Response of dog parathyroid glands to short-term alterations of serum calcium.

Parathyroid (PT) glands of dogs were exposed to low or high serum calcium by infusion of either EGTA or CaCl2. Infusion of EGTA resulted in an increase of parathyroid hormone (PTH) and infusion of CaCl2, in a decrease of this hormone. The PT glands excised either at the beginning or at the end of the infusions were examined by electron microsoopy. After infusion of EGTA, activated cells showed a dense matrix, prominent Golgi apparatus, rough endoplasmic reticulum (rER) with narrow cisternae, and an incrased tortuosity of the plasma membrane, accompanied by an enlargement of the intercellular spaces. Infusion of CaCl2 resulted in a distention of the rER cisternae, disorganization of the Golgi apparatus and a decreased tortuosity of the plasma membrane. It is concluded that (1) PT cells may contract in the course of activation; (2) storage capacity for PTH is low, and (3) PT cells may be stimulated or inhibited to promote biosynthesis of PTH within minutes.