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

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.