COMPARATIVE MECHANICAL STUDY OF ISOLATED PAPILLARY-MUSCLE FROM WISTAR-KYOTO AND WISTAR RATS

Isolated papillary muscles have often been used in myocardial mechanic al function studies. The objective of the present study was to compare the mechanical function of papillary muscle isolated from left ventri cle between Wistar (W) and Wistar-Kyoto (WKY) rats of different ages ( 1, 3, 6 and 12 months), in order to examine whether there is a differe nce in intrinsic mechanical properties of muscle between the two rat s trains. Muscles were perfused with Krebs-Henseleit solution at 28-degr ees-C and studied isometrically and isotonically at a stimulation rate of 0.2 Hz. The W and WKY showed statistically significant differences during both isometric and isotonic contractions. During isometric con traction, (1) the peak developed tension (DT) and + dT/dt were lower i n WKY rats in the 1 mo groups; 2) the resting tension (RT) was greater in WKY at 3, 6 and 12 mo, (3) time to peak tension (TPT) was greater in WKY at 3 and 12 mo, (4) time for tension to fall from peak to 50% o f peak tension (RT 1/2) was greater in WKY at 3 mo and (5) - dT/dt was lower in WKY at 1 and 3 mo. During isotonic contraction, (1) the peak shortening (PS) and dL/dt were lower in WKY at 12 mo, (2) the time to peak shortening (TPS) was greater in WKY at 3 and 12 mo; (3) + dL/dt was lower in WKY at 3, 6, and 12 mo and (4) the relative variation of length (Lmax-PS/Lmax was greater in WKY at 6 and 12 mo. These data sho wed a difference in mechanical behaviour of the papillary muscle betwe en Wistar and Wistar-Kyoto rats of different age.