Repeated sympathetic stimuli elicit the decline and disappearance of prostaglandin modulation and an increase of vascular resistance in humans

Effect of cyclooxygenase inhibition on the inspiratory muscle metaboreflex-induced cardiovascular consequences in men

Inspiratory muscle metaboreflex activation increases mean arterial pressure (MAP) and limb vascular resistance (LVR) and decreases limb blood flow (Q̇_L). Cyclooxygenase (COX) inhibition has been found to attenuate limb skeletal muscle metaboreflex-induced increases in muscle sympathetic nerve activity. We hypothesized that compared with placebo (PLA), COX inhibition would attenuate inspiratory muscle metaboreflex-induced 1) increases in MAP and LVR and 2) decreases in Q̇_L Seven men (22 ± 1 yr) were recruited and orally consumed ibuprofen (IB; 10 mg/kg) or PLA 90 min before performing the cold pressor test (CPT) for 2 min and inspiratory resistive breathing task (IRBT) for 14.9 ± 2.0 min at 65% of maximal inspiratory pressure. Breathing frequency was 20 breaths/min with a 50% duty cycle during the IRBTs. MAP was measured via automated oscillometry, Q̇_L was determined via Doppler ultrasound, and LVR was calculated as MAP divided by Q̇_L Electromyography was recorded on the leg to ensure no muscle contraction occurred. The 65% IRBT led to greater increases (P = 0.02) in 6-keto-prostaglandin-F_1α with PLA compared with IB. IB, compared with PLA, led to greater (P < 0.01) increases in MAP (IB: 17 ± 7 mmHg vs. PLA: 8 ± 5 mmHg) and LVR (IB: 69 ± 28% vs. PLA: 52 ± 22%) at the final minute of the 65% IRBT. The decrease in Q̇_L was not different (P = 0.72) between IB (-28 ± 11%) and PLA (-27 ± 9%) at the final minute. The increase in MAP during the CPT was not different (P = 0.87) between IB (25 ± 11 mmHg) and PLA (24 ± 6 mmHg). Contrary to our hypotheses, COX inhibition led to greater inspiratory muscle metaboreflex-induced increases in MAP and LVR.NEW & NOTEWORTHY Cyclooxygenase (COX) products play a role in activating the muscle metaboreflex. It is not known whether COX products contribute to the inspiratory muscle metaboreflex. Herein, we demonstrate that COX inhibition led to greater increases in blood pressure and limb vascular resistance compared with placebo during inspiratory muscle metaboreflex activation.

Cyclooxygenases 1 and 2 differentially regulate blood pressure and cerebrovascular responses to acute and chronic intermittent hypoxia: implications for sleep apnea

Background

Obstructive sleep apnea (OSA) is associated with increased risk of cardiovascular and cerebrovascular disease resulting from intermittent hypoxia (IH)‐induced inflammation. Cyclooxygenase (COX)‐formed prostanoids mediate the inflammatory response, and regulate blood pressure and cerebral blood flow (CBF), but their role in blood pressure and CBF responses to IH is unknown. Therefore, this study's objective was to determine the role of prostanoids in cardiovascular and cerebrovascular responses to IH.

Methods and Results

Twelve healthy, male participants underwent three, 6‐hour IH exposures. For 4 days before each IH exposure, participants ingested a placebo, indomethacin (nonselective COX inhibitor), or Celebrex^® (selective COX‐2 inhibitor) in a double‐blind, randomized, crossover study design. Pre‐ and post‐IH blood pressure, CBF, and urinary prostanoids were assessed. Additionally, blood pressure and urinary prostanoids were assessed in newly diagnosed, untreated OSA patients (n=33). Nonselective COX inhibition increased pre‐IH blood pressure (P≤0.04) and decreased pre‐IH CBF (P=0.04) while neither physiological variable was affected by COX‐2 inhibition (P≥0.90). Post‐IH, MAP was elevated (P≤0.05) and CBF was unchanged with placebo and nonselective COX inhibition. Selective COX‐2 inhibition abrogated the IH‐induced MAP increase (P=0.19), but resulted in lower post‐IH CBF (P=0.01). Prostanoids were unaffected by IH, except prostaglandin E₂ was elevated with the placebo (P=0.02). Finally, OSA patients had elevated blood pressure (P≤0.4) and COX‐1 formed thromboxane A₂ concentrations (P=0.02).

Conclusions

COX‐2 and COX‐1 have divergent roles in modulating vascular responses to acute and chronic IH. Moreover, COX‐1 inhibition may mitigate cardiovascular and cerebrovascular morbidity in OSA.

Clinical Trial Registration

URL: www.clinicaltrials.gov. Unique identifier: NCT01280006

Cyclooxygenase inhibition augments central blood pressure and aortic wave reflection in aging humans

The augmentation index and central blood pressure increase with normal aging. Recently, cyclooxygenase (COX) inhibitors, commonly used for the treatment of pain, have been associated with transient increases in the risk of cardiovascular events. We examined the effects of the COX inhibitor indomethacin (Indo) on central arterial hemodynamics and wave reflection characteristics in young and old healthy adults. High-fidelity radial arterial pressure waveforms were measured noninvasively by applanation tonometry before (control) and after Indo treatment in young (25 ± 5 yr, 7 men and 6 women) and old (64 ± 6 yr, 5 men and 6 women) subjects. Aortic systolic (control: 115 ± 3 mmHg vs. Indo: 125 ± 5 mmHg, P < 0.05) and diastolic (control: 74 ± 2 mmHg vs. Indo: 79 ± 3 mmHg, P < 0.05) pressures were elevated after Indo treatment in older subjects, whereas only diastolic pressure was elevated in young subjects (control: 71 ± 2 mmHg vs. Indo: 76 ± 1 mmHg, P < 0.05). Mean arterial pressure increased in both young and old adults after Indo treatment (P < 0.05). The aortic augmentation index and augmented pressure were elevated after Indo treatment in older subjects (control: 30 ± 5% vs. Indo 36 ± 6% and control 12 ± 1 mmHg vs. Indo: 18 ± 2 mmHg, respectively, P < 0.05), whereas pulse pressure amplification decreased (change: 8 ± 3%, P < 0.05). In addition, older subjects had a 61 ± 11% increase in wasted left ventricular energy after Indo treatment (P < 0.05). In contrast, young subjects showed no significant changes in any of the variables of interest. Taken together, these results demonstrate that COX inhibition with Indo unfavorably increases central wave reflection and augments aortic pressure in old but not young subjects. Our results suggest that aging individuals have a limited ability to compensate for the acute hemodynamic changes caused by systemic COX inhibition.

Exaggerated local hand sympathetic but not renin-angiotensin system activation in patients with primary Raynaud's phenomenon

In Raynaud's disease (RD), an overactivity of sympathetic nervous system (SNS) was hypothesized but only indirect proofs were obtained. Complex interactions between the renin-angiotensin system (RAS) and SNS were reported without clear demonstrations of a RAS involvement. Recently, the use of ACE inhibitors and AT1 receptor antagonists in RD patients showed mixed results. The study of total and regional kinetics of tritiated noradrenaline (NA) and the measurements of local Angiotensin (Ang) I and II arterial-venous gradient were performed in 10 RD patients and 10 controls both in rest conditions and following a cold pressor test (CPT). Hand blood flow (HBF) was measured by strain-gauge plethysmography. Baseline HBF was slightly lower in patients than in controls, but during CPT, it significantly decreased only in RD patients (P < 0.01). Total (3H)-NA clearance and spillover were similar in the two groups throughout the study. On the contrary, baseline hand NA spillover was higher in RD patients than in controls and the difference further increased during CPT. Hand NA spillover was linearly related to HBF (P < 0.001). Arterial-venous Ang I and Ang II gradients were positive without difference between controls and patients throughout the study. In conclusion in RD patients, a pathological waste of NA from sympathetic nervous endings of the hand region, exaggerated by sympathetic stimulation, occurs but an enhanced local Ang II formation was not demonstrable.

Excessive vasoconstriction after stress by the aging kidney: inadequate prostaglandin modulation of increased endothelin activity

The adaptive capacity of the aging kidney to stimulation of the sympathetic nervous system, as induced by a 30-minute mental stress (MS), was assessed in 8 elderly healthy women (68 to 82 years of age) and compared with that of 8 younger women (24 to 40 years of age). The study encompassed 4 consecutive 30-minute periods (baseline, mental stress, recovery 1, and recovery 2). In the elderly subjects, baseline effective renal plasma flow (ERPF)(iodine 131-labeled hippurate clearance) was lower and glomerular filtration rate (GFR)(iodine 125-labeled iothalamate clearance) was proportionally less reduced than in the younger group; the filtration fraction (FF) was higher. The elderly group excreted more endothelin 1 (ET-1) (P < .05), prostaglandin E2 (PGE2), and 6-keto-prostaglandin F1alpha (6-keto PGF1alpha)(P < .001 for both)(radioimmunoassay). Mental stress induced similar increases in blood pressure, heart rate, and plasma catecholamines in the 2 age groups, limited to the stimulation period. In the elderly group, mental stress caused a prolonged decrease in ERPF that reached its maximum 60 minutes after mental stress (-33%, P < .05), while GFR remained constant during the whole experiment, so that FF increased. In the younger subjects, renal hemodynamic changes were limited to the mental stress period. ET-1 increased during mental stress and the first recovery period in the elderly group (+50% and +25%, P < .05) as it did in the younger group, but the elderly group differed from the younger in that vasodilating prostaglandins increased only during mental stress. In conclusion, the aging kidney reacts to adrenergic stimulation with more-pronounced and -prolonged vasoconstriction that is probably caused by a defect in prostaglandin modulation of endothelin activity. Autoregulation of GFR is maintained at the expense of increased intraglomerular pressure.

The effect of indomethacin on the circulatory and plasma noradrenaline responses to cold pressor testing in normal subjects

Prostaglandins may alter neuronal noradrenaline release or vascular responsiveness to sympathoexcitation. The purpose of this study was to determine if indomethacin, a prostaglandin synthesis inhibitor, influences the sympathetic and circulatory adjustments to a commonly utilized laboratory stressor in the clinical assessment of autonomic function, the cold pressor test. Venous plasma noradrenaline levels (n = 8), mean arterial pressure and heart rate (n = 10) were measured in healthy male subjects during immersion of the non-dominant hand in cold water (1 degree C) for 90 s. The subjects were given either placebo or indomethacin (100 mg) in a double-blind manner. The order of administration was counterbalanced and a 1 week period was given for systemic clearance of the drug. The absolute level of mean arterial pressure was elevated during the resting control period after indomethacin treatment (88 in placebo vs. 92 mmHg in indomethacin). Both heart rate and venous plasma noradrenaline levels were similar between trials during the resting control period. Mean arterial pressure and heart rate increased similarly during cold pressor testing in both indomethacin and placebo. Venous plasma noradrenaline levels increased during cold pressor testing 162 +/- 39 vs. 200 +/- 69 pg/ml in indomethacin vs. placebo (p > 0.05), respectively. In addition, perceived pain (peak level = 7 +/- 1 vs. 6 +/- 1 units; indomethacin vs. placebo, respectively) was not different between the trials. These results suggest that administration of indomethacin in a maximal single therapeutic dose, does not affect the sympathetic nervous system or circulatory responsiveness to cold pressor testing. It may not be necessary to discontinue indomethacin prior to autonomic function testing.