Prostaglandins and blood pressure control

Effect of non-steroidal anti-inflammatory drugs on control of hypertension by beta-blockers and diuretics

The effect of sulindac on renal function and blood pressure was compared with those of placebo, piroxicam, and naproxen in 20 patients with primary hypertension being treated with a diuretic and a beta-blocker. Although the three non-steroidal anti-inflammatory drugs (NSAIDs) did not differ in their effect on renal function (weight, glomerular filtration rate, creatinine clearance) or on serum thromboxane and plasma 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha), blood pressure was significantly lower with sulindac than with placebo, piroxicam, or naproxen. These differences were associated with less renal cyclooxygenase inhibition by sulindac (reflected by urinary thromboxane B2 and 6-keto PGF1 alpha) than by other NSAIDs. The findings suggest that the blood pressure differences reflect vasodilation due to differences in the balance between systemic and renal effects of the NSAIDs.

Renal prostaglandins

Contradictions persist as to the role of PG in the regulation of renal blood flow and function. Many conflicting data can now be explained by the fact that anesthetized animals often yield different results from conscious, chronically instrumented animals. Further utilization of conscious animals and the continued development of more specific assays and inhibiting agents promises to better characterize the actions of these hormones.

The arthritic patient with hypertension: selection of an NSAID

Vasodilator prostaglandins produced in the renal medulla have a role in blood pressure regulation, beyond modulation of sodium and water retention. Systemic vasodilation resulting from effects of renomedullary prostaglandins lowers systemic vascular resistance, and administration of NSAIDs elevates blood pressure in hypertensive patients treated with diuretics and/or beta blockers, in patients with myocardial infarction, and in patients taking sympathomimetic agents such as phenylpropanolamine. Aspirin, which appears in the urine as salicylic acid (which has no effect on cyclooxygenase) has not been implicated as a drug which attenuates blood pressure control. Similarly, sulindac, the active sulfide metabolite of which is not filtered, does not inhibit renal synthesis of prostaglandins, though given in doses sufficient to inhibit serum thromboxane and 6-keto PGF 1-alpha. In a double-blind complete crossover study of blood pressure and renal function in hypertensive patients controlled with timolol-hydrochlorothiazide, sulindac lowered blood pressure significantly, whereas naproxen and piroxicam significantly raised blood pressure, in the absence of any effect on GFR, plasma renin, weight, creatinine clearance, or urinary sodium. It is suggested that for arthritic patients with hypertension, the NSAIDs of choice are aspirin and sulindac.

Interference by sulphinpyrazone with the antihypertensive effects of oxprenolol

The interfering effect of sulphinpyrazone, a uricosuric agent which reduces the activity of cyclo-oxygenase, with the antihypertensive activity of oxprenolol, a non-cardioselective beta-blocker with sympathomimetic activity, has been evaluated. Ten patients with primary arterial hypertension of mild to moderate degree entered a randomized double-blind cross-over study versus placebo. They were given oxprenolol + placebo or oxprenolol + sulphinpyrazone for 15 days, and then the treatments were crossed-over for a further 15 days. Oxprenolol significantly reduced blood pressure (161 +/- 3/101 +/- 1 vs 149 +/- 4/96 +/- 2 mmHg) and heart rate (72 +/- 3 vs 66 +/- 3 beats/min). During administration of the combination with sulphinpyrazone the blood pressure increased to its pretreatment level (156 +/- 5/101 +/- 2 mmHg). The effect of oxprenolol on heart rate was not influenced by the combined treatment (67 +/- 6 beats/min). The results may be explained by 1) sulphinpyrazone-induced inhibition of prostaglandin synthesis, which could interfere with the antihypertensive activity of oxprenolol, or 2) sulphinpyrazone-induced acceleration of the metabolism of oxprenolol.

Presence of negative inotropic agents in canine plasma during positive end-expiratory pressure

Application of positive end-expiratory pressure (PEEP) will reduce cardiac output (CO). Humoral mediation of this event by circulating negative inotropic agents was examined using a rat papillary muscle bioassay. Twenty-seven dogs were anesthetized with an iv pentobarbital infusion. Plasma was obtained before and after 30 minutes of PEEP. The plasma was oxygenated in a small (4.5-ml) papillary muscle chamber using a diffusion membrane. An average PO2 of 416 mm Hg was achieved. PEEP plasma reduced developed tension (Tpd) from 2.16 +/- 1.0 to 1.90 +/- 1.05 g (P less than 0.0001). A fall in Tpd was observed whether or not CO was maintained constant with fluid infusion. Resting tension was unchanged. The percent reduction in Tpd correlated with the fall in CO (r = 0.63, P less than 0.01) when fluid was not infused to maintain CO. Reapplication of control plasma restored Tpd. Barbiturate levels in anesthetized dogs rose from 17.3 to 19.4 microns/ml during PEEP (P less than 0.1). Addition of pentobarbital to normal plasma led to a slight decrease in Tpd only when the concentration exceeded 99 microns/ml. In three experiments on ex vivo perfused hearts, application of PEEP led to lowering of peak systolic pressure (PSP) within 5 minutes. Removal of PEEP restored PSP in a similar time. The results support the hypothesis that the decline in CO with PEEP is mediated in part by a circulating negative inotropic agent.

Blood pressure and adipose tissue linoleic acid

In a natural, "free-living population" of 650 men, surveyed with the purpose of health assessment within an epidemiological design, a strongly significant negative correlation between the relative linoleic acid composition of adipose tissue and blood pressures was found (P less than 0.001). This correlation remained significant when age and weight were statistically controlled for. Thus, dietary, lipid-lowering linoleic acid seems to effect blood pressures as well in a favorable way.

Changes in hormonal activities relative to the severity of essential hypertension

Endocrine activity in patients with essential hypertension was studied by measuring the urinary excretion of catecholamines, prostaglandin E (PGE) and cyclic adenosine monophosphate (cAMP). Simultaneously, plasma renin activity, concentrations of serum sodium, potassium, blood urea nitrogen (BUN) and creatinine were determined. Systolic blood pressure and BUN increased progressively with age until the sixth decade. Urinary excretion of norepinephrine was correlated with the systolic blood pressure. In contrast, plasma renin activity and urinary excretion of PGE decreased progressively with the increase in systolic blood pressure. Although the cause of essential hypertension is not known, it is suggested that hypertension accelerates the aging process in the kidney and thus decreases renal PGE synthesis. This decrease of PGE in turn causes a reduction of plasma renin activity, possibly either by accelerating the retention of sodium and water or by failing to stimulate renin synthesis. A decrease of PGE may also potentiate the vasopressor action of norepinephrine.

Central cardiovascular and thermal effects of prostaglandin F2 alpha in rats

Administration of PGF2 ALPHA (0.2--6.4 micrograms) into the lateral cerebral ventricle (i.c.v.) induced dose-dependent increases in blood pressure, heart rate and body temperature in urethane-anaesthetised rats, but had no effect on these parameters when the same dose range was administered intravenously. Peripheral pretreatment with sodium meclofenamate (50 mg/kg s.c.) shifted all the dose-response curves for PGF2 alpha (i.c.v.) to the left, but indomethacin (50 mg/kg s.c.) did not significantly affect those changes. Central pretreatment with sodium meclofenamate or indomethacin (1.25 mg per rat i.c.v.) failed to modify significantly the effects of centrally administered PGF2 alpha. The results support previous suggestions that PGF2 alpha may participate in the central control of the cardiovascular and thermoregulatory systems, and also suggest that there may be differences in the sites and/or modes of action between sodium meclofenamate and indomethacin.

Perspectives in coronary prevention

The seeds of premature coronary heart disease are often sown in childhood and it is the developing arteries of children which are the most susceptible. Paediatricians and all who work with them have the earliest and most promising opportunities for prevention. Coronary protection can be added to the potential advantages of breast feeding and to ensure appropriate fatty acid balance throughout weaning. It is reasonable to accept the strong consensus of opinion on diet reflected in the reports of the eighteen national committees. They are: to reduce total fat intake to 30-35% of the energy, to restrict consumption of saturated fat, cholesterol, sugar, and salt, to increase unrefined carbohydrate and polyunsaturated fat, and to maintain a P/S balance of 1.0-1.5:1. Food is the fundamental coronary risk factor, but others may add insult to injury. Smoking, hypertension, obesity, lack of exercise, and stress, each of which is related to behaviour, may start in childhood. Smoking doubles the overall risk CHD and increases it ten times in males under 45 years old. Good habits, including food preferences and eating patterns learned early, are those most likely to be continued. School meals require and should match revised nutritional education. The co-operation of the food industry is essential and can be anticipated, but it requires a clear lead by paediatricians. The nutritional advice should come from the medical profession. Every contact with children and their parents provides an opportunity for enquiry and giving advice.

Bartter's syndrome: an overview

Bartter's syndrome, which is characterized by hypokalemic hypochloremic alkalosis, renal juxtaglomerular hyperplasia, elevated renin and aldosterone, and normal or low blood pressure, has been ascribed to a variety of etiologies. Most recently, the prostaglandins have been in the forefront of the pathophysiologic discussion. Two cases with appropriate renal biopsies are reviewed, as are the clinicopathologic pathways. It is important that strict criteria be applied, and confirmation by renal biopsy is urged.