Morphometric analysis of parathyroid glands in neonatal and growing dogs

In dogs and aged 6 days or 5 months, the parathyroid (PT) glands exhibited differences of both the distribution and ultrastructure of dark and light cells. Morphometric estimates of cytoplasm, nucleus, mitochondria, rough endoplasmic reticulum (rER), Golgi apparatus, secretory granules, lysosomes and plasma membranes of both dark and light cells were obtained by point counting volumetry from PT glands of dogs of the two age groups and calculated per one hypothetical average PT cell. It was evident that in the PT glands of 6-day-old puppies the volume of the average PT cell was significantly smaller than in the PT glands of the 5-month-old dogs, but the cell surface was not significantly different. The volume of mitochondria, rER and lysosomes was higher in the average PT cell of the 5-month-old dogs, whereas the surface of Golgi apparatus and rER did not differ. Though the difference of the cellular and mitochondrial volume is probably related to the age difference between the two groups, the findings on Golgi apparatus, plasma membranes and lysosomes suggest that the secretory activity or at least the potency for the secretion of parathyroid hormone was higher in PT glands of the 6-day-old dogs than in the 5-month-old dogs.