Impairment of nitric oxide-mediated relaxations in anaesthetized autoperfused streptozotocin-induced diabetic rats

Abstract

This work was designed to determine in vivo the influence of the metabolic control of streptozotocin-induced diabetic rats, measured by the levels of haemoglobin glycosylation in blood (HbA1c), on developing vascular endothelial dysfunction. For this, the vasoactive responses to basal and stimulated endothelial nitric oxide (NO) were studied using the technique of the anaesthetized autoperfused rat, analyzing the responses to acetylcholine (ACh) and N(G)-nitro-L-arginine methyl ester (L-NAME) in non-diabetic and diabetic rats with different degrees of metabolic control (four groups with HbA1c levels of 5.5-7.4%, 7.5-9.4%, 9.5-12%, and >12%, respectively). When administered over a noradrenaline-induced vasopressor tone, ACh (0.25, 0.75, 2.5, 7.5 and 25 microg kg(-1)) induced dose-dependent vasodilatatory responses in all rat groups, reducing both mean arterial pressure and perfusion pressure of the left hindlimb. These responses were similar in non-diabetic and in diabetic rats with good metabolic control (HbA1c 5.5-7.4%), while diabetic rats with levels of HbA1c higher than 7.5% showed significantly lower vasodilatatory responses to ACh. In untreated diabetic rats, the relaxant responses evoked by the NO donor sodium nitroprusside were also impaired. On the other hand, increasing doses of L-NAME (0.1 to 10 mg kg(-1)) enhanced both mean arterial pressure and left hindlimb perfusion pressure in diabetic and non-diabetic rats. As with ACh, the responses to L-NAME were significantly reduced in diabetic rats with HbA1c levels higher than 7.5%. To determine the mechanism underlying the NO-mediated endothelial dysfunction, the responses to ACh in untreated diabetic rats (HbA1c >12%) were studied in the presence of the NO substrate L-arginine, in the presence of the oxygen-derived free radical scavenger superoxide dismutase (SOD), or in the presence of both compounds. Both L-arginine and SOD produced a partial improvement of the ACh-induced vasodilatatory responses, but the effects of these agents were not additive. In this group of animals, SOD also induced a partial recovery of the L-NAME-evoked vasoconstrictions. In non-diabetic and untreated diabetic rats, the plasma levels of NO derivatives and arginine were measured. No significant differences were obtained in the amount of nitrites plus nitrates, while plasma levels of arginine were markedly reduced in the untreated diabetic animals. The results indicate that the endothelial dysfunction associated to diabetes is closely related to the level of metabolic control of the disease. Therefore, it is possible to establish a threshold for developing endothelium impairment from percentages of HbA1c higher than 7.5%. As the responses to the NO synthase blocker L-NAME were analogously impaired, it is reasonable to suggest that diabetic endothelial dysfunction is related to the interference with mechanisms linked both to stimulated and basal production of NO. We suggest that this interference is partially due to a deficit in the substrate availability for NO and to an increas...

Enhancement of endothelial nitric oxide synthase production reverses vascular dysfunction and inflammation in the hindlimbs of a rat model of diabetes

“…Therefore we measured in vivo peripheral endothelial function in the femoral artery and ex vivo endothelial function in isolated aortic rings. In agreement with our previous studies [11,16] and with that of others [18] we also demonstrated under both in vivo and ex vivo conditions the presence of an impaired endothelial function under streptozotocin-diabetic conditions. Under diabetic conditions, endothelial dysfunction is a phenomenon that is often recognised in clinical and experimental settings [28,29].…”

“…In vivo assessment of vascular function and left ventricular BP in vivo For in vivo assessment of vascular function, we used the autoperfused hindlimb model in the rat as described previously [16][17][18]. Briefly, the rats were anaesthetised (chloral hydrate, 400 mg/kg body weight, i.p.…”

Endothelial dysfunction in diabetes

“…Defective endothelium-dependent relaxation was restored 4 weeks after pancreatic transplantation, performed in rats after 12 weeks of diabetes (Pieper et al, 1998a). A close relationship between endothelial dysfunction and metabolic control was found in streptozotocin-diabetic rats in which the degree of hyperglycaemia was manipulated with subcutaneous insulin implants (Angulo et al, 1998). Conversely, acute exposure to high glucose concentrations induces endothelial dysfunction similar to that in diabetic animals (Tesfamariam et al, 1990;Tesfamariam & Cohen, 1992;Bohlen & Lash, 1993;Mayhan & Patel, 1995).…”

“…In accordance, an increased NO synthase activity, measured by conversion of 3 H-L-arginine to 3 H-L-citrulline, was demonstrated in diabetic rat heart endothelium (RoÈ sen et al, 1996). Exogenous L-arginine (partially) restored endotheliumdependent vasodilatation in certain (Pieper & Peltier, 1995;Fulton et al, 1996;Matsunaga et al, 1996;Angulo et al, 1998), but not all studies (Heygate et al, 1995;Koltai et al, 1997;Mayhan et al, 1997). These variable results may relate to an aspeci®c e ect of L-arginine: this amino acid is known to release insulin, which by itself may stimulate endothelium-dependent vasodilatation (MacAllister et al, 1995).…”

“…Markedly reduced serum arginine levels have been observed in diabetic rats (Pieper & Peltier, 1995;RoÈ sen et al, 1996;Angulo et al, 1998) and have been attributed to enhanced consumption of L-arginine due to an increased NO synthesis. In accordance, an increased NO synthase activity, measured by conversion of 3 H-L-arginine to 3 H-L-citrulline, was demonstrated in diabetic rat heart endothelium (RoÈ sen et al, 1996).…”