Left ventricular pressure-volume relationships during normal growth and development in the adult rat - Studies in 8- and 50-week-old male Wistar rats

Aims: Left ventricular (LV) pressure-volume relations provide relatively load-independent indexes of systolic and diastolic LV function, but few data are available on pressure-volume relations during growth and development in the normal adult heart. Furthermore, to quantify intrinsic ventricular function the indexes should be normalized for heart weight. However, in many studies the indexes are reported in absolute terms, or body weight-correction is used as a surrogate for heart weight-correction. Methods: We determined pressure-volume relations in young (8-week-old, n = 13) and middle-aged (50-week-old, n = 19) male Wistar rats in relation to their heart and body weights. The animals were anaesthetized and a 2F pressure-conductance catheter was introduced into the LV to measure pressure-volume relations. Results: Heart and body weights were significantly higher in the 50-week-old rats, whereas the heart-to-body weight ratio was significantly lower (2.74 ± 0.32 vs. 4.41 ± 0.37 mg g^-1, P < 0.001). Intrinsic systolic function, quantified by the slopes of the end-systolic pressure-volume relation (E_ES), the dP/dt_MAX vs. end-diastolic volume relation (S-dP), and the preload recruitable stroke work relation (PRSW), normalized for heart weight, was slightly decreased in the 50-week-old rats (S-dP: -6%, P < 0.004; PRSW: -3%, P < 0.06). Heart weight-corrected diastolic indexes were not significant different. The absolute indexes qualitatively showed the same results, but body-weight corrected pressure-volume indexes showed improved systolic function and significantly depressed diastolic function. Conclusions: Intrinsic systolic function slightly decreases from the juvenile to the middle-aged period in normal male Wistar rats. Furthermore, correction of pressure-volume indexes for body weight is not an adequate surrogate for heart weight-correction in these animals.