Colloid in the anterior pituitary of helmet guinea fowl (Numida meleagris galeata): morphometric analysis and pattern of occurrence in relation to apoptosis.

Colloidal accumulations in the pars distalis of helmet guinea fowls at various ages from 1 to 450 days were examined by Periodic acid-Schiff reaction, immunohistochemistry and electron microscopy. Round, ovoid and elongated colloids were observed. Colloids (69.5 +/- 2.997) with 0.169 +/- 0.014 microm mean diameter were already present in a 1-day-old bird. Numerous colloids were encountered in 450 days old birds (2931.333 +/- 29.847) with 2.263 +/- 0.078 microm mean diameter of round colloids. A significant difference in the mean colloidal number and diameter between young and adult birds was observed. In young birds (aged 1-30 days) both Periodic acid-Schiff reaction positive colloids and S-100 positive folliculostellate (FS) cells were found to appear first on or near the posterolateral region. In adult birds, FS cells were found to completely surround the colloids. We examined the biochemical components of colloids and the relationship with apoptosis by immunohistochemistry. Results showed that the colloids are composed of clusterin protein. Apoptotic cells detected by single stranded DNA (ssDNA) were abundant and localized preferentially near colloids. To define clearly the type of cells undergoing apoptosis in the anterior pituitary, we performed electron microscopy. Numerous endocrine cells at different stages of apoptosis were found engulfed by FS cells that were in close association with the colloidal accumulations. The occurrence of extremely large number of colloids in relation to apoptotic profiles in anterior pituitary of helmet guinea fowl is discussed.