Morphology and function of the parathyroid gland of the caiman, Caiman crocodilus

Abstract

The juvenile caiman, Caiman crocodilus, possesses two to six parathyroid glands which are embedded in the thymus, one to three on either side of the body. The number is subject to individual variation. In specimens having three parathyroids on one side of the body, the smallest may be designated as an accessory parathyroid. The parathyroid gland is composed of parenchymal cells arranged in cords among which rich connective tissue and blood capillaries are present. The general features of the parathyroid histology of the present specimens resemble those reported in other groups of reptiles. Normal serum calcium, sodium, and phosphorus concentrations are 15.2 ± 0.30, 332.7 ± 2.42, and 3.4 ± 0.32 mg/100 ml, respectively. Surgical parathyroidectomy caused a significant decrease of serum calcium concentration (about 50–60% of the normal) 5 and 10 days after the operation together with simultaneous occurrence of tetanic convulsions. However, no changes were observed in serum sodium concentrations. Serum phosphorus concentration increased 5 days after parathyroidectomy. Administration of mammalian parathyroid extract (0.2 USP units/g body wt) partially corrected the hypocalcemia which was caused by parathyroidectomy. The present results suggest that the role of the crocodilian parathyroid gland in serum calcium and phosphorus homeostasis is very similar to that of the Squamata but somewhat different from that of the Chelonia.