Structural and ultrastructural immunocytochemical study of somatomammotrophs in ovine adenohypophysis: age and lactation influences.

The influences of age and lactational period on the distribution, number and structure of somatomammotrophs (SMTs) and the relationships to changes in somatotroph and lactotroph populations in ovine were studied using immunocytochemical procedures with light and electron microscopy as well as morphometric techniques. Adenohypophyseal glands of 15 individuals of the Segureña bread (female lambs and ewes in anoestrus or at different stages of milk production) were used. SMTs were always seen in the adenohypophysis of sheep, but were scarce in number and more frequently distributed in the anterior area of the gland. Their number decreased with age, increased at the beginning of the lactation, and decreased again in late lactation. Ultrastructurally these cells showed variable morphology and stored GH and PRL in different secretory granules. Data presented in this report suggest that SMTs are a stage between PRL and GH producing cells.