Efeito da toxina A do clostridium difficile na atividade contrátil do musculo liso intestinal de coelho

Abstract

The effects of the toxin A (TxA) of the Clostridium difficile, on the mechanical properties of the intestinal smooth muscle has been hitherto neglected. In this study the effects of the TxA on the mechanical properties of the intestinal smooth muscle and its underlying mechanisms of action were evaluated. The time course of these effects were evaluated to 2, 6 and 18 h, after rabbit isolated intestinal loops were injected with TxA (1 pg/ml/loop). Isolated loops injected with PBS were used as internai control, whereas their neighboring loops were injected with TxA. Surgical handling-induced effects were evaluated using rabbit isolated loops injected only with PBS (externai control). Intestinal loops from sham-operated animais were also used. It was evaluated: amplitude of the spontaneous-, K+- (7.5 - 120 mM) or ACh-induced (0.1 - 300 pM) phasic contractions. In relation to spontaneous contractions, only PBSP6 group showed a signifícant increase compared to SC group. The time course of these contractility parameters was altered by TxA in two phases. For TxATIS and PBST18 groups, there were gradual effects: TxAT18 < PBST18 < PBSP18. The differences between TxAT18 and PBST18 were defrned as local effects (effect of the TxA in the directly exposed loop) and between PBST18 and PBSP18, as systemic effects (TxA-induced effects in neighboring loops far from those where it was originally injected). Dexametasone (2 mg/Kg) fully blocked the depressor TxA-induced effects on the intestinal contractility. On the other hand, quinacrine (20 mg/kg)-induced blockade was only partial. Indometacine (2 mg/Kg), celecoxibe, (20 mg/Kg), sodium montelukast (10 mg/Kg), talidomide (50 mg/kg) and pentoxifiline (50 mg/kg) also fully blocked the TxA-induced effects. The hexamethonium (10 mg/Kg)- induced protection of the intestinal contractility against the TxA-induced effects strongly suggests an important enteric nervous system, as well as a cholinergic role in the TxA- induced effects on intestinal smooth muscle. The essential oil of Croton zehntneri (OECz) was efficient, in small doses (compared by the LD50), in blocking the TxA-induced effects on intestinal contractility. The present study showed that the TxA (1 pg/ml/loop) of the C. difficile induced alterations on intestinal contractility, which were associated to inflammatory processes. Alterations of the enteric nervous system activity are in coherence with the absence of TxA receptors in longitudinal and circular smooth muscle cells.