Rapid increase of calcitonin-specific mRNA after acute hypercalcemia

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Abstract
The regulation of calcitonin (CT) secretion by Ca was studied by measuring CT mRNA extracted from thyroids of normal rats subjected to acute Ca stimulation in vivo. The 15,000-MW primary translation product of CT mRNA was identified by immunoprecipitation using specific antibodies. While total mRNA and total radioactivity incorporated after translation of total mRNA remained unaffected by the Ca stimulation, a 4-fold increase in radioactivity incorporated in CT primary translation product occurred as early as 2 min after Ca administration. This peak coincided with a rise in plasma levels of the hormone and preceded a detectable decrease in tissue stores. Apparently, Ca ion, either directly or indirectly via its action on intracellular stores or the hormone or its precursors, causes a rapid increase in cell levels of translatable CT mRNA. In view of the extremely short time (2 min) in which this increase occurs, the action is probably at the post-transcriptional level as no increase in CT mRNA levels could be detected by hybridization assay using a specific c[complementary]DNA probe for human CT mRNA.