The influence of serotonin on follicular cells FRTL-5 in vitro

Serotonin is an aromatic monoamine found in parafollicular cells of rats, bats and in a human medullary thyroid carcinoma cell line. We have examined the hypothesis that serotonin stimulates follicular cells. The effect of serotonin in presence and absence of thyrotropin was studied in a cell line of rat follicular cells FRTL-5 (Fischer Rat Thyroid cells in Low serum) by measuring [3H]thymidine incorporation into cell DNA (growth assay) and by transmission electron microscopy. The cell line was used to avoid the contamination with serotonin secreted from parafollicular cells. Results show that serotonin at 3 microM, 10 microM, 30 microM, and 100 microM concentrations increases [3H]thymidine incorporation into cell DNA. Serotonin at a 1000 microM concentration reduces sharply the [3H]thymidine incorporation into cell DNA. All cytoplasmic organelles completely disappear, only a thin fibrous membrane remains. The toxic effect of serotonin is observed in the nuclei, too. As expected, thyrotropin stimulates follicular cells. Serotonin does not have any influence on that stimulative effect of thyrotropin. Rough endoplasmic reticulum consists of round vesicles, several mitochondria are present in the cytoplasm. From the surface few pseudopodia extend into the culture medium.