In situ analysis of adenohypophysis proliferative activity in beagle dogs. Preliminary results

Mitotic activity of the pars intermedia in the female mouse: age-associated variations in proliferation rate and circadian periodicity

We previously reported daily variations in the mitotic activity of the endocrine cells in the pars intermedia of 21- and 28-day-old male mice. Since cellular proliferation might be affected by factors such as sex and age, we undertook the present experiments to study the mitotic activity of the pars intermedia from 14-, 28-, and 150-day-old female mice. Inbred C3H/S mice, grouped according to age, were housed under standard conditions (12h each of light and dark [LD 12:12]) for periodicity analysis and were killed in lots of 5-11 animals every 4h over a single 24h cycle, with each mouse receiving 2 microg/g of colchicine 4h before decapitation. Pituitaries were excised, extracted, fixed in buffered formaldehyde, embedded in celloidin-paraffin, sectioned at 5 microm, and stained with hematoxylin and eosin. We counted the total number of nuclei to estimate the total number of cells monitored and then calculated the mitotic index (metaphases/1000 nuclei). Differences were analyzed for statistical significance by the Student t test. While the 14-day-old animals manifested no significant changes in mitotic activity during the 24h cycle, the 28- and 150-day-old mice showed higher mitotic indices during the period of darkness. The average mitotic activity over the entire cycle, however, was higher in the two groups of younger animals than in the 150-day-old mice. Moreover, the averages for the 28-day-old females were higher than the corresponding values previously reported by us for male mice of the same age.

Mitosis and apoptosis in the pituitary gland: tumour formation or hyperplasia?

Direct analyses of trophic activity in the pituitary have been hampered by the lack of normal human tissue to study and by the short duration of the histologically overt phases of mitosis and apoptosis, which renders significant trophic events difficult to quantify. In rats and dogs, pituitary cell turnover is rapid in youth, declines markedly with age and virtually ceases by 'late middle age'. Specific stimuli superimpose brief but dramatic trophic events on this active background. There is little convincing evidence, as yet, for plasticity, i.e. the persistence of cell population changes after transient stimuli have passed. In contrast to spontaneous pituitary adenomas in rats, human pituitary tumours show relatively modest increases in mitotic activity. In the light of these observations, this chapter examines the accepted models of pituitary adenoma formation and propagation, with special reference to trophic activity, clonality and tumour behaviour.