ROLE OF NACL INTAKE ON REGULATION OF RENI N EXPRESSION IN KIDNEYS ANDADRENAL-GLANDS

The influence of dietary NaCl intake on renin gene expression was stud ied in adult Sprague-Dawley rats. Animals were kept at low (0.14 mg/g Na+), normal (2.5 mg/g Na+) or high salt diet (18 mg/g Na+) for 5, 10, 15 or 20 days with free access to water. Blood pressure (arterial cat heter in conscious animals), plasma renin activity and the relative ab undance of renin mRNA (RNase protection assay) in renal and adrenal ti ssue was assessed at the end of each feeding period. Arterial pressure was not influenced by the different salt diets. Plasma renin activity increased in animals kept on low salt diet to about three-fold of con trol at 10 days with a slight decline during the third week. Renal ren in mRNA levels paralleled the changes of plasma renin activity. Conver sely, in animals kept on high salt diet, plasma renin activity decreas ed transiently. Renin mRNA decreased to about 50% of control values (p < 0.05) and remained suppressed. Abundance of renin mRNA in adrenal g lands was estimated to be about 1% of that in kidneys. Changes of reni n expression in adrenal glands were similar to those in kidneys under the different diets studied. To assess whether the changes in renin ex pression are mediated by renal nerval input, animals were studied unde r the different diets after unilateral denervation utilizing a mechani cal and chemical protocol. Renal denervation caused a 50% decrease in renin mRNA in rats under normal diet. In animals under low salt diet d enervation did not prevent the rise in renin mRNA levels, while under high salt diet renin mRNA was further decreased in denervated kidneys. Conclusion: Renin secretion and renin expression are inversely relate d to the amount of salt intake. Since renal and adrenal renin expressi on change in parallel we hypothesize the existence of a humoral factor that may link renin expression to the rate of salt intake. Renal nerv es play no significant role in the salt-dependent regulation of renin- expression. Essential sentence: Salt-dependent relation of renin-expre ssion is similar in kidneys and adrenal glands probably mediated by a humoral factor.