Distribution of NPY, SP, CGRP in rat thyroid and change under condition of acute experimental hyperthyroidism(In English)

Previous work has shown that peptidergic nerve fibers of the thyroid gland contain vasoactive intestinal polypeptide (VIP), substance P (SP) and neuropeptide Y (NPY). They contact vessel walls and epithelial cells of follicles and regulate the activity of the smooth muscle and epithelium of the follicle. It is generally accepted that the hypothalamic- pituitary -thyroid axis regulates the activity of thyroid follicles. The action of NPY, CGRP and SP, especially in hyperthyroidism, is poorly understood. The acute hyperthyroidism rat model was induced by injection of thyroxine (T4). NPY, CGRP, SP were tested by RIA. The location and distribution of NPY, CGRP and SP were studied using immunohistochemistry. NPY positive nerve fibers surrounded the small blood vessels, and their terminals contacted endothelial cells of blood vessels. Some NPY and SP positive nerve fibers were localized in connective tissue between follicles, and their terminals contacted follicular epithelial cells. No CGRP positive nerve fibers were detected. CGRP positive cells were distributed within the epithelium of follicles or adjacent to follicles. Radioimmunoassay revealed a higher level of NPY and SP in experimental rats following T4 application as compared with control rats, but the level of CGRP was lower than in controls. In hyperthyroidism, increased vasoconstriction caused by increasing of NPY overcomes the weakened vasodilation effects of CGRP decreasing to decrease blood flow and controls T4 into blood circulation. This balance may be considered as one of homeostasis mechanism under process of pathology [Acta Zoologica Sinica 54(5): 830–835, 2008].