Hypertrophy In Spontaneously Hypertensive Rats Research Articles

Cardiac hypertrophy and characteristic impedance in spontaneously hypertensive rats.

Characteristic impedance and systemic arterial compliance were evaluated in 12 anaesthetized spontaneously hypertensive rats (SHR) from analysis of phasic records of pressure and flow in the ascending aorta. Cardiac hypertrophy expressed as the ratio of the left ventricular weight to the body weight was not correlated with arterial blood pressure (systolic, diastolic or mean). In contrast, there was a significant relationship between the left ventricular weight to body weight ratio and the characteristic impedance, suggesting that increased arterial stiffness contributes to left ventricular hypertrophy in SHR.

Influence of blood pressure on development of aortic medial smooth muscle hypertrophy in spontaneously hypertensive rats.

The hypothesis that a primary stimulus for aortic medial hypertrophy in spontaneously hypertensive rats (SHR) is increased blood pressure was tested by determining whether development of smooth muscle cell hypertrophy and hyperploidy in SHR could be dissociated from blood pressure levels in rats treated with various antihypertensive drugs with different mechanisms of action. Wistar-Kyoto rats (WKY) and SHR were treated between 2 and 5 months of age with captopril (375 mg/L), hydralazine (40 mg/L), or propranolol (1.5 mg/L) administered in their drinking water. Smooth muscle hypertrophy and hyperploidy were analyzed by morphometric evaluation of medial smooth muscle content, flow cytometric analysis of the frequency of polyploid smooth muscle cells, and biochemical estimates of smooth muscle cell number. All drugs significantly lowered blood pressure in SHR compared with untreated controls (order of efficacy: captopril greater than hydralazine greater than propranolol). Captopril also was most effective at changing blood pressure in WKY, while propranolol and hydralazine had similar blood pressure-lowering effects. The efficacy of drugs in preventing the development of smooth muscle cell polyploidism and medial hypertrophy in SHR was the same as their efficacy in lowering blood pressure, although propranolol had no effect on medial smooth muscle hypertrophy despite lowering blood pressure by 26 mm Hg. Regression analyses showed a high degree of correlation between blood pressure and the frequency of polyploid smooth muscle cells and medial smooth muscle content. These results are consistent with the hypothesis that aortic medial hypertrophy may be, in part, a response to increased blood pressure or wall stress. However, analysis of covariance and two-stage multiple regression analyses indicated that captopril had an effect over and above that predicted by its blood pressure-lowering effect. Furthermore, propranolol lowered blood pressure but did not affect medial hypertrophy. These results suggest that smooth muscle hypertrophy is not simply a response to increased blood pressure, but that other factors, such as angiotensin II, may be important in modulating aortic medial hypertrophy in SHR.

Depressor effect of diabetes in the spontaneously hypertensive rat: associated changes in heart performance.

Effects of streptozotocin-induced diabetes (8 weeks) on the performance of perfused hearts from spontaneously hypertensive (SH) rats were compared with effects on normotensive Wistar-Kyoto (WK) and Sprague-Dawley (SD) rat hearts. Diabetes markedly decreased systolic arterial pressure (SAP) of SH rats in vivo but did not affect SAP of either of the normotensive strains. Diabetes also reduced heart size of SH and normotensive rats and reversed absolute left ventricular hypertrophy (wall-to-lumen ratios and left-to-right ventricular weight ratios) of SH rats. Heart perfusion at the end of the 8-week period revealed that diabetes (i) reduced hydraulic work at high pressure loads and efficiency of contraction (work/mu LO2 consumed) of SH rat hearts but not of WK or SD hearts, and (ii) depressed left ventricular pulse pressure development (LVPP) and contractility (LV + dP/dt) of SH hearts more extensively than it reduced these variables in either of the normotensive control groups. Effects of diabetes which were similar in hypertensive and normotensive hearts were reductions in stroke work at high volume loads and depressions in LV-dP/dt. Attendant hypothyroidism probably contributed to the reductions in SAP, heart size, LVPP, LV+ and -dP/dt, and stroke work but not to the decreased efficiency or reversal of hypertrophy of SH rat hearts. Malnutrition of SH rats, like hypothyroidism, also decreased heart size without reversing hypertrophy but had no effect on SAP and only reduced LV-dP/dt. The results show that diabetes reversed hypertrophy and selectively reduced contraction efficiency, contractility, and LVPP of SH hearts, but otherwise the effects of diabetes in hypertensive and normotensive rat strains were similar to each other.(ABSTRACT TRUNCATED AT 250 WORDS)

Increased sensitivity to alpha-adrenoceptor stimulation but intact purinergic and muscarinergic effects in prehypertensive cardiac hypertrophy of spontaneously hypertensive rats.

The effects of phenylephrine, isoprenaline and adenosine, (-)-N6-phenylisopropyladenosine (PIA) or carbachol alone and in the presence of isoprenaline on force of contraction were studied in isolated electrically driven papillary muscles of spontaneously hypertensive rats (SHR) and age-matched Wistar control rats. In SHR an increased heart to body weight ratio was observed when blood pressure was not yet elevated. During this stage of the syndrome (i.e. between the 27th and 35th day of life) phenylephrine was about 3.4 times more potent to increase force of contraction in SHR (mean EC50: 2.8 mumol l-1) than in control rats (mean EC50: 9.4 mumol l-1). The positive inotropic effect of isoprenaline was similar in SHR and control rats. Also no difference could be detected in the isoprenaline-antagonistic effect of adenosine, the adenosine receptor agonist PIA or carbachol. We conclude that an increased sensitivity to cardiac alpha-adrenoceptor stimulation might be related to prehypertensive cardiac hypertrophy in SHR.

Cilazapril Prevents Hypertension in Spontaneously Hypertensive Rats

Chronic daily administration of cilazapril (1 X 10 mg/kg/day p.o., from age 4 to 14 weeks) to young spontaneously hypertensive rats (SHR) prevented the development of hypertension. The antihypertensive effect of a single dose of cilazapril persisted greater than 24 h. Discontinuation of long-term treatment resulted in an increase of systolic arterial blood pressure (SAP) to control hypertensive levels within 4 days. Following 10 weeks of drug administration, comparative hemodynamic studies were carried out on age-matched (14 weeks) control SHR and cilazapril-treated SHR. Cilazapril-treated SHR had a significantly lower mean arterial blood pressure (MAP) and total peripheral vascular resistance than did control SHR. The antihypertensive effect of cilazapril was not associated with changes in heart rate (HR). The myocardial performance parameters, cardiac output, and stroke volume, were similar in treated and control SHR, suggesting that the antihypertensive effect of cilazapril following chronic administration to SHR is mainly due to a reduction in peripheral vascular resistance. Vasopressor responses to angiotensin I were significantly lower in cilazapril-treated SHR than in control SHR. By contrast, pressor responses to angiotensin II and a high dose of norepinephrine (1.0 microgram/kg i.v.) were significantly enhanced. Isoproterenol elicited a fall in blood pressure in both groups, the extent of which was dependent upon the magnitude of basal blood pressure levels. Chronic cilazapril treatment resulted in a reduction of heart weight, suggesting that the drug may prevent development of cardiac hypertrophy in SHR. Kidney and adrenal weights were unaffected by the chronic treatment. Specific renin activities (SRA) in tissues of SHR were increased by factors of 20 (plasma) or 2 (kidney and adrenal) following cilazapril administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of Nifedipine on Renin Release and Renal Function in Anesthetized Dogs

The effects of nifedipine, classed as a calcium entry blocker, on urinary excretion and renin release were investigated in anesthetized dogs. Nifedipine was infused into one renal artery for three consecutive 10-min periods, at incremental rates of 0.3, 1, and 3 micrograms/min. Intrarenal infusion of nifedipine (3 micrograms/min) produced marked increases in urine flow rate (by 200%) and in urinary sodium (by 210%) and potassium (by 40%) excretion rates of the infused kidney without changes in mean systemic blood pressure, heart rate, glomerular filtration rate, and filtration fraction. Urinary osmolarity was slightly decreased by the drug, but this change was not statistically significant. There were no consistent changes in these parameters for the contralateral noninfused kidney. Renin secretion rate was increased to three times the preinfusion level during infusion of the highest nifedipine dose. The blood flow to the infused kidney was increased, and ipsilateral renal vascular resistance was simultaneously decreased upon nifedipine infusion. These results suggest that a nonhypotensive dose of nifedipine causes an increase in renin secretion and that this drug has a striking effect on the reabsorption of sodium and water by the renal tubules.

Exercise-induced myocardial capillary growth in the spontaneously hypertensive rat

Spontaneously hypertensive rats (SHR) were studied to test the hypothesis that endurance exercise training can stimulate capillary growth and offset the decrement associated with the development of myocardial hypertrophy. The exercise group (SHR-T) was trained on a treadmill for 10 weeks at 70–90% maximum V ̇ O 2 and compared to nontrained SHR and normotensive Wistar-Kyoto (WKY) at 16 weeks of age. Thus, the training program coincided with the development of hypertension and hypertrophy in SHR. Image analysis was used to study capillaries in one micron thick left ventricular tissue samples from perfuse-fixed hearts. Training did not affect left ventricular mass or blood pressure, but reversed the characteristic decrements in capillary surface area (CSA), volume (CV), and numerical density (CD). CSA and CV were most markedly affected by exercise, as mean values for these parameters increased by 31 and 40%, respectively, compared to SHR. The magnitude of these changes approximated the magnitude of hypertrophy as evidenced by left ventricular weight/body weight ratios (42% in SHR and 37% in SHR-T). Anatomical intercapillary distance was also normalized by training ( x ± SEM ): SHR-T, 11.65 ± 0.31; SHR, 13.97 ± 0.37; WKY, 11.19 ± 0.37. These data indicate that exercise stimulates capillary growth in the face of developing hypertension and its related left ventricular hypertrophy.

Cardiovascular pharmacology of nicardipine in animals.

The haemodynamic, antianginal and antihypertensive effects of nicardipine, a vascular selective calcium antagonist, were studied in experimental animals. In the canine isolated coronary artery, nicardipine relaxed potassium-induced contraction and suppressed 3,4-diaminopyridine-induced rhythmic contractions more effectively than nifedipine, verapamil or diltiazem. In anaesthetised rats, nicardipine prevented the elevation of ST segment induced by intracoronary injection of methacholine. In anaesthetised dogs, nicardipine produced a greater vasodilatation in vertebral, carotid, and coronary vessels than in mesenteric, femoral, and renal vessels and did not affect myocardial oxygen consumption. In conscious monkeys, nicardipine given intravenously lowered blood pressure and gave rise to reflex tachycardia but did not prolong the A-V conduction time. Nicardipine given orally lowered blood pressure in spontaneously hypertensive rats (SHR), renal hypertensive rats (RHR), and deoxycorticosterone acetate/salt hypertensive rats (DOCA/Salt), as well as in normotensive rats. Long-term treatment with nicardipine given orally for 12 weeks effectively lowered high blood pressure in the three types of hypertensive rats, reduced cardiac hypertrophy in SHR and DOCA/Salt rats, and prevented mortality from stroke in DOCA/Salt rats. Combined treatment with nicardipine and a beta-adrenoceptor blocking agent (indenolol) showed an antihypertensive effect similar to that obtained with nicardipine alone. Conscious renal hypertensive dogs given repeated oral administration of nicardipine for 14 days did not develop tolerance to the hypotensive activity of nicardipine. Under the same conditions, tolerance to hydralazine developed within 4 days.

Regression of Cardiac Hypertrophy After Therapy in Animal Hypertension

Studies on spontaneously hypertensive rats (SHR), which represent a model of genetically determined arterial hypertension, revealed that cardiac hypertrophy can be controlled by blood pressure normalization by use of various antihypertensive drugs such as hydralazine, captopril, metoprolol, guanethidine, and alpha-methyldopa. Adrenergic influences seem to play a part except for left ventricular (LV) systolic unloading on cardiac hypertrophy, because LV hypertrophy was quantitatively less expressed after a combined therapy with both metoprolol and hydralazine than after a single hydralazine treatment, although blood pressure was not different between the groups. To study whether nifedipine can cause an already existing cardiac hypertrophy to regress, 20-week-old SHR were treated with nifedipine for a period of 20 weeks. After nifedipine treatment, LV muscle mass/body weight ratio was significantly less than before therapy (2.13 +/- 0.18 vs. 2.37 +/- 0.30 mg/g; p less than 0.05). Mass to volume ratio, i.e., quotient of LV muscle mass and LV end-diastolic volume, dropped from 3.40 +/- 0.66 to 3.07 +/- 0.30 mg/microliters (p less than 0.05) after therapy. Accordingly, an antihypertensive treatment with the calcium channel blocker nifedipine can cause an already existing LV hypertrophy in SHR to regress. Because blood pressure reduction resulting from therapy with beta-receptor-blockers, vasodilators, sympatholytic drugs, angiotensin converting enzyme inhibitors, and calcium channel blockers has qualitatively similar effects with respect to causing regression of hypertrophy, reversal of cardiac hypertrophy seems to be mainly related to the reduced LV systolic load. Specific pharmacodynamic effects may only modulate the extent of LV mass reduction along with blood pressure normalization.

Increase of cardiac .BETA.-adrenergic receptors in young spontaneously hypertensive rats.

The authors studied the number of myocardial beta-adrenergic receptors and the cyclic nucleotide concentration in both male spontaneously hypertensive rats (SHR) and Wistar Kyoto rats (WKY) at 4 to 5, 10 to 15, 20 to 25 and 35 to 55 weeks of age. A potent beta-adrenergic antagonist, (125I) iodohydroxybenzylpindolol was used to estimate the number and affinity of beta-adrenergic receptors. beta-adrenergic receptors in cardiac membranes from SHR of 4 to 5 weeks and 10 to 15 weeks numbered 63.1 +/- 4.6 and 51.6 +/- 4.6 f mol/mg protein, respectively. These were significantly (p less than 0.02) greater than the number in WKY at 4 to 5 weeks and 10 to 15 weeks (42.2 +/- 5.1 and 31.5 +/- 5.4 f mol/mg protein, respectively). The dissociation constant in the membranes was the same in WKY and SHR, and no significant differences were found in the number of receptors and affinity of SHR and WKY at 20 to 25 weeks or 35 to 55 weeks of age. Also, there was no difference in the concentration of myocardial cyclic nucleotides at the various ages. Since cardiac hypertrophy in SHR had appeared before the onset of hypertension at about 7 weeks, the present results suggest that the SHR heart is hypersensitive to catecholamines and hemodynamically hyperkinetic due to the increased numbers of beta-receptors in the pre- and early stages of hypertension.

Measurement of cardiac output by the thermodilution method in conscious spontaneously hypertensive rats.

The usefulness of the thermodilution method for measuring cardiac output (CO) was evaluated in awake rats by comparison with electromagnetic flowmetry. CO was measured in 3- and 6-month-old conscious spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto rats (WKY). The correlation co-efficient between CO obtained by the two methods was 0.66 (p less than 0.01). Although CO values obtained by the thermodilution technique tended to be overestimated in comparison with those determined by electromagnetic flowmetry, this method was shown to be useful for measuring CO in unanesthetized rats because of its technical simplicity. Left ventricular mass (LVM) and the ratio of CO to LVM were significantly greater in SHR than in WKY at both ages and CO/LVM increased with increasing age in SHR. The ratio of heart work (HW) to body weight (HW/BW) was increased only in 3-month-old SHR compared with WKY and there was no difference in HW/LVM in 3- and 6-month-old SHR compared with age-matched WKY. The present results suggest that the development of cardiac hypertrophy in SHR is an adaptation to the increased HW due to high afterload.

The effects of beta adrenoceptor blockade with atenolol on myocardial cellular and subcellular hypertrophy in spontaneously hypertensive rats.

In this study we investigated the effects of chronic beta adrenoreceptor blockade with atenolol on cellular and subcellular hypertrophy in spontaneously hypertensive rats (SHR). Atenolol was injected subcutaneously (20 mg/kg) twice daily commencing in four-week-old rats. The treated animals (SHR-A) were compared to their nontreated controls and normotensive, Wistar-Kyoto (WKY) controls at the age of 16 weeks. A group of atenolol-treated WKY was also studied. Chronic drug treatment was effective in attenuating the rise in systolic blood pressure characteristic of SHR, but did not normalize the values to those of WKY. Cardiac hypertrophy, characteristic of SHR, was modified by drug treatment as evidenced by left ventricular weights as well as myocardial cell size. The cells from the subendocardium underwent selective hypertrophy in SHR which was attenuated by about 50% after atenolol treatment. Stereological analysis of electron micrographs showed that while relative mitochondrial volume was not affected by treatment, relative myofibrillar volume (%) decreased in both subepicardium (SHR = 63.28 +/- 1.25; SHR-A = 56.72 +/- 1.37) and subendocardium (SHR = 66.53 +/- 1.27; SHR-A = 58.30 +/- 1.51). This change raised the mitochondrial/myofibrillar volume ratio, which is characteristically low in SHR compared to WKY. Sarcoplasm, which included all cell constituents except mitochondria, increased with atenolol treatment, but water concentration remained unchanged. The data suggest that attenuation of hypertrophy in SHR after beta blockade is associated with selective effects on the myocardial cell involving primarily the myofibrillar cell compartment.

Prevention of the development of heart failure and the regression of cardiac hypertrophy by captopril in the spontaneously hypertensive rat.

The spontaneously hypertensive rat (SHR) exhibits both a compensated phase of cardiac hypertrophy in which forward output is maintained despite persistently elevated systemic arterial pressures and a decompensated phase in which cardiac performance has deteriorated in spite of further hypertrophic growth. To determine whether chronic antihypertensive therapy prevents the development of heart failure and the progression of cardiac hypertrophy in SHR with advanced hypertension, captopril (2 g/l of drinking water), a converting enzyme inhibitor, was administered to 14 month old female SHR and normotensive American Wistar rats (NWR) for 10 months. The severe left ventricular hypertrophy of the 24 month old untreated SHR (4.37 +/- 0.2 mg/g v. 2.50 +/- 0.06 mg/g, untreated NWR) was markedly reduced (P less than 0.02) by captopril (3.01 +/- 0.1 mg/g). Chronic therapy prevented the reduction of both baseline and maximal cardiac indices in SHR, but did not alter blood flow in NWR. Left ventricular dilatation was present in 24 month old SHR and, as peak stroke volume index was diminished, the ejection fraction index of the SHR was reduced. Captopril restored this index in SHR to normal. The relation of ejection fraction index and afterload (peak systolic wall stress) was depressed in untreated SHR, but was normal in treated SHR. Thus, chronic therapy with captopril prevented the development of severe cardiac dysfunction and produced a marked regression of cardiac hypertrophy in SHR with advanced hypertensive heart disease.

Effect of converting enzyme inhibitor (SQ14,225) on myocardial hypertrophy in spontaneously hypertensive rats.

The potent converting enzyme inhibitor (CEI) SQ14,225, which is known to prevent the formation of angiotensin II (AII) has been used to evaluate the role of AII in the development and reversal of cardiac hypertrophy. The present study describes the effect of CEI on blood pressure (BP) and myocardial hypertrophy (prevention and reversal) in the spontaneously hypertensive rat (SHR). A group of 3-week- and 8-week-old male SHR was treated with CEI (30 mg/kg in drinking water) for 6 weeks. An additional group of SHR was also treated with a combination of CEI and a diuretic (hydrochlorothiazide, 500 mg/liter). Heart weight, BP, deoxyribonucleic acid (DNA), ribonucleic acid (RNA), hydroxyproline, myocardial catecholamines, and plasma renin activity (PRA) were determined. In the prevention study, we found a significant reduction in the ratio of heart weight to body weight along with the prevention of hypertension (200 vs 145 mm Hg, p less than 0.001). Similar reductions in BP and heart weights were obtained with the reversal group. A better BP control was noted in the CEI and hydrochlorothiazide group. The reduction of heart weight was associated with a reduction in RNA and hydroxyproline content. In all groups, we found a significant increase in PRA (p less than 0.001) and a slight increase in tissue catecholamine concentration. No change in kidney weight was found in any group. Data clearly showed that oral administration of CEI prevented and reversed cardiac hypertrophy in SHR. Reversal was associated with a decrease in myocardial collagen content. These data indicate that prevention of AII formation in combination with BP control can prevent and reverse cardiac hypertrophy in SHR. Of course, whether or not CEI acts only through the renin angiotension system is still speculative.

ULTRASTRUCTURAL ASPECT OF LEFT VENTRICULAR HYPERTROPHY IN SPONTANEOUSLY HYPERTENSIVE RATS : A QUALITATIVE AND QUANTITATIVE STUDY

The morphology of the left ventricular myocardium of spontaneously hypertensive rats (SHR) (Okamoto and Aoki) was studied with light and electron microscopes, with special reference to a quantitative analysis of subcellular organelles and a description of the characteristics of the capillaries in myocardium. Paired groups of SHR and control Wistar-Kyoto rats were sacrificed at 3, 5, 9, 11, 15 and 21 weeks and one year of age. In the left ventricular lateral wall of SHR, starting at the age of 11 weeks, the cardiocytes became progressively thicker as the blood pressure rose and exhibited various ultrastructural alterations. In these cardiocytes, the proliferation of Z-band materials was occasionally present in the myofibrils, and was closely associated with the subsarcolemmal area and intercalated discs. Convolutions and extensive foldings of the intercalated discs were prominent. Mitochondrial abnormalities consisted of fragmentation and stacks of cristae, aggregates of small mitochondria and intramitochondorial α-glycogen rosettes. In one-year-old SHR, malaligned cardiocytes as well as myofibrils were seen in certain areas of the myocardium. In some cardiocytes, streaming and clumping of Z-band material, myofibrillolysis and proliferation of sarcoplasmic reticulum appeared. In addition, there were clusters of spherical microparticles, tubular aggregates and intramitochondrial inclusions, suggestive of degenerative changes. Stereological analysis of subcellular organelles in the hypertrophied cardiocytes of SHR revealed an increase of myofibrillar volume fractions and a decrease of mitochondrial volume fractions, resulting in an increase in the ratio of myofibrils to mitochondria. These findings differed from those in the posterior papillary muscle of the left ventricle in the same animal hearts. Thus, it is apparent that myocardial hypertrophy varies in each area of the myocardium due to different stresses during the course of its development. In the hypertrophied myocardium of SHR, the capillaries were seen to proliferate with the appearance of a "tunnel capillary", while interstitial fibrosis and hypertensive vascular lesions progressed with aging. The capillary proliferation maintained a constant diffusion distance from the capillary to the cardiocyte, probably as one of adaptation in cardiac hypertrophy in SHR.

Catecholamines, Blood Pressure, Renin and Myocardial Function in the Spontaneously Hypertensive Rat

1. Neither nerve-growth-factor antiserum (NGFAS) administered subcutaneously nor 6-hydroxydopamine administered intraventricularly to immature spontaneously hypertensive rats (SHR) inhibited the development of the hypertensive syndrome. In contrast, NGFSA did not affect blood pressure in normotensive Kyoto/Wistar rats. 2. Peripheral vascular resistance was increased and cardiac index decreased in both NGFAS and 6-hydroxydopamine-treated SHR despite preservation of normal blood pressure. 3 NGFAS treatment did not influence the development of left ventricular hypertrophy in SHR, despite the lowering of blood pressure. In contrast, 6-hydroxydopamine caused an attenuation in the development of left ventricular hypertrophy. 4. Indices of left ventricular contractility were depressed by NGFAS treatment but not by 6-hydroxydopamine. 5. Plasma renin activity was unaffected by NGFAS treatment and increased by 6-hydroxydopamine.

Cardiac hypertrophy in spontaneously hypertensive rats.

The energy metabolism of cardiac hypertrophy in spontaneously hypertensive rats (SHR) was studied chronologically by histochemical and in part chemical methods. The activities of various enzymes, such as glucose-6-phosphate dehydrogenase (G6PDH), lactate dehydrogenase (LDH), isocitrate dehydrogenase, succinate dehydrogenase, beta-hydroxybutylate dehydrogenase (beta-HBDH) and monoamine oxidase (MAO) in the cardiac muscle were determined histochemically. beta-HBDH activity was greatly increased in the stage of developing hypertension in SHR. LDH activity increased simultaneously with the rise of beta-HBDH activity. Moreover, MAO activity increased markedly in later stages when the blood pressure was already elevated in SHR. To confirm the histochemical findings of beta-HBDH activity, the mitochondrial fraction of cardiac muscle was subjected to chemical assay. The chemical findings of myocardial beta-HBDH in SHR corresponded well with the histochemical findings. The myocardial beta-HBDH activity in SHR increased markedly at the age of 5 to 9 weeks, while no or minimal activity was found in controls of the same age. No significant difference of beta-HBDH activity was observed between SHR and controls in the mitochondrial fraction from the diaphragm and liver. The increase of beta-HBDH activity in the cardiac muscle of SHR prior to the development of cardiac hypertrophy suggests that the metabolism of ketone bodies may play an important role in providing the energy necessary for the development of cardiac hypertrophy in SHR.