Oxygen dependence and energy turnover in normal and hypertrophic rat portal vein

Oxygen consumption (J₀₂), lactate production (J_LA), and active force were studied on rat portal veins that had hypertrophied in response to a 5 days period of increased transmural pressure. The vessels were mounted in vitro at optimum lengths for force development. The walls of the hypertrophic (H) veins had in comparison to their controls (C) an increased cross-sectional area (1.14plusmn;0.05 vs. 0.46±0.03 mm², S.E., n= 12). The H veins had a diminished or absent spontaneous contractile activity in contrast to C. The influence of surrounding P_O2 on amplitude of K⁺-induced contractures was studied in an open organ bath. For both Cand H veins a decline in force was seen at P_O2levels around 275 mmHgand below. Energy metabolism was studied in a closed glass chamber (volume 1.2 ml) at a P_O2of 290 mmHg. In comparison to recordings at 690 mmHg, J_LA and active force were unaltered in both groups indicating a sufficient O₂ supply. For veins relaxed in Ca²⁺-free solution J_O2and J_LA were higher in H veins compared to C if expressed per unit vessel length (J_O2: 0.47±0.03 vs. 0.20±0.02, J_LA: 0.66±0.09 vs. 0.22±0.03 nmol/min×mm, n= 6). When the comparisons were made per unit weight J_O2 was similar, about 0.38 μmol/min×g whereas J_LA was higher in the H group (0.53±0.04 vs. 0.38±0.05 μmol/min×g). Contractures were elicited in high-K⁺solutions with varied amounts of Ca²⁺added. Maximal force per unit area was lower for H veins compared to C (9.5 ± 1.6 vs. 16.3±3.3 mN/mm²). For both groups J_O2 increased with active force. J_LA increased with force for C but was unaltered for H veins. The relation between calculated ATP production and force was less steep for H indicating a lower metabolic tension cost.