Neurogenic and non‐neurogenic responses in the urinary bladder of hibernating hamster

Abstract

1 Purinergic and cholinergic components of parasympathetic neurotransmission and contractile responses to exogenous a,b-methylene ATP, acetylcholine, substance K, substance P, calcitonin generelated peptide, vasoactive intestinal polypeptide and capsaicin have been investigated in the urinary bladder of hibernating hamsters (4 weeks), cold exposed (4 weeks) and age-matched controls. 2 Electrical ®eld stimulation (EFS) evoked increased frequency-dependent contractions in the detrusor strips from hibernating hamsters compared with those obtained from cold-exposed and age-matched animals. Tetrodotoxin (10 76 M) completely blocked the frequency-dependent contractions in all groups. 3 The purinergic component of the parasympathetic neurotransmission was not a ected in hibernating and cold-exposed animals while the cholinergic component was increased with respect to age-matched animals. The neurogenic response to EFS, still present after incubation with atropine (10 76 M) and suramin (10 74 M), was attenuated by indomethacin (10 76 M) and blocked by tetrodotoxin (10 76 M). 4 Exogenous administration of a,b-methylene ATP elicited a signi®cantly reduced contraction in strips from hibernating and cold-exposed hamsters relative to age-matched animals. The contractile response to exogenous acetylcholine was greater in the detrusors from hibernating hamsters than in cold-exposed and age-matched animals. Substance K elicited reduced contractions in preparations from hibernating animals compared with cold-exposed and control animals. Calcitonin gene-related peptide, vasoactive intestinal polypeptide, substance P and capsaicin did not elicit any relaxant or contractile response either at resting tone or in carbachol (5610 77 M)-precontracted tissues. 5 In summary, our ®ndings indicate that 4 weeks of hibernation can signi®cantly increase neurogenic responses in the hamster urinary bladder. This appears to be due to an increase in postjunctional responses to acetylcholine. In contrast, there was a decrease of the postjunctional responses to the parasympathetic cotransmitter ATP and also to the sensory-motor neurotransmitter substance K.

Purinergic signalling in the urinary tract in health and disease

“…5) [560]. Perhaps surprisingly, 4 weeks of hibernation significantly increased both cholinergic and purinergic neurogenic responses of the hamster urinary bladder.…”

“…In cold-exposed and hibernating hamsters α,β-meATP elicited decreased contractions (ANOVA, P <0.05; n =6). (Reproduced from [560], with permission from Wiley) potency was: α,β-meATP = ADPβS > 2-MeSATP > ATP >> UTP. In addition, it was reported that responses to α,β-meATP and ADPβS were additive and that the P2 antagonist p -chloromercuribenzene sulphonic acid [724] antagonised ADPβS-induced contractions, but was inactive against α,β-meATP, while Reactive blue 2 had no effect against ADPβS contractions [541].…”

The role of sensory neuropeptides in motor innervation of the hamster isolated urinary bladder

“…The last is the most efficient since the contractile responses were strongly reduced by purinergic antagonist and unaffected or barely affected by cholinergic antagonist (Pinna et al 1998;this paper). Now we have demonstrated that a sensory component is also present and functionally active in this organ.…”

“…Pinna et al (1998) found that CGRP or capsaicin did not elicit any contractile or relaxant response either on the resting tone or on the tone produced by carbachol. In our hands the effect on the tone is very small as compared to the effect on the twitches and this may suggest a role, at prejunctional level of parasympathetic fibers, for the peptides released from sensory nerves which cannot be observed in unstimulated preparations.…”

“…Little or no information is available about the effect of CGRP which apparently does not produce intrinsic effects on the bladder from hibernating hamster (Pinna et al 1998), but it could be responsible for the relaxation produced by capsaicin administration (Maggi et al 1987). Specific binding to vanilloid receptor has been detected in hamster urinary bladder (Szallasi et al 1993), although in a relatively small amount, being approximately one-fifth of the amount found in the rat bladder.…”