Platelet neuropeptide Y in spontaneously hypertensive rats

To investigate the pathological role of platelet neuropeptide Y (NPY) in genetically hypertensive rats, we measured the platelet content and plasma concentration of immunoreactive (ir)-NPY in hypertensive and normotensive rats and examined the aggregating ability of rat platelets and the NPY releasing reaction in each of these rat types. In addition, we purified platelet NPY and determined its amino acid sequence.

To characterize immunoreactive NPY in rat platelets, rat platelet NPY was purified to homogeneity and the purified peptide was analysed by gas-phase sequencer. Platelet content and plasma concentration of NPY was measured by a sensitive radioimmunoassay for NPY. Aggregating ability was examined by a turbidimetric method; aggregation was recorded for 5 min and the maximum aggregation was read.

Rat platelet NPY was purified and the amino acid sequence was determined to be YPSKPDNPGEDAPAEDMARYYSALRHYINLITRQRY. The platelet content of ir-NPY in 5-, 10-, and 15-week-old spontaneously hypertensive rats (SHR) was higher than that in Wistar-Kyoto (WKY) rats of the same age. The platelet content of ir-NPY in 10-week-old stroke prone-SHR was also higher than that in 10-week-old WKY rats. No differences were observed between any of the pairs in any WKY rats, SHR or stroke-prone SHR group with regard to the plasma concentration of ir-NPY. Ir-NPY was not released from rat platelets when adenosine diphosphate was used for aggregation. However, NPY was released from the platelets when they were aggregated by collagen and, furthermore, in this case the amount of NPY released from platelets was greater in SHR than in WKY rats.

That the platelet content of NPY in SHR (and stroke-prone SHR) was higher than that in WKY rats seems to be an important genetic characteristic of SHR. As NPY is a potent vasoconstrictor, it may be involved in the progression of vascular lesions.