Ultrastructural evaluation of ultimobranchial glands from normal and osteopetrotic chickens
Ultimobranchial glands of young, rapidly growing chickens were evaluated ultrastructurally and compared to findings in chickens of the same age with severe naturally occurring osteopetrosis. Secretory cells were present in actively synthesizing and storage phases of their secretory cycle in both groups. Stellate cells extended long cytoplasmic processes between adjacent secretory cells and had features suggestive of a supportive rather than a secretory function. Follicular structures with single or multiple layers of lining cells were a prominent feature of the ultimobranchial gland. The presence of secretory and stellate cells in various stages of differentiation in the basilar regions of multilayered follicles suggested a mechanism of cell renewal from follicular epithelium. Although viral particles were present in the intercellular and extracellular spaces, viral replication was not observed within the secretory cells of chickens with osteopetrosis. Densely granulated secretory cells in the storage phase of the secretory cycle were more numerous in ultimobranchial glands of normal chickens, whereas actively synthesizing cells predominated in diseased birds. These changes in secretory activity could be explained either by a direct interaction between the leukosis virus and secretory cells or be secondary to alterations in blood calcium.