Effect of Cyclooxygenase Inhibition on Peripheral Venous Distension Reflex in Healthy Humans.

BACKGROUND: Peripheral venous distension evokes a pressor reflex (venous distension reflex). Afferent group III and IV nerves innervating veins are suggested as the afferent arm of the venous distension reflex. Prostaglandins stimulate/sensitize group III/IV nerves. We hypothesized that inhibition of prostaglandin synthesis by local COX (cyclooxygenase) blockade would attenuate the muscle sympathetic nerve activity (MSNA) and blood pressure responses to venous distension.

METHODS: Nineteen healthy volunteers (age, 27±5 years) participated in the study with 2 visits. To induce venous distension, a volume of solution (saline alone or 9 mg ketorolac tromethamine in saline) was infused into the vein in the antecubital fossa of an arterially occluded forearm. During the procedure, beat-by-beat heart rate , blood pressure and MSNA were recorded simultaneously. The vein size was measured with ultrasound.

RESULTS: In both visits, the venous distension procedure significantly increased blood pressure, heart rate, and MSNA (all, P <0.05). The increase in mean arterial pressure and MSNA in the ketorolac visit was significantly lower than in the control visit (∆ mean arterial pressure, 7.0±6.2 versus 13.8±7.7 mm Hg; ∆MSNA, 6.0±7.1 versus 14.8±7.7 bursts/min; both, P <0.05). The increase in vein size induced by the infusion was not different between visits.

CONCLUSIONS: The presented data show that COX blockade attenuates the responses in MSNA and blood pressure to peripheral venous distension reflex. The results suggest that COX products play a key role in evoking afferent activation responsible for the venous distension reflex.