Early changes induced in the left ventricle by pressure overload. An experimental study on swine heart

The purpose of this study was to evaluate the early changes in sarcoplasmic reticulum (SR) function and the parallel morphological and hemodynamic mod ifications occurring in the heart following pressure overload. As regards S R function, we also explored the levels of acylphosphatase, an enzyme which might have a regulatory effect on the SR Ca2+ pump by hydrolyzing the phos phorylated intermediate of this transport system. Pigs subjected to pressur e overload by aortic stenosis for 6, 12, 24, 48, 72, and 96 h were compared to sham-operated controls. At each of the considered times both SR Ca2+-AT Pase activity and Ca2+ uptake, as well as acylphosphatase activity, were si gnificantly enhanced in the pressure overloaded compared to the control hea rts, with a maximal increase at 6 h: moreover, a positive and significant c orrelation was found between these parameters, The modifications in the act ivities of Ca2+-ATPase and acylphosphatase reflected an increased expressio n of these proteins, while phospholamban did not show significant changes i n its concentration nor in its phosphorylation status, As for hemodynamic p arameters, rapid changes in the left ventricular function were observed and especially the early hours following the aortic stenosis appeared to be cr ucial for the adjustment of heart function, The most relevant morphological Ending was a focal disarrangement of the myofibrillar pattern which was ve ry evident at Gh, and progressively attenuated at later times, Taken togeth er our data suggest that an early adaptation to the increased hemodynamic w orking overload is a consistent activation of the contractile apparatus whi ch reflects, at least in part, an enhanced SR Function. Besides the changes in Ca2+ pump protein expression, increased acylphosphatase levels might al so contribute to this effect. (C) 2000 Academic Press.