Electrodes were implanted in dogs in the dorsal portion of the medulla oblongata near the obex. A week or more later, the electrodes were stimulated while changes in plasma renin activity, plasma epinephrine and norepinephrine, and blood pressure were monitored. Stimulation of 20 points in 16 dogs produced clear-cut increases in plasma renin activity. In almost all instances, these increases were associated with marked increases in blood pressure. There was also a small increase in circulating epinephrine without a significant change in plasma norepinephrine. Stimulation of the medulla 4 h after renal denervation was not associated with any increase in plasma renin activity even though the pressor response was comparable to that before denervation. The response was also absent in dogs stimulated two week after renal denervation. The data show that renin secretion can be increased in association with marked increases in blood pressure. They also show that the increase produced by stimulation of the medulla oblongata is mediated via the renal nerves.

The α-adrenergic blocking agent, phenoxybenzamine, was found to have no effect on the increase in renin secretion produced by stimulation of the ‘pressor area’ of the medulla oblongata in dogs. The β-adrenergic blocking agent, propranolol, reduced the response when administered at two different dose levels. Administration of propranolol plus phenoxybenzamine completely abolished the increase. The data are consistent with the hypothesis that renin secretion is controlled, at least in part, by β-adrenergic receptors in the kidney.

Dopaminergic neurons arising from cell bodies in the rostral arcuate nucleus of the hypothalamus have been shown to make axoaxonic contact with neurohypophyseal neurosecretory axons. In this study, electrical stimulation of the rostral arcuate nucleus depresses multiunit electrical activity recorded from neurosecretory axons within the neurohypophysis. After a single 5-s stimulus train, neurohypophyseal electrical activity is reduced to 6% of control. The superfusion of dopamine (5 micrograms/microliters) onto the neurohypophysis also has an inhibitory effect. Superfusion directly onto the neurohypophysis of the dopamine-receptor antagonist, pimozide (1 micrograms/microliters), abolishes the inhibitory effect of arcuate nucleus stimulation. These findings suggest that the dopaminergic innervation of the neurohypophysis may have an inhibitory influence on the release of neurohypophyseal hormones.

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