Angiotensin II binding and extracellular matrix remodelling in a rat model of myocardial infarction.

Clinical evidence points to a role for angiotensin II (Ang II) in the post-infarction remodelling of cardiac hypertrophy. The present study was designed to investigate the remodelling process in an animal model of myocardial infarction (MI) using the following criteria: 1) histological studies to examine the re-vascularisation process and collagen deposition in different regions of the myocardium; 2) histological evidence to investigate the cell type distribution using cell-specific markers; 3) histological and Western blot analysis to localise Ang II receptor subtypes (AT(1)-receptor and AT(2)-receptor) and to study their regulation; 4) kinetics of the binding of Ang II to its receptors in a heart perfusion model; and 5) to assess the effect of the Ang II antagonist (losartan) on these parameters. MI was induced by ligation of the left anterior descending coronary artery of Sprague-Dawley rats. Four different animal groups were established: 1) sham-operated, non-treated; 2) sham-operated, treated with losartan; 3) myocardial infarct, non-treated; and 4) myocardial infarct, treated with losartan. In infarcted rat hearts, fibroblasts and collagen types I and III increased in the remnant viable region of the left ventricle compared with sham-operated rats. One month of losartan treatment in myocardial infarcted rats revealed insignificant changes in fibroblasts and collagen types I and III compared with sham controls. Also, myocardial infarction increased AT(1)-receptor protein levels compared with sham-operated controls, as judged by Western blotting. In losartan-treated myocardial infarct animals, no changes were detected at the level of AT(1)-receptor expression compared with non-treated myocardial infarct rats. Binding studies of Ang II on endothelial cell lining and directly on myocytes in sham-operated and infarcted perfused rat hearts revealed that, in myocardial infarcted-animals, Ang II binding affinity increased both in the endothelium and in myofibres. This may be considered a major putative effect of the peptide in potentiating the pharmacodynamics of hypertrophy. In losartan-treated myocardial infarcted-animals, a marked increase in the binding affinities of Ang II for the AT(2)-receptor subtype was observed. Hence, potential cardioprotective effects of the AT(1)-receptor antagonist are proposed.

Characterization of insulin-resistance: role of receptor alteration in insulin-dependent diabetes mellitus, essential hypertension and cardiac hypertrophy.

Insulin-resistance is associated with a number of disease states such as diabetes, syndrome X, and hypertension. These situations may be coupled to insulin-resistance through the insulin signaling system as a common pathway. The purpose of this study was to investigate the receptor binding alterations in streptozotocin-induced diabetic rats, spontaneously hypertensive rats and aortocaval shunted rats (eccentric cardiac hypertrophy). A physical model describing a 1:1 stoichiometry of ligand binding with its receptor is proposed describing reversible binding of [(125)I]insulin or [(125)I]IGF-1 at the microvascular endothelial as well as with the cardiac myocytes after CHAPS-treatment. Analysis of the collected effluents are curve-fitted with a conservation equation and a first-order Bessel function which allowed the calculation of the forward binding constants (k(n)), the reversible constants (k(-n)), the dissociation constants (k(d)) and the residency time constants (tau). The results showed that streptozotocin-induced diabetic rats showed insulin-resistance through alterations in the kinetics of insulin receptor binding. The normotensive controls of the spontaneously hypertension rats (SHR) carry themselves insulin-resistant receptors whose binding to insulin worsens in the hypertensive SHR. Negative cooperativity between insulin-like growth factor IGF-1 and insulin receptors could be a causative factor predisposing for insulin-resistance in the aortocaval shunted rats to insulin resistance. The defects may be occurring at the receptor level in insulin-dependent diabetes mellitus, Wistar-Kyoto rats and spontaneously hypertensive rats. In conclusion, alterations in the kinetics of insulin binding to its receptor seem to play a central role for the initiation of insulin-resistance during the various pathophysiological states.

Insulin-receptor binding characteristics in perfused SHR and WKY rat hearts.

This work uses a new heart-perfusion technique to measure 125I-insulin binding on capillary endothelium and myofiber cell membranes in Wistar-Kyoto and spontaneously hypertensive rats. Ringer-Lock buffer was infused at a rate of 1 ml min-1 in the presence of 20 meq l-1 K+ and 125I-insulin through an aortic cannula. The effluent was collected through a catheter introduced into the right atrium. The capillary endothelial lining was removed by detergent treatment to expose the cardiac myocyte surfaces. A physical model describing a 1:1 binding stoichiometry of 125I-insulin with its receptors is proposed and the derived mathematical equations allow for the calculation of binding constants (kn), unbinding constants (k-n), dissociation constants (kd), and residency time constants (tau). The results showed that in the spontaneously hypertensive rats' hearts significant alterations were not noticed in the kinetics of insulin binding with its receptor at the capillary endothelial site compared to hearts of the normotensive control Wistar-Kyoto rats. However, at the myocyte site and in the spontaneously hypertensive rats, steric, configurational, and/or structural modifications for insulin binding with the receptor were observed as indicated by changes in insulin affinity for its receptor. Hence, alterations in insulin binding rather than reduction in insulin receptor number due to hyperinsulinemia, can be considered among the peculiarities of insulin resistance in the spontaneously hypertensive rats. Hyperinsulinemia, therefore, may be considered an upregulatory process as a consequence of insulin-resistance. The results support the hypothesis that insulin-resistance on the myocytes could be a pathophysiologic defect in insulin-receptor structure, function and affinity, and therefore myocardial function.

Treatment of hypertension in the elderly with captopril.

Fifteen elderly hypertensives aged fifty-nine to seventy-four years received captopril either as a monotherapy (group I, n=7) or as an addition to other antihypertensive drugs (group II, n=8) for twelve to fourteen months. Both the mean supine and erect blood pressure fell from 173.3 +/- 3.4/93.3 +/- 6.6 to 143.3 +/- 3.4/78.3 +/- 1.7 and from 166.7 +/- 8.6/98.3 +/- 4.4 to 146.7 +/- 12.0/85.0 +/- 2.9 mm Hg, respectively, in group I, and from 165.6 +/- 10.5/104.9 +/- 4.4 to 128.8 +/- 4.7/84.1 +/- 1.7 and from 154.0 +/- 10.1/107.8 +/- 3.3 to 126.3 +/- 6.0/88.8 +/- 1.2 mm Hg, respectively, in group II. There was a slight but insignificant reduction in pulse rate and body weight. Side effects were minimal. All patients experienced a sense of well-being. There was no impairment of renal function in most patients and no reduction in serum K. This study suggests that, in elderly hypertensives, captopril reduces blood pressure safely and effectively without impairing perfusion to the brain, heart, and kidneys and without causing edema or hypokalemia.

High blood pressure: definitions, prognostic, and therapeutic implications.

Although it is well established that high blood pressure (BP) levels of 140/90 mmHg or higher are associated with increased cardiovascular morbidity and mortality it has not been as well appreciated that lower BP levels, namely those considered to be in the "normotensive" range, also confer an increased risk of cardiovascular disease. Recent data from the Framingham Heart Study have demonstrated that high normal levels (i.e. SBP = 130-139 and/or DBP = 85-89 mmHg) frequently progress to hypertension, are associated with structural and functional cardiovascular alterations, an atherogenic metabolic profile and/or a comorbid condition, and an increased risk of cardiovascular outcomes. Factors that predispose to progression to hypertension include higher SBP and body weight at baseline and weight gain. In low risk subjects with high normal BP, nonpharmacologic measures, especially salt restriction and weight reduction are often adequate to lower BP to < or = 130/80. In those with a high cardiovascular risk profile, BP should be reduced to < or = 120/80 with nonpharmacologic measures and pharmacotherapy.

Regulation of Na+-K+ pump activity in erythrocytes and blood pressure in anephric rats.

This study was designed to explore factors involved in the regulation of Na-K pumps in erythrocytes and blood pressure in anephric Sprague-Dawley female rats. Twenty-four hours following bilateral nephrectomy, the rats were given a 1-h infusion of 1 ml of either 0.9% or 5.4% saline, or 5% or 30% glucose. At the completion of the infusion, tail blood pressure was determined and blood was drawn for the measurement of the ouabain-furosemide-sensitive sodium efflux rate constant in erythrocytes. Infusion of 5.4% saline or 30% glucose caused a significant reduction in the erythrocyte sodium efflux rate constant, more pronounced with the former, and an elevation in blood pressure. Nephrectomy or infusion of 0.9% saline or 5% glucose had no effect on either parameter. These findings suggest that in anephric rats (1) extracellular fluid hyperosmolality rather than extracellular fluid volume expansion inhibits the Na-K pump in all cells; (2) a Na-K pump inhibitor is involved in the genesis of hypertension.