Carotid vascular control of ACTH secretion in lambs

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Abstract
To test the hypothesis that changes in carotid vascular pressure influence ovine ACTH and corticosteroid secretion, 6-7 wk-old conscious lambs were subjected to bilateral carotid occlusion with or without prior vagosympathetic blockade. Reversible vagosympathetic blockade, produced by injection of 2% lidocaine onto the vagosympathetic trunks, inhibited the reflex changes in heart rate after i.v. injection of phenylephrine or during carotid occlusion. Vagosympathetic blockade by itself did not alter arterial pressure or heart rate but did increase circulating levels of ACTH and corticosteroids. Afferent fibers in the vagosympathetic trunks tonically inhibit the secretion of ACTH. Bilateral carotid occlusion did not change plasma ACTH or corticosteroid concentrations. Bilateral carotid occlusion plus prior vagosympathetic blockade stimulated increases in plasma ACTH and corticosteroid concentrations that were larger than responses to vagosympathetic blockade alone. Changes in carotid vascular pressure influence ovine ACTH and corticosteroid secretion only during vagosympathetic blockade. Carotid vascular mechanoreceptors apparently interact with other mechanoreceptors having vagosympathetic afferent fibers.

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