DIFFERENT ULTRASTRUCTURAL-LOCALIZATION OF VIP AND PROLACTIN IN ANTERIOR-PITUITARY-CELLS OF RATS CHRONICALLY TREATED WITH ESTROGEN

In the present study we investigated the effect of a long-term estroge n treatment on the intracellular distribution of VIP immunoreactivity in pituitary prolactin cells using double-labeling immunocytochemistry . With the use of pre-embedding ABC method it was found that VIP immun oreactivity was associated with the outer surface of membrane-bound or ganelles, and was not found in secretory granules. However, prolactin immunoreactivity demonstrated by postembedding immunogold technique wa s mainly associated within the secretory granules of the same cells. T he discrepancy between our and Hsu et al.'s results (1989), who observ ed VIP immunoreactivity in secretory granules of human anterior pituit ary cells, may be owing to the overstimulation of VIP cells by estroge n. It is possible that estrogen treatment depleted the VIP content of the secretory granules and enhanced the cytosolic VIP. The appearance of an alternative form of VIP in estrogen-treated vats with preferenti al distribution in the cytosol cannot be excluded.