FAILURE OF PROSTAGLANDINS TO MODULATE THE TIME-COURSE OF BLOOD-FLOW DURING DYNAMIC FOREARM EXERCISE IN HUMANS

The time course and magnitude of increases in brachial artery mean blo od velocity (MBV; pulsed Doppler), diameter (D; echo Doppler), mean pe rfusion pressure (MPP; Finapres), shear rate (gamma = 8 . MBV/D), and forearm blood flow (FBF = MBV . 7 pi r(2)) were assessed to investigat e the effect that prostaglandins (PGs) have on the hyperemic response on going from rest to rhythmic exercise in humans. While supine, eight healthy men performed 5 min of dynamic handgrip exercise by alternate ly raising and lowering a 4.4-kg weight (similar to 10% maximal volunt ary contraction) with a work-to-rest cycle of 1:1 (s/s). When the exer cise was performed with the arm positioned below the heart; the rate o f increase in MBV and gamma was faster compared with the same exercise performed above the heart. Ibuprofen (Ibu; 1,200 mg/day, to reduce PG -induced vasodilation) and placebo were administered orally for 2 days before two separate testing sessions in a double-blind manner. Restin g heart rate was reduced in Ibu (52 +/- 3 beats/min) compared with pla cebo (57 +/- 3 beats/min) (P < 0.05) without change to MPP. With place bo, D increased in both arm positions from similar to 4.3 mm at rest t o similar to 4.5 mm at 5 min of exercise (P < 0.05). This response was not altered with Ibu (P > 0.05). Ibu did not alter the time course of MBV or forearm blood flow (P > 0.05) in either arm position. The gamm a was significantly greater in Ibu vs. placebo at 30 and 40 s of above the heart exercise and for all time points after 25 s of below the he art exercise (P < 0.05). Because PG inhibition altered the time course of gamma at the brachial artery, but not FBF, it was concluded that P Gs are not essential in regulating the blood flow responses to dynamic exercise in humans.