BJU International (1999), 83, 113–122 Increased expression of endothelin B receptors in the diabetic rabbit urinary bladder: functional relevance F.H. MUMTAZ, M.R. DASHWOOD*, C.S. THOMPSON*, M.E. SULLIVAN†, D.P. MIKHAILIDIS* and R.J. MORGAN Departments of Urology, *Chemical Pathology and Human Metabolism, Royal Free Hospital and School of Medicine, London and †Royal Battle Hospital, Reading, UK Objectives To determine the eCect of diabetes mellitus Results ET A and ET B receptor binding sites were localized to both the urothelium and smooth muscle of the on the density and distribution of endothelin A (ET A ) and endothelin B (ET B ) receptor subtypes in the rabbit detrusor and bladder neck. There were significantly more ET B receptor binding sites in the diabetic detrusor urinary bladder, and to assess the in vitro functional properties of endothelin-1 (ET-1) receptors in bladder and bladder neck sections than in controls. ET-1 smooth muscle contractile responses were ET A recep- smooth muscle strips from diabetic and healthy rabbits. tor-mediated. The smooth muscle contractile responses to ET-1 were unaltered in the detrusor, but signifi- Materials and methods Diabetes mellitus was induced in six male New Zealand White rabbits with alloxan cantly impaired in the bladder neck of diabetic animals compared with controls. and their urinary bladders excised 6 months after the induction of diabetes. On serial detrusor and bladder Conclusion Alteration in the expression of ET B receptors and in vitro contractile smooth muscle responses to neck sections, low- and high-resolution autoradio- graphy was performed using radioligands for ET-1, ET-1 in the diabetic rabbit urinary bladder neck may play a role in the pathophysiology of diabetic ET A and ET B receptors; these sections were then ana- lysed densitometrically. The results were compared cystopathy. Keywords Endothelin A, endothelin B, rabbit, urinary with those from six age-matched healthy control rabbits. Functional responses were investigated using bladder, diabetes mellitus isometric tension studies. bovine [13] and rat lung [14], respectively. These recep- Introduction tors have been detected in the rabbit lower urinary tract using SDS-PAGE and characterized based upon diCeren- Alterations in bladder function (e.g. atonic or hyper- reflexic bladders) are increasingly recognized in diabetic tial binding aBnities of sarafotoxin 6c (S6c) and a cyclic pentapeptide, BQ123, at 125I-ET-1 binding sites [15,16]. patients [1,2]. These complications are thought to be due to abnormal function of sensory and autonomic These studies indicated that there are regional diCerences in the density and distribution of ET receptors in the innervation to the bladder [3,4], detrusor hypertrophy [5,6] and alterations in the density of various receptors rabbit urinary tract, suggesting that the specific functions of ET-1 depend on the region of the urinary tract. Whilst [7]. Endothelin-1 (ET-1) (a 21 amino-acid peptide, orig- these studies provide a possible physiological role for ET-1 in the urinary bladder, the exact function of its inally identified in the culture medium of porcine endo- thelial cells) [8], has been shown to elicit smooth muscle receptor subtypes is unclear. In the vascular bed, ET A receptors mediate vasoconstriction and cellular prolifer- contraction in the lower urinary tract of various animal species including humans [9,10]. In addition, ET-1 is ation, whereas ET B receptors, predominantly found on endothelial cells, mediate vasodilatation via the pro- mitogenic and has a growth promoting eCect on diCerent cell types [11,12]. Two ET receptor subtypes, ET A and duction of nitric oxide (NO) and prostacyclin (PGI 2 ) (although ET B -mediated vasoconstriction is also well ET B , have been characterized and recently cloned from established) [17]. Recently, the enhancing eCects of glucose and insulin Accepted for publication 18 August 1998 on ET-1 release from endothelial cells and mesenteric arteries has been described in diabetic animals [18]. The preliminary findings of this study were presented to the 52nd Annual meeting of BAUS, 24 June 1997 Up-regulation of ET receptor expression has been shown 113 © 1999 BJU International