induced H ypertension and nephrotoxicity are major side effects of cyclosporine-induced vasoconstriction. Vasoconstriction induced by cyclosporine is both acute in onset and persistent during chronic administration of the agent.12 Administration of a single dose of cyclosporine to healthy individuals produces an abrupt 20% to 30% decrease in renal blood flow and glomerular filtration rate over the course of 2 hours. 1 Similarly, renal blood flow and glomerular filtration rate increase after cyclosporine is stopped in subjects who have received the drug for more than a year.3 The mechanism or mechanisms responsible for cyclosporineinduced vasoconstriction remain poorly understood. Three mechanisms have received the most attention: (1) an increase in intracellular calcium with enhancement of vasoconstrictor responses, 4 -5 (2) activation of the sympathetic nervous system, 6 and (3) cyclosporine-induced endothelial dysfunction. 79 Studies described in this report will focus on the effects of cyclosporine on endothelial function. Endothelial cells modulate vascular smooth muscle tone in large part by regulated production of endothelium-derived nitric oxide (EDNO) and to a lesser extent of vasodilating prostaglandins. relaxations in cyclosporine-treated arteries were normalized by pretreatment of the arteries with superoxide dismutase (150 IU/mL; pD 2 , 3.6±0.1; P<.Q5); superoxide dismutase had no effect on relaxations in control arteries. SQ 29,548, an inhibitor of prostaglandin H 2 /thromboxane A, receptors; H-7, an inhibitor of protein kinase C; and indomethacin did not alter relaxations in response to acetylcholine in either group of arteries. Cyclosporine-treated arteries were more sensitive than control arteries to nitroprusside, an agent that induces relaxation via nitric oxide (pD 2 , 1.3 and 6.2 /unol/L, respectively; P<.05). Thus, cyclosporine impairs relaxations mediated by endothelium-derived nitric oxide in mesenteric arteries via enhanced production of f...

Vascular relaxations are impaired in adult spontaneously hypertensive rats (SHRs) because of increased production of an endothelium-derived, cyclooxygenase-dependent contractile factor or factors. To test the hypothesis that alterations in endothelial function precede and contribute to the development of overt hypertension in SHRs, we compared in myographs endothelium-mediated relaxations of mesenteric resistance arteries from 4-week-old SHRs and Wistar-Kyoto (WKY) rats. Acetylcholine (10(-9) to 10(-4) M) induced comparable relaxations in SHR and WKY arteries precontracted (ED50) with norepinephrine. In arteries obtained from SHRs but not from WKY rats, relaxations were replaced by contractile responses with higher concentrations of acetylcholine (10(-6) to 10(-5) M). The contractile responses were endothelium dependent, were augmented by nitro L-arginine (10(-4) M), and were prevented by pretreatment with indomethacin (10(-5) M) or 3-amino-1,2,4-triazole (10(-3) M), an inhibitor of superoxide anion production via the cyclooxygenase pathway. Inhibition of thromboxane synthetase (CGS-13080, 5 x 10(-5) M) and antagonism of prostaglandin H2/thromboxane A2 receptors (SQ-29,548, 5 x 10(-5) M) failed to block the contractile response to acetylcholine in SHR arteries. Acetylcholine-mediated relaxations were significantly impaired in mesenteric arteries from 16-week-old SHRs but not from WKY rats. Endothelium-independent relaxations produced by sodium nitroprusside and contractile responses to norepinephrine and endothelin were comparable in arteries from SHRs and WKY rats of all ages. In summary, endothelium-dependent relaxations of mesenteric arteries from "prehypertensive" SHR rats were impaired by the production of a contractile factor (or factors) that appears to be superoxide anions.

No abstract

Vascular resistance is increased in the kidneys of spontaneously hypertensive rats (SHR).Imbalanced production of relaxing and contracting factors by the endothelium may play an important role in both the initiation and the maintenance of the abnormal vasoconstriction characteristically seen in humans with essential hypertension and in genetic models of hypertension in animals. 4-5 Endothelium-dependent relaxations are impaired in the aorta and mesenteric resistance arteries of spontaneously hypertensive rats (SHR).6 -11 In both vessels, the impaired relaxations result from enhanced production of a cyclooxygenasedependent endothelium-derived contracting factor (EDCF) that antagonizes the relaxing properties of endothelium-derived nitric oxide.6 -11 More than one EDCF may be produced in SHR arteries.12 Two recent reports suggest that the EDCF produced by the SHR aorta may be prostaglandin H 2 (PGH 2 ) or thromboxane A 2 (TXA,).10 - 11From the Department of Medicine, Division of Nephrology and Hypertension, University of Kansas Medical Center, Kansas City, Kan. The objectives of the studies described in this report were twofold: 1) to determine if endothelium-mediated relaxations were impaired in resistance arteries isolated from kidneys of young SHR and 2) to characterize the nature of the factor(s) that promotes enhanced constriction in resistance arteries. EDCFs may function by inactivating the endothelium-derived relaxing factor nitric oxide, 13 by direct activation of contractile responses in vascular smooth muscle cells, or by a combination of the two mechanisms. MethodsMale, 5-6-week-old SHR and normotensive WistarKyoto (WKY) rats were obtained from Harlan Laboratories, Boston, Mass. The rats were maintained four per cage at constant temperature (24±1°C), with a 12-hour dark/light cycle and standard rat chow. All procedures followed were in accordance with institutional guidelines. Systolic blood pressure was measured in conscious, prewarmed, restrained rats by the tail-cuff method by using plethysmography and a physiograph recorder (model 11 TC, Innovators in Instrumentation, Woodland Hills, Calif.). Vessel PreparationRats were anesthetized with ether. The abdominal aorta was cannulated to enable in situ perfusion of the aorta and renal and superior mesenteric arteries with