Mechanisms underlying systemic hemodynamic responses to experimental coronary artery occlusion. A preliminary study with hexamethonium

The hemodynamic changes induced by coronary occlusion were investigated in anesthetized dogs. Coronary occlusion elicited an immediate but transient increase in the systemic blood pressure and in the vascular resistance of the hind limb perfused at constant flow. Thereafter, systemic hypotension and vasodilatation in the perfused region were observed. Vagotomy abolished the initial increase of the systemic and perfusion pressure and reduced significantly the late vasodilator response both systemically and in the perfused hind limb. After the subsequent administration of hexamethonium the vasodilatation in the hind limb was no longer manifest but the fall in blood pressure was unmodified. These results seem to suggest that multiple mechanisms are involved in the hemodynamic response to coronary occlusion.

Non-invasive evaluation by thermistor plethysmography of left ventricular performance during dynamic exercise. Comparison with echocardiography

The purpose of this study was to evaluate the reliability of two non-invasive techniques (STI and echocardiography) in assessing cardiovascular response during exercise. STI were obtained using a new carotid pulse transducer (thermistor pulse) proved to be reliable in exercise recording. The study population included 12 male rowers (age 15-20 years), who performed supine bicycle exercise; STI and echocardiographic recording of left ventricle were simultaneously obtained at rest and continuously throughout the exercise period. A negative linear correlation (r=-0.782; p less than 0.001) was found between PEP (pre-ejection period) and %LVID (fractional shortening of left ventricle), reliable indexes of cardiac contractility measured by the two techniques. A lower, but significant correlation (r=0.643; p less than 0.001) was present between ETI (left ventricular ejection time corrected by heart rate) and SV (stroke volume) indexes of pump function. The present study shows that STI measured with this new technique, can be employed in evaluating left ventricular function in those patients in whom a good echocardiogram is difficult to record during exercise.

Development of cardiac hypertrophy in rats exposed to acute hypobaric hypoxia. - Studies with protein synthesis inhibitors

The study is based on the experimental model of myocardial hypertrophy in rats. Male Sprague-Dawley adult rats were exposed to acute hypoxia in a hypobaric chamber (0.40 atmospheres of air for 24 hours). Myocardial hypertrophy was detected by wet and dry heart weight values when calculated on the basis of total body weight; i.e., ratio heart weight in mg to body weight in 100 g. The behaviour of myocardial hypertrophy was assessed after treatment of intact animals with Puromycin (10 mg/rat i.p.) or Actinomycin-D (100 micrograms/rat i.p.). The experimental results showed the following dry heart weight values (mean +/- SEM): room pressure 60.5 +/- 1.5; hypoxia 69.2 +/- 0.9; Actinomycin-D + hypoxia 63.5 +/- 0.6; Puromycin + hypoxia 62.4 +/- 1.5, (P less than 0.001). From the comparison of data reveals that inhibitors of protein synthesis completely inhibit the myocardial hypertrophy due to hypoxia. Thus it is documented that acute hypobaric hypoxia is able to induce in the rat an actual myocardial hypertrophy condition as expressed of the enhanced protein synthesis.

Echocardiographic evaluation of acute administration of oxyfedrine in patients with coronary artery disease

In order to assess the effects of oxyfedrine in ischaemic heart disease, echocardiographic evaluation of left ventricular function was performed 2,5,10,15 and 20 minutes after the intravenous administration of 12 mg oxyfedrine in 15 patients with coronary artery disease without angiographic abnormalities of left ventricular wall motion. The following parameters were measured: heart rate, mean arterial blood pressure, internal dimension in diastole (LVIDd) and in systole (LVIDs) of the left ventricule and the percentage shortening of the LVID (%LVID). There was a significant increase in %LVID (peak 10 minutes after drug administration; p less than 0.001) indicating improved left ventricular function, associated with slight changes in pre-load (LVIDd) and in heart rate, and no variation in mean blood pressure. No abnormalities of contraction were observed after the administration of oxyfedrine. These results suggest that oxyfedrine exerts a direct positive inotropic effect of the myocardium in patients with significant coronary artery stenoses.

His bundle electrogram recording using a multipolar electrode catheter via the arm veins

In eighteen patients with atrioventricular conduction disturbance, His bundle electrograms were studied via the arm vein. A 6F Berkovits-Castellanos USCI hexapolar electrode catheter was introduced into the right atrium and looped across the tricuspid valve in a "golf club" shape. The main aim was to leave the two distal electrodes in contact with the atrial endocardium to perform atrial pacing, while displaying the other four electrodes along the superior angle of the tricuspid valve for proximal and distal His bundle recordings. His bundle electrograms were successfully obtained in all cases. The arm approach provides an alternate route whenever the femoral approach is not feasible. Moreover, the use of an hexapolar electrode catheter provides some practical advantages: 1) it enables atrial pacing to be performed, as well as proximal and distal His bundle recording to be obtained, by using the same multipolar electrode catheter; and 2) it allows long-term monitoring of His bundle potentials, in view of the stability of His bundle recordings. Finally, the arm approach could be the method of choice for the study of His bundle electrograms during leg supine exercise in selected patients.

Disopyramide and mexiletine: which is the agent of choice in the long term-oral treatment of lidocaine-responsive arrhythmias? Efficacy comparison in a randomized trial

Forty patients with serious lidocaine-responsive ventricular arrhythmias were randomly assigned to treatment with either oral disopyramide (100 mg 4 times daily) or mexiletine (200 mg 4 times daily) for 3 weeks. A satisfactory arrhythmias control (greater than 75 % reduction of premature ventricular complexes per minute as compared to the control period prior to lidocaine administration) was achieved in 19 patients in the mexiletine group and in 16 in the disopyramide treated patients. Furthermore, disopyramide failed to maintain the reduction of the number of ventricular extrasystoles per minute obtained with lidocaine, while mexiletine succeeded. Finally, the number of ventricular extrasystoles per minute in the mexiletine treated group was significantly lower than in the other group. Gastrointestinal disturbances were more frequent during mexiletine administration.

Inhibition of hypoxia-induced cardiac hypertrophy by verapamil in rats

Male Sprague-Dawley rats (200-220 g) were employed to study the effect of a calcium antagonistic drug on hypoxia-induced myocardial hypertrophy. The hypoxic condition was obtained by exposure of animals to reduced barometric pressure in a hypobaric chamber. The rats, divided in groups, were exposed to acute or chronic intermittent hypoxia (0.42 atmospheres of air for 24 hrs or 0.42 atm for 12 hrs per day for 10 days, respectively). Verapamil (VRP) was given subcutaneously in a total dose of 200 mg/kg/b.w./rat. In hypoxic rats, the drug significantly reduced the values of dry heart weight calculated on the basis of its relationship to total body weight. This phenomenon is probably due to: (1) reduced activation of the contractile system and a thereby resulting decrease in ATP breakdown as a result of blocking of Ca++ inflow into myocardial cells; (2) the effect of Verapamil on hypoxia-induced pulmonary hypertension and/or (3) a direct effect of the drug on the myocardial cell.

Hemoglobin synthesis in individual bursts from normal adult blood: all bursts and subcolonies synthesize G gamma-and A gamma-globin chains

Gamma-globin chain synthesis has been evaluated in individual bursts and subcolonies that were generated by normal adult blood BFU-Es in methylcellulose cultures containing semipurified erythropoietin (Ep) and then analyzed via either isoelectric focusing (IEF) of globin chains or immunofluorescence techniques. At variance with previously reported results, based on plasma clot culture and immunofluorescence, all bursts and subcolonies analyzed synthesize gamma-globin chains. Identification of gamma-chains has been confirmed by preparative IEF of HbF, followed by either carboxymethylcellulose chromatography or IEF analysis of the resulting globin chains. In all bursts analyzed, the relative synthesis of the two types of gamma-globin chains (G gamma and A gamma) shows an adult ratio (i.e., approximately 1:1). The results obtained via IEF have been confirmed by immunofluorescence studies, which apparently showed presence of at least some HbF-positive cells within all scrutinized bursts or subcolonies. The significance of these studies is discussed in the light of current hypotheses on mechanism(s) underlying HbF synthesis in normal adults.

Myocardial hypertrophy in the rat. Correlation between two experimental models

Two different conditions responsible for cardiac hypertrophy in the rat were investigated: the first one is isoproterenol-induced myocardial infarct, the second is exposure to hypoxia (0.42 atmospheres/24 h) in hypobaric chamber. To demonstrate that in both experimental models stimulation of protein synthesis is an absolute requirement to induce cardiac hypertrophy, a variety of techniques were employed including: evaluation of dry heart weight value, concentration of radiothallium (201T1) in the heart and effects of inhibitors of protein synthesis (Puromycin). Experimental results have showed: (A) a significant increase (p<0.001 as compared to control group) of dry heart weight values both in isoproterenol-treated and hypoxic rats; (B) a significant increase over control group (p<0.001) in myocardial 201T1 concentration in isoproterenol-treated rats; (C) total inhibition of cardiac hypertrophy in Puromycin treated group subjected to hypoxia. Finally, on the basis of different mortality observed in infarcted (85.0%) or hypoxic (5.0%) rats treated with Puromycin (40 mg/Kg body weight i.p.) a different role of cardiac hypertrophy in 2 experimental conditions is postulated: in the case of infarct-like lesions the cardiac hypertrophy has compensatory significance; under hypoxic stimulus is only due to increased cardiac work.

Long term comparative study of guanfacine and alpha-methyldopa in essential hypertension

The hypotensive action of guanfacine and alpha-methyldopa has been compared in 30 patients wth moderate essential hypertension. After 2 weeks of placebo treatment, the patients were randomly allocated to a 12 week treatment with either of the two drugs. The treatment was started with guanfacine, 1 mg twice daily p.o., or alpha-methyldopa, 250 mg three time a day p.o. This dose of guanfacine was able to induce a satisfactory control of blood pressure in all patients while the dose of alpha-methyldopa was gradually increased to a predetermined maximum daily dose (2 g) in those patients with unsatisfactory blood pressure control, i.e., systolic blood pressure above 160 mmHg and diastolic above 95 mmHg. Then the two treatments were dicontinued for one week. Both drugs induced a significant reduction of systolic and diastolic blood pressure. However, guanfacine induced a more marked decrease in systolic blood pressure after the 14th day of treatment while the reduction of diastolic blood pressure was significantly higher only at the end of the final wash-out period, thus indicating a longer lasting effect of guanfacine as compared to alpha-methyldopa. Two patients treated with guanfacine developed dryness of the mouth and three of those in the alphamethyldopa group complained of excessive sedation.

Effects of intravenous disopyramide on myocardial function in patients with different degrees of cardiac failure

The effects of intravenous disopyramide phosphate on myocardial function were evaluated by non-invasive indices of cardiac performance (systolic time intervals, STI) in 15 patients with atherosclerotic heart disease and different degrees of cardiac failure. Disopyramide (1.5 mg/Kg) was given intravenously over a period of 5 min. This drug induced in patients in I-II classes of NYHA a significant decrease of LVETc, while PEP, ICT, and PEP/LVET ratio rose significantly. STI were affected much more markedly in patients in III-IV classes of NYHA. Particularly affected were contractility indices (PEP, ICT, PEP/LVET), which were reduced significantly more in patients in III-IV classes as compares to patient in I-II classes. In contrast, LVETc, which correlates to stroke volume and cardiac output, was similarly worsened by the drug in the 2 groups of patients. Therefore, this study shows that disopyramide has relevant depressant effects on myocardial performance, simultaneously reducing stroke volume and contractility, and that the effect on contractility is more marked in patients with severe left ventricular impairment.

Globin chain synthesis in single erythroid bursts from cord blood: studies on gamma leads to beta and G gamma leads to A gamma switches

Erythroid bursts from cord or adult blood were grown in methylcellulose cultures (3 international units of erythropoietin per plate). On day 13, single bursts were picked up and reincubated for 16-24 hr with [3H]leucine. Radioactive globin chains [alpha,beta,G gamma, and A gamma (Ala-136)] were analyzed by either isoelectric focusing on polyacrylamide gels and fluorography or carboxymethylcellulose chromatography. In all cases, alpha to non-alpha globin radioactivity ratios were close to 1. In single cord blood bursts, the values of both gamma-to-beta and G gamma-to-A gamma ratios were spread over a large spectrum and further characterized by a continuous rather than a bimodal distribution. Morever, the G gamma-to-A gamma ratios demonstrated in single bursts appeared to be directly correlated with the respective gamma-to-beta ratios. These data suggest that both the gamma leads to beta and the G gamma leads to A gamma switches are mediated via mechanisms modulating the relative activities of the different genes in the non-alpha globin gene cluster rather than via selection of clones committed to the preferential synthesis of beta and A gamma globins. In contrast with the results obtained with cord blood, individual adult blood bursts synthesize a lower and hence relatively more uniform amount of gamma globin chains.

Hemodynamic response to exercise after propranolol in patients with mitral stenosis

Hemodynamic response to exercise before and 10 minutes after propranolol (5 mg intravenously) was studied in 10 young patients with pure mitral stenosis who had normal sinus rhythm and no cardiac failure. After propranolol the mean heart rate and cardiac index at rest were lower than during the control state (respectively, 95 +/- 4 versus 82 +/- 3 beats/min, P less than 0.005; 3.4 +/- 0.2 versus 2.8 +/- 0.1 liters/min per m2, P less than 0.025). As a result, the mean pulmonary wedge pressure and mean mitral valve gradient at rest were lower (respectively, 22 +/- 2 versus 18 +/- 2 mm Hg, P less than 0.005; 24 +/- 2 versus 17 +/- 2 mm Hg, P less than 0.001). During exercise after propranolol the values of pulmonary wedge pressure and mitral valve gradient were lower than control values during exercise (respectively, 39 +/- 3 versus 30 +/- 2 mm Hg, P less than 0.005; 44 +/- 3 versus 32 +/- 3 mm Hg, P less than 0.005), again because of the lower heart rate and cardiac index (130 +/- 6 versus 104 +/- 6 beats/min, P less than 0.001; 4.6 +/- 3 versus 3.7 +/- 2 liters/min per m2, P less than 0.01). Left ventricular end-diastolic pressure and stroke index showed no significant changes. Thus, propranolol may benefit patients with pure mitral stenosis with sinus rhythm and no cardiac failure whose symptoms occur during those reversible conditions characterized by an increase in heart rate or cardiac output, or both.

Protective effects of propranolol on the exercise-induced reduction of blood flow in arteriopathic patients

The vascular steal phenomenow, that is, the shunting of blood from ischemic to normally perfused areas, is commonly observed during exercise in the affected limbs of patients with peripheral arterial insufficiency. Propranolol was administered to 18 arteriopathic patients before the exercise to ascertain whether the reverse situation can be induced. The results indicate that before propranolol administration, Jantsch's index (used to quantify the plethysmographic waves) decreased from 0.53 +/- 0.05 to 0.33 +/- 0.04 (P less than 0.001) at 1 minute, and to 0.38 +/- 0.04 (P less than 0.001) at 5 minutes after the end of the exercise. When the exercise was repeated after propranolol, Jantsch's index did not change. These findings indicate that propranolol can inhibit exercise-induced vascular steal.

Effect of furosemide on plasma concentration and beta-blockade by propranolol

Although propranolol and furosemide are used together for hypertension, the effects of furosemide on plasma levels and beta-blocking action of propranolol are not known. Ten healthy subjects received propranolol 40 mg orally; the mean plasma propranolol levels in 60, 90, 180, and 300 min were 85 +/- 16, 90 +/- 7, 82 +/- 8, and 58 +/- 8 ng/ml. Propranolol was then given together with furosemide (25 mg orally) and the propranolol blood level was measured. Mean propranolol plasma levels were 106 +/- 11 ng/ml at 60 min, 120 +/- 12 ng/ml at 90 min (p less than 0.01), 102 +/- 8 ng/ml at 180 min (p less than 0.05), and 78 +/- 8 ng/ml at 300 min (p less than 0.01). Six additional subjects were given an infusion of 1 microgram/min isoproterenol increased by 0.5 microgram/min every 2 min until the heart rate rose by 25% after oral administration of furosemide 25 mg. This procedure was repeated after propranolol (40 mg orally) and propranolol with furosemide (25 mg orally). The amount of isoproterenol which raised the heart rate by 25% was 2.6 +/- 0.3 micrograms after furosemide alone and 17.7 +/- 2 micrograms after propranolol (p less than 0.01). After propranolol with furosemide the dose of isoproterenol required to elevate heart rate by 25% was 109 +/- 15 micrograms (p less than 0.001).