Activity of centrally truncated analogues of neuropeptide Y at Y1 and Y2 receptor subtypes in vivo

Neuropeptide Y1- and Y2-receptor-mediated cardiovascular effects in the anesthetized guinea pig, rat, and rabbit

Neuropeptide Y (NPY) causes vasoconstriction through Y1-receptors and inhibits vagal bradycardia through presynaptic Y2-receptors. These effects of NPY were investigated in anesthetized guinea pigs, rats, and rabbits to find the most suitable species for evaluation of Y1- and Y2-active agents in vivo. The increase in blood pressure (through Y1) of lower doses of NPY was similar in the three species (ED50, 0.9 +/- 0.13, 0.8 +/- 0.39, and 0.6 +/- 0.09 nmol/kg, respectively), but higher doses had depressor effects in four of six rats. Vagal bradycardia, induced by electrical stimulation of the right cervical vagus nerve, was inhibited by NPY in the guinea pig and in the rat (ED35, 3.5 +/- 0.46 and 11.2 +/- 1.79 nmol/kg, respectively; p < 0.05) but not in the rabbit. In the guinea pig, the Y2-receptor-preferring fragment NPY(3-36) and the selective Y1-receptor antagonist H 409/22 were used to confirm that the increase in blood pressure was mediated solely through the Y1-receptor and the vagal inhibition solely through the Y2-receptor. Aside from the cardiovascular effects, NPY caused a decrease in the body temperature and inhibited vagal bronchoconstriction in this species. Considering that NPY may cause depressor effects in the rat and has no effect on the vagal bradycardia in the rabbit, the guinea pig is preferable to both these species for assessment of Y1- and Y2-receptor-active agents in vivo.

Aspects of the molecular structure and dynamics of neuropeptide Y

Human neuropeptide Y (hNPY) and the Q34-->P34 mutant (P34-hNPY) have been characterized by CD spectroscopy. hNPY self-associates in aqueous solution with a dimerization constant in the micromolar range. The self-association correlates with an increase in secondary-structure content which was studied as a function of concentration, temperature and pH. The effects of temperature were measured in water (5-84 degrees C) and in ethanediol/water (2 : 1) (-90 degrees to +90 degrees C). A single-residue mutation, Q34-->P34, affects the pH, thermal and self-association properties of NPY. The CD results are correlated with photochemically induced dynamic nuclear polarization NMR experiments which show that the tyrosines at the interface between two monomer units present limited accessibility to a photoreactive dye. An equilibrium state is described, involving a PP-fold monomer form and a handshake dimer form, that accommodates the physicochemical properties of NPY.