Hypothalamic and plasma total nitrate/nitrite concentrations in spontaneously hypertensive rats.

Stable end-products of nitric oxide (NO) metabolism, nitrates and nitrites, were measured in hypothalamic extracts and plasma samples of Okamoto spontaneously hypertensive (SH) rats. The mean total nitrate/nitrite concentration was significantly lower in the hypothalami of SH rats compared with the normotensive Wistar Kyoto (WKY) control animals (P < 0.01). In contrast, their plasma concentrations were significantly higher (P < 0.05). These results indicate that the hypertensive state in SH rats is associated with a diminished production of hypothalamic NO, while the raised plasma nitrate/nitrite levels could reflect an increased compensatory endothelial NO synthase activity in these animals compared with the WKY controls.