Explants of eggshell with and without the chorioallantoic membrane were tak
en from fertile chicken eggs on day 16 of incubation and exposed in vitro t
o inhibitors (acetazolamide and benzolamide) of carbonic anhydrase to deter
mine if enzyme inhibition affected release of calcium from the shell. A sep
arate experiment examined the effect of the metabolic poison dinitrophenol
(DNP) on release of calcium from explants. Explants with the chorioallantoi
s in situ released more calcium than those lacking the epithelium, but neit
her the enzyme inhibitors nor DNP affected release of calcium. The lack of
effect of the enzyme inhibitors could indicate that activity of carbonic an
hydrase is not as important to the release of calcium from the eggshell as
has been assumed. However, the absence of an effect of DNP instead indicate
s that release of calcium mediated by the chorioallantois in vitro simply l
acks physiological relevance. Thus, results of this investigation raise dou
bts that the mechanism underlying release of calcium from the eggshell can
be assessed in vitro. (C) 1999 Elsevier Science Inc. All rights reserved.