Contribution of bradykinin to the beneficial effects of ramipril in the fructose-fed rat

Inhibition of CatA: an emerging strategy for the treatment of heart failure

The lysosomal serine carboxypeptidase CatA has a very important and well-known structural function as well as a, so far, less explored catalytic function. A complete loss of the CatA protein results in the lysosomal storage disease galactosialidosis caused by intralysosomal degradation of β-galactosidase and neuraminidase 1. However, mice with a catalytically inactive CatA enzyme show no signs of this disease. This observation establishes a clear distinction between structural and catalytic functions of the CatA enzyme. Recently, several classes of orally bioavailable synthetic inhibitors of CatA have been identified. Pharmacological studies in rodents indicate a remarkable influence of CatA inhibition on cardiovascular disease progression and identify CatA as a promising novel target for the treatment of heart failure.

Metabolic actions of angiotensin receptor antagonists: PPAR-gamma agonist actions or a class effect?

Accumulating basic and clinical data support the hypothesis that angiotensin receptor blockers have beneficial effects on glucose and lipid metabolism that are not shared by other classes of antihypertensive agents. These metabolic actions might only partially be shared by angiotensin-converting enzyme inhibitors. Specific benefits beyond those of other angiotensin receptor blockers have been claimed for telemesartan and, to a lesser extent, irbesartan based on a partial agonist action on PPAR-gamma receptors. Although the evidence is strong in vitro, specific actions not shared by other angiotensin receptor blockers have not yet been convincingly demonstrated in vivo or in clinical trials. In many cases, a full range of doses has not been compared, and the apparent superiority of telmesartan could be an artifact of its higher receptor binding affinity, greater tissue penetration owing to lipophilicity, and longer half life.

Metabolic effects of antihypertensive agents: role of sympathoadrenal and renin-angiotensin systems

Reports of beneficial, neutral and adverse impacts of antihypertensive drug classes on glucose and lipid metabolism can be found in human data. Furthermore, mechanisms for these diverse effects are often speculative and controversial. Clinical trial data on the metabolic effects of antihypertensive agents are highly contradictory. Comparisons of clinical trials involving different agents are complicated by differences in the spectrum of metabolic disturbances that accompany hypertension in different groups of patients. Two physiological systems are predominant at the interface between metabolic and cardiovascular regulation: the sympathetic nervous system (SNS) and the renin-angiotensin system (RAS). These two systems are major targets of antihypertensive drug actions, and also mediate many of the beneficial and adverse effects of antihypertensive agents on glucose and lipid metabolism. Thiazides and beta-adrenergic antagonists can adversely affect glucose and lipid metabolism, which are frequently compromised in human essential hypertension, and increase the incidence of new cases of diabetes. Laboratory studies confirm these effects, and suggest that compensatory activation of the SNS and RAS may be one mechanism. Other antihypertensives directly targeting the SNS and RAS may have beneficial effects on glucose and lipid metabolism, and may prevent diabetes. Resolution of the controversies surrounding the metabolic effects of antihypertensive agents can only be resolved by further laboratory studies, in addition to controlled clinical trials.

Changes in blood glucose and plasma insulin levels induced by bradykinin in anaesthetized rats

1. The influence of bradykinin (BK) on blood glucose and plasma insulin levels was investigated in anaesthetized rats. 2. Blood glucose level was dose-dependently increased by intravenous infusion of BK. This effect of BK was enhanced by captopril, an inhibitor of angiotensin-converting enzyme (ACE). Des-Arg9-bradykinin (DABK), a kinin B1 receptor agonist, did not modify blood glucose levels while the effect of BK was inhibited by Hoe-140, a kinin B2 receptor antagonist. 3. The effect of BK was reduced by the NO-synthase inhibitor, N(omega)-nitro-L-arginine methyl ester (L-NAME), and by the cyclo-oxygenase inhibitor, indomethacin. The effect of BK was suppressed by the association of propranolol with phentolamine or phenoxybenzamine. It was also reduced by hexamethonium, a ganglion-blocking drug. In adrenalectomized rats, the infusion of BK slightly decreased blood glucose levels. 4. The hyperglycaemic effect of adrenaline was suppressed by propranolol associated with phentolamine or phenoxybenzamine, but it was not modified by L-NAME. 5. Infusion of BK did not modify plasma insulin levels. However, after phentolamine and propranolol, BK induced a transient 2 fold rise in plasma insulin levels. The release of insulin was dose-dependent and inhibited by Hoe-140. 6. We conclude that infusion of BK induces, via a stimulation of B2 receptors, the release of NO and of prostanoids. The latter agents activate through a reflex pathway the release of catecholamines from the adrenal medulla. This release increases blood glucose levels and reduces plasma insulin levels. After adrenoceptor inhibition, BK induces a secretion of insulin, via the stimulation of B2 receptors.

Effects of quinapril and losartan on insulin sensitivity in genetic hypertensive rats with different metabolic abnormalities

This study was designed to investigate the effects of the angiotensin-converting enzyme (ACE) inhibitor quinapril and the angiotensin II-receptor antagonist losartan on insulin sensitivity in two types of genetic hypertensive rats with insulin resistance. Quinapril (3 mg/kg) and losartan (10 mg/kg) decreased the systolic blood pressure to almost the same extent in both spontaneously hypertensive rats (SHRs) and Dahl salt-sensitive (Dahl S) rats. Quinapril increased the glucose requirement for the euglycemic clamp test in both SHRs and Dahl S rats, whereas losartan increased it in SHRs but not in Dahl S rats. The severity of the metabolic abnormalities may be responsible for the failure of losartan to improve the insulin sensitivity in Dahl S rats because serum insulin, total cholesterol, triglyceride, and free fatty acids (FFAs) were higher in the Dahl S rats than in SHRs. A kinin antagonist, Hoe 140, inhibited the increase in the glucose requirement by quinapril without affecting the depressor effect of quinapril in SHRs. In conclusion, quinapril improved the insulin sensitivity more effectively than did losartan in the genetic hypertensive rats with insulin resistance and relatively severe metabolic abnormalities. Based on our findings, one of the mechanisms underlying the difference between quinapril and losartan may thus be endogenous kinins.

Angiotensin-converting enzyme gene and diabetes mellitus

AIMS

The association of the insertion/deletion polymorphism in the angiotensin-converting enzyme (ACE) gene with cardiovascular disease and diabetic nephropathy remains a controversial issue. This review aims to give an overview of the research to date assessing the impact of the ACE polymorphism in Type 1 and Type 2 diabetes mellitus (DM).

METHODS

A systematic review of the literature was performed in the databases of MEDLINE, PubMed and EMBASE for the key words 'diabetes mellitus', 'diabetic nephropathy', 'ACE polymorphism' and 'genotype' and relevant articles were considered.

RESULTS

A meta-analysis assessing the influence of the ACE polymorphism on disease susceptibility demonstrated significant odds ratios in individuals with the DD genotype for coronary heart disease, myocardial infarction and both diabetic and nondiabetic renal disease. No association was found for left ventricular hypertrophy or hypertension in nondiabetic subjects.

CONCLUSIONS

The ACE polymorphism appears to have a significant impact on the progression of diabetic nephropathy and may have therapeutic implications for identifying those individuals resistant to the effects of ACE inhibitors. It also appears to be indicative of an increased vascular risk in diabetic patients; however, larger prospective studies are required to clarify this situation.