Hyperinsulinemia induces myocardial infarctions and arteriolar medial hypertrophy in spontaneously hypertensive rats

Endothelial dysfunction in diabetes: multiple targets for treatment

Robert Furchgott's discovery of the obligatory role that the endothelium plays in the regulation of vascular tone has proved to be a major advance in terms of our understanding of the cellular basis of diabetic vascular disease. Endothelial dysfunction, as defined by a reduction in the vasodilatation response to an endothelium-dependent vasodilator (such as acetylcholine) or to flow-mediated vasodilatation, is an early indicator for the development of the micro- and macroangipathy that is associated with diabetes. In diabetes, hyperglycaemia plays a key role in the initiation and development of endothelial dysfunction; however, the cellular mechanisms involved as well as the importance of dyslipidaemia and co-morbidities such as hypertension and obesity remain incompletely understood. In this review, we discuss the mechanisms whereby hyperglycaemia, oxidative stress and dyslipidaemia can alter endothelial function and highlight their effects on endothelial nitric oxide synthase (eNOS), the endothelium-dependent hyperpolarising factor (EDHF) pathway(s), as well as on the role of endothelium-derived contracting factors (EDCFs) and adipocyte-derived vasoactive factors such as adipose-derived relaxing factor (ADRF).

The roles of insulin resistance, hyperinsulinemia, and thiazolidinediones in cardiovascular disease

Although it is difficult to distinguish between the relative effects of insulin resistance and hyperinsulinemia, insulin resistance is clearly associated with significantly increased cardiovascular and cerebrovascular risk. This effect is consistent across the spectrum of worsening glycemic control, from the onset of impaired glucose tolerance to the development of clinical diabetes. It is more difficult to discriminate between the roles of elevated circulating insulin and proinsulin levels; the association between insulin levels and cardiovascular risk is weak. The thiazolidinediones (TZDs) significantly improve insulin sensitivity and exert numerous effects on the vascular bed, including improved endothelial function, decreased vascular inflammation, decreased plasma free fatty acid levels, improved dyslipidemic profiles, and inhibition of vascular smooth muscle proliferation. These findings provide increasing evidence to suggest that the TZDs may have a beneficial effect on atherosclerosis and may reduce the incidence and severity of adverse cardiovascular outcomes. These effects remain to be substantiated by the results of large outcomes studies to evaluate the impact of glycemic control and reversal of insulin resistance on cardiovascular events.

The use of beta-blockers in the treatment of chronic heart failure

The use of beta-blockers in addition to digoxin, diuretics, and ACE inhibitors was shown to be beneficial for patients with chronic heart failure. Benefits include decreased hospitalizations, decreased need for heart transplant, and decreased mortality. The fact that beta-blockers may improve a sense of well-being, as well as quality of life, for patients with chronic heart failure, is perhaps the greatest advantage to including these drugs in HF therapy.

Structural alterations in subcutaneous small arteries of normotensive and hypertensive patients with non-insulin-dependent diabetes mellitus

BACKGROUND

It is not presently known whether non-insulin-dependent diabetes mellitus (NIDDM) is associated with the presence of structural alterations in small arteries or whether the combination of hypertension and NIDDM may have an additive effect on endothelial dysfunction. Therefore, we investigated subcutaneous small arteries in 12 normotensive subjects (NT group), 18 patients with essential hypertension (EH group), 13 patients with NIDDM, and 11 patients with NIDDM and EH (NIDDM+EH group).

METHODS AND RESULTS

Subcutaneous small arteries were evaluated by a micromyographic technique. The internal diameter, the media-to-lumen ratio, remodeling and growth indices, and the collagen-to-elastin ratio were calculated. Concentration-response curves to acetylcholine, bradykinin, the endothelium-independent vasodilator sodium nitroprusside, and endothelin-1 were performed. The media-to-lumen ratio was higher in the EH, NIDDM, and NIDDM+EH groups compared with the NT group. EH patients showed the presence of eutrophic remodeling, whereas NIDDM and NIDDM+EH patients showed 40% to 46% cell growth. The collagen-to-elastin ratio was significantly increased in the EH and NIDDM+EH groups compared with the NT group. The vasodilatation to acetylcholine and bradykinin was similarly reduced in EH, NIDDM, and NIDDM+EH groups compared with the NT group. The contractile responses to endothelin-1 were similarly reduced in EH, NIDDM, and NIDDM+EH patients.

CONCLUSIONS

Our data suggest that the effects of NIDDM and EH on small artery morphology are quantitatively similar but qualitatively different and that the presence of hypertension in diabetic patients has little additive effect on small artery morphology and none on endothelial dysfunction.

Role of glucose utilization in the restoration of hypophysectomy-induced hepatic cytochrome P450 2E1 by growth hormone in rats

Growth hormone and insulin are the primary determinants for cytochrome P450 2E1 (CYP2E1) expression. The role of glucose on the induction of CYP2E1 by hypophysectomy and on the restorative effect by growth hormone was investigated in the rat liver. Western and Northern blot analyses revealed that hypophysectomy induced CYP2E1 by 5-fold at 1-4 weeks, relative to control, with a concomitant increase in CYP2E1 mRNA. Hypophysectomized rats (HXR) showed a 20% reduction in the plasma glucose level. Hypophysectomy-induced increase in the CYP2E1 mRNA was completely abolished by glucose feeding in drinking water (10%) for 7 days. Treatment of HXR with hGH (2 I.U./kg, twice a day, for 7 days) inhibited the increases in CYP2E1 protein and mRNA levels with restoration of the plasma glucose level. In contrast to the effect of human growth hormone (hGH) on CYP2E1 in HXR with free access to foods, CYP2E1 expression failed to be restored by hGH in starving HXR. However, glucose feeding of starving HXR abolished the induction of CYP2E1. Effects of hypophysectomy and hGH treatment were studied in streptozotocin-induced diabetic rats. Insulin, but not hGH, prevented an increase in CYP2E1 mRNA in diabetic rats. The hepatic CYP2E1 induction in hypophysectomized diabetic rats was inhibited by hGH treatment, indicating that the hGH effect on CYP2E1 expression did not involve insulin production. These results provide evidence that the induction of hepatic CYP2E1 by hypophysectomy may result from reduced glucose utilization, and that the effect of hGH on CYP2E1 expression may be mediated with enhanced glucose utilization, but not with insulin production.

Relative influence of insulin resistance versus blood pressure on vascular changes in longstanding hypertension. ICARUS, a LIFE sub study. Insulin Carotids US Scandinavia

BACKGROUND

Insulin resistance is associated with hypertension. The relative influences of hyperinsulinaemia and high blood pressure on vascular hypertrophy and carotid distensibility is unclear in patients with longstanding hypertension.

METHODS

In 88 unmedicated patients with stage II-III hypertension and left ventricular hypertrophy on electrocardiogram we measured blood pressure, minimal forearm vascular resistance (MFVR) using plethysmography, intima-media thickness (IMT) and the wall distensibility of the common carotid arteries using ultrasound, and insulin sensitivity using a 2-h isoglycaemic hyperinsulinaemic clamp.

RESULTS

IMT was positively correlated to systolic blood pressure (r= 0.26, P < 0.05), whole body glucose uptake index (M/IG; r= 0.22, P< 0.05), age (r= 0.24, P< 0.05) and negatively correlated to body mass index (r= -0.24, P < 0.05); IMT did not correlate to fasting serum insulin (r= -0.14, NS). In men (n = 64) MFVR was positively correlated to systolic blood pressure (r = 0.30, P < 0.05), but was unrelated to M/G and serum insulin. The distensibility of the common carotid arteries was negatively correlated to systolic blood pressure (r = -0.40, P< 0.001) and in untreated patients (n = 22) positively correlated to M/IG (r = 0.47, P < 0.05).

CONCLUSIONS

High systolic blood pressure was related to vascular hypertrophy, whereas hyperinsulinaemia and insulin resistance were not, suggesting that longstanding high blood pressure is a far more important determinant for structural vascular changes than insulin resistance at this stage of the hypertensive disease. However, hyperinsulinaemia and insulin resistance were associated with low distensibility of the common carotid arteries in the subgroup of never treated hypertensive patients.