SA GENE-EXPRESSION IN THE PROXIMAL TUBULE OF NORMOTENSIVE AND HYPERTENSIVE RATS

Previous studies have shown that the SA gene is expressed at higher le vels in the kidney of genetically hypertensive rats than in control st rains and that in hybrid crosses of genetically hypertensive rats and normotensive controls, markers in or close to the SA gene cosegregate with blood pressure. The present studies examine the localization of t he SA gene product in the kidney by semiquantitative reverse transcrip tion-polymerase chain reaction (RT-PCR). cDNA was prepared from microd issected nephron segments from Sprague-Dawley (SD) rats, spontaneously hypertensive rats (SHRs), and Wistar-Kyoto (WKY) rats, and RT-PCR was performed using specific primers. In all three strains, SA gene mRNA was found to be abundantly expressed in proximal tubules. SA PCR produ ct was occasionally detected at approximately 100-fold lower abundance in glomeruli, while no signal was obtained from the collecting duct, thick ascending limb of the loop of Henle, or arcuate artery. Within t he proximal tubule of normotensive rats, distribution of SA mRNA was f ound to be strain dependent: in SD rats it was expressed at high level s in the proximal convoluted tubule, whereas in WKY rats it was restri cted to the proximal straight tubule. In SHRs, SA PCR product was dete cted along the entire proximal tubule. Induction of hypertension by re nal artery clamping (two-kidney, one-clamp Goldblatt model) did not al ter the pattern of expression observed in the SD rat. These results in dicate that an extension of SA gene expression to the full length of t he proximal tubule accompanies spontaneous hypertension and that in no nhypertensive animals the pattern of gene product expression is more r estricted but shows substantial strain variability.