Heat shock of cultured gc cells enhances the level of triiodothyronine induced growth hormone (gh) and gh messenger ribonucleic acid

We have previously proposed that the effects of heat shock on thyroid hormone-responsive rat pituitary tumor (GC) cells may be a model relevant to the in vivo effects of nonthyroidal disease on thyroid hormone action. To determine the effects of heat shock on thyroid hormone responses, GC cells (normally cultured at 37 C) were studied after incubation at 41 C. After 18 h at 41 C there was enhanced synthesis of proteins (mol wt, 70,000 and 90,000) considered to be universal markers of the cellular response to heat shock. Incubation at 41 C also resulted in a significant decrease in GC cell viability and (after 24 h) arrest of GC cell growth. However, the induction of GH synthesis by T₃ was significantly enhanced in GC cells stressed by incubation at 41 C. The addition of 5 nM T₃ to thyroid hormone-depleted GC cells resulted in a significantly greater (P ≪ 0.001) accumulation of GH (2642 ± 280 ng/18 h) during 41 C incubation than during 37 C incubation (1223 ± 175 ng/18 h). The enhanced T₃-induced production of GH was coincident with a proportional increase (P ≪ 0.05) in cellular GH mRNA determined by dot hybridization analysis. Thus, the stress of 41 C incubation elicits a heat shock response in GC cells characterized by decreased viability and growth arrest, but enhanced accumulation of GH mRNA in response to T₃. Our recent report on the identical effects due to the stress of implantation of the Walker 256 carcinoma on T₃-induced rat pituitary GH mRNA in vivo suggests that heat shock of cultured GC cells is a valid in vitro model of nonthyroidal disease.