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We investigated the effects of visceral stimulation by colorectal distension (CRD) on mean arterial blood pressure (MAP) and renal sympathetic nerve activity (RSNA), the latter of which is an index of vasoconstrictor activity, in anesthetized central nervous system (CNS)–intact and C2 spinalized rats. The CRD stimulation was induced by distention of a balloon that was inserted into the colorectum. In CNS-intact rats, there were significant reductions in MAP and RSNA in response to intra-balloon pressures of 60 and 80 mmHg, but not 20 and 40 mmHg. However, spinalized rats demonstrated significant increases in MAP in response to intra-balloon pressures of 60 and 80 mmHg, and increases in RSNA in response to intra-balloon pressures of 40, 60 and 80 mmHg. These results suggest that noxious visceral stimulation at lower spinal levels reduces MAP by inhibiting sympathetic output in CNS-intact anesthetized rats. On the other hand, such stimulation results in an increase in sympathetic-induced MAP in spinalized anesthetized rats.
