Antihypertensive Treatment and Renal Damage

Alterations of M 2,3 -Muscarinic Receptor Protein and mRNA Expression in the Bladder of the Fructose Fed Obese Rat

PURPOSE

The effects of metabolic syndrome on bladder function and M2,3-muscarinic receptor expression were studied using the fructose fed obese rat.

MATERIALS AND METHODS

Male Wistar rats were divided into 2 groups, including group 1-normal control rats and group 2-6-week fructose fed rats. In vivo cystometry using anesthesia was performed. In vitro the bladder was divided into the urothelium and muscle layer by microdissection. Tissue M2,3-muscarinic receptor protein levels were measured by Western blotting. Expression of the mRNAs that encode M2,3-muscarinic receptors was estimated using reverse transcriptase-polymerase chain reaction.

RESULTS

Premicturition unstable bladder contractions suggestive of detrusor overactivity were noted in 62.5% of fructose fed rats but in no controls. M2,3-muscarinic receptor protein and mRNA expression was noted in the urothelium and muscle layer of the rat bladder. In control rats the M2-to-M3-muscarinic receptor protein expression ratio was 1:0.68 in urothelium and 1:0.28 in the muscle layer, and that for mRNA expression was 1:0.32 and 1:0.36, respectively. Compared to controls bladder M2,3-muscarinic receptor protein expression in the urothelium and muscle layer of 8 preparations each was significantly increased in fructose fed rats by 89% and 90% for M2-muscarinic receptor (each p <0.001), and by 35% and 93% for M3-muscarinic receptor (p <0.01 and <0.001, respectively). Correspondingly M2,3-muscarinic receptor mRNA expression in the fructose fed rat bladder urothelium and muscle layer of 8 preparations each was also significantly increased by 31% and 49% for M2-muscarinic receptor (each p <0.01), and by 121% and 117% for M3-muscarinic receptor (each p <0.001, respectively).

CONCLUSIONS

Metabolic syndrome induces increased expression of M2,3-muscarinic receptor mRNA and protein in the urothelium as well as the muscle layer of the bladder in 6-week fructose fed rats. The receptor alterations are associated with functional evidence of detrusor overactivity.

Relationship between renal and cardiovascular changes in a murine model of glucose intolerance

Nutrition is an important variable which may affect the risk for renal disease. We previously showed that a high fructose diet in mice produced hypertension and sympathetic activation [8]. The purpose of this study was to determine if a fructose diet altered renal function. A high fructose diet for 12 weeks impaired glucose tolerance, but caused no change in body weight, blood glucose or plasma insulin. Impairment in renal function was documented by the almost two fold increase in urinary protein excretion (

CONTROL

6.6+/-0.6 vs. Fructose: 15.0+/-0.7 mmol protein/mmol creatinine; p<0.05) which was also accompanied by increases in urinary volume. The diet produced little change in renal histology, kidney weight or kidney weight/body weight ratio. Urinary excretion of angiotensin II/creatinine (

CONTROL

78.9+/-16.6 vs. Fructose: 80.5+/-14.2 pg/mmol) and renal angiotensin converting enzyme activity (

CONTROL

9.2+/-1.6 vs. Fructose: 7.6+/-1.0 ACE units) were not different between groups. There was a positive correlation between mean arterial pressure (r=0.7, p=0.01), blood pressure variability (BPV) (r=0.7, p=0.02), low frequency BPV component (r=0.677, p=0.03) and urinary protein excretion. Results show that consumption of a high fructose diet in mice had deleterious effects on renal function, which were correlated with cardiovascular changes.

Physiologic evidence of renoprotection by antihypertensive therapy

PURPOSE OF REVIEW

Hypertension is vastly prevalent worldwide and constitutes the second leading cause of end-stage renal disease. Therefore, treating hypertension and protecting the kidney from deterioration are exceedingly important. Although previous studies have explored the renal effects of various antihypertensive drugs in animal models and humans, recent clinical trials are all the more convincing. This review summarizes the latest data demonstrating the physiologic evidence of renoprotection by antihypertensive therapy.

RECENT FINDINGS

Experimental studies in various models of hypertension with renal injury have demonstrated clearly that angiotensin-converting enzyme inhibitors, angiotensin II type 1 receptor blockers, or aldosterone antagonists promote beneficial renal actions, through hemodynamic and nonhemodynamic mechanisms. Of particular significance, recent clinical trials have demonstrated renoprotection by angiotensin II inhibition in patients with hypertension and chronic kidney disease. Angiotensin-converting enzyme inhibition and angiotensin II type 1 receptor blockade have provided equivalent renal benefits, and their dual action seems to confer greater renoprotection. The available data on the renal outcomes of other antihypertensive drugs such as calcium antagonists have been inconsistent.

SUMMARY

The results of the numerous experimental and clinical studies have established the renoprotective properties of renin-angiotensin-aldosterone inhibitors, which confer greater benefit by virtue of their effects over and beyond blood pressure reduction. These findings provide the convincing basis for the recommendation of angiotensin-converting enzyme inhibitors, angiotensin II type 1 receptor blockers, or both as first-line therapy in hypertension with chronic kidney disease.

Blutdruckunabhängige Wirkungen von Antihypertensiva

Antihypertensive medications belong to different pharmacological classes. Besides blood pressure lowering properties, many substances, particularly ACE inhibitors and AT1-receptor antagonists but also in part calcium antagonists and aldosterone receptor antagonists, exert additional anti-inflammatory and antifibrotic effects as well as protective effects on endothelium. Delay of disease progression in chronic kidney disorders by inhibition of the renin-angiotensin system also as the result of blood pressure independent effects has been documented in clinical trials. On the other hand, in patients with essential hypertension without end-organ damage, it remains unclear whether the clinically proven blood pressure independent effects of antihypertensive agents are also clinically relevant. However, in clinical studies ACE inhibitors and AT1-receptor antagonists reduce the de novo occurrence of the diabetic metabolic state. Inhibition of the renin-angiotensin system decreases the incidence of diabetic nephropathy. This contribution presents currently available data on possible blood pressure independent effects of antihypertensive agents.

New insights into the pathophysiology of diabetic nephropathy: from haemodynamics to molecular pathology

Although debated for many years whether haemodynamic or structural changes are more important in the development of diabetic nephropathy, it is now clear that these processes are interwoven and present two sides of one coin. On a molecular level, hyperglycaemia and proteins altered by high blood glucose such as Amadori products and advanced glycation end-products (AGEs) are key players in the development of diabetic nephropathy. Recent evidence suggests that an increase in reactive oxygen species (ROS) formation induced by high glucose-mediated activation of the mitochondrial electron-transport chain is an early event in the development of diabetic complications. A variety of growth factors and cytokines are then induced through complex signal transduction pathways involving protein kinase C, mitogen-activated protein kinases, and the transcription factor NF-kappaB. High glucose, AGEs, and ROS act in concert to induce growth factors and cytokines. Particularly, TGF-beta is important in the development of renal hypertrophy and accumulation of extracellular matrix components. Activation of the renin-angiotensin system by high glucose, mechanical stress, and proteinuria with an increase in local formation of angiotensin II (ANG II) causes many of the pathophysiological changes associated with diabetic nephropathy. In fact, it has been shown that angiotensin II is involved in almost every pathophysiological process implicated in the development of diabetic nephropathy (haemodynamic changes, hypertrophy, extracellular matrix accumulation, growth factor/cytokine induction, ROS formation, podocyte damage, proteinuria, interstitial inflammation). Consequently, blocking these deleterious effects of ANG II is an essential part of every therapeutic regiment to prevent and treat diabetic nephropathy. Recent evidence suggests that regression of diabetic nephropathy could be achieved under certain circumstances.