Hypotensive effect of fasting: possible involvement of the sympathetic nervous system and endogenous opiates.

Fasting lowers blood pressure to a greater extent in spontaneously hypertensive rats than in normotensive rats. While fasting reduced cardiac sympathetic activity to an equivalent extent in both groups of animals, only in the hypertensive rats did fasting elicit an opiate-mediated vasodepressor response that was independent of sympathetic withdrawal. Both sympathetic nervous system suppression and endogenous opiate activation, therefore, may contribute to the hypotensive effect of fasting in the spontaneously hypertensive rat.