Role Of Nacl Intake On Regulation Of Renin Expression In Kidneys And Adrenal-Glands

The influence of dietary NaCl intake on renin gene expression was studied 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 catheter in conscious animals), plasma renin activity and the relative abundance of renin mRNA (RNase protection assay) in renal and adrenal tissue 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 control at 10 days with a slight decline during the third week. Renal renin mRNA levels paralleled the changes of plasma renin activity. Conversely, in animals kept on high salt diet, plasma renin activity decreased transiently. Renin mRNA decreased to about 50% of control values (p < 0.05) and remained suppressed. Abundance of renin mRNA in adrenal glands was estimated to be about 1% of that in kidneys. Changes of renin expression in adrenal glands were similar to those in kidneys under the different diets studied. To assess whether the changes in renin expression are mediated by renal nerval input, animals were studied under the different diets after unilateral denervation utilizing a mechanical and chemical protocol. Renal denervation caused a 50% decrease in renin mRNA in rats under normal diet. In animals under low salt diet denervation 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 related to the amount of salt intake. Since renal and adrenal renin expression change in parallel we hypothesize the existence of a humoral factor that may link renin expression to the rate of salt intake. Renal nerves play no significant role in the salt-dependent regulation of renin-expression. Essential sentence: Salt-dependent relation of renin-expression is similar in kidneys and adrenal glands probably mediated by a humoral factor.