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.