From: deputyfife23x@gmail.com   
      
   Science and technology    
      
   The microbiome and health    
   Sniffing out hypertension    
      
      
   Gut bacteria help regulate blood pressure    
   Feb 16th 2013    
      
      
   THE role of the microbiome, the complement of bacterial passengers carried   
   around by every human being, gets more intriguing by the month. Recent papers   
   have confirmed that having the wrong microbiome can cause malnutrition, and   
   that transplanting bugs    
   from one person to another, in the form of small amounts of faeces, can   
   abolish Clostridium difficile infection, a potentially fatal gut disease, even   
   when antibiotics have failed to do so.    
   The latest connection to be investigated between the microbiome and health is   
   that of gut bacteria to blood pressure. Work by Jennifer Pluznick of Johns   
   Hopkins University, in Baltimore, and her colleagues, published in the   
   Proceedings of the National    
   Academy of Sciences, confirms that this link exists--at least, in mice and   
   thus probably also in men. And an intriguing aside is that, in essence, the   
   reason is that the kidneys have a sense of smell.    
      
      
   What they are smelling is propionic acid, a substance that several species of   
   gut bacteria produce in quantity. Earlier work, by researchers at Imperial   
   College, London, suggests that formic acid--a similar but smaller   
   molecule--acts on the kidneys to    
   alter blood pressure, but the details are obscure. Dr Pluznick has shown that   
   as far as propionic acid is concerned, one of the detectors which regulates   
   the process is an olfactory-receptor protein of a type more familiarly seen in   
   people's noses.    
   Dr Pluznick had previously shown that at least six such nasal proteins are   
   made by kidney cells, too. Preliminary experiments led her to focus on one,   
   called Olfr78, and also on a second receptor protein, Gpr41, that is not found   
   in the nose.    
   The kidneys help to control blood pressure via an enzyme called renin, which   
   increases it. Dr Pluznick found that in normal, healthy mice propionic acid   
   regulates this process, causing blood pressure to drop. She then looked at the   
   role of Olfr78 and    
   Gpr41, and the link with the microbiome, by comparing normal mice with those   
   that have been genetically engineered to eliminate one or other of the genes   
   for the proteins in question.    
   She found, first, that when she injected engineered mice with propionic acid,   
   the blood pressure of those in which Olfr78 had been knocked out dropped more   
   than it did in normal mice. In those in which the knocked-out gene was Gpr41,   
   by contrast, it did    
   not fall at all. The two proteins thus seem to be acting in opposite ways.    
   That was intriguing, but did not absolutely prove the connection with gut   
   bacteria. The clincher was when she treated some mice with an antibiotic, to   
   kill off their gut bacteria. Mice so treated that had no gene for Olfr78   
   showed a significant rise in    
   blood pressure. Those that were genetically normal did not. (She has yet to do   
   the experiment on Gpr41-deficient mice.)    
   These results, it must be acknowledged, are confusing--indicating as they do   
   that propionic acid can push blood pressure in either direction, depending on   
   which receptor is involved. Almost certainly, other as-yet-unidentified   
   receptors are part of the    
   picture, too. It does look, though, as if something produced by gut bacteria,   
   probably propionic acid or a related molecule, is acting like a hormone and   
   regulating blood pressure. If the same were to prove true in people, it would   
   add a new layer of    
   complexity to the relationship between humans and their microbiomes.    
   How evolution came to give bugs the power to regulate the blood pressure of   
   their hosts is a fascinating question. A more pressing one, though, is whether   
   what seems true in mice really is true in people, and if so, how big the   
   effect is. Given the    
   amount of hypertension seen in modern humanity, knowing the answer to that is   
   really rather important.    
      
      
      
      
   http://www.economist.com/news/science-and-technology/21571844-gu   
   -bacteria-help-regulate-blood-pressure-sniffing-out-hypertension   
      
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