Modulation of noradrenaline and neuropeptide Y (NPY) release in the pig kidney in vivo: involvement of alpha2, NPY and angiotensin II receptors

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Abstract
The modulation of the release of noradrenaline (NA) and neuropeptide Y-like immunoreactivity (NPY-LI) was investigated in the pig kidney in vivo. Under control conditions a reproducible co-release of NA and NPY-LI was obtained upon stimulation of the renal nerves with 5 Hz for 1 min. Infusion of peptide YY (PYY, 1 μg/kg/min i.v.), which binds to NPY receptors, caused renal vasoconstriction and reduced the stimulation-evoked overflow of NA and NPY-LI by 24 ± 4 and 33 ± 11%, respectively (P < 0.01). The PYY effect was reversible and was absent 1 h after the infusion. The alpha2-adrenoceptor antagonist yohimbine (0.2 mg/kg i. v.) enhanced the overflow of NA and NPY-LI 2- to 3-fold. The angiotensin converting enzyme inhibitor captopril (5 mg/kg i. v.) did not significantly affect the overflow of NA or NPY-LI evoked by the nerve stimulation. Angiotensin II (0.5 μg/kg/min i. v.), on the other hand, induced a reversible enhancement of the overflow of both NA and NPY-LI by 71 and 77%, respectively (P2-adrenoceptors by endogenous NA. Furthermore, angiotensin II receptor stimulation facilitates the release whereas endothelin has no major effect on transmitter secretion.