Platelet neuropeptide Y and its vasoconstriction effect in rat

Specific radioimmunoassay showed that in rat neuropeptide Y (NPY) immuno--re-activities (IR) in platelets and platelet rich plasma (PRP) were respectively 90±16ng/10~7 platelets and 93±19 ng/ml. Both values were much greater than those in theplasma (1.2±0.1 ng/ml, P0.001) and platelet poor plasma (PPP) (1.7±0.3ng/ml, P0.001). The NPY--IR in rat platelets eluted at the same position as authen-tic NPY on reverse phase HPLC. The NPY-IR in the platelets prepared from the PRPaggregated maximally by collagen reduced to 34±5 ng/ 10~7 platelets, while the NPY-IR in the PPP prepared from the same PRP increased to 26±4 ng/ml. PPP 1.6 mlprepared from the aggregated PRP induced contraction of isolated rat caudal arterieswith the maximal tension of 380±80 mg; while the maximal contraction induced by1.6 ml of the same PPP pretreated with NPY anti--serum was only 190±40 mg (P0.001). Authentic NPY 1 nmol/L did not cause any contraction. The results indicatethat rat platelets contain a high concentration of NPY, which can be released during ir-reversible platelet aggregation. The NPY released can potentiate vasoconstriction re-sponses induced by co--released substances during platelet aggregation.