Local Intestinal ACE-Like Activity and Corticosterone Production in Hypertensive and Aging Rats

The renin angiotensin system (RAS) participates in inflammatory processes, as either a pro-inflammatory or an anti-inflammatory mediator. Components of RAS, such as angiotensin-converting enzyme (ACE), have been detected locally in the gut epithelium. In addition, the anti-inflammatory steroid, corticosterone, is produced in the gut. Hypertension and aging evoke a low-grade inflammatory process in the vascular endothelium. It is not known whether they induce a similar low-grade inflammation in the intestine and if the low-grade inflammation would evoke an activation of ACE and an elevation of corticosterone production. These two variables were measured in ileum and colon of 9- and 26-week old spontaneously hypertensive rats (SHR) and their normotensive Wistar-Kyoto (WK) controls. ACE-activity, measured via the formation of histidyl-leucine from hippuryl-histidyl-leucine in the tissue homogenate samples, was similar in the ileum and colon of young animals although the ileum of the young normotensive animals displayed the lowest level. In the old animals, the ACE activity was higher in the ileum than in the colon, especially in normotensive rats. Corticosterone production was measured as corticosterone concentration in the supernatants of ileum or colon after a 90-min ex vivo incubation. Corticosterone production was higher in ileum than in colon in both SHR and WK. No clear evidence was seen for age-dependency or for an effect of hypertension in the measured variables in the intestine. Thus, the putative low-grade inflammation in the intestine in aging or hypertension is not a strong enough stimulus to elevate corticosterone production or activate ACE.