Alteration of aortic function from streptozotocin-diabetic rats with KilhamÕs virus is associated with inducible nitric oxide synthase Matthew R. Nangle a, * , Mary A. Cotter b , Norman E. Cameron b a Pain Management Research Institute, University of Sydney, Royal North Shore Hospital, St. Leonards, NSW 2065, Australia b School of Medical Sciences, Institute of Medical Sciences, University of Aberdeen, Aberdeen AB25 2ZD, Scotland, United Kingdom Accepted 4 August 2005 Abstract KilhamÕs rat virus (KRV) is a parvovirus commonly known to affect laboratory rats. Qualitative immunohistochemical analysis revealed that aorta isolated from KRV-infected streptozotocin (STZ)-induced diabetic adult rats expressed markedly greater levels of inducible nitric oxide synthase (iNOS) than aorta from KRV-infected controls. In contrast with the prevailing literature, nitric oxide-mediated endothelium-dependent relaxation to acetylcholine was not blunted by STZ-diabetes, butwas comparable to relaxations of aorta from controls. However, with increasing ex vivo duration, a decreased response to acetylcholine was observed in the STZ-dia- betic aorta. In addition, whereas contraction responses to phenylephrine were not significantly altered over time in control tissue, aorta from STZ-diabetic rats developed increased tensions. The data suggest that increased iNOS-derived nitric oxide masks expected acetyl- choline-mediated relaxation deficits as a result of KRV-infection, and that the deficit is unmasked by iNOS turnover ex vivo. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Aorta; Diabetes mellitus; KilhamÕs rat virus; Inducible nitric oxide synthase; Endothelium 1. Introduction KilhamÕs rat virus (KRV) is a member of the parvovirus family and can manifest itself without any overt signs or symptoms (Kilham and Oliver, 1959). It is composed of three proteins and a linear single-stranded DNA molecule, and is particularly common in laboratory rats (Institute for Laboratory Animal Research, 1991). Independent serological testing of pathological markers by Surrey Diagnostics, Surrey, UK, confirmed the presence of KRV in our rat colony at the time of these experiments. Inducible nitric oxide synthase (iNOS), not normally present in healthy vascular tissue, is produced in response to cytokine stimulation in vast amounts as part of the inflammatory response (Shah, 2000). Aortas from strep- tozotocin (STZ)-induced diabetic rats develop reduced ni- tric oxide-mediated endothelium-dependent relaxation responses to agonists such as acetylcholine, compared to controls (Archibald et al., 1996; Cameron and Cotter, 1992; Durante et al., 1988), despite the induction of iNOS in STZ-diabetic, but not control, rat arteries (Bardell and MacLeod, 2001). As the immune system is suppressed by STZ-diabetes, we tested whether KRV-infection might af- fect endothelium-dependent nitric oxide-mediated func- tion of STZ-diabetic rat aorta and whether this might be associated with iNOS. 2. Materials and methods 2.1. Animals, diabetes induction and anaesthesia Diabetes was induced with a single 45 mg kg 1 strep- tozotocin intraperitoneal (IP) injection, dissolved in 1090-0233/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.tvjl.2005.08.014 * Corresponding author. Tel.: +61 2 9926 6860; fax: +61 2 9906 4079. E-mail address: stish@med.usyd.edu.au (M.R. Nangle). www.elsevier.com/locate/tvjl The Veterinary Journal 172 (2006) 455–459 The Veterinary Journal