Plasma catecholamines in man are not influenced by the inhibition of prostaglandin synthesis

Interactions between non-steroidal anti-inflammatory drugs and antihypertensives and diuretics

Non-steroidal anti-inflammatory drugs (NSAIDs) may increase blood pressure and antagonise the effects of antihypertensive agents. They can cause salt and water retention and an increase in extracellular volume. NSAIDs also cause a decrease in prostaglandin synthesis in blood vessel walls which removes a direct vasodilatory influence and also increases the vascular response to vasoconstrictor stimuli. The hypotensive effects of frusemide and captopril are due in part to their stimulation of prostaglandin synthesis. Hence the antagonism of the hypotensive effect of these agents is probably due to NSAID-induced inhibition of prostaglandin synthesis. However, the interactions of NSAIDs with the other antihypertensive agents may not be related to inhibition of antihypertensive-induced release of prostaglandin but to independent and opposing actions of the NSAIDs on the various physiological mechanisms which regulate blood pressure. Clinicians should remain alert to these potential drug interactions.

Active and acid-activable inactive renin during inhibition by indomethacin of prostaglandin synthesis in sodium-replete man

The effect of inhibition of prostaglandin synthesis by indomethacin on active renin and on acid-activable inactive renin was studied in nine healthy, sodium-replete men, both at rest and exercise. These volunteers were investigated after pretreatment with placebo or indomethacin, 150 mg daily for 3 days. Indomethacin induced a decrease in active (P = 0.004), total (P less than 0.001) and inactive (P = 0.02) renin at rest recumbent and at rest, sitting. Inhibition of prostaglandins with indomethacin reduced (P less than 0.001) active and total renin at each level of work load but not (P = 0.32) inactive renin. However the exercise-induced stimulation (P less than 0.05) of active and of total renin still occur during indomethacin. Indomethacin reduced (P less than 0.001) at rest, sitting and at maximal exercise the plasma concentrations of immunoreactive prostaglandins E2, prostaglandin F2 alpha and 13, 14-dihydro-15-keto-prostaglandin F alpha; the urinary excretion of immunoreactive prostaglandin E2 and F2 alpha were also reduced.

Influence of prostaglandin inhibition on dihydralazine induced acute effects in patients with essential hypertension

In order to determine whether vasodilator prostaglandins (PG) contribute to the acute vascular and endocrine responses to intravenously administered dihydralazine, we examined its effects on systolic and diastolic blood pressure (BP), heart rate (HR), plasma renin activity (PRA) and the plasma catecholamines (CA) noradrenaline (NA), adrenaline (A) and dopamine (DA) as well as on sodium, potassium and creatinine clearance (CNa, CK and CCr respectively), urinary flow rate, urinary catecholamines (NA, A, DA) and iPGE2 and i6-keto-PGF1 alpha excretion rate in six patients (three females, three males) with essential hypertension before and after PG synthesis inhibition by the nonsteroidal, anti-inflammatory agent diclofenac. Diclofenac, which reduced urinary iPGE2 and i6-keto-PGF1 alpha excretion by 62% (P = 0.026) and 45% (P = 0.037), respectively, antagonized dihydralazine induced diastolic BP reduction (P = 0.0009), HR increase (P = 0.01), noradrenaline and adrenaline increase in plasma (P = 0.02 and P = 0.05, respectively), increase in urine flow rate (P = 0.03), sodium clearance (P = 0.01) and tended to reduce PRA. We conclude that dihydralazine-mediated changes can be reduced by cyclo-oxygenase inhibition, most likely on the basis of a reduction of its effect on peripheral resistance, thereby leading to less reflex activation of the sympathetic nervous and renin-angiotensin systems.

Release and vasoactive actions of catecholamines during inhibition of prostaglandin synthesis in normal man

To assess the effect of prostaglandin inhibition upon the vasoactive actions of endogenous and exogenous catecholamines in healthy man, indomethacin (150 mg/day for 3 days) was administered to six healthy men in the sodium-repleted state. Pretreatment with indomethacin did not interfere with the response of blood pressure and pulse rate to orthostasis (10 minutes), a cold pressor test (2 minutes), and the intravenous (i.v.) administration of norepinephrine (NE) (50, 100, and 200 ng kg-1 min-1). Basal plasma concentrations of epinephrine (E) and NE as well as the concentrations of E during orthostasis and cold pressor test remained uninfluenced by pretreatment with indomethacin. While the release of NE during orthostasis appeared to be suppressed in the indomethacin-treated state, it was unchanged during the cold pressor test. These results indicate that inhibition of endogenous prostaglandin synthesis may suppress the release of NE, but does not have a major impact on the vasoactive actions of endogenous and exogenous catecholamines in normal men.

The effect of sulfinpyrazone on the response to sympathetic nervous system stimulation

The purpose of this study was to determine if sulfinpyrazone has a direct action on sympathetic nerve endings to prevent release of the transmitter. Pre-synaptic and post-synaptic events as well as direct sympathetic nervous system stimulation were tested in 15 alpha-chloralose anesthetized cats before and 1 hour after sulfinpyrazone (100 mg . kg-1, i.v.). Heart rate response to cardiac accelerator nerve stimulation or to increasing doses of isoproterenol was not significantly depressed by sulfinpyrazone. In addition, no alteration in the reflex activation of the sympathetic nervous system in response to histamine was observed following sulfinpyrazone. Both norepinephrine and epinephrine levels were similar to those levels reported previously by Smith and Robinson for (7) untreated cats. We conclude sulfinpyrazone has no direct depressing effect on the sympathetic nerve endings and that this mechanism cannot explain the reported beneficial effect of sulfinpyrazone on coronary occlusion induced arrhythmias.

Role of the prostaglandin in norepinephrine release during augmented renal sympathetic nerve activity in the dog

To determine the role of the prostaglandins on renal norepinephrine release, the effect of inhibition of prostaglandin synthesis was examined in anesthetized dogs during reflex activation of the renal adrenergic nerves. Hypotension increased the renal vein plasma concentrations of norepinephrine from 380 +/- 59 to 608 +/- 106 pg/ml (mean +/- SEM; P less than 0.01) and of PGE2 from 55 +/- 7 to 81 +/- 41 pg/ml (P less than 0.05). Subsequent administration of indomethacin or meclofenamate lowered the renal venous concentration of PGE2 to 26 +/- 3 pg/ml (P less than 0.01), had no significant effect on the norepinephrine concentration (620 +/- 89 pg/ml). Administration of indomethacin or meclofenamate to dogs with sodium depletion lowered renal venin plasma concentration of PGE2 from 108 +/- 40 to 20 +/- 3 pg/ml (0.05 less than P less than 0.1) but had no effect on the renal venous norepinephrine concentration (475 +/- 50 vs. 397 +/- 46 pg/ml). In dogs fed a normal salt diet, inflation of a balloon placed in the thoracic inferior vena cava lowered cardiac output and increased the renal venous concentrations of norepinephrine from 212 +/- 60 to 496 +/- 112 pg/ml (P less than 0.01) and of PGE2 from 28 +/- 5 to 96 +/- 18 pg/ml (P less than 0.01). Subsequent administration of indomethacin lowered the renal venous concentration of PGE2 to 16 +/- 5 pg/ml (P less than 0.01), but had no significant effect on the concentration of norepinephrine (548 +/- 91 pg/ml). During the three experimental conditions examined, renal blood flow was lowered by inhibition of prostaglandin synthesis. These results in the dog suggest that the attenuating effect that prostaglandins exert on the renal vascular action of the adrenergic nerves is not due to inhibition of norepinephrine release.

Effects of moderate short-term potassium depletion in normal humans. The role of prostaglandins

The role of prostaglandins (PG) in the effects of potassium (K+)depletion was studied in six normal women. A mean K+-deficit of 220 mEq was induced with and without concomitant treatment with indomethacin (150 mg/day). Mean serum K+ concentration decreased from 4.2 +/- (S.E.) 0.1 to 3.2 +/- 0.1 mEq/L without indomethacin and from 4.1 +/- 0.1 to 3.2 +/- 0.1 mEq/L with indomethacin. "Supine" and "upright" plasma renin activity (PRA) and plasma norepinephrine concentration (NE) were unaltered by K+ -depletion alone but decreased with indomethacin. Plasma aldosterone (PA) was suppressed during K+-depletion (control: 7.2 +/- 2.6 ng/dl supine, 19.3 +/- 8.1 ng/dl upright; K+-depletion: 2.6 +/- 0.3 ng/dl supine, 5.5 +/- 1.3 ng/dl upright) and was paralleled by a decrease in urinary aldosterone. K+- depletion decreased urinary PGE2 from 667 +/- 133 to 343 +/- 60 ng/day (P less than 0.025) without a change in PGF2 alpha. The dose of exogenous angiotensin II (A II) which increased diastolic blood pressure by 20 mm Hg (pressor dose) was 7.1 +/- 1.4 ng/kg/min during control and increased to 11.0 +/- 0.7 ng/kg/min during K+-depletion (P less than 0.05). Indomethacin increased the sensitivity to A II both during control (pressor dose: 4.9 +/- 0.6 ng/kg/min) and K+ - depletion (pressor dose: 6.0 +/- 1.0 ng/kg/min). These results indicate that in healthy subjects, moderate short-term K+-depletion does not affect PRA or NE but decreases production of aldosterone and PGE2 by the kidney. The changes in vascular sensitivity to exogenous A II during K+-depletion and indomethacin and the decreases in plasma NE and PRA during indomethacin may be explained by changes in vascular vasodilator PG.

Plasma dopamine: source, regulation, and significance

Plasma dopamine is present in free form in a concentration approximately equivalent to that of epinephrine and about 25% that of norepinephrine. It originates in a variety of tissues including sympathetic nerves and adrenal, and the percentage originating from the various sources remains unknown. Events that are associated with increases in sympathetic activity such as stress, exercise, standing, or hypovolemia are associated with increases in plasma dopamine concentration, although the responses may be of considerably smaller magnitude than those for plasma norepinephrine and epinephrine. The functional importance of dopamine in the periphery and of changes in circulating dopamine remain only poorly defined. These include possible roles in neurotransmission in sympathetic ganglia, altering renal vascular bed, modulation of aldosterone secretion and sodium excretion, mediation of certain stress responses, and others yet to be revealed.

Evidence against prostaglandin modulation of cardioaccelerator nerve activity in the anesthetized dog

The hypothesis that prostaglandins have a modulatory role in adrenergic neurotransmitter release was tested in the anesthetized dog. Inhibition of prostaglandin synthesis with indomethacin (10 mg/kg, i.v.) did not alter positive chronotropic responses to cardioaccelerator nerve stimulation or blood pressure responses to exogenous norepinephrine. In the presence of indomethacin, infusions of PGE, (0.01 and 0.1 microgram kg-1 min-1) also failed to influence the responses to cardioaccelerator nerve stimulation although the blood pressure responses to exogenous norepinephrine were reduced in a dose-related manner. It was concluded that endogenous prostaglandins and exogenous PGE2, the purported physiological inhibitor of neurotransmitter release in cardiac tissue, do not play a role in modulating chronotropic responses during cardioaccelerator nerve stimulation in the anesthetized dog.

Studies on the clinical pharmacology of prazosin. II: The influence of indomethacin and of propranolol on the action and disposition of prazosin

1 The possibility of pharmacodynamic and pharmacokinetic interactions of prazosin with indomethacin and with propranolol have been studied in healthy subjects. 2 In four out of nine individuals indomethacin considerably attenuated prazosin-induced hypotension, but noradrenaline concentrations were unchanged from the day when blood pressure fell greatly. The effect of prazosin in the other five subjects was not influenced by indomethacin. 3 Indomethacin prevented the rise in plasma renin activity seen following administration of prazosin alone. 4 Propranolol did not prevent the syncope associated with the first dose of prazosin. 5 Propranolol affected neither the absorption nor elimination of prazosin. 6 It is concluded that in certain subjects indomethacin can largely prevent the hypotensive effect of parazosin, possible by increasing adrenergic receptor sensitivity. The theoretical possibility that propranolol could influence prazosin disposition or syncope was not substantiated.