Ratios of alpha to beta TSH mRNA in normal and hypothyroid pituitaries and TSH-secreting tumors.

We have studied the relationship between the levels of the alpha and beta subunit of TSH and alpha and TSH-beta mRNA content in pituitaries from euthyroid, short-term, and long-term hypothyroid mice and in various mouse TSH-secreting tumors. TSH, alpha, and TSH-beta were determined by specific radioimmunoassay. alpha and TSH-beta mRNA content was measured by dot blot hybridization with labeled alpha or TSH-beta plasmid probes. Normal pituitaries contained an excess of both alpha protein and alpha mRNA compared to beta. However, in hypothyroidism there was an increase in TSH and in particular in beta such that the alpha/beta protein ratio approached 1. Similarly, a marked increase in TSH-beta mRNA led to an alpha/TSH-beta mRNA ratio of approximately 1. Ratios of alpha/TSH-beta protein and mRNA in TSH-secreting tumors varied widely. There was a fair, but imperfect, correlation between alpha and TSH-beta protein and mRNA levels. Although transcriptional control of alpha and TSH-beta production appears likely, posttranscriptional regulatory mechanisms also seem to be involved.