Expression of the parathyroid hormone-related peptide gene in rat tissues.

We have demonstrated that parathyroid hormone-related peptide (PTHrP) mRNA is expressed ubiquitously in normal tissues of the rat, including organs previously considered to be transcriptionally silent. We reverse transcribed PTHrP and PTH mRNA and amplified the resultant cDNA using the polymerase chain reaction. The level of transcriptional activity of PTHrP was highly variable in different tissues, suggesting tissue-specific regulation. Significant PTHrP gene activity in the nonlactating mammary gland of the pregnant rat suggests that PTHrP may be involved in mammary differentiation. PTHrP gene expression was detected throughout the gastrointestinal tract and in cardiovascular tissues, suggesting that it might act as an autocrine and/or paracrine regulatory factor and may be the natural ligand for the receptors discovered originally in these tissues using PTH analogs. In contrast, PTH gene activity is restricted to the parathyroids, under physiologic conditions.