Abstract
The effects of the pharyngeal non-noxious mechanical stimulation on the secretion of immunoreactive thyroxin (iT4), immunoreactive calcitonin (iCT), and immunoreactive parathyroid hormone (iPTH) into thyroid venous blood were examined in anesthetized rats. Secretion rates of iT4, iCT, and iPTH were calculated from their concentration in thyroid venous plasma and the plasma flow rate. A mechanical stimulation was delivered to the pharynx by a rubber balloon placed on the tongue that was intermittently pushed into the pharyngeal cavity. Pharyngeal stimulation increased iT4 and iCT secretion, but iPTH secretion was unchanged. The secretion responses were abolished by transecting the superior laryngeal nerves (SLNs) bilaterally. The activities of the thyroid parasympathetic efferent nerves and the afferent nerves in the SLN increased significantly during pharyngeal stimulation. These results indicate that pharyngeal mechanical stimulation promotes thyroxin and calcitonin secretion from the thyroid gland by a reflex increase in SLN parasympathetic efferent activity, triggered by excitation of SLN mechanoreceptive afferents.
Highlights
The autonomic nerve fibers’ distribution to widespread visceral organs contributes to the regulation of various physiological functions
superior laryngeal nerves (SLNs), that the sympathetic and parasympathetic efferent fibers antagonistically regulate the secretion of immunoreactive thyroxin, immunoreactive triiodothyronine, and immunoreactive calcitonin from the thyroid gland, whereas the sympathetic nerve promotes the secretion of immunoreactive parathyroid hormone from the parathyroid gland [6]
This study aimed to clarify whether pharyngeal mechanical stimulation promotes iT4 and immunoreactive calcitonin (iCT) secretion from the thyroid gland, without changes in immunoreactive parathyroid hormone (iPTH) secretion from the parathyroid gland, in anesthetized rats, and if so, whether the SLN is involved in that reflex using afferent and efferent pathways
Summary
The autonomic nerve fibers’ distribution to widespread visceral organs contributes to the regulation of various physiological functions. We have shown, by stimulating at a supramaximal intensity the cut peripheral portion of either CSTs or SLNs, that the sympathetic (inhibitory effects) and parasympathetic (excitatory effects) efferent fibers antagonistically regulate the secretion of immunoreactive thyroxin (iT4), immunoreactive triiodothyronine (iT3), and immunoreactive calcitonin (iCT) from the thyroid gland, whereas the sympathetic nerve promotes the secretion of immunoreactive parathyroid hormone (iPTH) from the parathyroid gland [6]. The majority of myelinated fibers in the SLN are afferent fibers [7], and pre- and postganglionic autonomic efferent fibers are unmyelinated in rats [7,8,9] These findings led us to hypothesize that excitation of sensory afferents in SLN may produce a reflex increase in the efferent activity of the SLN parasympathetic thyroid branches to promote hormonal secretion into thyroid venous blood
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