Distribution of thyroid, parathyroid, and ultimobranchial hypocalcemic factors in birds. II. Morphology, Histochemistry, and hypocalcemic activity of pigeon thyroid glands

Thyroid lobes from five common and six White Carneaux pigeons were cut into fragments which were assayed biologically for their calcitonin content. Pooled, alternate tissue slices from the individual thyroid lobes of 18 additional White Carneaux pigeons were assayed; the remaining tissue slices were prepared for light and electron microscopy or for demonstration of histochemical properties associated with the APUD system of polypeptide hormone‐producing cells, including: α‐glycerophosphate dehydrogenase, acetylcholinesterase, nonspecific cholinesterase, esterase, argyrophilia, and production of fluorogenic monoamines. Calcitonin was present at all cephalo‐caudal levels within pigeon thyroid lobes and was concentrated in peripheral, as opposed to central areas of the lobes. White Carneaux left thyroid lobes contained 34–225 MRC U of calcitonin/g tissue. Twelve of 18 right lobes lacked detectable calcitonin; the remaining six lobes contained 12–46 MRC U/g. Microscopy revealed a population of granulated cells that were found only in peripheral regions of lobes containing measurable calcitonin. These cells resemble mammalian thyroid parafollicular cells ultrastructurally. They appear to be surrounded by amine‐containing, argyrophilic nerve fibers. Of the histochemical characteristics of mammalian “C” cells tested, only amine‐precursor uptake could be correlated with the presence of calcitonin and granulated cells in the thyroid gland of the White Carneaux pigeon.