Light and ultrastructural immunocytochemical study of prolactin cells in ovine adenohypophysis. Influence of lactation and weaning.

The influence of lactation and weaning on the number, distribution, and structure of mammotroph cells (PRL cells) in ewes was studied using immunocytochemical procedures for light and electron microscopy, as well as morphometric and stereological techniques. The adenohypophyseal gland of 12 ewes of the Segureña breed at different stages of milk production and weaning were analysed, while the same organ of 3 ewes in anestrus served as control. During lactation, PRL cells increased in number and decreased in size. Ultrastructurally, these cells showed a well-developed rough endoplasmic reticulum (RER) and Golgi complex (GC), and large secretory granules. These findings point to increased synthesis and secretion activities during lactation, and a decrease after weaning. One day after weaning 'storage' cells increased in number, and crinophagy became evident 7 days after weaning, when the first 'inactive' cells were seen (10% of total cells). In anestrus these last cells represented 40% of the total, and showed scarce granules, signs of inactivity, lysosomes and lipid droplets.