Endocrine Abstracts

Colocalisation of hormones in the adult human pituitary has been demonstrated only for growth hormone (GH) and prolactin (PL) and only for adenomatous tissue. We have investigated whether colocalization occurs earlier in ontogenesis. Pituitaries from male human fetuses of 16–22 weeks gestational age fixed by immersion in 4% buffered formaldehyde and embedded in LR Gold were processed for immunocytochemical double labelling with GH/FSH or GH/LH anti-rat and anti-human primary antibodies, using both fluorescence and electron immunogold (particles 15, 5 nm) microscopic localization.

In the 16-weeks-old fetus, green-red superposition showed the colocalisation GH and FSH in most of the GH-positive cells. The colocalisation decreased in both intensity and number of colocalized cells from 16 to 20 and 22 weeks. In the 22-weeks-old fetus, islets of cells with either green (GH), or red (FSH) or yellow (GH+FSH) fluorescence were present. The superposition of fluorescence was rarely complete, with many cells showing punctuate green, yellow and red spots. The colocalization of fluorescence indicating GH and FSH was much more intense and frequent than that indicating GH and LH. In all the fetuses there were more GH-fluorescent than FSH- or LH-fluorescent cells. Electron microscopy revealed both 15 nm and 5 nm particles in presumed GH (15 nm) cells, usually in different granules. In the rare ‘small granule cells’, 15 nm (GH) and 5 nm (FSH) gold particles were found, seldom within the same granule. The intercellular spaces were almost free of non-specific labelling.

These data suggest that colocalization occurs in normal pituitary cells early during human ontogenesis and that this phenomenon decreases significantly from 16 to 22 weeks and is largely lost during adulthood. However, the potential for colocalization is preserved and can be reactivated in tumoral transformation.