Immunohistochemical and morphometric analysis of calcitonin distribution in anuran ultimobranchial glands.

The presence and distribution of immunoreactive calcitonin (iCT) in the anuran (Rana pipiens) ultimobranchial gland was examined with a specific antiserum to salmon calcitonin. Improved resolution of the distribution of iCT within individual cells allowed recognition of a iCT-negative [iCT(-)] early maturing cell, the primary iCT-positive [iCT-(+)] secretory cell with accumulation of iCT within the basal and apical cytoplasm, an iCT(-) cell that lacks a basal accumulation of secretory material, and a iCT(-) cell that borders the central lumen. A morphometric analysis was made of the entire glandular basal secretory surface area and a calculation was made of the relative area that contained iCT(+) secretory material (expressed as a basal index (BI)). For frogs kept in fresh water, the total basal area of a single gland was 0.335 mm2, with a BI of 0.72 and a total iCT(+) secretory surface of 0.241 mm2. A second group of frogs kept in a high calcium medium for 12 days had a BI of 0.74 with no significant increase in parenchyma volume or total basal area and therefore no increase in the total iCT(+) secretory area. A third group was kept in a high calcium medium for 12 days and given a single oral dose of vitamin D3 (500 IU/g body wt). The BI of this group remained unchanged at 0.75; however, there was a significant glandular hypertrophy concomitant with an increase in secretory surface area to 0.462 mm2. This resulted in a 43% increase in the iCT(+) secretory area to 0.345 mm2. A model is proposed to explain the increase in iCT in the gland in response to a vitamin D and high calcium challenge.