Volume overload influence on hypertrophied myocardium function.
The aim of this study was to demonstrate that hypertrophied cardiac muscle is more sensitive to volume-overload than normal cardiac muscle. We assessed the mechanical function of isolated left ventricular papillary muscle from male spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar-Kyoto rats (WKY) submitted to volume overload caused by aortocaval fistula (ACF) for 30 days. Muscles were perfused with Krebs-Henseleit solution at 28 degrees C and studied isometrically at a stimulation rate of 0.2 Hz. The ACF increased the right and left ventricular weight-to-body weight ratio in WKY rats; it also promoted right ventricular hypertrophy and further increased the basal hypertrophy in the left ventricle from SHR. The arterial systolic pressure was greater in SHR than in WKY rats, and decreased with ACF in both groups. Developed tension (DT) and maximum rate of DT (+dT/dt) were greater in the SHR-control than in the WKY-control (P < 0.05); the time from peak tension to 50% relaxation (RT 1/2) was similar in these animals. ACF did not change any parameters in the SHR group and increased the resting tension in the WKY group. However, the significant difference observed between myocardial contraction performance in WKY-controls and SHR-controls disappeared when the SHR-ACF and WKY-controls were compared. Furthermore, RT 1/2 increased significantly in the SHR-ACF in relation to the WKY-controls. In conclusion, the data lead us to infer that volume-overload for 30 days promotes more mechanical functional changes in hypertrophied muscle than in normal cardiac muscle.
Cicogna
Antonio Carlos
AC
Department of Internal Medicine, School of Medicine of Botucatu, State University Julio de Mesquita Filho, Botucatu, State of São Paulo, Brazil.
Matsubara
Beatriz Bojikian
BB
Matsubara
Luiz Shiguero
LS
Okoshi
Katashi
K
Gut
Ana Lúcia
AL
Padovani
Carlos Roberto
CR
Meyer
Mariana Monteiro
MM
Okoshi
Marina Politi
MP
D000818:Animals; D001696:Biomechanical Phenomena; D006321:Heart / Q000503:physiopathology*; D017379:Hypertrophy, Left Ventricular / Q000503:physiopathology*; D017380:Hypertrophy, Right Ventricular / Q000503:physiopathology; D066298:In Vitro Techniques; D007537:Isometric Contraction / Q000502:physiology*; D008297:Male; D010210:Papillary Muscles / Q000473:pathology / Q000503:physiopathology; D051381:Rats; D011918:Rats, Inbred SHR; D011921:Rats, Inbred WKY; D013318:Stroke Volume