Ultrastructural localization of thyrotropin (TSH) in the porcine anterior pituitary: a comparison between pre-embedding and post-embedding methods.

Two different immunocytochemical techniques based on specific antibodies against beta-subunits of porcine, rat and bovine TSH were applied at the ultrastructural level to identify the TSH cells in the porcine anterior pituitary and to compare the subcellular localization of the hormone. The post-embedding method on serial ultrathin sections revealed the localization of TSH beta in the granules of a special cell type, negative for the other hormones. TSH beta was found in polyhedral cells characterized (i) by their content of granules that were the smallest of all the cell types examined, and (ii) by their flattened or slightly dilated RER cisternae. The pre-embedding method applied to isolated cells permitted a good penetration of antisera and the maintenance of antigenicity in sites inaccessible to the post-embedding method. Thus, immunoreactivity of TSH beta was detected in the secretory granules, the cytoplasmic matrix and in portions of the rough endoplasmic reticulum, in association with some membranes and inside some saccular structures.