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The influence of lactation period and weaning on the distribution, number, and structure of somatotropic cells (GH 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 in different stages of milk production and weaning was studied, while three ewes in anoestrus served as controls. The size of secretory granules was heterogeneous in all stages, suggesting that this characteristic is not related to functional activity. During lactation and weaning the size of GH cells decreased, while the number of 'synthesis cells' increased. The rough endoplasmic reticulum and Golgi complex appeared more developed and small secretory granules showed lower gold particle labelling. These data suggest that GH cells are more active during lactation, particularly during late lactation.

We have studied the structural and ultrastructural changes that occur in growth hormone (GH), prolactin (PRL) and somatomammotroph (SMT) cells of female goats of the Murciano-Granadina breed during different physiological stages: prepuberty, anestrus, pregnancy and lactation. Serial sections were stained with double immunolabeling, alkaline phosphatase and avidin-biotin complex for light microscopy, and immunogold labeling was used for electron microscopy. These techniques allowed the identification of GH, PRL and SMT cells, which were evenly distributed throughout the whole pars distalis. PRL cells were the most frequent. Both PRL and GH cells showed morphological changes that may be related to a given physiological stage. These changes include the number of cells and the number and size of the secretory granules. SMT cells were clearly identified by having two types of monohormonal secretory granule showing single labeling, in spite of their similar ultrastructural characteristics to the other adenohypophysary cells. They are found in low percentages (0.6%). We postulate that cell aggregates which look like SMT syncytia may be artifacts caused by interdigitation of PRL and GH cells, and that cells which are normally taken to be SMT cells are not an interconversion stage between monohormonal cells.

The structural and ultrastructural characteristics of adenohypophyseal growth hormone (GH)-, prolactin (PRL)- and GH-PRL (SMT)-secreting cells were studied using immunocytochemical techniques in two normal and one lactating male goat. SMT cells were found in both types of males, which showed the same characteristics as those reported for the female. PRL and SMT cells were more frequent in the lactating male, which reflects their greater galactopoietic activity. GH cells did not seem to influence this process significantly.

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