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Thyroidal vascular responsiveness to parasympathetic stimulation is increased in hyperthyroidism
M Dey1, M Michalkiewicz, L J Huffman
1Department of Physiology, School of Medicine, West Virginia University, Morgantown 26506.
The American Journal of Physiology
|March 1, 1993
Summary
Thyroxine (T4) pretreatment enhances thyroid blood flow (TBF) response to parasympathetic nerve stimulation. This suggests hyperthyroidism increases thyroid vascular sensitivity to parasympathetic control.
Area of Science:
- Physiology
- Endocrinology
- Neuroscience
Background:
- Thyroid blood flow (TBF) regulation involves both sympathetic and parasympathetic nerves.
- Thyroxine (T4) pretreatment sensitizes the thyroid gland to thyrotropin.
- The effect of T4 on parasympathetic regulation of TBF is not well understood.
Purpose of the Study:
- To investigate if T4 pretreatment sensitizes the thyroid to parasympathetic stimulation of TBF.
- To determine the role of muscarinic receptors in mediating TBF changes.
Main Methods:
- Rats were pretreated with T4 or left untreated.
- Superior laryngeal nerves (SLN) were stimulated in anesthetized rats.
- Thyroid blood flow (TBF) measured by laser Doppler flowmetry (LDF).
- Thyroid vascular conductance (TVC) assessed using the microsphere technique.
- Muscarinic receptor blockade with atropine was employed.
Main Results:
- SLN stimulation did not affect TBF or TVC in untreated rats.
- T4 pretreatment significantly increased TBF (65 +/- 21%) and TVC upon SLN stimulation.
- Atropine administration blocked the T4-induced increase in TVC, indicating muscarinic receptor involvement.
Conclusions:
- Thyroidal vascular responsiveness to parasympathetic stimulation is enhanced in a hyperthyroid state.
- T4 pretreatment increases thyroid vascular sensitivity to parasympathetic nerve activity.
- Muscarinic receptor activation mediates the parasympathetic control of TBF in hyperthyroidism.