NEUROTENSIN MEDIATES RAT BLADDER MAST CELL DEGRANULATION TRIGGERED BY ACUTE PSYCHOLOGICAL STRESS N. ALEXACOS, X. PANG, W. BOUCHER, D. E. COCHRANE, G. R. SANT, AND T. C. THEOHARIDES ABSTRACT Objectives. An increased number of activated mast cells have been documented in interstitial cystitis (IC), a painful bladder disorder occurring primarily in women and exacerbated by stress. Mast cells in the bladder and in the intestine are often found in juxtaposition to neurons, where they are activated by neuropeptides and neurotransmitters as well as by acute psychological stress. This work was undertaken to investigate whether the neuropeptide neurotensin (NT) is involved in the activation of bladder mast cells by acute psychological stress. Methods. Male 300-g Sprague-Dawley rats were either kept on the bench in a quiet procedure room or stressed by confining them one at a time for 30 minutes in a clear Plexiglas immobilizer and then killed with carbon dioxide. The bladder was removed and fixed with 4% paraformaldehyde. Frozen sections were either stained with acidified toluidine blue or processed for NT immunocytochemical analysis. An immunosorbent assay was used to also measure NT in bladder homogenate before and after stress. Results. Bladder mast cell activation in control rats was 37.3  1.4%, as judged by extrusion of granule contents. Degranulation in stressed animals increased to 75.3  5.5% (P = 0.0003). Treatment of the animals neonatally with capsaicin decreased mast cell degranulation to 48.9  7.5% (P = 0.008), a 35.1% inhibition. Intraperitoneal administration of the nonpeptide NT receptor antagonist SR48692 sixty minutes before stress decreased bladder mast cell degranulation to 25.2  3.6% (P = 0.00007), a 66.5% inhibition. This value is 32.5% below control levels, indicating that NT is involved in basal mast cell degranulation. Stress also reduced the total bladder NT content. Conclusions. The present results indicate that NT mediates the effect of acute, nontraumatic psychological stress on bladder mast cell degranulation. They further suggest that NT receptor antagonists may be useful in subpopulations of patients with IC in whom symptoms worsen under stress. UROLOGY 53: 1035–1040, 1999. © 1999, Elsevier Science Inc. All rights reserved. R ecent studies have shown that acute psycho- logical stress can trigger mast cell degranula- tion, leading to release of vasoactive, proinflamma- tory, and nociceptive mediators that include histamine, cytokines, and proteolytic enzymes. 1 These findings have prompted speculations that mast cells are involved in neuroimmunoendocrine disorders. 2 High numbers of activated mast cells have been documented in the bladder of patients with interstitial cystitis (IC), 3 a sterile bladder con- dition that occurs primarily in women and is char- acterized by urinary frequency, urgency, burning, and suprapubic pain. 4–6 Patients with IC also have allergies, 7 as well as a variety of other neuroinflam- matory conditions, such as irritable bowel syn- drome and migraine headaches, 8 all of which are exacerbated by stress. 6 Mast cells are located close to neurons 9 –12 and are activated by neuropep- tides, 13–16 by antidromic nerve stimulation, 17 and by acute psychological stress. 1 Stress is a basic response to diverse real or per- ceived threatening stimuli. 18 Besides affecting ill- This work was supported by the Interstitial Cystitis Association, New York, New York; Kos Pharmaceuticals, Miami, Florida; and Farmalex, Athens, Greece. From the Department of Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, Boston, Mas- sachusetts; Department of Biology, Tufts University, Medford, Massachusetts; and Department of Urology, New England Medi- cal Center, Boston, Massachusetts Reprint requests: T. C. Theoharides, M.D., Ph.D., Department of Pharmacology and Experimental Therapeutics, Tufts Univer- sity School of Medicine, 136 Harrison Avenue, Boston, MA 02111 Submitted: May 18, 1998, accepted (with revisions): November 3, 1998 BASIC SCIENCE © 1999, ELSEVIER SCIENCE INC. 0090-4295/99/$20.00 ALL RIGHTS RESERVED PII S0090-4295(98)00627-X 1035