Neuropeptide K potently stimulates the hydrolysis of phosphatidylinositol in the rat spinal cord.

The accumulation of total [3H]inositol phosphates stimulated by neuropeptide K was investigated in rat spinal cord slices and compared with that of substance P and carbachol. The rank order of potency of the agonists in stimulating [3H]phosphatidylinositol (PI) hydrolysis was neuropeptide K > substance P > carbachol. The PI responses to neuropeptide K and substance P were significantly (P < 0.01) enhanced when slices were incubated with a mixture of bacitracin (30 microM), captopril (10 microM) and leupeptin (2 micrograms/ml), yet the order of potency remained unchanged. These results show for the first time that NPK can stimulate the PI hydrolysis in the adult rat spinal cord. The relatively greater degree of potency and efficacy of NPK over SP to stimulate PI hydrolysis does not appear to be entirely attributed to the metabolic stability of the peptide.