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

Oxygen consumption (Jo2), lactate production (JLA), 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 (1.14 +/- 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 Po2 on amplitude of K+-induced contractures was studied in an open organ bath. For both C and H veins a decline in force was seen at Po2 levels around 275 mmHg and below. Energy metabolism was studied in a closed glass chamber (volume 1.2 ml) at a Po2 of 290 mmHg. In comparison to recordings at 690 mmHg. JLA and active force were unaltered in both groups indicating a sufficient O2 supply. For veins relaxed in Ca2+-free solution Jo2 and JLA were higher in H veins compared to C if expressed per unit vessel length (Jo2:0.47 +/- 0.03 vs. 0.20 +/- 0.02, JLA:0.66 +/- 0.09 vs. 0.22 +/- 0.03 nmol/min x mm, n = 6). When the comparisons were made per unit weight Jo2 was similar, about 0.38 mumol/min x g whereas JLA was higher in the H group (0.53 +/- 0.04 vs. 0.38 +/- 0.05 mumol/min x g). Contractures were elicited in high-K+ solutions with varied amounts of Ca2+ added. Maximal force per unit areas was lower for H veins compared to C (9.5 +/- 1.6 vs. 16.3 +/- 3.3 mN/mm2). For both groups Jo2 increased with active force. JLA 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.