Detection of growth hormone, prolactin and human beta-chorionic gonadotropin messenger RNA in growth-hormone-secreting pituitary adenomas by in situ hybridization

Abstract

In a series of 39 adenomas from patients with the clinical hyperfunction syndrome of acromegaly and in one from a case of prolactinoma we studied the mRNA expression of growth hormone (GH), prolactin (PRL) and beta-human chorionic gonadotropin (HCG) by using this technique of in situ hybridization (ISH). This technique allows the direct identification and localization of cells expressing mRNA and thus synthesizing the respective hormone. The aim of our study was to demonstrate the frequent co-expression of PRL mRNA and HCG mRNA in pituitary adenomas of acromegalic patients. Probes for ISH of the above-mentioned hormones were obtained by subcloning cDNA fragments into pGEM plasmids. Subsequent Sp6-polymerase catalysed in vitro transcription with 35S-CTP revealed radiolabelled single-stranded antisense RNA probes [the probe for beta HCG detects beta-luteinizing hormone (beta LH) simultaneously because of a sequence homology of 90%]. To localize the labelled hybrids, autoradiography was carried out. Light microscopical evaluation of the tissue sections demonstrated positive signals in all cases for GH, in 80% of cases for PRL and in 25% of cases for HCG [LH] mRNA. The comparison of mRNA content shown by ISH with immunocytochemical (ICC) hormone detection revealed that in all cases the detection of GH corresponded to GH mRNA content of the cells. For PRL and HCG [LH] positive mRNA detection (ISH) and negative hormone detection (ICC) occurred in some cases (PRL 17.5%; HCG [LH] 15%). In contrast, negative mRNA detection (ISH) and positive hormone content (ICC) was also demonstrated (PRL 5%; HCG [LH] 37.5%). The remaining adenomas showed both mRNA and the respective hormone, as well as negative ISH and ICC.