This study sought to examine the involvement of prostaglandins and of nitric oxide (NO) in the macula densa-dependent activation of the renin system in vivo. For this purpose, male Sprague-Dawley rats were chronically infused with furosemide (12 mg/day) for 6 days to inhibit macula densa salt transport. To inhibit the synthesis of prostaglandins and of NO, animals were injected with indomethacin (2 mg/kg twice daily) and with nitro-L-arginine methyl ester (L-NAME; 40 mg/kg twice daily) for the last 2 days of the experiment, respectively. Furosemide infusion increased plasma renin activity (PRA) from 8.8 +/- 1.4 to 41 +/- 5.2 ng angiotensin I (ANG I).h-1.ml-1 and renin mRNA levels from 112 +/- 8 of standard to 249 +/- 18% of standard. After treatment with indomethacin, the furosemide-induced increases in renin mRNA levels was attenuated to 190 +/- 11% of standard. After injections of L-NAME, both the furosemide-induced increases of renin mRNA levels and of PRA were reduced to 126 +/- 14% of standard and 22 +/- 5 ng ANG I.h-1.ml-1, respectively. These findings suggest that activation of renin gene expression by blockade of the macula densa function is dependent on intact NO and prostaglandin formation, whereas for stimulation of renin secretion mainly intact NO formation appears to be necessary.