Protein expression of somatostatin receptor 2, somatostatin receptor 5 and dopamine D2 receptor in normal pituitary gland and ACTH-secreting pituitary adenoma in dogs

Res Vet Sci. 2018 Aug:119:61-66. doi: 10.1016/j.rvsc.2018.04.015. Epub 2018 May 4.

Abstract

Purpose: To evaluate the protein expression of somatostatin receptor (SSTR) 2, SSTR5 and dopamine D2 receptor (DA2R)-targets of somatostatin analogs and dopamine agonists-in normal canine pituitary and canine adrenocorticotropic hormone (ACTH)-secreting pituitary adenomas.

Methods: Six normal canine pituitary glands and 14 canine ACTH-secreting pituitary adenoma cases were included in this study. The protein expression of SSTR2, SSTR5 and DA2R was determined by double-label immunofluorescence staining of these receptors and ACTH.

Results: SSTR2, SSTR5, and DA2R proteins were expressed in the anterior and intermediate lobes of normal canine pituitary glands. In the anterior pituitary lobes, the percentages of SSTR2-, SSTR5-, and DA2R-positive cells among the ACTH-positive population were 27.0 ± 8.6%, 27.9 ± 5.9%, and 34.0 ± 9.4%, respectively. In contrast, the corresponding percentages in the intermediate pituitary lobes were 97.8 ± 1.5%, 94.1 ± 4.4%, and 96.1 ± 6.6%, respectively. Of the 14 ACTH-secreting pituitary adenoma cases, 11, 12, and 6 cases expressed SSTR2, SSTR5, and DA2R, respectively. Additionally, four cases showed strong positive staining for both SSTR2 and SSTR5. Two of these were ACTH-secreting pituitary adenomas likely derived from the intermediate pituitary lobe, because these are α-Melanocyte-stimulation hormone (α-MSH)-positive stains.

Conclusion: Immunohistological detection and characterization of SSTR2, SSTR5 and DA2R may provide useful additional information for determining treatment options when an ACTH-secreting pituitary adenoma cannot be completely resected, or in the case of recurrence.

Keywords: Canine Cushing's disease; Dopamine D2 receptor; Somatostatin receptor 2; Somatostatin receptor 5.

MeSH terms

  • ACTH-Secreting Pituitary Adenoma / metabolism
  • ACTH-Secreting Pituitary Adenoma / veterinary*
  • Adenoma / metabolism
  • Adenoma / veterinary*
  • Animals
  • Dog Diseases / metabolism*
  • Dogs
  • Pituitary Gland / metabolism*
  • Pituitary Neoplasms
  • Receptors, Dopamine D2 / metabolism*
  • Receptors, Somatostatin / metabolism*
  • Somatostatin

Substances

  • Receptors, Dopamine D2
  • Receptors, Somatostatin
  • Somatostatin
  • somatostatin receptor 2