Reciprocal effects of dexamethasone on vasodilatory responses to arachidonic acid and prostanoids in the isolated perfused rabbit kidney

Opposite effects of cyclooxygenase-1 and -2 activity on the pressor response to angiotensin II

Therapeutic use of cyclooxygenase-inhibiting (COX-inhibiting) nonsteroidal antiinflammatory drugs (NSAIDs) is often complicated by renal side effects including hypertension and edema. The present studies were undertaken to elucidate the roles of COX1 and COX2 in regulating blood pressure and renal function. COX2 inhibitors or gene knockout dramatically augment the pressor effect of angiotensin II (Ang II). Unexpectedly, after a brief increase, the pressor effect of Ang II was abolished by COX1 deficiency (either inhibitor or knockout). Ang II infusion also reduced medullary blood flow in COX2-deficient but not in control or COX1-deficient animals, suggesting synthesis of COX2-dependent vasodilators in the renal medulla. Consistent with this, Ang II failed to stimulate renal medullary prostaglandin E(2) and prostaglandin I(2) production in COX2-deficient animals. Ang II infusion normally promotes natriuresis and diuresis, but COX2 deficiency blocked this effect. Thus, COX1 and COX2 exert opposite effects on systemic blood pressure and renal function. COX2 inhibitors reduce renal medullary blood flow, decrease urine flow, and enhance the pressor effect of Ang II. In contrast, the pressor effect of Ang II is blunted by COX1 inhibition. These results suggest that, rather than having similar cardiovascular effects, the activities of COX1 and COX2 are functionally antagonistic.

The contribution of cytochrome P450-dependent arachidonate metabolites to integrated renal function

Arachidonic acid can be metabolized to diverse products which differ widely in their biological activities. These metabolites affect basic biological mechanisms such as vascular reactivity and transport function in critical nephron segments. Metabolism of arachidonic acid is discretely localized to specific cells and differs within segments of the nephron; for example, cells of the medullary ascending limb of Henle's loop have a considerable capacity to generate cytochrome P450-dependent arachidonate metabolites but have negligible cyclooxygenase activity. Arachidonic acid metabolites participate in fluid and electrolyte homeostasis, and in the regulation of tissue blood flow, and act as modulators of vasoactive hormones, and, thereby, make important contributions to integrated renal function.

Steroid inhibition of oedema formation in the rat skin

1. A model has been developed to compare the inhibitory effects of the topical steroid, betamethasone-17-valerate, to those of systemically administered betamethasone upon oedema responses induced by 5-hydroxytryptamine (5-HT), platelet activating factor (PAF) and zymosan-activated serum (ZAS) +/- prostaglandin E1 (PGE1), measured in the rat skin by use of 125I-labelled human serum albumin. 2. Systemic betamethasone had a selective, time- and dose-dependent inhibitory effect upon oedema treatment, with 1 mg kg-1 and a 3 h pretreatment having the greatest effect of the doses and times employed. 3. Topical betamethasone inhibited the oedema responses to all of the stimuli showing no apparent selectivity. 4. Topical betamethasone inhibits inflammatory stimuli in a different manner from systemic betamethasone. The broad spectrum of inhibition suggests that topical betamethasone acts by affecting a fundamental feature of the inflammatory response common to all of the stimuli.