Alterations in myocardial collagen content affect rat papillary muscle function

We investigated the influence of myocardial collagen volume fraction (CVF, %) and hydroxyproline concentration (mu g/mg) on rat papillary muscle funct ion. Collagen excess was obtained in 10 rats with unilateral renal ischemia for 5 wk followed by 3-wk treatment with ramipril (20 mg . kg(-1) . day(-1 )) (RHTR rats; CVF = 3.83 +/- 0.80, hydroxyproline = 3.79 +/- 0.50). Collag en degradation was induced by double infusion of oxidized glutathione (GSSG rats; CVF 5 2.45 +/- 0.52, hydroxyproline = 2.85 +/- 0.18). Nine untreated rats were used as controls (CFV = 3.04 +/- 0.58, hydroxyproline = 3.21 +/- 0.30). Active stiffness (AS; g . cm(-2) . %L-max(-1)) and myocyte cross-se ctional area (MA; mu m(2)) were increased in the GSSG rats compared with co ntrols [AS 5.86 vs. 3.96 (P< 0.05); MA 363 +/- 59 vs. 305 +/- 28 (P< 0.05)] . In GSSG and RHTR groups the passive tension-length curves were shifted do wnwards, indicating decreased passive stiffness, and upwards, indicating in creased passive stiffness, respectively. Decreased collagen content induced by GSSG is related to myocyte hypertrophy, decreased passive stiffness, an d increased AS, and increased collagen concentration causes myocardial dias tolic dysfunction with no effect on systolic function.