Prostaglandins

Prostaglandins are unsaturated fatty acid compounds synthesized from cell membrane phospholipids. They exert their main effects in close proximity to the site of production. The main prostaglandins synthesized in the kidney are PGE 2 (the main renal medullary prostaglandin), PGF 2 , PGD 2 , prostacyclin (PGI 2, the main renal cortical prostaglandin) and thromboxane A 2.

Prostaglandins are important in the maintenance of renal blood flow and glomerular filtration rate in the face of reductions induced by vasoconstrictor stimuli such as angiotensin II, catecholamines and α-adrenergic stimulation. In the presence of renal underperfusion, inhibition of prostaglandin synthesis by non-steroidal anti-inflammatory drugs results in a further reduction in GFR, sometimes sufficiently severe as to cause acute renal failure.

Renal prostaglandins also have a natriuretic renal tubular effect and antagonize the action of antidiuretic hormone. Renal prostaglandins do not regulate salt and water excretion in normal subjects, but in some circumstances, such as chronic renal failure, prostaglandin-induced vasodilatation is important in maintaining renal blood flow.

Patients with chronic renal failure are thus vulnerable to further deterioration in renal function on exposure to non-steroidal anti-inflammatory drugs, as are elderly patients in many of whom renal function is compromised by renal vascular disease and/or the effects of ageing upon the kidney.

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Health Tip

Foods high in substances called purines increase levels of uric acid in the blood, and foods to be avoided include poultry, strawberries, shellfish, game, caffeine and alcohol.