Growth regulation of porcine thyroid follicles in-vitro by growth factors.

Primarily intact thyroid follicles were isolated from explanted thyroid glands of hogs immediately after sacrifice. These intact thyroid follicles had a preserved polarity, still contained thyroglobulin, could be liberated from contaminating mesenchymal single cells and could be kept in culture for at least 14 days. They respond to bovine TSH (1 mU/ml) with a 10-fold increase in cAMP production within 15 min, trapp and organify iodine and secrete thyroid hormones. In contrast to thyroid monolayers, prepared from these thyroid follicles, intact thyroid follicles did not proliferate in response to bTSH (1-1000 uU/ml) stimulation. When thyroid follicles, however, were stimulated with EGF (1-5 ng/ml) a dose dependent increase in cell number as well as [3H]-thymidine incorporation into acid precipitable DNA was seen. The growth response of thyroid follicles to EGF (5 ng/ml) in comparison to thyroid monolayer cells was 275% versus 145% increase in cell number within 6 days. With IGF I, a proliferative response of thyroid follicles was found, and this was synergistic with simultaneous incubation with EGF. When thyroid follicles were incubated with EGF together with TSH, a dose dependent inhibition of [3H]-thymidine incorporation as well as cell number with increasing amounts of TSH (1-1000 mU/ml) occurred. The comparable effect was found, when thyroid follicles were stimulated to growth with IGF I (100 ng/ml).(ABSTRACT TRUNCATED AT 250 WORDS)