Ultrastructure of parathyroid glands of growing chickens with vitamin D deficiency rickets.

Ultrastructural studies were conducted on the parathyroid glands (PTG) of 2- to 7-week-old nontreated control growing broiler chickens (group A, 6 chickens); the same aged chickens with experimentally induced vitamin D deficiency rickets (18 morbid chickens each from groups B, C, and D); and in 4- to 9-week-old chickens naturally affected with rickets (group E, 8 chickens). Four types of principal cells were classified in the PTG of clinically normal birds and in PTG of birds with secondary hyperparathyroidism as follows: Type I cell (small cell in the resting phase); type II cell (medium-sized cell with well-developed rough-surfaced endoplasmic reticulum in the synthesizing phase); type III cell (large cell with well-developed Golgi apparatus and cytoplasmic organelles in the packaging and secretory phase); and type IV cell (medium-sized cell with poor cytoplasmic organelles in the involuting phase). Many coated vesicles were observed in type II and type III cells. In young control chickens, principal cells of the PTG were considered in the resting phase; in older control chickens, there were increased numbers of cells in the synthesizing phase. In the vitamin D deficiency groups, principal cells were in the synthesizing and packaging and secretory phases. In birds with naturally occurring rickets, principal cells were in packaging and secretory phases, with a small number of cells in the involuting phase. The ultrastructural changes of the PTG from the initial to final phases in growing chickens with secondary hyperparathyroidism were demonstrated.