Hypertension in rats is associated with an increased permeability of the colon to TMA, a gut bacteria metabolite.

An increased blood trimethylamine N-oxide (TMAO) has emerged as a marker of cardiovascular mortality, however, the mechanisms of the increase are not clear. We evaluated if hypertension was associated with changes in the colon permeability to trimethylamine (TMA), a TMAO precursor. We did experiments on male, 24-26-week-old normotensive Wistar-Kyoto rats (WKY), spontaneously hypertensive rats (SHR) and SHR treated with enalapril, an antihypertensive drug (SHR-E). To check the colon permeability and liver TMA clearance, blood was collected from the portal vein and hepatic veins confluence, at baseline and after the intracolonic administration of TMA. Arterial blood pressure (BP) and intestinal blood flow (IBF) recordings and histological assessment of the colon were performed. SHR showed an increased gut-blood barrier permeability to TMA. Namely, at baseline SHR had a higher BP and portal blood TMA, but a lower IBF than WKY. After the intracolonic administration of TMA, SHR had a significantly higher portal blood TMA and higher TMA liver clearance than WKY. In SHR the arteriolar walls of the colon mucosa were significantly thicker than in WKY. Furthermore, SHR showed a significant decrease in the height of the mucosa. In contrast, SHR-E had lower portal blood TMA, lower BP and smaller thickness of arteriolar walls, but higher IBF than SHR, which indicates improved function of the gut-blood barrier in SHR-E. All groups had similar immunostaining of occludin and zonula occludens-1, markers of tight junctions. In conclusion, hypertensive rats show an increased permeability of the colon to TMA, which is accompanied by morphological and hemodynamic alterations in the colon. Therefore, cardiovascular diseases may be characterized by an increased permeability of the gut-blood barrier to bacterial metabolites such as TMA

Metabolic data and TMA/TMAO excretion.

<p>Metabolic data and TMA/TMAO excretion.</p

Assessment of intestinal blood flow and blood pressure.

<p>Intestinal (upper mesenteric vein) blood flow, systolic arterial blood pressure, diastolic arterial blood pressure and heart rate in anaesthetized normotensive Wistar-Kyoto rats (WKY) (n = 6), spontaneously hypertensive rats (SHR) (n = 6) and enalapril-treated SHR (SHR-E) (n = 6) at baseline (0) and after the intracolonic administration of 0.25 mL of 0.9% NaCl (↓ saline) and TMA (100 mg/kg BW) dissolved in 0.25 mL of 0.9% NaCl (↓ TMA). ^$- p<0.05 for SHR vs WKY, ^#- p<0.05 for SHR vs SHR-E comparison.</p

Inflammatory changes in the mucosa of the colon in WKY (normotensive Wistar Kyoto rats), SHR (spontaneously hypertensive rats) and SHR-E (SHR treated with enalapril).

<p><b>A, B, C</b>–The colonic mucosa in WKY, SHR and SRE-E, respectively, (x 40 objective lens). <b>B</b>—Significant infiltration of mononuclear cells under the epithelium, similar to cryptopatches, (x 40 objective lens). <b>D, E</b>—Active GALT lymph nodes (Peyer's patches) were present only in SHR, (x 4 objective lens).</p

Immunohistochemistry stain of zonula occludens-1 (ZO-1) and occludin in colon mucosa.

<p><b>A, B, C</b>–The colonic mucosa with the immunostaining of ZO-1 in WKY (Wistar Kyoto rats), SHR (spontaneously hypertensive rats) and SHR-E (enalapril-treated SHR). <b>E, F, G—</b>The colonic mucosa with the immunostaining of occludin in WKY, SHR and SHR-E. <b>D, H–</b>Changes of mean signal of fluorescence in epithelium of the colonic mucosa (arbitrary units of fluorescence).</p

TMA and TMAO liver clearance.

<p>TMA and TMAO liver clearance.</p

Histopathological and morphometric parameters in the colon of WKY (Wistar Kyoto rats), SHR (spontaneously hypertensive rats) and SHR-E (enalapril-treated SHR).

<p><b>A, B, C–</b>The mucosa of the colon with haematoxylin and eosin (x10 objective lens). <b>E, F, G–</b>Larger arterioles of mucosa with haematoxylin and eosin (x100 objective lens). <b>I, J, K–</b>Larger arterioles of mucosa with van Gieson stain (x100 objective lens). <b>D–</b>The height of the colonic mucosa– μm (x10 objective lens). <b>H–</b>The width of the tunica media of larger arterioles– μm (x40 objective lens). <b>L—</b>The width of the tunica media of smaller arterioles– μm (x100 objective lens). <b>*-</b> p<0.05.</p