Interaction of prostaglandins with the renin-angiotensin system

COX-2-derived PGE2 triggers hyperplastic renin expression and hyperreninemia in aldosterone synthase-deficient mice

Pharmacological inhibition or genetic loss of function defects of the renin angiotensin aldosterone system (RAAS) causes compensatory renin cell hyperplasia and hyperreninemia. The triggers for the compensatory stimulation of renin synthesis and secretion in this situation may be multimodal. Since cyclooxygenase-2 (COX-2) expression in the macula densa is frequently increased in states of a defective RAAS, we have investigated a potential role of COX-2 and its derived prostaglandins for renin expression and secretion in aldosterone synthase-deficient mice (AS^−/−) as a model for a genetic defect of the RAAS. In comparison with wild-type mice (WT), AS^−/− mice had 9-fold and 30-fold increases of renin mRNA and of plasma renin concentrations (PRC), respectively. Renin immunoreactivity in the kidney cortex of AS^−/− mice was 10-fold higher than in WT. Macula densa COX-2 expression was 5-fold increased in AS^−/− kidneys relative to WT kidneys. Treatment of AS^−/− mice with the COX-2 inhibitor SC-236 for 1 week lowered both renal renin mRNA and PRC by 70%. Hyperplastic renin cells in AS^−/− kidneys were found to express the prostaglandin E₂ receptors EP2 and EP4. Global deletion of EP2 receptors did not alter renin mRNA nor PRC values in AS^−/− mice. Renin cell-specific inducible deletion of the EP4 receptor lowered renin mRNA and PRC by 25% in AS^−/− mice. Renin cell-specific inducible deletion of the EP4 receptor in combination with global deletion of the EP2 receptor lowered renin mRNA and PRC by 70–75% in AS^−/− mice. Lineage tracing of renin-expressing cells revealed that deletion of EP2 and EP4 leads to a preferential downregulation of perivascular renin expression. Our findings suggest that increased macula densa COX-2 activity in AS^−/− mice triggers perivascular renin expression and secretion via prostaglandin E₂.

Anti-inflammatory pharmacotherapy during pregnancy

NSAIDs or cyclooxygenase inhibitors (COX inhibitors), including aspirin, are widely used to treat pain, fever and the articular symptoms of chronic rheumatic diseases. Manifestations of connective tissue or autoimmune diseases are commonly treated with glucocorticosteroids. The effect and side effects of NSAIDs depend on the isoforms of cyclooxygenases that they preferentially or selectively inhibit. The use of COX inhibitors has recently been associated with infertility and miscarriage. The classical nonselective COX inhibitors, including aspirin, do not increase the risk of congenital malformations in humans but administered in the latter part of gestation, they can affect pregnancy and the fetus. The ability of nonselective and selective COX inhibitors to prolong gestation has been used by obstetricians to inhibit premature delivery. The vascular effects of prostaglandin inhibitors can cause constriction of the fetal ductus arteriosus and reduce renal blood flow. These complications have been described for most nonselective COX inhibitors but are increasingly reported also for the selective COX-2 inhibitors. Aspirin, which causes irreversible inhibition of cyclooxygenases, differs from other NSAIDs with regard to indication, effects and side effects. Prematurity, which is increased in pregnancies of women with connective tissue diseases, is an additional risk factor for adverse effects of antenatal exposure to NSAIDs. Therefore, treatment with COX inhibitors should be discontinued at week 32 of gestation. The ability of NSAIDs to compromise reproductive function by inhibition of ovulation and as causative agents for miscarriage is still under debate. Glucocorticosteroids given in early pregnancy are a risk factor for the development of oral clefts. Therefore, the daily dose should be kept to <or= 15 mg during the first trimester. High doses of glucocorticosteroids in the second and third trimester are reserved for flares of autoimmune diseases. Intrauterine fetal growth restriction and premature delivery are possible side effects of high doses.