We previously found that deletion of connexin 40 (Cx40) causes a misdirection of renin expressing cells from the media layer of afferent arterioles to the perivascular tissue, extraglomerular mesangium, periglomerular and peritubular interstitium. The mechanisms underlying this aberrant renin expression are unknown. We here questioned the relevance of COX-2 activity for aberrant renin expression in Cx40-deficient kidneys. We found that COX-2 mRNA levels were three-fold increased in the renal cortex of Cx40-deficient kidneys relative to wildtype (wt) kidneys. In wt kidneys, COX-2 immunoreactivity was minimally detected in the juxtaglomerular region, but renin expression was frequently associated with COX-2 immunoreactivity in Cx40-deficient kidneys. Treatment with COX-2 inhibitors for one week lowered renin mRNA levels in wt kidneys by about 40%. In Cx40-deficient kidneys, basal renin mRNA levels were increased two-fold relative to wt kidneys and these elevated mRNA levels were reduced to levels of untreated wt mice by COX-2 inhibitors. In parallel, renin immunoreactive areas were clearly reduced by COX-2 inhibitors such that renin expression vanished decreased significantly in the periglomerular and peritubular extensions. Notably, COX-2 inhibitor treatment lowered plasma renin concentration (PRC) by about 40%, but did not affect the highly elevated PRC levels in Cx40-deficient mice. These findings suggest that aberrant renin producing cells in-Cx40-deficient kidneys express significant amounts of COX-2, which contribute to renin expression in these cells, in particular, those in the periglomerular and peritubular position. Apparently, these disseminated cells do not contribute to the enhanced renin secretion rates of Cx40-deficient kidneys.