REN and polyarteritis nodosa: However, reductions in Ang II levels and renin activity do not appear to be important mechanisms associated with PAN-NS sodium retention, the reasons are as follows: (1) The decrease of urinary sodium excretion in PAN-NS rats was earlier than that of Ang II level and renin activity; (2) No correlation between plasma Ang II level and renin activity and urinary sodium excretion was found throughout the experimental period.