Figure 1. Effect of hypercapnia on SND and PND in vago-sino-aortic denervated rats.

A, effect produced by step-wise increases in end-expiratory CO₂ on splanchnic SND (sSND) and PND in one rat. The ganglionic blocker hexamethonium (Hex) was used to define baseline SND. Inset shows the peri-event average of sSND triggered on the ascending phase of iPND. B, steady-state relationship between sSND and end-expiratory CO₂ under halothane (11 rats) or urethane anaesthesia (8 rats). sSND recorded at 3.3–3.8% CO₂ was defined as 100 units. The noise (0 unit) was defined by the hexamethonium method. C, steady-state relationship between mvPND (1 normalized unit equals the maximum value of the signal) and end-expiratory CO₂ for the rats shown in B. D, evidence that the animals were completely barodenervated (Phe, phenylephrine, 5 μg kg⁻¹i.v.; SNP, sodium nitroprusside 30 μg kg⁻¹i.v.).