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Biomedical subjects

H G Zimmer

Publications and source records attributed to H G Zimmer.

At least 55 records · Page 3Linked to original sources
PubMed1992

Development and modulation of experimental right ventricular hypertrophy in rats.

Two models of right ventricular (RV) hypertrophy in rats have been created and characterized: chronic myocardial infarction and pulmonary artery stenosis. A Millar ultraminiature catheter pressure transducer designed specifically for right heart catheterization was used for the measurement of RV function in closed-chest, anesthetized rats. Four weeks after coronary artery ligation, left ventricular (LV) function was depressed as evidenced by the reduction of LV systolic pressure (LVSP), the maximal rate of rise in LV pressure (LV dp/dtmax), cardiac output, and by the elevation of LV end-diastolic pressure (LVEDP). There was an increase in RVSP and an elevation in RV dp/dtmax as well as an increase in the RV weight/body weight ratio. Myocytes isolated from the RV 4 weeks after coronary artery ligation had a greater volume and cross-sectional area. In addition, 14 days after pulmonary artery stenosis, there also was an elevation in RVSP and in RV dp/dtmax. In this model, the effect of angiotensin-converting enzyme (ACE) inhibition with ramipril (1 mg/kg daily) was examined. The increase in RVSP from 35 +/- 2 to 61 +/- 4 mm Hg after pulmonary artery stenosis was not influenced by ramipril (63 +/- 4 mm Hg), neither was the elevation of RV weight. However, the increase in cell volume and cross-sectional area of myocytes isolated from the RV was less pronounced in the ramipril-treated group (+27% compared with +58% in untreated animals). Thus, ACE inhibition with ramipril altered the hypertrophic response at the cellular level.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1992

Energy metabolism of the hypertrophied heart studied by 31P nuclear magnetic resonance.

We report studies on the isolated hearts of rats treated with triiodothyronine (0.2 mg/kg daily) for 14 days, on spontaneously hypertensive rats (12 and 21 weeks old, Lyon strain) and on their respective controls. A 30% increase in cardiac weight was developed with triiodothyronine and a 40% increase in heart weight in the presence of spontaneous hypertension. The hearts were perfused in the presence of 2 mM pyruvate and the intracellular content of phosphocreatine, inorganic phosphate and ATP measured by nuclear magnetic resonance spectroscopy with 31P. The left ventricular developed pressure was measured with an intraventricular balloon. Changes in contractile strength were induced by stepwise modifications of the extracellular concentration of calcium from 0.5 mM to 1.0, 1.5 and 2.0 mM. In all experimental groups, each increase in the extracellular calcium induced an increase in the developed pressure, together with a decrease in phosphocreatine and an increase in inorganic phosphate; the ATP level remained unchanged. These metabolic changes increased progressively with the increase in developed pressure. In the hearts of animals treated with triiodothyronine and of the 21 weeks old hypertensive rats, the extent of changes in phosphocreatine and inorganic phosphate was the same as in the controls; but, in the hearts of 12 weeks old hypertensive rats, the changes were significantly greater than in their controls. These observations suggest that, during the development of cardiac hypertrophy from spontaneous hypertension, there is a transitory deficiency in the capacity for aerobic ATP production relative to the rate of hydrolysis of ATP induced by an inotropic effect.

Adenosine Triphosphate↗
PubMed1991

Effect of inosine on function and adenine nucleotide content of the isolated working rat heart: studies of postischemic reperfusion.

Inosine added to the perfusion medium for isolated working rat heart induced a dose-dependent coronary vasodilator and positive functional effect. Inosine increased coronary flow (ml/min) from 11.8 +/- 0.5 (control, n = 16) to 15.6 +/- 0.6 (0.1 mM, n = 10), to 18.2 +/- 1.1 (0.5 mM, n = 6), and to 18.4 +/- 0.8 (1.0 mM, n = 14). Left ventricular systolic pressure was increased (LVSP, mm Hg) from 72.5 +/- 1.1 (control) to 75.4 +/- 1.7 (0.1 mM) to 78.7 +/- 2.1 (0.5 mM) and to 82.6 +/- 1.5 (1.0 mM). and cardiac output (CO, ml/min) from 26.4 +/- 2.0 (control) to 29.6 +/- 2.3 (0.1 mM), to 30.2 +/- 3.5 (0.5 mM), and to 37.4 +/- 2.0 (1.0 mM). At the end of 30-min reperfusion after a 15-min period of global total ischemia (n = 9), the functional parameters were significantly reduced (coronary flow 8.5 +/- 0.4 ml/min, LVSP 63 +/- 1.9 mm Hg, CO 13.6 +/- 1.9 ml/min). When inosine was present in the perfusion medium during the entire experimental protocol, coronary flow and heart function were also enhanced in a dose-dependent manner. The content of cardiac ATP (mumol/g) was decreased at the end of the 15-min ischemic period (1.89 +/- 0.17, n = 7; control 3.85 +/- 0.05, n = 4), and inosine had no effect. At the end of the 30-min postischemic reperfusion period, the ATP pool had recovered to an appreciable extent (3.01 +/- 0.11, n = 9) and was higher when 1.0 mM inosine had been infused (3.44 +/- 0.11, n = 7). Thus, inosine increased coronary flow dose dependently and, as a consequence, the function of the isolated perfused working heart both under control conditions and during the postischemic reperfusion period.

Adenine Nucleotides↗
PubMed1991

Effect of angiotensin converting enzyme inhibition on pressure-induced left ventricular hypertrophy in rats.

The influence of angiotensin converting enzyme inhibition on the development of left ventricular (LV) hypertrophy due to stenosis of the aortic arch was studied in female Sprague-Dawley rats. The aortic arch was banded to an outer diameter of 1.0 mm. After 14 days, LV and right ventricular functional parameters and transstenotic pressure gradient were measured in anesthetized rats. In addition, regional heart weights were determined, and myocytes of three different heart regions were isolated and subjected to morphometric analysis. To inhibit the angiotensin converting enzyme, ramipril was administered orally by gavage in a single daily dose of 1 mg/kg. Rats with aortic stenosis showed a marked increase in LV systolic pressure, mean prestenotic aortic pressure, and LV stroke work compared with sham-operated rats and demonstrated a systolic transstenotic pressure gradient of 82 mm Hg. This increase in LV hemodynamic load was paralleled by the development of LV hypertrophy as determined by a 37% increase in LV weight and by a 20% increase in cell volume of isolated LV myocytes. Concomitant ramipril treatment did not significantly affect LV functional parameters. The transstenotic pressure gradient was the same as in untreated rats with aortic stenosis. Likewise, the weight gain of the LV as well as the development of cellular hypertrophy of the LV were not influenced. Thus, in this model, angiotensin converting enzyme inhibition did not reduce the development of LV hypertrophy independent of the hemodynamic load.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1991

Nucleotide precursors modify the effects of isoproterenol. Studies on heart function and cardiac adenine nucleotide content in intact rats.

In closed-chest rats, isoproterenol (ISO, 25 mg/kg), 5 hours after subcutaneous administration, increased heart rate by 53%, left ventricular (LV) dP/dtmax by 80%, and cardiac output by 37%. LV systolic pressure (LVSP, -10%), mean arterial pressure (MAP, -12%), and total peripheral resistance (TPR, -36%) were diminished. In separate experiments, continuous intravenous infusion of adenine (50 mg/kg/hr) for 5 hours reduced heart rate (-11%), LVSP (-16%), MAP (-20%), TPR (-33%), and LV dP/dtmax (-20%). Cardiac output was increased (+20%). Inosine has been shown to have similar effects, except for a decline in cardiac output. Adenine (50 mg/kg/hr) attenuated the ISO-induced increase in heart rate and LV dP/dtmax and aggravated the decline in LVSP, MAP, and TPR. The increase in cardiac output was not changed. Inosine (200 mg/kg/hr) modified the ISO effects to a similar extent. Ribose (200 mg/kg/hr) added to the adenine infusion did not have functional effects. However, it aggravated the modifying influence of inosine on LVSP, LV dP/dtmax, and MAP. ISO reduced the cardiac ATP content (mumol/g) from a control value of 5.02 +/- 0.06 (n = 12) to 3.51 +/- 0.13 (n = 10). Adenine (3.56 +/- 0.21, n = 7) and ribose (3.64 +/- 0.11, n = 9) alone did not affect it, but inosine attenuated it (4.33 +/- 0.08, n = 8). Adenine and inosine in combination with ribose abolished the ISO-induced ATP decline (5.18 +/- 0.23, n = 7, and 4.76 +/- 0.10, n = 8, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine↗
PubMed1991

[Right ventricular hypertrophy in rats: effect of ACE inhibitors].

Models of right ventricular hypertrophy in rats have been created and characterized: Daily injections of triiodothyronine, irradiation of the lung in Brown-Norway rats, chronic myocardial infarction, and pulmonary artery stenosis. A new Millar ultraminature catheter pressure transducer designed for right heart catheterization allowed the measurement of right ventricular function. All models were characterized by an increase in right ventricular systolic pressure, by an elevation in the RNA/DNA ratio in the right ventricle, and by an increase in the right ventricular weight/body weight ratio. Myocytes isolated from the right ventricle 4 weeks after coronary artery ligation had a greater volume and cross sectional area. Similar results were obtained 14 days after pulmonary artery stenosis. In this model, the effect of angiotensin converting enzyme inhibition with ramipril (1 mg/kg, daily) was examined. The increase in right ventricular systolic pressure from 35 +/- 2 mm Hg to 61 +/- 4 mm Hg (without ramipril) was not influenced by ramipril (63 +/- 4 mm Hg), neither was the elevation of right ventricular weight. However, the increase in cell volume and cross-sectional area of myocytes isolated from the right ventricle was less pronounced in the ramipril-treated group (+27% compared to +58% in untreated animals). Thus, angiotensin converting enzyme inhibition with ramipril altered the hypertrophic response at the cellular level.

Angiotensin-Converting Enzyme Inhibitors↗
PubMed1991

[Mechanisms of the effect of allopurinol on the metabolism of adenine nucleotides].

The effect of repeated administration of allopurinol (50 mg.kg-1 48, 24, and 4 hours before analysis) on the activity of enzymes of degradation and resynthesis of adenine nucleotides was studied. The activity of xanthine dehydrogenase and xanthine oxidase was inhibited in the heart, liver and kidney and the activity of membrane-bound 5'-nucleotidase was particularly elevated in the heart and brain, suggesting that membrane transport processes may be affected. The increase in the activity of hypoxanthine guanine phosphoribosyl transferase in the liver is indicative of a potential mechanism of positive action of allopurinol upon restoring the purine nucleotide store. The authors present their hypothesis on the mechanism of allopurinol action upon the metabolism of adenine nucleotides. The suggested mechanisms might become operative in protecting tissues against ischemia and reperfusion induced damage.

Adenine Nucleotides↗
PubMed1991

Heart function and morphology in rats with chronic large myocardial infarction.

Large transmural myocardial infarctions were created in rats by occlusion of the descending branch of the left coronary artery. Four weeks after surgery, parameters of left and right ventricular function and of peripheral circulation were measured in the closed-chest, anesthetized animals and compared with those obtained in sham-operated controls. The morphology of the hearts was examined both at the macroscopic and cell size level. Cardiac output, LVSP, and the LV weight/body weight ratio were markedly lower than in sham-operated controls. LVEDP was elevated up to 32 +/- 2 mm Hg. On the other hand, RVSP, RV dp/dtmax, the right ventricular weight/body weight ratio, and the volume of myocytes isolated from the right ventricular free wall were increased. Histological examination of the lungs revealed marked thickening of the tunica media of small pulmonary arteries with narrowing of the lumen. These changes are considered to represent the morpohological basis for the increased pulmonary vascular resistance which was associated with right ventricular pressure overload and hypertrophy.

Animals↗
PubMed1990

Changes in heart function and cardiac cell size in rats with chronic myocardial infarction.

Myocardial infarctions were induced in rats by ligation of the left anterior descending (LAD) coronary artery. After 4 weeks, parameters of left (LV) and right ventricular (RV) function and of peripheral circulation were measured in the intact, anesthetized animals. The morphology of the heart chambers was examined at the macroscopic and cell size level. In animals with slight reduction in LV function, LVEDP was elevated from 3.4 +/- 0.8 to 8.8 +/- 1.5 mmHg, LV stroke work was reduced by 14%, and dP/dtmax of both ventricles was depressed by 10% compared with sham-operated controls. Myocytes isolated from the LV and RV were elongated to some extent and had a greater cell volume, but there was no change in heart weight. These rats had infarctions that were small or medium in size. In rats with severe depression in left heart function, cardiac output, LVSP, LV stroke work, mean arterial pressure, and the LV weight/body weight ratio were markedly lower than in sham-operated controls. LVEDP was elevated up to 32 +/- 2 mmHg. These rats had large infarctions. RVSP, RV weight/body weight ratio, and the volume of myocytes isolated from the RV were doubled. RV stroke work was increased by 58%. Myocytes from the LV, RV and from the septum were elongated to about the same extent. The septum had developed a 23% hypertrophy. Histological examination of the lungs revealed marked thickening of the tunica medica of small pulmonary arteries with narrowing of the lumen. These changes are considered to represent the morphological basis for the increased pulmonary vascular resistance that was associated with RV pressure overload and hypertrophy.

Animals↗
PubMed1990

Hemodynamic effects of inosine in combination with positive and negative inotropic drugs: studies on rats in vivo.

Inosine applied as a continuous i.v. infusion of 400 mg/kg/h for 20 min had a negative chronotropic and inotropic effect in closed-chest, anesthetized rats. In the presence of adenosine deaminase (ADA, 133 U/kg/h), the reduction in heart rate was abolished indicating that adenosine is responsible for that effect. However, the negative inotropic effect persisted. It was characterized by a 38 and 56% decrease in left ventricular systolic pressure (LVSP) and diastolic aortic pressure, respectively, a 24% decline in LV dp/dtmax and a 16% fall in cardiac output. Total peripheral resistance was diminished by 38%. Inosine in combination with ADA antagonized the noradrenaline-induced positive inotropic effect and the increase in cardiac output. On the other hand, i.v. bolus injection of noradrenaline in rats pretreated with inosine and ADA did not increase blood pressure and total peripheral resistance. Inosine administered in animals pretreated with the beta-receptor blocker metoprolol or with the calcium antagonist verapamil aggravated the negative inotropic effect. Inosine in combination with ADA caused a decline in cardiac output in metoprolol-pretreated rats that was more pronounced than that induced by inosine alone. However, in rats pretreated with verapamil, inosine did not cause a reduction in cardiac output.

Adenosine Deaminase↗
PubMed1990

Influence of ramipril on right ventricular hypertrophy induced by pulmonary artery stenosis in rats.

The influence of the angiotensin-converting enzyme (ACE) inhibitor ramipril (1 mg/kg orally in a single daily dose) on right ventricular (RV) hypertrophy was studied in Sprague Dawley rats. The pulmonary artery was banded to an outer diameter of 1.7 mm. After 14 days, left (LV) and RV hemodynamic parameters were measured in anesthetized animals. Furthermore, regional heart weights were determined, and myocytes of three different heart regions were isolated and subjected to morphometric analysis. Pulmonary artery stenosis caused a marked increase in RV systolic blood pressure (SBP) without alteration of LV functional parameters as compared with sham-operated animals. Correspondingly, the weight of the RV free wall as well as the RV cell volume were increased to about the same extent, while the LV weight was unchanged. Administration of ramipril to pulmonary artery-constricted animals slightly reduced LV SBP and LVdP/dtmax as compared with banded animals without treatment. The increase in RV SBP and the weight gain of the RV free wall were not affected, however. In contrast, the increase in cell volume of isolated myocytes was less pronounced in this group (+27% as compared with +58% in untreated animals). Because there were no differences in water content of the tissue, interstitial or cellular edema cannot be responsible for this discrepancy. Thus, ACE inhibition with ramipril appears to blunt the cellular hypertrophy in this model without affecting the weight gain of the RV.

Analysis of Variance↗
PubMed1990

Beta-adrenergic agonists stimulate the oxidative pentose phosphate pathway in the rat heart.

The oxidative pentose phosphate pathway is poorly developed in the rat heart compared with other organs, since the activity of glucose-6-phosphate dehydrogenase (G-6-PDH), the first and rate-limiting enzyme of the oxidative pentose phosphate pathway, is low. As a consequence, the available pool of 5-phosphoribosyl-1-pyrophosphate and the rate of adenine nucleotide biosynthesis are limited. Isoproterenol, 24 hours after subcutaneous administration at 0.1, 1, and 25 mg/kg, stimulated the activity of G-6-PDH in whole hearts dose-dependently from 4.3 +/- 0.16 (control) to 6.6 +/- 0.35, 10.3 +/- 0.82, and 11.5 +/- 0.56 units/g protein, respectively. The activity of 6-phosphogluconate dehydrogenase, another of the enzymes in the oxidative pentose phosphate pathway, remained unchanged. G-6-PDH activity started to increase 12 hours after isoproterenol application, when the glycogenolytic and functional response was over, and reached a peak value between 24 and 48 hours. This stimulating effect was also demonstrated in cardiac myocytes that were isolated 28 hours after isoproterenol application. beta-receptor blockade with atenolol reduced the isoproterenol-induced increase in cardiac G-6-PDH activity by 90%. Cycloheximide, which inhibits translation, and actinomycin D, which interferes with transcription, attenuated it by 83% and 78%, respectively. These results indicate that cardiac beta-adrenergic receptors and enzyme protein synthesis are involved in this effect. Other beta-sympathomimetic agents such as dopamine, dobutamine, fenoterol, salbutamol, and terbutaline also stimulated myocardial G-6-PDH activity in a time- and dose-related manner. The calcium antagonist D 600 (gallopamil) reduced the isoproterenol-elicited stimulation by 65%, and verapamil blunted the fenoterol-induced increase by 50%. This suggests that Ca2+ ions also contribute to the stimulation of the cardiac oxidative pentose phosphate pathway.

Adenine Nucleotides↗
PubMed1989

Differential effects of triiodothyronine on rat left and right ventricular function and the influence of metoprolol.

The influence of triiodothyronine (T3) on right ventricular functional parameters was tested and compared to the alterations induced in the left ventricle. Female Sprague-Dawley rats received daily injections of T3 (0.2 mg/kg s.c.) for 3 days and a constant i.v. infusion of 0.9% NaCl or the beta 1-receptor blocker metoprolol (1 mg/kg/h). The hyperthyroid state after 3 days administration of T3 was characterized by an increase in heart rate and cardiac output and a decrease in the systemic peripheral resistance. However, pulmonary vascular resistance was unchanged. Beta-Receptor blockade reduced heart rate to the control level without affecting the elevation in cardiac output. The T3 group showed a marked increase in right ventricular systolic pressure (RVSP) and mean pulmonary artery pressure, whereas left ventricular systolic pressure (LVSP) and mean aortic pressure were not significantly changed. Metoprolol had no effect on LVSP, and attenuated the increase in RVSP. Furthermore, T3 induced a considerable increase in dP/dtmax in both ventricles, which was reduced nearly to control level by concomitant metoprolol infusion. The T3-induced percentage weight gain of the right ventricular free wall (RV) was more pronounced than that of the left ventricle (LV) as indicated by the significant increase in the RV/LV weight and the RNA/DNA ratios. Metoprolol did not affect significantly the T3-induced left and right ventricular hypertrophy, but attenuated slightly the elevated RV/LV weight ratio. Our results indicate a different action of T3 on systemic and pulmonary circulation.

Animals↗
PubMed1989

Functional and metabolic effects of ribose in combination with prazosin, verapamil and metoprolol in rats in vivo.

Ribose improves the function of the rat heart in various pathological conditions through its effects on cardiac energy metabolism, while having no direct haemodynamic actions. We therefore studied its functional and metabolic effects in closed chest rats when given in combination with prazosin, verapamil or metoprolol, all of which have direct effects on the circulation. Ribose administration for 24 h at 200 mg.kg-1.h-1 did not affect heart function but increased the available pool of 5-phosphoribosyl-1-pyrophosphate in heart (four fold) and skeletal muscle (1.7-fold), as assessed by the incorporation of 14C-adenine into the adenine nucleotides. The utilisation of adenine for adenine nucleotide synthesis, expressed as the ratio of adenine nucleotide radioactivity to tissue extract radioactivity, was 70% in heart and 20% in skeletal muscle under control conditions, and 97% and 88% after 24 h of ribose administration. Ribose decreased the 14C-adenine incorporation into the adenine nucleotides in kidney, lungs and liver. After 24 h infusion of prazosin (100 micrograms.kg-1.h-1), heart rate and LVdP/dtmax were not changed, but LVSP (-20%), mean aortic pressure (-16%) and peripheral resistance (-40%) were decreased. Cardiac output was enhanced (+40%). Verapamil (2mg.kg-1.h-1) and metoprolol (2mg.kg-1.h-1) infused for 24 h decreased the pressure-rate and pressure-volume product of the left ventricle to the same extent (-40%). Verapamil had no influence on cardiac output, while metoprolol depressed it (-30%). Simultaneous administration of prazosin, verapamil or metoprolol with ribose did not affect the ribose induced increase in the myocardial 5-phosphoribosyl-1-pyrophosphate pool.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenine Nucleotides↗
PubMed1989

Effect of calcium antagonists and other drugs on the hypoxia-induced increase in rat right ventricular pressure.

The effect of four calcium antagonists (nifedipine, nitrendipine, nisoldipine, and verapamil) on hypoxia-induced changes in right ventricular parameters were examined in anesthetized closed-chest rats using an ultraminiature catheterization technique. The effect of the calcium antagonists was compared to the alpha-adrenoceptor blocker prazosin, the beta-adrenoceptor blocker propranolol, the angiotensin-converting enzyme (ACE) inhibitor captopril, and the vasodilator nitroglycerin. The animals were exposed to two successive 5-min hypoxic periods separated by a normoxic interval of 60 min, during which the animals received an intravenous (i.v.) infusion of the substances tested. Hypoxia caused a marked rise in right ventricular systolic pressure (RVSP) and a moderate increase in RVdP/dtmax. Heart rate (HR) was only slightly enhanced. The functional response to the second hypoxic period did not differ from the first one in NaCl-infused animals. All calcium antagonists reduced the hypoxic pressure increase in a dose-dependent manner and ultimately abolished it. Nisoldipine was the most effective substance, followed by nifedipine, nitrendipine, and verapamil. In contrast, prazosin and propranolol did not influence the hypoxic pressure response. Administration of captopril and nitroglycerin attenuated the increase in RVSP. Thus, as compared with the other substances tested, calcium antagonists were the most effective drugs that antagonized the hypoxia-induced increase in RVSP.

Animals↗
PubMed1989

Inotropic response of the rat heart during development and regression of triiodothyronine-induced hypertrophy.

The inotropic response of rat hearts in vivo was tested by infusion of 2 mmol/kg/h calcium chloride after 14 days of daily 3,3',5-triiodo-L-thyronine (T3) treatment and 14 days following discontinuation of T3 treatment. The hyperthyroid state was characterized by marked cardiac hypertrophy (57% increase in the heart weight/body weight ratio) which was more pronounced in the right ventricle (63% increase). Heart rate and cardiac output index were elevated by 56 and 63%, respectively, and total peripheral resistance was reduced by 40%. Left ventricular systolic pressure (LVSP) was elevated by 15%, the maximal rate of rise in left ventricular pressure (LV dp/dtmax) by 106%, and LV pressure-volume performance by 192%. Right ventricular systolic pressure (RVSP) was elevated by 71%, RV dp/dtmax by 126%, and RV pressure-volume performance by 371%. Intravenous infusion of calcium induced an elevation in heart rate and LV dp/dtmax, the increase of the latter was less pronounced than in the control heart. After 14 days subsequent to discontinuation of T3 treatment, there was a regression of cardiac hypertrophy. However, the LV was still hypertrophied by 12% and the RV by 24%. Heart rate and contractility were normal. The pressure-volume performance of both LV and RV was still enhanced by 24 and 18%, respectively. The inotropic response of the LV to calcium infusion was similar to that of the normal heart. Thus, 14 days after discontinuation of T3 treatment, the regression of cardiac hypertrophy was not complete, although heart rate and contractility as well as the inotropic response to calcium, were normal. The remaining cardiac hypertrophy correlated with the still existing elevation in the pressure-volume performance.

Adrenergic beta-Agonists↗
PubMed1989

Significance of myocardial alpha- and beta-adrenoceptors in catecholamine-induced cardiac hypertrophy.

The role of alpha- and beta-adrenoceptors in the development of catecholamine-induced cardiac hypertrophy in vivo was investigated. Rats received a constant intravenous infusion of norepinephrine or sodium chloride (control) for 3 days. The norepinephrine infusion was combined with the alpha-blocker prazosin, the beta-blocker metoprolol, or both blockers. For modulation of the work load of the heart, the calcium channel blocker verapamil was added to the norepinephrine infusion. A further group of animals was treated with the alpha-adrenergic stimulator norfenephrine, which also was combined with prazosin or verapamil. Norepinephrine induced significant increases in mean aortic pressure, left ventricular dP/dtmax, heart rate, and total peripheral resistance. The left ventricular weight/body weight ratio was significantly elevated and was accompanied by an increase in the RNA concentration and the RNA/DNA ratio. Prazosin as well as metoprolol partially antagonized the increase in left ventricular weight and RNA concentration, whereas simultaneous prazosin and metoprolol treatment prevented the norepinephrine-induced alterations. Although combination of norepinephrine with verapamil resulted in considerable reduction of all functional parameters, the development of cardiac hypertrophy and the elevated RNA/DNA ratio were not significantly influenced. Stimulation of alpha-receptors with norfenephrine elicited an increase in total peripheral resistance and in left ventricular weight, which was abolished by prazosin. Verapamil did not affect the norfenephrine-induced cardiac hypertrophy, although it normalized essentially all functional parameters. Thus, the rapid development of cardiac hypertrophy in the norepinephrine model seems to be directly mediated by stimulation of myocardial alpha- and beta-adrenoceptors rather than by hemodynamic changes.

Adrenergic alpha-Antagonists↗