p75 and TrkC neurotrophin receptors demonstrate a different immunoreactivity profile in comparison to TrkA and TrkB receptors in human normal pituitary gland and adenomas

BACKGROUND/AIMS

Recent knowledge indicates that neurotrophins play a significant role in neuroendocrine systems through their specific receptors TrkA, TrkB, TrkC and low-affinity p75(NTR) receptor. TrkA and TrkB receptors have been previously detected in numerous endocrine cells in human anterior pituitary and adenomas. In the present study, the localization of p75(NTR) and TrkC along with TrkA and TrkB receptors was investigated.

METHODS

Semi-serial paraffin-embedded sections of 5 human normal pituitaries and 30 adenomas were immunostained using specific antibodies.

RESULTS

Expression of p75(NTR) receptor was demonstrated in the intricate capillary and reticulin network in the anterior pituitary and in the pericapillary tissue and pituicytes in the posterior lobe. p75(NTR) immunoreactivity was absent from all adenomas. In normal anterior pituitary, a few scattered cells showed weak TrkC immunoreactivity in contrast to a high percentage of endocrine cells distributed throughout the pars distalis and pars intermedia which exhibited strong TrkA and/or intermediate TrkB immunoreactivity. Double immunohistochemistry demonstrated TrkA immunoreactivity in more than 80% of lactotropes and 70% of corticotropes and to a lesser extent in other cell types. Furthermore, in the majority of adenomas, independently of type, sex and age, a high percentage of TrkA- and/or TrkB-positive cells was detected. Interestingly, TrkC expression appeared to be increased in some adenomas compared to normal pituitary. Endothelial cells and perivascular connective tissue were always TrkB-immunostained.

CONCLUSION

The above findings support a potential role of all neurotrophins, through their different receptors, in pituitary functions.