John C. Yates

Ventricular dysfunction and necrosis produced by adrenochrome metabolite of epinephrine: relation to pathogenesis of catecholamine cardiomyopathy.

We have examined the effects of adrenochrome and other metabolites of epinephrine on the ultrastructure and contractile activity of isolated rat hearts perfused under conditions in which the heart rate and coronary flow were controlled. Perfusion of hearts with epinephrine or metanephrine significantly increased contractile force; vanillylmandelic acid and dihydroxymandelic acid did not alter contractile force development, whereas adrenochrome (50 mg/L) declined contractile force with epinephrine (50 mg/L) was associated with increased resting tension and maximum rates of force development and relaxation, and decreased time for peak tension development and 1/2 relaxation. On the other hand, hearts perfused with adrenochrome showed early decline followed by steady increase in resting tension; maximum rates of force development and relaxation were reduced and times for peak tension development and 1/2 relaxation were increased. Hearts perfused or 10 minutes or more with adrenochrome (50 mg/L), but not epinephrine, metanephrine, dihydroxymandelic acid or vanillylmandelic aicd, showed ultrastructural damage. Adrenochrome concentrations of 10 or 25 mg/L altered the appearance of mitochondria after 30 minutes of perfusion. Infusion of epinephrine (1 mg/L) during perfusion with adrenochrome partially maintained contractile force during the first 15 minutes of perfusion but did not alter the severity of ultrastructural changes due to adrenochrome. These results are consistent with the concept that oxidation products of catecholamines such as adrenochrome are partly responsible for inducing myocardial necrosis and failure following massive catecholamine injections in intact animals.

Structural and functional changes associated with failure and recovery of hearts after perfusion with Ca2+-free medium.

Abstract The electrical and mechanical functions and ultrastructure of isolated rat hearts were studied during perfusion with Ca2+-free medium and during reperfusion with normal medium following various intervals of Ca2+-free perfusion. Contractile force declined to zero within 30 s of perfusion with Ca2+-free medium. No ultrastructural changes were observed within 3 min of Ca2+-free perfusion; however, separation of the intercalated discs was noted after 5 min or longer of Ca2+-free perfusion and upon reperfusion with normal medium after 3 min of Ca2+-free perfusion. The ability of hearts to recover contractile force upon reperfusion with normal medium was dependent upon the duration of the Ca2+-free perfusion. The resting tension was increased during the Ca2+-free perfusion and was further increased upon reperfusion with normal medium after 2 min. Reperfusion with normal medium after 5 min or longer of Ca2+-free perfusion also resulted in contracture of sarcomeres and extensive ultrastructural damage. Irreversible changes in surface electrical activity occurred after 3 to 4 min of Ca2+-free perfusion. Reducing the Na+ concentration of the Ca2+-free medium delayed failure of contractility, augmented the recovery of contractility, and prevented the separation of the intercalated discs. Reducing the Mg2+ concentration of the Ca2+-free medium also delayed failure of contractility but did not affect recovery. Reducing the K+ concentration did not alter the time-course of failure but diminished the recovery of contractile force after 3 min of Ca2+-free perfusion. These results clarify the sequence of structural and functional changes occurring during Ca2+ deprivation and support the view that extracellular Na+ plays a deleterious role during failure of Ca2+-deprived hearts. It is suggested that isolated heart perfused with Ca2+-free medium forms an interesting model for studying the pathogenesis of two types of heart failure namely failure due to “intracellular calcium deficiency” and failure due to “intracellular calcium overload”.

Induction of necrosis and failure in the isolated perfused rat heart with oxidized isoproterenol

Abstract The effects of fresh and oxidized isoproterenol (100 mg/l) on mechanical function and ultrastructure of the isolated perfused rat heart were studied. In contrast to fresh isoproterenol, isoproterenol oxidized for 6 to 8 h decreased developed contractile tension, maximum rate of tension development and maximum rate of relaxation. The hearts perfused with oxidized isoproterenol were unable to generate contractile force in about 35 min, and showed a marked increase in resting tension. Although fresh isoproterenol at high concentrations employed in this study did not show an increase in the developed contractile force, the maximum rates of tension development and relaxation were increased in comparison to the control. Both fresh and oxidized isoproterenol decreased times for peak tension and for 1 2 relaxation. The hearts perfused with oxidized isoproterenol, but not with fresh isoproterenol, showed disrupted myofilaments, swollen mitochondria and other ultrastructural damage which is commonly seen in myocardial necrosis. The ability of the solution of isoproterenol oxidized for 16 to 24 h to depress cardiac function and induce necrosis was markedly less than that of the one oxidized for 6 to 8 h. These results are consistent with the view that oxidized products of catecholamines, but not catecholamines per se , are responsible for inducing myocardial necrosis and failure.

Functional and subcellular changes in the isolated rat heart perfused with oxidized isoproterenol

Abstract The isolated rat heart failed to generate contractile force within 10, 15 and 60 min upon perfusion with medium containing 100, 50 and 20 mg/l oxidized isoproterenol respectively, whereas the contractile force was depressed by about 85% of control following a 90 min perfusion with 10 mg/l oxidized isoproterenol. Swelling of mitochondria and sarcoplasmic reticulum, and disruption of the contractile proteins were seen in all hearts failing due to oxidized isoproterenol. Furthermore, calcium uptake activity, but not calcium binding of the microsomal fraction from hearts perfused with oxidized isoproterenol was depressed, whereas mitochondrial calcium binding and uptake activities were unaffected. Perfusion of the hearts with oxidized isoproterenol did not change the mitochondrial or microsomal ATPase activities; however, mitochondrial phosphorylation rate, state 3 respiration and RCI values were significantly depressed. These results indicate changes in subcellular mechanisms during the induction of myocardial necrosis and contractile failure due to oxidized isoproterenol.

The suitability of the antimony electrode for pH determinations in mammalian heart.

Antimony electrode provides a stable and reproducible means for the determination of intramuscular pH. Large changes in bicarbonate or phosphate concentrations are required before a significant alteration in electrode response is observed and thus is quite suitable for physiological measurements. However, dramatic shift in mv-pH relationship for this electrode was seen upon changing pO2 of the medium. When the electrode was employed to monitor intramuscular pH in isolated perfused rat heart, it was found that Na+ or K+ free medium produced a severe acidosis (pH < 6.5) along with loss of contractility. Ca2+ free perfusion, on the other hand, resulted in a failure of contractility within 30 sec without any change in interstitial pH. Upon stretching the heart when the perfusion rate was maintained at constant level, an increase in both contractile force and pH occurred. Norepinephrine along with increased perfusion flow produced an increase in both rate and force of contraction without any significant change in interstitial pH. However, at constant perfusion rate, the interstitial pH increased dramatically. Similarly, global ischemia resulted in a decline in contractile force and initial increase and subsequent decrease in interstitial pH. No decrease in pH was noted when coronary flow was reduced gradually. These results suggest that the antimony electrode is only suitable in situations which are not associated with larger changes in pO2.