Quantification of growth hormone mRNA in blood.

Abstract Background Growth hormone (GH) is present in human lymphocytes and the relative concentration of GH mRNA in circulating cells is reportedly increased in patients with acromegaly. No quantitative assay has been described to measure GH in circulating cells. Methods To measure GH mRNA, we used real-time reverse-transcriptase (RT) quantitative PCR (qPCR) with nested primers, a synthetic nucleotide standard and SYBR Green I detection. Blood samples from volunteers with and without pituitary disorders were collected in PAXgene Blood RNA tubes. Essential MIQE guidelines were followed during sample preparation and assay development. Results RT-qPCR assay was specific for GH mRNA and was linear from ≤ 90 to ≥ 90,000 copies of GH mRNA per reaction. Day-to-day imprecision (CV) was 31%–46% at mean concentrations of 3400 and 2630 copies/mL of blood, respectively (n = 10). The variability (CV) of results in samples collected from a single individual over a year and assayed in a single run was 28% (n = 17 samples). The mean concentrations of GH mRNA in blood were statistically indistinguishable in patients with acromegaly, control subjects, and patients receiving replacement doses of recombinant GH. Moreover, GH mRNA concentrations in blood were not correlated with concentrations of insulin-like growth factor-I in plasma. Conclusions The RT-PCR assay quantifies GH mRNA at concentrations present in circulating cells. The present study suggests that the absolute concentration of GH mRNA in circulating cells is not altered in patients with acromegaly.