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Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-27T11:17:31Z No. of bitstreams: 0Bitstream added on 2014-05-27T14:28:12Z : No. of bitstreams: 1 2-s2.0-0027572997.pdf: 49390 bytes, checksum: d4ef74947d7759c47359d756b77a9d3f (MD5) Made available in DSpace on 2014-05-27T11:17:31Z (GMT). No. of bitstreams: 0 Previous issue date: 1993-04-01 PURPOSE--To evaluate the effects of age on mechanical performance of rat myocardium. METHODS--Left ventricular papillary muscles were isolated from male Wistar rats at 1, 3, 6 and 12 months of age. Muscles were studied isometrically and isotonically, stimulated at 0.2 Hz, perfused with Krebs-Henseleit solution having an external calcium concentration of 2.52 mM, and maintained at 28 degrees C. RESULTS--Peak isometric developed tension was significantly higher in 1 month than 3, 6 and 12 months. Peak rate of isometric tension rise decreased substantially between 1, 3 and 12 months. Time to peak isometric developed tension showed a significant increase of both 3 and 12 months of age. Time to half relaxation increased significantly from 3 to 6 and from 3 to 12 months. Maximum rate of tension decline decreased from 3 to 6 and from 3 to 12 months. No difference in resting tension was noted among any group. Isotonically, peak shortening and time to peak shortening increased from 1 to 3 months of age. Time to half re-lengthening increased from 3 to 6 and from 3 to 12 months of age. No difference in peak shortening velocity, peak relaxation velocity and relative change in muscle length was noted among any groups. CONCLUSION--The maturation affects the mechanical performance of cardiac muscle.