Inhibition by locally applied alpha-adrenoreceptor blocking drugs of the depressor response to stimulation of the anterior hypothalamus

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Abstract
Summary Cats were anaesthetized with pentobarbital sodium and the anterior hypothalamus was superfused with artificial cerebrospinal fluid through a push-pull cannula. Electrical stimulation of the superfused area with the tip of the cannula elicited a fall of the arterial blood pressure which was dependent on frequency and voltage. Maximal depressor response was obtained at 60 Hz with 2–4 V; further increase of the voltage often led to a rise of the arterial blood pressure. Superfusion of the anterior hypothalamus with the alpha-adrenoreceptor blocking drugs tolazoline, piperoxan, yohimbine or phentolamine caused a dose-dependent inhibition of the depressor response to hypothalamic stimulation. Tolazoline was less effective than the other drugs. Superfusion of the anterior hypothalamus with the alpha-sympathomimetic drug phenylephrine prior to and during superfusion with phentolamine abolished the inhibitory action of the latter drug. It is concluded that alpha-adrenoreceptors are present in the anterior hypothalamus and involved in the depressor response to electrical stimulation of this hypothalamic area.

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