Interactions of renal prostaglandins with the renin-angiotensin system

Effects of indomethacin and (+/-)-propranolol on the cardiovascular and renin responses to vasoactive intestinal polypeptide (VIP) infusion in man

The mechanisms of the cardiovascular and renin responses to vasoactive intestinal polypeptide (VIP) are unclear. Rabbit studies suggest that VIP-induced tachycardia is largely beta-adrenoceptor mediated, but that the renin response may be partially prostaglandin-dependent. To examine the relative importance of prostaglandins and reflex sympathetic activation in the haemodynamic and renin responses to VIP infusion in man, we completed two randomised single-blind crossover studies in two groups of six healthy male volunteers (aged 24-35 years). We recorded the effects of indomethacin and propranolol pretreatment on VIP-related changes in heart rate (HR), blood pressure (BP), forearm vascular resistance (FVR), plasma renin activity (PRA), plasma noradrenaline (PNA) and plasma arginine vasopressin (AVP) concentrations. Intravenous VIP (calculated dose: 6 pmol kg-1 min-1) produced cutaneous flushing, increased HR and PRA, decreased FVR, but did not alter mean arterial BP or AVP levels. Indomethacin (375 mg over 3 days) lowered basal PRA and propranolol (circa 40 mg i.v. over 60 min) decreased resting HR and increased FVR. Although indomethacin and propranolol reduced the absolute rise in PRA and HR, respectively, during VIP infusion, the percentage changes were no different from control. Neither drug altered the flush response to VIP and propranolol did not affect the fall in FVR. We conclude that the measured cardiovascular responses to VIP infusion in man are probably direct and do not involve a significant contribution from reflex sympathetic stimulation, nor prostaglandin release.

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.

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.

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.

Chemically induced renal papillary necrosis and upper urothelial carcinoma. Part 1

In the past, renal papillary necrosis (RPN) has been commonly associated with long-term abusive analgesic intake, but over recent years a wide variety of industrially and therapeutically used chemicals have been shown to induce this lesion experimentally or in man. Destruction of the renal papilla may result in: (1) secondary degenerative cortical changes which precede chronic renal failure or (2) a rapidly metastasizing upper urothelial carcinoma, which has a very poor prognosis. This article will briefly review the published data on the morphology, function, and biochemistry of the normal renal medulla and the pathology associated with RPN, together with the secondary changes which give rise to cortical degeneration or epithelial carcinoma. It will then examine in detail those chemicals which have been reported to cause RPN in an attempt to delineate structure-activity relationships. Finally, the many different theories that have been proposed to explain the pathophysiology of RPN will be examined and an hypothesis will be put forward to explain the primary pathogenesis of the lesion and its secondary consequences.

Chemically induced renal papillary necrosis and upper urothelial carcinoma. Part 2

In the past, renal papillary necrosis (RPN) has been commonly associated with long-term abusive analgesic intake, but over recent years a wide variety of industrially and therapeutically used chemicals have been shown to induce this lesion experimentally or in man. Destruction of the renal papilla may result in: (1) secondary degenerative cortical changes which precede chronic renal failure or (2) a rapidly metastasizing upper urothelial carcinoma, which has a very poor prognosis. This article will briefly review the published data on the morphology, function, and biochemistry of the normal renal medulla and the pathology associated with RPN, together with the secondary changes which give rise to cortical degeneration or epithelial carcinoma. It will then examine in detail those chemicals which have been reported to cause RPN in an attempt to delineate structure-activity relationships. Finally, the many different theories that have been proposed to explain the pathophysiology of RPN will be examined and an hypothesis will be put forward to explain the primary pathogenesis of the lesion and its secondary consequences.

Studies on the renin response to vasoactive intestinal polypeptide (VIP) in the conscious rabbit

Vasoactive intestinal polypeptide (VIP) has been found within the renal cortex and is believed to be a neurotransmitter. Although it produces systemic vasodilatation and renin release, the exact mechanism of the latter response is uncertain. When infused into conscious rabbits, VIP elicits a rise in plasma renin activity (PRA) and an increase in heart rate. The rise in PRA is unaltered by pretreatment with propranolol, but is attenuated by indomethacin. The tachycardia is inhibited by propranolol, but unaffected by indomethacin. We conclude that the renin response to VIP is in part prostaglandin-dependent and that the heart rate response is due to direct or reflex beta-adrenoceptor stimulation.

Mononuclear phagocyte system of the mouse defined by immunohistochemical localization of antigen F4/80. Identification of resident macrophages in renal medullary and cortical interstitium and the juxtaglomerular complex

Macrophages have been identified in mouse kidney by immunohistochemical localization of the macrophage-specific antigen F4/80. They constitute the majority of the renal medullary interstitial cell population and are also found in contact with cortical distal and proximal tubules and Bowman's capsule. They are a physical component of the juxtaglomerular complex.