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Open access

Shinsuke Uraki, Hiroyuki Ariyasu, Asako Doi, Hiroto Furuta, Masahiro Nishi, Takeshi Usui, Hiroki Yamaue and Takashi Akamizu

Summary

A 54-year-old man had gastrinoma, parathyroid hyperplasia and pituitary tumor. His family history indicated that he might have multiple endocrine neoplasia type 1 (MEN1). MEN1 gene analysis revealed a heterozygous germline mutation (Gly156Arg). Therefore, we diagnosed him with MEN1. Endocrinological tests revealed that his serum prolactin (PRL) and plasma adrenocorticotropic hormone (ACTH) levels were elevated to 1699 ng/mL and 125 pg/mL respectively. Immunohistochemical analysis of the resected pancreatic tumors revealed that the tumors did not express ACTH. Overnight 0.5 and 8 mg dexamethasone suppression tests indicated that his pituitary tumor was a PRL-ACTH-producing plurihormonal tumor. Before transsphenoidal surgery, cabergoline was initiated. Despite no decrease in the volume of the pituitary tumor, PRL and ACTH levels decreased to 37.8 ng/mL and 57.6 pg/mL respectively. Owing to the emergence of metastatic gastrinoma in the liver, octreotide was initiated. After that, PRL and ACTH levels further decreased to 5.1 ng/mL and 19.7 pg/mL respectively. He died from liver dysfunction, and an autopsy of the pituitary tumor was performed. In the autopsy study, histopathological and immunohistochemical (IHC) analysis showed that the tumor was single adenoma and the cells were positive for ACTH, growth hormone (GH), luteinizing hormone (LH) and PRL. RT-PCR analysis showed that the tumor expressed mRNA encoding all anterior pituitary hormones, pituitary transcription factor excluding estrogen receptor (ER) β, somatostatin receptor (SSTR) 2, SSTR5 and dopamine receptor D (D2R). PRL-ACTH-producing tumor is a very rare type of pituitary tumor, and treatment with cabergoline and octreotide may be useful for controlling hormone levels secreted from a plurihormonal pituitary adenoma, as seen in this case of MEN1.

Learning points:

  • Although plurihormonal pituitary adenomas were reported to be more frequent in patients with MEN1 than in those without, the combination of PRL and ACTH is rare.

  • RT-PCR analysis showed that the pituitary tumor expressed various pituitary transcription factors and IHC analysis revealed that the tumor was positive for PRL, ACTH, GH and LH.

  • Generally, the effectiveness of dopamine agonist and somatostatin analog in corticotroph adenomas is low; however, if the plurihormonal pituitary adenoma producing ACTH expresses SSTR2, SSTR5 and D2R, medical therapy for the pituitary adenoma may be effective.

Open access

Etienne Larger, Nicolai J Wewer Albrechtsen, Lars H Hansen, Richard W Gelling, Jacqueline Capeau, Carolyn F Deacon, Ole D Madsen, Fumiatsu Yakushiji, Pierre De Meyts, Jens J Holst and Erica Nishimura

Summary

Glucagon stimulates hepatic glucose production by activating specific glucagon receptors in the liver, which in turn increase hepatic glycogenolysis as well as gluconeogenesis and ureagenesis from amino acids. Conversely, glucagon secretion is regulated by concentrations of glucose and amino acids. Disruption of glucagon signaling in rodents results in grossly elevated circulating glucagon levels but no hypoglycemia. Here, we describe a patient carrying a homozygous G to A substitution in the invariant AG dinucleotide found in a 3′ mRNA splice junction of the glucagon receptor gene. Loss of the splice site acceptor consensus sequence results in the deletion of 70 nucleotides encoded by exon 9, which introduces a frame shift and an early termination signal in the receptor mRNA sequence. The mutated receptor neither bound 125I-labeled glucagon nor induced cAMP production upon stimulation with up to 1 µM glucagon. Despite the mutation, the only obvious pathophysiological trait was hyperglucagonemia, hyperaminoacidemia and massive hyperplasia of the pancreatic α-cells assessed by histology. Our case supports the notion of a hepato–pancreatic feedback system, which upon disruption leads to hyperglucagonemia and α-cell hyperplasia, as well as elevated plasma amino acid levels. Together with the glucagon-induced hypoaminoacidemia in glucagonoma patients, our case supports recent suggestions that amino acids may provide the feedback link between the liver and the pancreatic α-cells.

Learning points:

  • Loss of function of the glucagon receptor may not necessarily lead to the dysregulation of glucose homeostasis.

  • Loss of function of the glucagon receptor causes hyperaminoacidemia, hyperglucagonemia and α-cell hyperplasia and sometimes other pancreatic abnormalities.

  • A hepato–pancreatic feedback regulation of the α-cells, possibly involving amino acids, may exist in humans.