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Abnormalities in contractile proteins in myocardium from chronic diabetic animals
j Mol Cell Cardiol 18 (Supplement 3) (1986) AND FUNCTIONAL ABNORMALITIES IN M Y O C A R D I A L ISCHEMIA. S c h a p e r a n d B. Ito, M a x - P l a n c k - I n s t i t u t e , Bad Naubeim, FRG We investigated the problem whether dyskinesia at r e p e r f u s l o n following relatively s h o r t p e r i o d s of c o r o n a r y o c c l u s i o n are c a u s e d b y defective energy generation or t r a n s p o r t . We occluded the l e f t a n terior descending coronary artery in a n e s t h e t i z e d dogs, measured regional contractile function w i t h 2 p a i r s of s o n o m i c r o m e t e r crystals, and measured coronary and collateral blood flow with tracer microspheres. Coronary venous oxygen saturation was continuously measured in t w o r e g i o n a l v e i n s . F i f t e e n m i n u t e s of c o r o n a r y occlusion followed by reperfusion l e a d to a 50 % d e c r e a s e of r e g i o n a l contractile function, to a 25 % d e c r e a s e in r e p e r f u s i o n c o r o n a r y f l o w (at 60 m i n ) , a n d to a 25 % d e c r e a s e in m y o c a r d i a l oxygen consumption. Reactive hyperemia responses remained unimpaired. We conclude that stunned myocardium down-regulates its b l o o d f l o w b e c a u s e of d e c r e a s e d oxygen need. Stimulation with intracoronary calcium completely restores contractile reserve which indicates that ATP-production or its intracellular transport is n o t r e s p o n s i b l e for dysfunction at r e p e r f u s i o n . METABOLIC
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ABNORMALITIES IN CONTRACTILE PROTEINS IN MYOCARDIUMFROMCHRONIC DIABETIC ANIMALS. J. Scheuer, P. Pollack, A. Malhotra. Montefiore Hospital - Albert Einstein College of Medicine. Streptozocin and alloxan-induced diabetes in rats causes decreased contractile function and parallel depressions in actomyosin and myosin ATPases which can be explained by shifts in cardiac myosin heavy chain isoenzymes from a predominant V1 pattern to a predominant V3 pattern. Similar contractile protein abnormalities have been demonstrated in genetically diabetic BB rats. These physiological and biochemical abnormalities are prevented by insulin therapy, and once established are also reversed in a dose-dependent and time-dependent manner with insulin therapy. Reversal of the myosin abnormalities with insulin therapy can occur while hyperglycemia persists; therefore hyperglycemia is not the cause of the abnormality. Methyl palmoxirate and fructose administration are reported to p a r t i a l l y or completely reverse the myosin abnormalities in diabetic rats. Therefore the myosin changes are not solely related to insulin a v a i l a b i l i t y . Unlike the r a t , rabbit cardiac myosin is predominantly V3 myosin and, therefore, more l i k e ventricular myosin in man. Alloxan diabetes in rabbits alters mechanical function, myosin ATPase a c t i v i t y and isoenzymes in the same direction as in the diabetic rat. The predominant V3 pattern becomes almost exclusively V3. Mechanical, isoenzyme and ATPase changes can be reversed by treatment with insulin. The role of thyroid hormone w i l l be discussed.
HEART XANTHINE OXIDOREDUCTASE ACTIVITY INCREASES WITH AGE; THE ENZYME IS ABSENT FROM MYOCYTES. B. Schoutsen, E. Keijzer, J.W. de Jong. Cardlochemical Laboratory, Thoraxcenter, Erasmus University, Rotterdam, The Netherlands. Xanthine oxidoreductase activity (XOD) could be involved in the 02-paradox, inducing post-anoxlc damage by free O~-radlcals. However, the O2-paradox is absent in neonatal rats. Therefore, we studied ~OD in rat hearts of various ages, in addition to its localization. We measured XOD with a radioenzymatlc HPLC assay in homogenates of hearts and in homogenates of cultured neonatal myocytes and non-muscular (F) cells, separated with differential attachment. XOD in hearts increased linearly with age from 23 • 4 mU/g protein (age I-3 h; means • SD, n = 3) to 960 • 170 mU/g (age 15 w). In a culture of myocytes (purity: 85-95%) XOD rose from 4.2 • 1.6 mU/g (2nd day of culture) to 17 • 4 mU/g (4th day). In F-cells XOD increased much more, from I0.I • I.I mU/8 (2nd day) to 117 • 25 mU/g (4th day). Thus in neonates XOD is extremely low; the activity increases with age. This offers an explanation for the absence of the O -paradox in neonatal hearts It has been reported that, in bovine heart, XOD is 2 located solely in the endothellum of capillaries. In the myocyte fraction of rat heart cells we find a very low XOD, which can be accounted for by contamination with F-cells. The large XOD increase in F-cells may be caused by biosynthetic regulation or by rapid endothelial cell growth. We conclude that xanthlne oxldoreductase is not located in myocytes, making damage to myocytes by free 02-radlcals generated by XOD unlikely.
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ABNORMALITIES IN CONTRACTILE PROTEINS IN MYOCARDIUMFROMCHRONIC DIABETIC ANIMALS. J. Scheuer, P. Pollack, A. Malhotra. Montefiore Hospital - Albert Einstein College of Medicine. Streptozocin and alloxan-induced diabetes in rats causes decreased contractile function and parallel depressions in actomyosin and myosin ATPases which can be explained by shifts in cardiac myosin heavy chain isoenzymes from a predominant V1 pattern to a predominant V3 pattern. Similar contractile protein abnormalities have been demonstrated in genetically diabetic BB rats. These physiological and biochemical abnormalities are prevented by insulin therapy, and once established are also reversed in a dose-dependent and time-dependent manner with insulin therapy. Reversal of the myosin abnormalities with insulin therapy can occur while hyperglycemia persists; therefore hyperglycemia is not the cause of the abnormality. Methyl palmoxirate and fructose administration are reported to p a r t i a l l y or completely reverse the myosin abnormalities in diabetic rats. Therefore the myosin changes are not solely related to insulin a v a i l a b i l i t y . Unlike the r a t , rabbit cardiac myosin is predominantly V3 myosin and, therefore, more l i k e ventricular myosin in man. Alloxan diabetes in rabbits alters mechanical function, myosin ATPase a c t i v i t y and isoenzymes in the same direction as in the diabetic rat. The predominant V3 pattern becomes almost exclusively V3. Mechanical, isoenzyme and ATPase changes can be reversed by treatment with insulin. The role of thyroid hormone w i l l be discussed.
HEART XANTHINE OXIDOREDUCTASE ACTIVITY INCREASES WITH AGE; THE ENZYME IS ABSENT FROM MYOCYTES. B. Schoutsen, E. Keijzer, J.W. de Jong. Cardlochemical Laboratory, Thoraxcenter, Erasmus University, Rotterdam, The Netherlands. Xanthine oxidoreductase activity (XOD) could be involved in the 02-paradox, inducing post-anoxlc damage by free O~-radlcals. However, the O2-paradox is absent in neonatal rats. Therefore, we studied ~OD in rat hearts of various ages, in addition to its localization. We measured XOD with a radioenzymatlc HPLC assay in homogenates of hearts and in homogenates of cultured neonatal myocytes and non-muscular (F) cells, separated with differential attachment. XOD in hearts increased linearly with age from 23 • 4 mU/g protein (age I-3 h; means • SD, n = 3) to 960 • 170 mU/g (age 15 w). In a culture of myocytes (purity: 85-95%) XOD rose from 4.2 • 1.6 mU/g (2nd day of culture) to 17 • 4 mU/g (4th day). In F-cells XOD increased much more, from I0.I • I.I mU/8 (2nd day) to 117 • 25 mU/g (4th day). Thus in neonates XOD is extremely low; the activity increases with age. This offers an explanation for the absence of the O -paradox in neonatal hearts It has been reported that, in bovine heart, XOD is 2 located solely in the endothellum of capillaries. In the myocyte fraction of rat heart cells we find a very low XOD, which can be accounted for by contamination with F-cells. The large XOD increase in F-cells may be caused by biosynthetic regulation or by rapid endothelial cell growth. We conclude that xanthlne oxldoreductase is not located in myocytes, making damage to myocytes by free 02-radlcals generated by XOD unlikely.
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