NEUROGENIC AND NON-NEUROGENIC RESPONSES IN THE URINARY-BLADDER OF HIBERNATING HAMSTER

1 Purinergic and cholinergic components of parasympathetic neurotransm ission and contractile responses to exogenous alpha,beta-methylene ATP , acetylcholine, substance K, substance P, calcitonin gene-related pep tide, vasoactive intestinal polypeptide and capsaicin have been invest igated in the urinary bladder of hibernating hamsters (4 weeks), cold exposed (4 weeks) and age-matched controls. 2 Electrical field stimula tion (EFS) evoked increased frequency-dependent contractions in the de trusor strips from hibernating hamsters compared with those obtained f rom cold-exposed and age-matched animals. Tetrodotoxin (10(-6) M) comp letely blocked the frequency-dependent contractions in all groups. 3 T he purinergic component of the parasympathetic neurotransmission was n ot affected in hibernating and cold-exposed animals while the choliner gic component was increased with respect to age-matched animals. The n eurogenic response to EFS, still present after incubation with atropin e (10(-6) M) and suramin (10(-4) M), was attenuated by indomethacin (1 0(-6) M) and blocked by tetrodotoxin (10(-6) M). 4 Exogenous administr ation of alpha,beta-methylene ATP elicited a significantly reduced con traction in strips from hibernating and cold-exposed hamsters relative to age-matched animals. The contractile response to exogenous acetylc holine was greater in the detrusors from hibernating hamsters than in cold-exposed and age-matched animals. Substance K elicited reduced con tractions in preparations from hibernating animals compared with cold- exposed and control animals. Calcitonin gene-related peptide, vasoacti ve intestinal polypeptide, substance P and capsaicin did not elicit an y relaxant or contractile response either at resting tone or in carbac hol (5 x 10(-7) M)-precontracted tissues. 5 In summary, our findings i ndicate that 4 weeks of hibernation can significantly increase neuroge nic responses in the hamster urinary bladder. This appears to be due t o an increase in postjunctional responses to acetylcholine. In contras t, there was a decrease of the postjunctional responses to the parasym pathetic cotransmitter ATP and also to the sensory-motor neurotransmit ter substance K.