Absolute numbers versus proportions in the assessment of differentiation of beta-cells in the embryonic avian pancreas.

Environmental factors may influence the proliferation and differentiation of embryonic pancreatic endocrine cells, creating a need for the quantification of such effects. The explanted dorsal pancreatic bud (DPB) of the 5-day chick embryo is a useful in vitro model. Since all explants cannot be assumed to have the same number of endocrine cells at the start of culture, the proportion of beta-cells with respect to alpha-cells may be a more meaningful measure than absolute numbers. This study aimed to establish baseline values for the proportion of beta-cells in both intact and mesoderm-depleted DPBs before culture. Buds were excised from 12 chick embryos and the surrounding mesoderm was removed from 6 buds following collagenase treatment. All the buds were freeze-dried, fixed in parabenzoquinone vapour, embedded in resin and sectioned at 1 micro m. alpha- and beta-cells were detected by an indirect immunoenzyme method. alpha-cells outnumbered beta-cells in 9 of the 12 buds. The proportion of beta-cells in the intact buds varied from 16% to 64% (mean 39.5%) and in the mesoderm-depleted buds from 17% to 66% (mean 39%). There was no significant difference between the absolute numbers or the proportions of cells in either case. The proportions of beta-cells in the 5-day DPBs were higher than those in buds cultured in previous studies for 7 days under various conditions. This result may reflect the role of apoptosis in response to the culture conditions.