Contents and release of human growth hormone1-43 (hGH1-43) in human pituitary glands and hGH-producing pituitary adenoma cells

Abstract

Human growth hormone1—43 (hGH1—43) is an amino terminal fragment of 22 kilodalton hGH (hGH1—191). In the present study, we developed a specific sandwich-type enzyme linked immunosorbent assay (ELISA) of hGH1—43. The minimal detectable dose was 3.5 × 10−4 pmol/well. hGH1—191 did not show any crossreactivity to hGH1—43 in the assay up to the dose of 0.25 pmol/well. Using this assay, we investigated the quantitative relationship between hGH1—191 and hGH1—43 in contents of normal human pituitary gland and hGH-producing adenoma cells. We also studied the release of hGH1—191 and hGH1—43 from cultured hGH-producing pituitary adenoma cells. Means (±SD) ratios of hGH1—43/hGH1—191 in the cytosolic fractions were 0.02 ± 0.01% in the normal pituitary and 0.07 ± 0.04% in hGH-producing adenoma cells, respectively. In static experiments, the ratio of hGH1—43/hGH1—191 was 1.21 ± 0.50% in the culture medium of hGH-producing pituitary adenoma cells. hGH1—191 and hGH1—43 were released in parallel in response to TRH, and the hGH1—43/hGH1—191 ratio was 1.37% in perifusion experiments. These observations suggest that the hGH1—43/hGH1—191 ratio in cell content is much lower than previously reported. It was also suggested that the ratio of hGH1—43/hGH1—191 is higher in the releasable pool of hGH in the pituitary and hGH1—43 might be secreted in a similar fashion to hGH1—191.