Effects Of Renovascular Hypertension Research Articles

EFFECT OF RENOVASCULAR HYPERTENSION ON CARDIAC RESPONSE TO SUBMAXIMAL EXERCISE IN DOGS

Effects of renovascular hypertension (RVH) on the cardiac and coronary response to exercise was examined in seven (7) dogs chronically instrumented to measure left ventricular systolic pressure (LVSP), mean arterial pressure (MAP), +dP/dtmax, heart rate (HR), cardiac output (CO), coronary blood flow (CBF) and myocardial oxygen consumption (MVO2). Data were collected at rest and during submaximal exercise, before (normotensive, NT) and after development of RVH produced by unilateral renal artery stenosis. Cardiac data are shown in the table:TableThe slope of the relationships between +dP/dtmax, CO and CBF versus MVO2 were significantly decreased after RVH. These data indicate that RVH attenuates the ability to increase myocardial contractile function in response to sympathetic stimulation during exercise. This could be due to coronary hypoperfusion, altered left ventricular β-receptor response to sympathetic stimulation, functional and/or metabolic changes in the left ventricle. (Funded by HL59405)

Effects of renovascular hypertension on myocardial protein patterns: analysis by computer-assisted two-dimensional gel electrophoresis.

Hypertensive heart disease caused by renovascular hypertension reflects the response of the heart to an increased afterload and neurohormonal stimulation. We hypothesized that in this condition the composition of the myocardial proteins of rats was altered. To identify yet unknown quantitative and qualitative differences in myocardial proteins in renovascular hypertensive heart disease, we analyzed protein patterns by computer-assisted two-dimensional polyacrylamide large gel electrophoresis. Renovascular hypertension was induced by placing a silver clip on the left renal artery in 9-week-old rat siblings. Sham-operated animals served as controls. Systolic blood pressure (197 +/- 19 mm Hg) and heart/body weight ratios (0.36 +/- 0.04%) were significantly increased in the hypertensive animals. Twenty protein patterns from the left ventricle of five hypertensive and five control rats were compared. The molecular mass and isoelectric point (pI) of proteins spots ranging from 13 to 100 kDa and from 4.5 to 8.5, respectively, were determined using marker proteins. In total, 761 +/- 88 protein spots were resolved in all twenty gels. For the quantitative data analysis a univariate (Mann-Whitney test) as well as a multivariate statistical approach (correspondence analysis) were applied. Only one myocardial protein spot (molecular mass = 41.3 kDa; pI = 6.3) was decreased by more than twofold (p < 0.05) in renovascular hypertension. The vast majority of spots did not indicate a significant alteration of intensity. Left ventricular hypertrophy in early renovascular hypertension induces a form of myocardial hypertrophy that conserves the naturally occurring protein expression pattern.

Decreased expression of Kv4.2 and novel Kv4.3 K+ channel subunit mRNAs in ventricles of renovascular hypertensive rats.

Hypertension-induced cardiac hypertrophy is associated with alterations in ventricular action potentials. To understand molecular mechanisms underlying this electrical abnormality, expression of cardiac voltage-gated K+ channel subunit genes was examined in ventricles of renovascular hypertensive rats. While generating a rat Kv4.3 probe, we discovered a previously unreported 19-amino acid insertion in the C-terminal intracellular region of the channel subunit. RNase protection assays indicated that this novel isoform is predominant in rat lung and heart. Effects of renovascular hypertension were then determined by using renal artery clipping models: two-kidney, one clip (2K-1C) rats, a model of high-renin hypertension with a normal plasma volume, and one-kidney, one clip (1K-1C) rats, a model of normal renin with a raised plasma volume. Expression of Kv4.2 and Kv4.3 mRNAs was diminished by > 50% in ventricles of 2K-1C rats; however, no changes in the expression of Kv1.2, Kv1.4, Kv1.5, Kv2.1, or KvLQT1 mRNAs were detected. Similar downregulation of Kv4.2 and Kv4.3 mRNAs was detected in 1K-1C rats. Chronic administration of captopril, an angiotensin-converting enzyme inhibitor, blocked the development of hypertension and the suppression of Kv4 subfamily channel mRNA expression in 2K-1C rats. Furthermore, captopril administration to sham-operated rats significantly increased Kv4.2 mRNA. These results indicate that renovascular hypertension causes specific reductions in Kv4 subfamily channel mRNA expression and that this effect is likely to be mediated primarily by an increase in cardiac afterload.

ACE in three tunicae of rat aorta: expression in smooth muscle and effect of renovascular hypertension.

Angiotensin I-converting enzyme (ACE) is known to be present at the surface of endothelial cells and also in the adventitia in large vessels. The presence of ACE in the vascular smooth muscle remains controversial. We microdissected segments of adventitia and media with or without endothelium from a region devoid of collateral arteries. The membrane-bound ACE activity in the media averaged 41% (pmol [glycine-1-14C]hippuryl-L-histidyl-L-leucine hydrolyzed.g tissue-1.min-1) of the values found in the whole aorta, whereas the adventitia contained only 6%. Immunoreactive ACE in media was characterized by Western blotting. ACE mRNAs were detected and characterized after polymerase chain amplification in isolated media. Angiotensin I and angiotensin II were equally able to contract medial rings, and the response to angiotensin I was blocked by enalaprilat. In aortas of two-kidney, one-clip hypertensive rats, there was an increase in ACE mRNA estimated by ribonuclease protection assay (P = 0.02) and in ACE activity at 15 days and 1 and 3 mo after clipping. This corresponded to a 1.5- to 2-fold increase in the ACE activity of both the media and the adventitia compared with sham-operated rats (P < or = 0.02). Thus ACE gene expression occurs in smooth muscle of rat aorta, which contains roughly the same amount of enzyme as the endothelium and readily converts angiotensin I to angiotensin II. ACE in the medial layer and the adventitia is upregulated in renovascular hypertension.

Myocardial biochemical, contractile, and electrical performance after imposition of hypertension in young and old rats.

The effects of renovascular hypertension on the biochemical, contractile, and electrical performance of myocardial tissue from rats of various ages has been examined. Male Fischer rats, 2, 7, 12, and 17 months old, were made hypertensive by constriction of the left renal artery. Ten weeks after the onset of hypertension, left ventricular papillary muscles were isolated from those four groups when 5, 10, 15, and 20 months old, respectively. Mechanical performance and transmembrane electrical events were recorded simultaneously. Contractile protein enzyme activity was determined in the same hearts from which papillary muscles were used for acquisition of mechanical and electrical information. There was a slight increase in blood pressure in control groups as a function of age while blood pressure maintained a range of approximately 179-188 mm Hg for all hypertensive groups. Heart weight of control animals increased significantly from 5 months to 20 months of age from 539 +/- 26 to 1088 +/- 56 mg, representing an increase of 101%. In hypertensive animals, heart weight increased 50% in 5-month-, 15% in 10-month-, 50% in 15-month-, and 11.7% in 20-month-old animals. Although control groups revealed alterations in mechanical, electrical, and biochemical parameters that increased as a function of age, the magnitude of the biochemical, contractile, and electrical response to hypertension varied monotonically with the extent of myocardial hypertrophy, rather than age per se. Adaptation to the stress of hypertension was observed in each age group, and was revealed as prolongation of mechanical and electrical timing parameters, depression of the load-velocity relation, and contractile protein enzyme activity. Thus, the stress of hypertension, which was tolerated by the 10- and 20-month-old animals with lesser relative hypertrophy and lesser changes in measured parameters, may represent a differential adaptation to the stress of hypertension.

Contractile behavior of rat myocardium after reversal of hypertensive hypertrophy.

The effects of renovascular hypertension and its reversal on the contractile performance of papillary muscles from rats has been examined. Hypertension of 10 wk duration caused a 48% increase in heart weight and significant prolongations of isometric time to peak tension (TPT), time to half relaxation, and time to peak shortening (TPS). A significant depression in the velocity of shortening was observed in the 10-wk group. However, muscles from hypertensive rats were still able to maintain normal levels of peak isometric developed tension and peak shortening; this may be due to the observed prolongation of TPT and TPS, respectively. In addition, calcium-activated actomyosin ATPase activity was depressed in hearts of hypertensive animals. Reversal of hypertension was studied at 20 wk after the onset of hypertension (10 wk of hypertension followed by 10 wk of normotension). Contractile and biochemical alterations observed in hypertensive animals were reversed in rats undergoing this regime. Thus reversal of a gradually applied pressure overload resulted in the regression of mechanical and biochemical abnormalities associated with the pressure overload myocardial hypertrophy.

Effect of renovascular hypertension on the morphology of oral blood vessels

Renovascular hypertension was created in twenty adult male rats to study the effects of systolic hypertension on the morphology of vessels supplying the gingiva, periodontal membrane, pulp tissue, and alveolar bone. Gingival arterioles showed changes consisting mainly of proliferation of the intima and elastic layers, some hyalinization of the wall, and reduction of the lumen. Similar but less frequent changes were observed in the vessels feeding the periodontal membrane; however, pulp tissue and alveolar arterioles were unaltered.