The effects of age and spontaneous adenoma formation on trophic activity in the rat pituitary gland: a comparison with trophic activity in the human pituitary and in human pituitary adenomas

The effects of ageing on trophic activity in the pituitary gland and the mo lecular events that underlie pituitary tumour formation are poorly understo od. In the present study we have used an extremely accurate system to analy se trophic activity in human pituitary tumours and compared our findings wi th trophic activity in spontaneous rat pituitary adenomas and with changes in basal rates of turnover as the animals age. Thin, hematoxylin and eosin- stained pituitary sections from groups of male Wistar rats aged 6 weeks to 16 months, killed at 90-min intervals after receiving a single intraperiton eal bolus of colchicine to block cellular passage through mitosis, were eva luated histologically. Extremely accurate quantification of small changes i n the prevalence of trophic events, and thus the rate of cell turnover, was achieved using a dedicated computerized aid to manual cell counting. Resul ts were compared with the prevalence of mitotic activity in 24 spontaneous rat pituitary adenomas and with a series of 97 archival human pituitary ade nomas and 24 normal human pituitary glands obtained at autopsy. In rats, av erage basal pituitary cell turnover declined by over 95% between 6 weeks an d 16 months of age. Concurrent with this decline was a marked increase in t he prevalence of adenoma formation. The prevalence of mitotic activity in s pontaneous rat pituitary adenomas averaged almost twice that seen in normal , young rat pituitary and exceeded 16 times that seen in the pituitary of a ged animals. In contrast, when compared to normal human pituitary tissue, a verage trophic activity in human pituitary adenomas remained extremely low.