Mitotic Activity of the Pars Intermedia in the Female Mouse: Age-Associated Variations in Proliferation Rate and Circadian Periodicity

Abstract

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.

Effects of tumors on the daily mitotic activity of mouse pars intermedia

“…Just as the MA is lower, so the PI mitotic index of adult mice is less than that previously reported in younger male mice. This observation is consistent with the proliferative activity of the PI epithelium in female mice (Barbeito et al, 2000) and of rat adenohypophysial cells (Oishi et al, 1993).…”

“…Like many biological processes, the degree of cellular proliferation often exhibits circadian variations, which may differ according to the cell population under study (Barbeito et al, 2003;Bjarnason and Jordan, 2002;Smaaland, 1996). In previous papers we have demonstrated a nocturnal mitotic peak in the epithelial cells of the pars intermedia (PI) of the hypophysis (Echave Llanos et al, 1987;Barbeito et al, 2000). Grafted tumors may generate quantitative changes in cell proliferation.…”