Endocrine Abstracts

New research claims, for the first time, that gut microbiota affect hypertension in rats but authors were unaware of historical research indicating this link. The urine steroid metabolome by gas chromatography of a patient with congenital adrenal hyperplasia from 17-hydroxylase (CYP17) deficiency was reported in 1978. Many of the steroids were 21-deoxy products of corticosterone and could be hypertensinogenic or glycerrhitinic acid like factors. Further studies in CYP17 deficient patients supported an enterohepatic circulation of corticosterone. 21-dehydroxylation of corticosterone by bacteria was characterised in 1969 by Sjovall and Gustafsson from comparisons of normal and germ free rats. In studies in 1982-1985 hypertension was induced by corticosterone or adrenocorticotrophin administration to Sprague Dawley rats. The increase in blood pressure was attenuated by antibiotic treatment. The normal development of high blood pressure in spontaneously hypertensive rats (SHR) was also attenuated by antibiotic administration. Full characterisation of the gut microbiome was difficult then, especially for the anaerobes. The gut microbiota is now much easier to study using bacterial 16S ribosomal RNA analysis. An imbalance of gut microbiota is called dysbiosis. Experiments involving the transplantation of caecal contents between rat strains support the link of gut dysbiosis with hypertension. Elevated blood pressure is associated with a decrease in bacteria involved in acetate (Holdemania and Coprobacillus) and butyrate production (Clostridia). An increase in lactate production (Lactobacilli) is also seen. Short chain fatty acids activate G-protein coupled receptors and affect vaso-reactivity and renin secretion. The microbiota of human hypertensive patients has a dysbiotic pattern similar to the SHR. The maintenance of blood pressure is a complex process. The kidney and caecum are important sites of salt absorption under steroid control. Further analysis of the gut microbiome in hypertension is needed. In the future, dietary intervention to adjust gut bacteria could be an innovative strategy for treating hypertension.