Hypoxic Acclimation Negatively Impacts the Contractility of Steelhead Trout (Oncorhynchus mykiss) Spongy Myocardium.
Cardiac stroke volume (SV) is compromised in Atlantic cod and rainbow trout following acclimation to hypoxia (i.e., 40% air saturation; ~ 8 kPa O2) at 10-12oC, and this is not due to changes in heart morphometrics or maximum achievable in vitro end-diastolic volume. To examine if this diminished SVmay be related to compromised myocardial contractility, we used the work loop method to measure work and power in spongy myocardial strips from normoxia- and hypoxia-acclimated steelhead trout when exposed to decreasing PO2levels (21 to 1.5 kPa) at several frequencies (30 - 90 contractions min-1) at 14oC (their acclimation temperature). Work required to lengthen the muscle, as during filling of the heart, was strongly frequency dependent (i.e., increased with contraction rate), but was not affected by hypoxic acclimation or test PO2. In contrast, while shortening work was less frequency dependent, this parameter and net work (and power): 1) were consistently lower (by ~ 30 - 50 and ~ 15%, respectively) in strips from hypoxia-acclimated fish; and 2) fell by approximately 40 - 50% in both groups from 20 to 1.5 kPa PO2, despite the already reduced myocardial performance in the hypoxia-acclimated group. In addition, strips from hypoxia-acclimated trout showed a poorer recovery of net power (by ~ 15%) when returned to normoxia. These results strongly suggest that hypoxic acclimation reduces myocardial contractility, and in turn, may limit SV(possibly by increasing end-systolic volume), but that this diminished performance does not improve the capacity to maintain myocardial performance under oxygen limiting conditions.
PubMed Abstracts
PubMed Abstracts