ABSTRACT
Local renin-angiotensin systems (RAS) are found in many tissues. The main physiological effects of RAS are driven by the balance between two pathways: the angiotensin-converting enzyme I - angiotensin II receptor type 1 (ACE1-AT1R) axis and the angiotensin-converting enzyme 2 - Mas-receptor (ACE2-MAS) axis. The local intestinal RAS functions both as a paracrine regulator and as a regulator of inflammation. The expression of local RAS is known to change with age in many tissues, but age-related changes in the intestinal RAS have not been studied comprehensively. The present study characterized age-related changes in two main pathways of local RAS in the jejunum and colon of young and adult rats, in normotensive and hypertensive strains. The main finding was that 33-week-old rats exhibit an increased ratio of ACE1/ACE2 activities and protein quantity ratios compared to young rats. As the relationship of ACE1 and ACE2 mediated pathways drives the total physiological effects of RAS, the results indicate that the function of intestinal RAS changes with age. It is possible that age-related increase in ACE1-AT1R axis introduces more pro-inflammatory and fibrogenic conditions in the intestine.
Subject(s)
Hypertension/physiopathology , Intestines/physiology , Renin-Angiotensin System/physiology , Angiotensin I/metabolism , Angiotensin II/metabolism , Angiotensin-Converting Enzyme 2 , Animals , Blood Pressure/physiology , Hypertension/metabolism , Peptidyl-Dipeptidase A/metabolism , Rats , Rats, Inbred SHR , Receptor, Angiotensin, Type 1/metabolism , Renin/metabolismABSTRACT
The effects of angiotensin-converting enzyme (ACE) inhibition by an antihypertensive drug, captopril, and milk casein-derived ACE-inhibiting bioactive tripeptide isoleucine-proline-proline (Ile-Pro-Pro), on local renin-angiotensin system (RAS) and glucocorticoid production in the intestine were studied in the dextran sodium sulfate induced colitis in mice. Mice received water or 3% dextran sodium sulfate with or without either 15.7 mg/l captopril or 833 mg/l Ile-Pro-Pro for 7 days. Captopril and Ile-Pro-Pro were found to have distinct effects on local renin-angiotensin system and mRNA expression of glucocorticoid synthesis components in colon in vitro. Captopril reduced intestinal mRNA expression of angiotensin-converting enzyme, angiotensinogen and Cyp11b1, whereas Ile-Pro-Pro reduced angiotensin-converting enzyme protein shedding from colon. Neither captopril nor Ile-Pro-Pro changed the expression of glucocorticoid-synthesis driving transcription factor Lrh-1 expression or intestinal glucocorticoid production. Contrary to previous studies, captopril did not alleviate DSS-induced colitis. Furthermore, Ile-Pro-Pro was mildly pro-inflammatory as exhibited by increased pro-inflammatory cytokine interleukin-1ß (IL-1ß) and tumor necrosis factor-α (TNF-α) levels in colon. The nutritional component Ile-Pro-Pro had different effect on intestinal RAS and glucocorticoid (GC) synthesis pathway than ACE inhibitor captopril, which suggests that the bioactivity of Ile-Pro-Pro is not limited to inhibition of ACE.
Subject(s)
Angiotensin-Converting Enzyme Inhibitors/pharmacology , Captopril/pharmacology , Colitis/metabolism , Corticosterone/metabolism , Oligopeptides/pharmacology , Renin-Angiotensin System/drug effects , Administration, Oral , Animals , Colitis/chemically induced , Colitis/genetics , Colitis/pathology , Colon/drug effects , Colon/metabolism , Colon/pathology , Cytochrome P-450 CYP1B1/genetics , Dextran Sulfate , Interleukin-1beta/metabolism , Interleukin-6/metabolism , Male , Mice, Inbred BALB C , Peptidyl-Dipeptidase A/genetics , Peptidyl-Dipeptidase A/metabolism , Tumor Necrosis Factor-alpha/metabolismABSTRACT
BACKGROUND: We have previously shown in mice that the fecal proportion and concentration of the hydrophobic bile acid deoxycholic acid (DCA) is elevated with high-fat feeding and that these changes are able to disrupt the intestinal barrier function. The aim of this study was to investigate whether these changes are mediated by the enteric nervous system (ENS). METHODS: The function of the ENS in the small intestinal tissues of mice was compromised by two different methods: by removing the seromuscular layer and by incubating the intact tissues with tetrodotoxin (TTX), a neural conduction blocker, before DCA treatment. Tissues with or without functional plexuses were mounted into a Ussing chamber system and treated with 3 mM DCA for 20 min. After DCA treatment, the intestinal permeability to fluorescein was assessed. Short-circuit current (Isc ) and transepithelial resistance (TER) were recorded throughout the experiment. KEY RESULTS: DCA increased intestinal fluorescein permeability only in tissues where the seromuscular layer was removed. In tissues with intact seromuscular layer, DCA induced a significant increase in TER, which was attenuated by blocking of the neural function by TTX. CONCLUSIONS & INFERENCES: The results of this study suggest that the DCA-induced increase observed in fluorescein permeability is not mediated through neural pathways, but more due to a direct effect on the epithelium. However, as TTX was able to attenuate the DCA-induced increase in TER, it can be speculated that DCA is also able to elicit responses through neural pathways.
