Neuropeptide Y and pancreatic polypeptide: effects on thyroid hormone secretion in the mouse.
Neuropeptide Y (NPY) is known to occur in adrenergic nerves within the thyroid gland and may thus be released concomitantly with noradrenaline upon adrenergic activation. In this study, the effects of combined administration of NPY and noradrenaline on thyroid hormone secretion were investigated under in vivo conditions in the mouse. Mice were pretreated with radioiodine and thyroxine: the subsequent release of radioiodine into blood upon stimulation is a reflection of the release of thyroid hormones since more than 90% of the released radioiodine is in the form of thyroid hormones. It was found that TSH enhanced the radioiodine levels in blood to 197 +/- 8% (P less than 0.01). Noradrenaline inhibited the TSH-induced thyroid hormone secretion to 168 +/- 6% (P less than 0.01), and NPY potentiated this inhibitory action of noradrenaline (P less than 0.01): the TSH-induced thyroid hormone secretion was only 19 +/- 6% after administration of both noradrenaline and NPY. Furthermore, alpha-adrenoceptor blockade by phentolamine abolished the effect of noradrenaline on TSH-induced thyroid hormone secretion and, during alpha-adrenoceptor blockade, NPY potentiated the secretory response to TSH. To study the specificity of the effects exerted by NPY, the influences of avian pancreatic polypeptide (APP) and bovine pancreatic polypeptide (BPP), which both show structural similarities to NPY, were also studied. However, in contrast to NPY, neither APP nor BPP had any effects on TSH-stimulated thyroid hormone secretion. Interestingly, an inhibitory action on non-stimulated radioiodine release (= TSH-independent thyroid hormone secretion) was seen in response to APP and BPP. This effect was not exerted by NPY.(ABSTRACT TRUNCATED AT 250 WORDS)
D000595:Amino Acid Sequence; D000818:Animals; D005260:Female; D007457:Iodine Radioisotopes; D051379:Mice; D009478:Neuropeptide Y / Q000494:pharmacology*; D009638:Norepinephrine / Q000494:pharmacology; D010191:Pancreatic Polypeptide / Q000494:pharmacology*; D013963:Thyroid Hormones / Q000378:metabolism*; D013972:Thyrotropin / Q000494:pharmacology; D013974:Thyroxine / Q000494:pharmacology
D007457:Iodine Radioisotopes; D009478:Neuropeptide Y; D013963:Thyroid Hormones; D010191:Pancreatic Polypeptide; D013972:Thyrotropin; D013974:Thyroxine; D009638:Norepinephrine