Cooling-induced bladder contraction: Studies on isolated detrusor muscle preparations in the rat

Objectives. Detrusor muscle contraction and uninhibited micturition after i ntravesical instillation of ice water is interpreted as a sign of upper mot or neuron lesions. The basic mechanism of cooling-induced contraction (CIC) at the level of smooth muscle, however, has not been satisfactorily explai ned. We therefore designed model experiments with cooling of rat detrusor m uscle. Methods. We recorded isometric tension from strips of rat urinary detrusor muscle in organ baths during stepwise cooling. CIC was tested before and af ter addition of various standard agents interfering with known neurogenic ( autonomic blockers, tetrodotoxin, capsaicin) and myogenic mechanisms of con traction (calcium channel blockers). Results. Stepwise cooling (37 degrees to 5 degrees C) of detrusor muscle in duced reproducible graded contractions, inversely proportional to temperatu re. CIC was not dependent on a neural mechanism (not blocked by tetrodotoxi n or capsaicin) or the release of neurotransmitters but was linked to trans location of calcium. It was reduced by calcium channel blockers and Ca2+-fr ee solution. Blockage of the Ca2+-adenosine triphosphatase pump, which inhi bits the extrusion of calcium, also plays a significant role in the process and enhances CIC. Conclusions. Cooling of detrusor muscle preparations induces a graded myoge nic contraction inversely proportional to the temperature. The mechanism is not dependent on local nervous control but is related to calcium transloca tion. (C) 1999, Elsevier Science Inc. All rights reserved.