Cyclooxygenases 1 and 2 and thromboxane synthase in kidneys of Lyon hypertensive rats

Compared with their two normotensive (LN and LL) controls, genetically hype rtensive rats of the Lyon strain (LH) exhibit increased renal vascular resi stance and a blunted pressure natriuresis function as well as an increased urinary excretion of vasoconstrictor prostanoids. The aim of this study was to assess in the kidneys of these animals the synthesis of vasoconstrictor or sodium-retaining prostanoids. The relative abundance of the mRNAs of cy clooxygenases (COX) 1 and 2 and of thromboxane A, synthase (TXS), was measu red by reverse-transcription polymerase chain reaction (RT-PCR) in renal co rtex and medulla dissected in groups of male LH, LN, and LL rats either in baseline conditions or after 1 week of salt loading (1.5% NaCl in the drink ing water). In basal conditions, at 3 and 11 weeks of age COX1 was expresse d in the kidneys of all rats more markedly in medulla than in cortex. COX2 was poorly expressed in the whole kidney. TXS expression was usually too lo w to be quantified. No difference could be observed among LH, LN, and LL ra ts. After salt loading, the expression of COX1 was enhanced in the medulla and that of COX2 reduced in the cortex. LH rats differed from controls by a significantly more marked increase in medullary COX1 expression. The prese nt work excludes any primary generalized increase in the renal expression o f the genes that control the synthesis of vasoconstrictor prostanoids in LH rats, but suggests that medullary COX1 is upregulated by salt in these ani mals. (C) 2000 American Journal of Hypertension, Ltd.