Evaluation of pituitary gland anatomy and histopathologic findings in clinically normal horses and horses and ponies with pituitary pars intermedia adenoma.

The research examined the role of pituitary gland size and weight in normal horses versus those with pituitary pars intermedia adenoma (PPIA), seeking associations related to sex and age, and exploring potential implications for issues like insulin resistance and laminitis.

Methodology of the Research

• The team used pituitary gland samples from 100 horses without noticeable PPIA symptoms and 36 horses and ponies that were diagnosed with PPIA.
• The glands were weighed, measured, and then subjected to histologic examination, using H&E staining. Masson trichrome and periodic acid-Schiff staining were utilized when necessary.
• Different types of histologic lesions in two parts of the pituitary, the pars intermedia and the pars distalis, were identified and characterized as no significant lesions, single or multiple cysts, focal or multifocal hyperplasia, single or multiple microadenomas, and adenoma.
• To maintain consistency, the relative pituitary weight (RPW) was calculated with the formula: RPW = pituitary weight (grams) / body weight (grams).

Key Findings

• The prevalence of pituitary lesions increased with age in geldings, mares, and non-pregnant mares, implicating the role of age in the pathogenesis of these lesions.
• The study found no significant difference in the RPW between horses and ponies diagnosed with PPIA, indicating that the ailment impacts both species similarly in terms of pituitary gland size.
• The maximum recorded pituitary weight in a horse with PPIA was 13.9 grams, with an RPW of 2.9 X 10(-5).
• A positive correlation was identified between plasma glucose concentration and RPW in ponies diagnosed with PPIA, suggesting that the disease may be linked to metabolic disorders such as insulin resistance.

Conclusions and Implications

• The findings suggest that pituitary lesions can be a factor in horses experiencing problems like insulin resistance and laminitis, even before the physical manifestation of PPIA symptoms.
• The study also speculates a potential role of ovarian steroids in the formation of lesions in the pars intermedia, indicating a need for further investigation into the hormone-related pathogenesis of pituitary diseases in horses.