Colloid in the pituitary pars distalis of viscacha (Lagostomus maximus maximus): ultrastructure and occurrence in relation to season, sex, and growth

The Anatomical Record
Fabian H MohamedRamón Piezzi


Randomly distributed extracellular colloidal accumulations were observed in the pars distalis of viscacha (Lagostomus maximus maximus). They were preferentially located in the peripheral zone of the gland and showed variability in shape and size. Two different types of colloidal accumulations were found by electron microscopy: 1) those surrounded by nongranulated follicular cells that correspond to characteristic follicles, and 2) those surrounded by granulated cells. In the follicles lined by nongranulated follicular cells, long, prominent microvilli and cytoplasmic processes protruded into the lumen. The frequency of these accumulations varies during the year in adult male animals, showing an increase in number during summer and a decrease during winter. The lowest value was registered in August (winter). The mean follicular diameter did not vary seasonally. The number of colloidal accumulations did not vary seasonally in adult female viscachas, but a significant difference in the mean follicular diameter between pregnant and non-pregnant females was observed. Pituitaries of immature animals contain fewer colloidal accumulations than those of adults. In fetuses, these accumulations were absent. The administration of melatonin...Continue Reading


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Age Factors
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