Changes in the mRNA and peptide levels of neuropeptide Y (NPY) in the adrenal gland and brain areas of spontaneously hypertensive rats (SHR) and of age-matched normotensive rats were investigated. The level of adrenal NPY mRNA of SHR decreased during progression of hypertension and was lower than that of Wistar-Kyoto (WKY) and Sprague-Dawley (SD) rats in the early stage of hypertension, while the level of adrenal NPY was unchanged or even higher than that of control rats. These findings suggest that both the biosynthesis and release of vasoconstrictive NPY peptide in the adrenal glands of SHR might decrease during progression of hypertension. In contrast, the NPY mRNA level neither decreased remarkably until week 17 in the cerebral cortex of SHR, nor changed at all in the other brain areas. This late decrease in cerebral NPY gene expression might be related to the disturbance in behavior and memory of SHR.