Time-dependent effects of ischaemia on neuropeptide Y mechanisms in pig renal vascular control in vivo

We have investigated the effects of ischaemia on neuropeptide Y (NPY) mechanisms involved in sympathetic vascular control of the pig kidney in vivo. Reperfusion after 2 h of renal ischaemia was associated with local overflow of noradrenaline (NA) but not of NPY‐like immunoreactivity (‐LI). Renal sympathetic nerve stimulation 10 min into reperfusion evoked markedly reduced vasoconstrictor effects and significantly less overflow of NA (reduced by 70% from the pre‐ischaemic conditions), whereas NPY‐LI overflow was unaltered. Renal vasoconstrictor responses to exogenous peptide YY (PYY), phenylephrine and angiotensin II were strongly attenuated after this ischaemic period, while vasoconstriction to α,β‐methylene ATP was maintained to a larger extent. The renal vascular responses and NA overflow had become partially normalized within a 2 h recovery period. In contrast, the renal vasoconstrictor response and the overflow of NPY‐LI upon sympathetic nerve stimulation were enhanced after 15 min of renal ischaemia. In parallel, the PYY‐evoked renal vasoconstriction was selectively and markedly prolonged after the 15 min of ischaemia. In the presence of the NPY Y1 receptor antagonist BIBP 3226, the augmented vascular response to nerve stimulation was significantly attenuated. We conclude that reperfusion after 2 h of renal ischaemia is associated with local overflow of NA, whereas the sympathetic nerve‐evoked release of NA and the reactivity of the renal vasculature to vasoconstrictor stimuli are reversibly reduced. Furthermore, possibly due to an impaired local degradation, the role of neurogenically released NPY in renal sympathetic vasoconstriction is enhanced after short‐term (15 min) ischaemia compared with control conditions.