ANTAGONISTIC EFFECT OF D-MYO-INOSITOL-1,2,6-TRISPHOSPHATE (PP56) ON NEUROPEPTIDE Y-INDUCED VASOCONSTRICTION IN THE FELINE DENTAL-PULP

Intra-arterial injection of neuropeptide Y (NPY) (1.3-2.0 mu g/kg) res ulted in decreases of pulpal blood flow by 37.7 +/- 5.7% (mean +/- SEM ). The intra-arterial injection of D-myo-inositol-1,2,6-trisphosphate (PP56) (0.3 mg/kg) alone changed pulpal blood dow by 1.0%. The effect of NPY in the presence of PP56 resulted in significantly smaller decre ases in pulpal blood flow ranging from 27.2 +/- 5.4 to 16.6 +/- 3.5% f rom control as compared with NPY alone. In effect, PP56 partially bloc ked the decreases in pulpal blood flow caused by NPY. The electrical s timulation of the sympathetic nerve alone resulted in decreases in pul pal blood flow of 41.7 +/- 6.2%. The electrical stimulation of the sym pathetic nerve following the intra-arterial administration of PP56 dec reased pulpal blood dow by 23.1 +/- 6.0% from control, significantly l ess than the sympathetic nerve stimulation alone. PP56 attenuated the decrease in pulpal blood flow caused by the sympathetic nerve stimulat ion by 44.4 +/- 11.0%. Similarly, the combination of PP56 and phentola mine followed by electrical stimulation of the sympathetic nerve reduc ed the decrease in pulpal blood dow caused by the sympathetic nerve st imulation alone by 43.0 +/- 8.6%. These results provide evidence that the non-peptide PP56 is capable of antagonizing vasoconstriction cause d by NPY in the feline dental pulp. In addition, they show functional evidence that NPY as well as noradrenaline are released from the sympa thetic nerve endings during its stimulation and cause vasoconstriction . Copyright (C) 1996 Published by Elsevier Science Ltd.