A study of pituitary thyrotropin, its subunits, and messenger ribonucleic acids in nonthyroidal illness

We studied serum TSH, pituitary TSH and alpha and beta-subunits of TSH and their messenger ribonucleic acids (mRNAs) in three models of nonthyroidal illness (NTI) in the rat, ie diabetes mellitus (1 wk after 65 micrograms streptozotocin/g BW IP), turpentine oil-injection (8 to 48 hours after after a dose of 5 microliter/g bw SC), and complete fasting for 72 hours. Euthyroid, hypothyroid (two months after thyroidectomy) and hyperthyroid rats (30 micrograms T4/d X 7, SC) were also studied for comparison. Pituitary TSH, alpha and beta subunits and serum TSH, T4, and T3 were measured by RIA. Pituitary mRNAs coding for common delta and TSH-beta subunits were determined by cytoplasmic dot hybridization technique using specific [32P]-cDNA probes. In all NTI models there were significant decreases in serum levels of TSH, T4, and T3, but no significant changes were observed in the pituitary content of TSH, and alpha and TSH-beta subunits. Hypothyroid rats had an increase in serum TSH, pituitary TSH, and pituitary TSH-beta subunit and a decrease in pituitary alpha subunit. On the other hand, hyperthyroid rats showed a decrease in serum TSH, pituitary TSH, and pituitary TSH-beta subunit, while there was no change in the alpha subunit. A significant reduction in the pituitary TSH-beta mRNA levels was observed in all NTI models and hyperthyroidism, while TSH-beta mRNA was increased in thyroidectomized rats. alpha-mRNA was increased only in the pituitary of hypothyroid rats; there was no appreciable change in the pituitary alpha-mRNA in the various other pituitary groups.(ABSTRACT TRUNCATED AT 250 WORDS)