Histamine may directly contract urinary bladder smooth muscle

Abstract

Mast cell degranulation and histamine release contribute to painful bladder syndrome, urinary tract infections, interstitial cystitis and other bladder disorders. The effects of histamine are well‐studied in other tissues, but little is known about the role of histamine and histamine receptors within the bladder. Since other smooth muscle cells express H1 (contractile) and H2 (relaxant) histamine receptors, we tested the hypothesis that histamine causes contraction of the urinary bladder smooth muscle in mice. All procedures followed institutional guidelines and were approved by the Institutional Animal Care and Use Committees of Michigan State University. Six to 12‐week‐old C57Bl/6 mice were euthanized and dissected bladders were cut into approximately 2 mm wide bladder strips, with or without the urothelium attached, for isometric contractility experiments. Both histamine H1 and H2 receptors were expressed in bladder smooth muscle cells. Increasing concentrations of histamine (100 nM – 300 μM) did not contract strips without urothelium and minimally contracted bladder strips with urothelium. However, bolus administration of 200 μM histamine caused a rapid but transient contraction in strips with and without urothelium. The H1 receptor blocker fexofenadine (5 – 10 μM) blocked these contractions (P<0.05; N=5), whereas the H2 receptor blocker cimetidine (5 – 10 μM) had no effect. In addition, transient receptor potential vanilloid 1 (TRPV1) channel blocker capsazepine significantly reduced histamine‐induced contractions only in bladder strips without urothelium, whereas the Na+ channel blocker tetrodotoxin (TTX) had no effect in any tissue (P < 0.05; N= 3–5). The mast cell activator compound 48/80 (10 μg/ml) contracted urinary bladder smooth muscle, and this contraction was also unaffected by TTX. These results indicate that H1 receptors on urinary bladder smooth cells likely modulate histamine‐induced bladder contraction, and sufficient amounts of histamine can be released from mast cells to cause a contraction. Support or Funding Information This research is supported by NIH K01‐DK103840 (NRT) and NIH R01‐DK119615 (NRT & GCM).