Storage and release of secretory granules in human prolactinomas: modification by bromocriptine.

Electron microscopic morphometric evaluation of the effects of bromocriptine on human prolactinomas during and after short-term parenteral (7 days) and long-term peroral (4-6 weeks) treatment showed that a reduction in size of prolactinoma cells occurs within a few days (half-time to maximum shrinkage, 2.2 days). The number of secretory granules discharged into the intercellular space increased after short-term treatment by a factor of three but the total volume of stored secretory granules did not change significantly. The total volume of cellular lysosomes, both primary and secondary, decreased significantly to about one-half of the pretreatment value. The amount of stored lipoids, end-products of lysosomal activity, decreased in specimens treated for 7 days, but returned to pretreatment levels in specimens treated for 4-6 weeks, suggesting that lysosomal material is discharged from the cells together with the secretory material.