Prostaglandin contribution to postexercise hyperemia is dependent on tissue oxygenation during rhythmic and isometric contractions

The role of prostaglandins (PGs) in exercise hyperemia is controversial. We tested their contributions in moderate intensity forearm exercise, whether their release is oxygen (O ₂)-dependent or affected by aging. A total of 12 young (21 ± 1 years) and 11 older (66 ± 2 years) recreationally active men performed rhythmic and isometric handgrip contractions at 60% maximum voluntary contraction for 3 min during air breathing after placebo, after cyclooxygenase (COX) inhibition with aspirin, while breathing 40% O ₂ and during their combination (aspirin + 40% O ₂). Forearm blood flow (FBF) was recorded with venous occlusion plethysmography (forearm vascular conductance (FVC): FBF/mean arterial pressure). Venous efflux of PGI ₂ and PGE ₂ were assessed by immunoassay. Postcontraction increases in FVC were similar for rhythmic and isometric contractions in young and older men, and accompanied by similar increases in efflux of PGI ₂ and PGE ₂. Aspirin attenuated the efflux of PGI ₂ by 75%–85%, PGE ₂ by 50%–70%, (p <.05 within group; p >.05 young versus. older), and postcontraction increases in FVC by 22%–27% and 17%–21% in young and older men, respectively (p <.05 within group and young versus. older). In both age groups, 40% O ₂ and aspirin + 40% O ₂ caused similar inhibition of the increases in FVC and efflux of PGs as aspirin alone (p <.05 within group). These results indicate that PGs make substantial contributions to the postcontraction hyperemia of rhythmic and isometric contractions at moderate intensities in recreationally active young and older men. Given PGI ₂ is mainly released by endothelium and PGE ₂ by muscle fibers, we propose PG generation is dependent on the contraction-induced falls in O ₂ at these sites.