Fine structure of chick embryonic parathyroid glands cultured on media with different concentrations of calcium.

An electron microscopical study of parathyroid glands from 13-day old chick embryos cultured for 2 days on media with different concentrations of calcium was conducted. The same as in non-cultured embryonic glands, the cells in all cultures contained a moderate amount of rough endoplasmic reticulum and a large Golgi complex with many cisternae, vacuoles, vesicles, coated vesicles and small prosecretory granules. In addition, large secretory granules, which are very rare in the non-cultured controls appeared frequently in the cultures and were especially numerous in the glands cultured on high-calcium medium. The fact that the amount of secretory granules varied according to the concentration of calcium in the medium is interpreted as indicating that the rate of parathyroid hormone secretion in the embryo is already responsive to variations in the concentration of calcium. To the extent that in vitro results may be accepted as representative of what happens in vivo these results support the idea that the embryonic gland may be controlled by variations in the calcemia as the adult gland does.