The actions of neuropeptide Y and peptide YY on the hepatic arterial and portal vascular beds of the anaesthetized dog

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Abstract
1 The vascular actions of the two peptides, neuropeptide Y (NPY) and peptide YY (PYY) were compared with the transmitter noradrenaline (NA) on the arterial and portal vascular beds of the in situ liver of the anaesthetized dog. 2 The sole vascular response of the hepatic arterial vasculature to intra-arterial administration of either NPY or PYY was vasoconstriction; the duration of these responses was longer than that to NA. 3 The maximum hepatic arterial vasoconstrictor responses to PYY and to NPY were significantly different and they were both significantly less than the maximum to NA (P > 0.001). 4 In contrast to its activity on the splenic arterial vasculature PYY was not more potent, on a molar basis, than NPY as an hepatic arterial vasoconstrictor agent. However, both peptides were significantly more potent than NA (P > 0.005). 5 Neither peptide, when injected intraportally, caused any change in intrahepatic portal inflow resistance. 6 Both peptides when administered intraportally in doses which were free of systemic effects caused hepatic arterial vasoconstriction.