Acute intravesical infusion of a cobalt solution stimulates a hypoxia response, growth and angiogenesis in the rat bladder.
OBJECTIVE
Experimental partial bladder outlet obstruction of rats induces a bladder growth and remodeling process similar to that in humans with benign prostatic hyperplasia. Previously we have proposed that bladder hypoxia associated with partial bladder outlet obstruction is a stimulus of this bladder growth process. We report our results of testing the acute effects of a simple chemical agent (cobaltous ion) known to mimic hypoxia in the rat bladder. We measured its ability to effect bladder gene expression, angiogenesis and growth processes.


METHODS
Adult rats were divided into 2 groups. One group (controls) received intravesical saline 3 times for 30 minutes in 6 days and the other received intravesical saline with 100 microM. CoCl(2) at the same times. All animals also received continuous infusion of BrdU for the 6-day period through an implanted osmotic pump. Portions of the bladders from these rats were fixed, sectioned, stained for microscopic analysis and immunohistochemically stained to identify BrdU positive cells and vascular elements via factor VIII staining. Other portions were frozen, extracted for proteins and the proteins were comparatively analyzed for the expression of hypoxia inducible factor-1alpha and vascular endothelial growth factor on Western blots.


RESULTS
Bladders infused with CoCl(2) showed extensive expansion of the submucosal region, which was significant compared with that in saline infused bladders. Cells in this expanded region as well as cells within the urothelium were found to be extensively labeled with BrdU, in contrast to control bladders, which had rare BrdU labeled cells in any region. Immunohistochemical analysis for factor VIII showed that the submucosal region of cobalt treated rats contained numerous small vessels and microvessels that were not apparent in controls. These cellular changes were consistent with our finding of increased hypoxia inducible factor-1alpha and vascular endothelial growth factor protein expression in cobalt treated bladders compared with controls.


CONCLUSIONS
Acute intravesical instillation of cobalt ion solution into the rat bladder initiated a hypoxia response accompanied by increased bladder angiogenesis and growth. This finding supports the idea that hypoxia is a stimulus for bladder growth subsequent to partial bladder outlet obstruction.
Buttyan
Ralph
R
Department of Urology, Columbia University Health Sciences, New York and Albany College of Pharmacy, Albany, New York, USA.
Chichester
Paul
P
Stisser
Brian
B
Matsumoto
Seiji
S
Ghafar
Mohamed A
MA
Levin
Robert M
RM
D000283:Administration, Intravesical; D000818:Animals; D015153:Blotting, Western; D002455:Cell Division / Q000187:drug effects; D015687:Cell Hypoxia / Q000187:drug effects; D003035:Cobalt / Q000008:administration & dosage / Q000494:pharmacology*; D004268:DNA-Binding Proteins / Q000378:metabolism; D016228:Endothelial Growth Factors / Q000378:metabolism; D005169:Factor VIII / Q000032:analysis; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D007150:Immunohistochemistry; D036341:Intercellular Signaling Peptides and Proteins / Q000378:metabolism; D008222:Lymphokines / Q000378:metabolism; D008297:Male; D018919:Neovascularization, Physiologic / Q000187:drug effects*; D009687:Nuclear Proteins / Q000378:metabolism; D009929:Organ Size / Q000187:drug effects; D051381:Rats; D017207:Rats, Sprague-Dawley; D014157:Transcription Factors; D001743:Urinary Bladder / Q000098:blood supply / Q000187:drug effects* / Q000378:metabolism / Q000473:pathology; D001748:Urinary Bladder Neck Obstruction / Q000473:pathology / Q000503:physiopathology; D019459:Urothelium / Q000473:pathology; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors
D004268:DNA-Binding Proteins; D016228:Endothelial Growth Factors; C497444:Hif1a protein, rat; D051793:Hypoxia-Inducible Factor 1; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D036341:Intercellular Signaling Peptides and Proteins; D008222:Lymphokines; D009687:Nuclear Proteins; D014157:Transcription Factors; D042461:Vascular Endothelial Growth Factor A; D042442:Vascular Endothelial Growth Factors; D003035:Cobalt; D005169:Factor VIII; C018021:cobaltous chloride