Immunocytochemical localization of prolactin and growth hormone in the equine pituitary.

The research article investigates the cellular characteristics of prolactin and growth hormone cells within the pituitaries of intact pony mares, revealing two types of lactotrope cells, somatotrope cells, and another subset of cells containing both hormones.

Research Methods and Findings

• The research was conducted at an electron microscopic level, examining the ultrastructural and immunoreactive staining characteristics of cells containing prolactin (lactotropes) and growth hormone (GH; somatotropes) in the anterior pituitaries of pony mares.
• The lactotrope cells consisted of two morphological subsets labeled as Type I and Type II. Type I cells had larger sizes with large, dense, polymorphic granules scattered within the cytoplasm. In contrast, Type II cells were smaller and had small, dense, polymorphic granules predominantly found in peripheral cellular areas.
• The study found that these lactotrope cells made up between 5 to 16% of the total cell count in the pituitary.
• Somatotrope cells, on the other hand, were medium-sized and contained large and dense secretory granules. These somatotropes had the largest secretory granules found in the pituitary and made up 11 to 26% of the total cell count.

Further Findings and Conclusion

• Type I lactotropes and somatotropes presented distinctive characteristics even without immunocytochemical staining, implying the inherent differences between the cells.
• Double-labeling of pituitary sections showed that some cells contained both prolactin and GH. These cells, dubbed mammosomatotropes, looked morphologically similar to Type I lactotropes and constituted 6.5 to 16.5% of the total cell count.
• The study established that there are two cell populations that contain prolactin only (Type I and II lactotropes), one cell population containing GH only (somatotropes), and an additional cell subset that contains both GH and prolactin in the equine pituitary.