Hypothalamic Control of Adrenergic Outflow to the Stomach in the Cat

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Abstract
Experiments were performed on chloralosed, adrenalectomized cats with recording of gastric volume, blood pressure and skeletal muscle blood flow. The vagal nerves were cut, but the vagal excitatory fibres to the stomach could be activated by electric stimulation. Topical stimulation of the hypothalamic defence area, or surrounding “pressor” areas, produced not only the characteristic known circulatory responses, but also a prompt and often complete inhibition of a vagally induced increase of gastric motility.‐But when the stomach was not under the influence of continuous vagal excitatory activity, corresponding stimulation of the hypothalamus rarely had any effect on gastric volume, and then only an insignificant and sluggish increase despite considerable “myogenic” tone of the stomach. Stimulation of the adjacent hypothalamic sympatho‐inhibitory area, on the other hand, augmented the vagally induced gastric motility and thereby suggested the presence of a centrally induced suppression of a prevailing sympathetic inhibitory influence on the stomach.‐All the above mentioned effects on gastric volume, produced by central nervous stimulation, could be blocked by guanethidine in these vagotomized cats. It is concluded that the hypothalamus contains neural mechanisms, which can affect stomach motility by changing in both directions the impulse frequency in the inhibitory adrenergic outflow to this organ. Simultaneous activity of vagal excitatory fibres to the stomach was found to be a prerequisite for reducing significantly gastric motility and tone when the adrenergic fibres were excited. This is compatible with the hypothesis that the adrenergic fibres exert their inhibitory effect mainly, or only, by acting on the parasympathetic ganglionic cells, which mediate the vagal excitatory influence to the gastric smooth muscles.