Substance P:: immunohistochemical localization and possible function in thyroid gland of the lizard Podarcis sicula (Reptilia, Lacertidae)

Tachykinins, such as substance P (SP), are a family of regulatory peptides involved in the modulation of the morphophysiology of the thyroid gland. The paper investigated by light microscopy techniques and radioimmunoassay the effects of SP on Podarcis sicula thyroid gland morphology and release of thyroid hormones (T3 and T4) and thyroid-stimulating hormone (TSH). Substance P significantly increased the plasma T3 and T4 levels and reduced TSH release. In agreement with these results, the morphology of the thyroid gland also appeared influenced after treatment with SP. Besides, SP was immunolocalized in the thyroid gland of P. sicula with the ABC complex. Substance P-immunoreactive fibres ran between the follicles and SP-immunoreactivity was evenly distributed on the apical cytoplasm of follicular cells. The results obtained indicate that this peptide may participate in the paracrine control of the P. sicula thyroid gland.