Differential expression of α_2D-adrenoceptor and eNOS in aortas from early and later stages of diabetes in Goto-Kakizaki rats

Abstract

Kobayashi, Tsuneo, Takayuki Matsumoto, Kazuyuki Ooishi, and Katsuo Kamata. Differential expression of ␣2D-adrenoceptor and eNOS in aortas from early and later stages of diabetes in Goto-Kakizaki rats. Am J Physiol Heart Circ Physiol 287: H135-H143, 2004; 10.1152/ajpheart.01074.2003.-The aim of the present study was to compare vascular dysfunction between the early (12 wk old) and later (36 wk old) stages of spontaneous diabetes in GotoKakizaki (GK) rats. We also evaluated the aortic expression of the ␣2D-adrenoceptor and endothelial nitric oxide synthase (eNOS). Vascular reactivity was assessed in thoracic aortas from age-matched control rats and 12-and 36-wk GK rats. Using RT-PCR and immunoblots, we also examined the changes in expression of the ␣2D-adrenoceptor and eNOS. In aortas from GK rats (vs. those from age-matched control rats): 1) the relaxation response to ACh was enhanced at 12 wk but decreased at 36 wk; 2) the relaxation response to sodium nitroprusside was decreased at both 12 and 36 wk, 3) norepinephrine (NE)-induced contractility was decreased at 12 wk but not at 36 wk, 4) the expressions of ␣1B-and ␣1D-adrenoceptors were unaffected, whereas those of ␣2D-adrenoceptor and eNOS mRNAs were increased at both 12 and 36 wk; and 5) NE-and ACh-stimulated NOx (nitrite and nitrate) levels were increased at 12 wk, although at 36 wk ACh-stimulated NOx was lower, whereas NE-stimulated NOx showed no change. These results clearly demonstrate that enhanced ACh-induced relaxation and impaired NE-induced contraction, due to NO overproduction via eNOS and increased ␣2D-adrenoceptor expression, occur in early-stage GK rats and that the impaired AChinduced relaxation in later-stage GK rats is due to reductions in both NO production and NO responsiveness (but not in eNOS expression).Type 2 diabetes; ␣2D-adrenoceptor; endothelium; nitric oxide synthase; relaxation DIABETES MELLITUS is an important risk factor for the development of atherosclerosis. Numerous epidemiological studies have indicated that the insulin resistance and hyperinsulinemia associated with Type 2 diabetes make important contributions to the development of hypertension and atherosclerotic lesions. Although an accumulating body of evidence indicates that endothelium-dependent relaxation is weaker both in a Type 1 diabetic model, namely, streptozotocin (STZ)-induced diabetic rats (11, 26, 32, 39 -41), and in Type 2 diabetic rats (28, 44, 50, 51), we (29) and others (6, 42) have noted an augmented or unaltered endothelium-dependent relaxation at an early stage in STZ-induced diabetes. In fact, there is clinical and experimental evidence of augmented blood flow at early stages of diabetes (9, 24). In the Type 1 model STZ-induced diabetic rat, Pieper (42) showed that there is an early (for 1 day) increase in endothelium-dependent relaxation, followed by a reversion phase (for 1-2 wk), in which relaxation is normal, and then a final phase (for 8 wk) of impaired relaxation. In a Type 2 model, the obese Zucker rat, the aorta has been reported to exhibit eith...

The PI3-K/Akt pathway: roles related to alterations in vasomotor responses in diabetic models

“…We and others have demonstrated that both aortic endothelial dysfunction and hypertension are present in type II spontaneously diabetic (db/db) mice and in fructose-fed insulin-resistant mice Kamata et al, 2001). However, our recent observation that both endothelial function and NO production are impaired in aortic strips from spontaneously type II diabetic Goto-Kakizaki rats seemed to conflict with our finding that the expressions of the mRNA and protein for endothelial NO synthase (eNOS) were increased in such aortae (Kobayashi et al, 2004a). Since endothelium-dependent relaxation seems to be attenuated in blood vessels in at least some diabetic models when the disease is wellestablished, it is possible that time-dependent changes in endothelial function may occur (e.g., a two-phase influence of diabetes over endothelium-dependent relaxation).…”

“…Jiang et al (1999) found that both vascular insulin-induced phosphorylation and activation of the components of insulin signaling from the receptor level downstream to Akt were blunted in these obese insulin-resistant rats. Our recent observation that both endothelial function and NO production are impaired in aortic strips from spontaneously type II diabetic Goto-Kakizaki rats seemed to conflict with our finding that the expressions of the mRNA and protein for endothelial NO synthase (eNOS) were increased in such aortae (Kobayashi et al, 2004a). However, a possible explanation may be that in the intact cells, NO synthesis is regulated independently of changes in eNOS enzyme activity.…”

Carotid Artery Stenosis is Exacerbated in Spontaneously Obese Model Rats with Diabetes

“…Hyperinsulinemia has been reported in OLETF rats in previous studies 7,8) . In the present analysis, metabolic correction with insulin notably reversed the enhanced endothelial function in the diabetic model rats, which may be due to the downregulation of endothelial nitric oxide synthase (eNOS)/heme oxygenase (HO)-1 9) . Insulin administration also resulted in intimal hyperplasia, particularly subendothelial thickening with the potential to impede the diffusion of nitric oxide into smooth muscle required to induce relaxation 10) .…”

Impairment of PI3-K/Akt Pathway Underlies Attenuated Endothelial Function in Aorta of Type 2 Diabetic Mouse Model

“…[3][4][5][6] Our recent observation that endothelial function and nitric oxide (NO) production are impaired in aortic strips from spontaneously type 2 diabetic GotoKakizaki rats seemed to conflict with our finding that the expressions of the mRNA and protein for endothelial NO synthase (eNOS) were increased in such aortas. 7 However, a possible explanation may be that in the intact cells, NO synthesis is regulated independently of changes in eNOS enzyme activity.…”