Diabetes mellitus and associated hypertension, vascular disease, and nephropathy. An update

Because considerable important information has been published since our previous review, this update concentrates on new findings with regard to cardiovascular and renal risk factors contributing to the striking morbidity and mortality of these coexisting diseases. For example, a large body of investigative data has recently emerged suggesting or delineating a pathogenic role for hyperglycemic-related glycosylation and oxidation of lipoproteins and vascular and renal tissues. Great strides have recently been made in the understanding of platelet, coagulation, lipoprotein, and endothelial abnormalities in the pathogenesis of cardiovascular and renal disease associated with diabetes mellitus and hypertension. Major progress has been made in clarifying the pathophysiology of glomerulosclerosis and other processes involved in the progression of diabetic nephropathy. Furthermore, accumulating data surveyed in this review address new and promising pharmacological interventions that specifically address these pathophysiological mechanisms.

Effects of lysophosphatidic acid, a novel lipid mediator, on cytosolic Ca2+ and contractility in cultured rat mesangial cells

Lysophosphatidic acid (LPA), the smallest and structurally simplest phospholipid, has the potential to modulate cellular signaling in diverse tissues and cell types, including fibroblasts. In the present study, we assessed the effects of LPA on cultured rat glomerular mesangial cells. Quantitative changes of [Ca2+]i in response to LPA were measured in monolayers of mesangial cells loaded with the fluorescent Ca2+ indicator fura 2. LPA (10 nmol/L to 100 mumol/L) increased [Ca2+]i in a dose-dependent manner and evoked inositol trisphosphate formation. LPA (1 mumol/L to 30 mumol/L) also elicited a marked, albeit transient, contractile response in mesangial cells cultured on collagen gel, as assessed by a decrease in cell surface area (CSA). The contraction persisted for 5 minutes (CSA decreased by 31%), whereupon the mesangial cells gradually relaxed with a consequent increase in CSA. Pretreatment of mesangial cells with isradipine (1 mumol/L), a dihydropyridine-sensitive Ca2+ channel blocker, completely blocked LPA-induced contraction. Isradipine also decreased resting [Ca2+]i levels as well as the peak and the subsequently sustained [Ca2+]i levels induced by LPA, suggesting that the contractile effects of LPA are dependent on Ca2+ entry through voltage-gated Ca2+ channels. Finally, LPA stimulated an increase in both prostaglandin E2 synthesis and cAMP accumulation, indicating that these mediators may modulate the contractile effects of LPA. Our study is the first demonstration that exogenous LPA induces mesangial cell contraction and suggests that the contraction is mediated by mobilization of intracellular Ca2+ by activation of the phosphoinositide cascade as well as by promotion of Ca2+ entry across the plasma membrane.

Non-visualized left anterior descending artery revealed on selective conus artery catheterization

Cardiac catheterization of a man with severe angina and anterior ischemia on exercise testing with perfusion imaging demonstrated normal anterior wall motion resting left ventriculography, but failed to visualize the left anterior descending (LAD) or conus artery on left and right coronary angiography. Selective contrast injection of a large conus artery originating from a separate ostium in the right aortic sinus demonstrated extensive collateral circulation to an LAD occluded at its origin from the left main coronary artery, thus providing essential information for subsequent patient management.

Renal sodium retention in liver disease

In many patients with cirrhosis, salt retention eventually culminates in ascites and edema. The pathogenesis probably involves several hormonal and neural effectors acting in concert. When conservative therapy with diet and diuretics fails to mobilize fluid, options for more intensive treatment include large-volume paracentesis and the transjugular intrahepatic portosystemic shunt.

Evolving concepts in the management of hypertension

Currently, a plethora of antihypertensive medications exists. One concern about the long-term use of many of these agents is that adverse effects may offset their benefits. Despite the availability of many newer agents, blood pressure continues to be inadequately controlled in the majority of treated hypertensive patients, and many still remain at higher risk of premature death than the general population. More than 60% of treated hypertensive patients fail to attain blood pressures of < 140/90 mmHg. The major factors that permit a rational choice of medication include demographic considerations such as race and age, coexisting disease, safety, patient acceptance (quality of life), potential drug interactions, and additional salutary effects. The role of nondiuretic monotherapy is an integral component of this discussion. Preliminary data indicate that the use of calcium-channel blockers, converting-enzyme inhibitors, and AII-receptor antagonists constitutes excellent therapy in many patients. The effects of medication on the metabolic and lipid profiles are also considered.

Release of kaliuretic peptide during immersion-induced central hypervolemia in healthy humans

Kaliuretic peptide, a new peptide hormone consisting of amino acids 79-98 of the 126 amino acid atrial natriuretic factor (ANF) prohormone, is synthesized in the heart and is a potent stimulator of potassium excretion. The mechanism(s) controlling the release of kaliuretic peptide heretofore has not been defined. Because water immersion to the neck provides an acute central volume expansion identical to that produced by 2 liters of saline but without the plasma compositional change, immersion to the neck (NI) was utilized to assess kaliuretic peptide responses to acute central blood volume expansion in seven seated sodium-replete normal subjects. Since atrial natriuretic factor (ANF; amino acids 99-126 of the prohormone) originates from the amino acids adjacent to kaliuretic peptide in the ANF prohormone but is proteolytically cleaved from the rest of the prohormone before release, measurement of ANF was incorporated into this study to determine if there are differences with respect to release of these two portions of the ANF prohormone. Both kaliuretic peptide and ANF increased promptly with NI, with ANF peaking at 1 hr of immersion, whereas kaliuretic peptide peaked at the 3rd hr of immersion. With cessation of immersion, ANF decreased to preimmersion levels within 0.5 hr while kaliuretic peptide was still significantly (P < 0.05) elevated at 1 hr postimmersion. These findings indicate that kaliuretic peptide and ANF are released simultaneously but that kaliuretic peptide peak circulating concentration and its return to preimmersion values are prolonged compared with ANF. These last findings suggest a slower clearance from the circulation for kaliuretic peptide. The diuretic peak response to NI corresponded in a temporal manner to the peak circulating concentration of kaliuretic peptide, suggesting a possible physiologic role for kaliuretic peptide in modulating volume homeostasis in humans.

Renal parenchymal disease and hypertension

Renal parenchymal disease is the most common cause of secondary hypertension, accounting for 2.5% to 5.0% of all cases. Hypertension associated with renal parenchymal disease occurs as a complication of a wide variety of glomerular and interstitial renal diseases and may accelerate the decline in renal function if inadequately controlled. Renal parenchymal hypertension most probably represents the combined interactions of multiple independent mechanisms: potential factors include impaired sodium handling leading to volume expansion, perturbations of the renin-angiotensin system, alterations in endogenous vasodepressor compounds, and possibly increased activity of vasoactive substances. The past several years have witnessed newer insights into both the pathophysiology and the therapeutics of this disorder. The characterization of endothelin and the nitric oxide (NO)-arginine pathway and their roles in biology and medicine has provided additional new insights with regard to the pathogenesis of hypertension in renal parenchymal disease. For example, methylated L-arginine derivatives that possess NO synthase inhibitor capabilities including NG-N-dimethylarginine and N-monomethyl-L-arginine are found in human plasma and in urine. Patients with chronic uremia have impaired elimination of these compounds, and circulating concentrations of these compounds may increase sufficiently to result in inhibition of NO production. Thus, accumulation of endogenous NO synthase inhibitors might contribute to the hypertension of advanced renal failure. Similarly, it has been proposed that increased endothelium-derived endothelin that results from hypertensive injury to vascular endothelium could lead to further vasoconstriction and worsening of hypertension. Additional insight into this fascinating problem must await further biochemical characterization of some of the mediators and a more precise delineation of their pathophysiological role.

Multiple factors contribute to acetylcholine-induced renal afferent arteriolar vasodilation during myogenic and norepinephrine- and KCl-induced vasoconstriction. Studies in the isolated perfused hydronephrotic kidney

Acetylcholine (ACh) elicits vasodilation by releasing a number of endothelium-derived relaxing factors (EDRFs). We used the isolated perfused hydronephrotic rat kidney to examine the characteristics of ACh-induced vasodilation of renal afferent arterioles during different types of underlying vasoconstriction. Basal arteriolar tone was increased by either elevating perfusion pressure to 180 mm Hg (myogenic), administering 0.3 mumol/L norepinephrine (NE), or elevating medium potassium concentration to 30 mmol/L (KCl). ACh (10 mumol/L) completely reversed myogenic and NE-induced vasoconstriction and reversed KCl-induced vasoconstriction by 80 +/- 5%. However, whereas ACh produced a sustained vasodilation during KCl- and NE-induced vasoconstriction, only a transient reversal of myogenic vasoconstriction was observed, and myogenic tone recovered within 5 to 10 minutes. ACh-induced vasodilation of arterioles preconstricted with KCl was markedly inhibited by either indomethacin (100 mumol/L) or nitro-L-arginine (100 mumol/L) and was completely abolished by pretreatment with both inhibitors. In contrast, indomethacin and nitro-L-arginine had no effect on the transient response to ACh observed during pressure-induced vasoconstriction. In vessels preconstricted with NE, nitro-L-arginine converted the normally sustained response to ACh to a transient vasodilation, which was refractory to both nitric oxide synthase and cyclooxygenase inhibition. Since this component was not observed during KCl-induced vasoconstriction, it may reflect the actions of an, as yet unidentified, endothelium-derived hyperpolarizing factor (EDHF). Our findings thus suggest that prostanoids, nitric oxide, and EDHF all contribute to ACh-induced renal afferent arteriolar vasodilation and that the relative contributions of these individual EDRFs depends on the nature of the underlying renal vascular tone.

Impairment of afferent arteriolar myogenic responsiveness in the galactose-fed rat

Previous studies from our laboratory have demonstrated impaired afferent arteriolar responsiveness to pressure in rats 4-6 weeks after the induction of diabetes mellitus. Although the responsible mechanisms mediating this renal autoregulatory defect have not been fully defined, increased polyol metabolism has been implicated as a possible factor involved in the pathogenesis of diabetic complications. We therefore investigated the possible role of this metabolic disturbance in renal autoregulation using the galactose-fed rat, a model characterized by increased polyol pathway activity independent of hyperglycemia or insulin deficiency. Hydronephrosis was induced to permit direct visualization of renal microvessels. Pressure-induced vasoconstriction of afferent arterioles was assessed by quantitating vessel diameter following stepwise increments of renal perfusion pressure (RAP; from 80 to 180 mm Hg) in the hydronephrotic kidneys from control rats and rats fed a 50% galactose diet for 2 or 4 weeks. Vessel diameters were measured from video images by computer-assisted image processing. Control rats exhibited progressive afferent arteriolar vasoconstriction when RAP was increased from 80 to 180 mm Hg (-17.3% +/- 1.0%; P < 0.001). In contrast, myogenic responses to increases in pressure were absent in the afferent arterioles of rats fed a 50% galactose diet for either 2 (-4.1% +/- 1.9%; not significant) or 4 weeks (-2.9 +/- 3.4%; not significant). Our demonstration that the impairment of afferent arteriolar responsiveness to increasing RAP in the normoglycemic galactose-fed rat was identical to that observed in the STZ-diabetic rat suggests that increased polyol accumulation may contribute to the impairment of renal autoregulation in the diabetic rat.

A prospective randomized clinical trial comparing a new oral sustained-release ritodrine with conventional tablets

OBJECTIVES

Evaluation of maternal metabolic and cardiovascular responses to treatment with the new sustained-release oral ritodrine as compared with the conventional tablets.

METHOD

Thirty-two pregnant patients who had successful intravenous tocolysis were randomly assigned to treatment with either ritodrine tablets or sustained-release capsules. After 5 days of the randomly determined first oral treatment each patient was shifted to the alternate ritodrine formulation for a further 5-day course. Each patient underwent metabolic and non-invasive hemodynamic evaluation.

RESULTS

Echocardiographic parameters during treatment with ritodrine tablets were not significantly different from during sustained-release capsules. Mean systolic blood pressure increased significantly during peak drug activity in patients treated with ritodrine tablets and not during treatment with the sustained-release form. Fasting plasma glucose levels were higher in patients on conventional tablets therapy than in patients on sustained-release ritodrine therapy (88.9 +/- 9 mg/dl vs. 78.7 +/- 8 mg/dl, P < 0.05) while levels following a 50-g oral glucose challenge test did not differ significantly (135 +/- 32 mg/dl vs. 124.5 +/- 27 mg/dl)

CONCLUSIONS

Because of fewer metabolic and cardiovascular side-effects, the new oral therapy offers some advantages over the presently available tablets.

Effects of calcium antagonists on renal hemodynamics and progression of nondiabetic chronic renal disease

In recent years, substantial investigative attention has focused on therapeutic regimens that could retard the progression of chronic renal insufficiency. Emphasis has been placed on the effects of antihypertensive treatment on renal hemodynamics and preservation of renal function. It has been suggested that some classes of antihypertensive agents may confer a greater renoprotective effect, especially agents that lower glomerular capillary pressure. Conversely, by virtue of their ability to preferentially dilate the afferent arteriole calcium antagonists theoretically could favor an increase in glomerular capillary pressure thereby accelerating the decline of renal function. In this review we survey the literature critically and conclude that in patients with essential hypertension and in patients with chronic renal insufficiency, calcium antagonists effectively reduce systemic blood pressure while maintaining glomerular filtration rate and effective renal plasma flow. Preliminary results from a few long-term studies suggest that calcium antagonists may even attenuate the decline in renal function of patients with chronic renal failure. The majority of studies in humans, however, have been nonrandomized, of too short duration, or confounded by investigative difficulties precluding definite conclusions whether calcium antagonists have renoprotective effects. Although the possibility that calcium antagonists may retard progression of renal disease remains to be ascertained, the available evidence indicates that calcium antagonists may be used in patients with renal functional impairment without further exacerbating renal function.