Immunocytochemical localization of adrenocorticotropic hormone-immunoreactive cells of the pars intermedia in thoroughbreds.

The research investigates the connection between the enlargement of the pituitary gland (specifically the pars intermedia region) and potential overproduction of ACTH hormone in Thoroughbred mares, and suggests that such a condition could be associated with hyperadrenocorticism.

Research Methodology

• The research involved analyzing 165 Thoroughbred mares that had been euthanatized or had died due to different causes. These mares showed no clinical signs of hyperadrenocorticism.
• Morphologic analysis of the pituitary gland was carried out post-mortem on eight randomly picked mares (between 5 and 15 years old), having normal-sized pituitary glands, and five older horses (between 17 to 25 years old), which demonstrated an enlarged pituitary gland.
• The research primarily focused on comparing the pituitary glands of horses with pituitary tumors (adenoma) of the pars intermedia (PI) with those that had normal pituitary glands.
• Immunocytochemistry and morphometry were applied in the analysis and characterization of any potential adenoma and hyperplasia of the PI.

Research Findings

• In horses where the pituitary gland was normal, the PI region was observed to have a complex network of capillaries or sinusoidal plexus, linking the pars distalis (PD) and pars nervosa (PN) regions. The PI cells stained slightly with ACTH antiserum, however, some cells on the borderline of the PD region showed a strong response to ACTH antiserum.
• Among the horses with enlarged pituitary glands, adenoma was detected, impacting the PI region. The cells around the borderline region were hypertrophied and responded strongly to the ACTH antiserum. The area and number of individual tumor cells in the PI borderline region were significantly increased when compared to those in the horses with normal-sized glands.
• The findings conclude that the PI-PD border region cells could secrete substantial quantities of ACTH due to stimulation by corticotropin-releasing factor.
• It also suggests the possibility that enlarged pituitary gland, specifically adenoma and hyperplasia of the PI region, in Thoroughbred mares could be associated with hyperadrenocorticism.

Research Implications

• This research provides significant insight into the potential role of the PI region of the pituitary gland in the overproduction of the ACTH hormone in Thoroughbred mares, a condition that could be correlated with hyperadrenocorticism.
• The significant increase in the area and number of tumor cells in horses with pituitary adenomas compared to those with normal glands aids in the understanding of the morphologic changes that occur in such cases.
• This research may help in the development of more accurate diagnostic techniques and targeted treatment strategies for equine pituitary gland disorders, specifically in the case of Thoroughbred mares.