Experimental and histological studies of the parathyroid glands of fresh-water turtles

Abstract

The structure and function of the parathyroid glands of fresh-water turtles, Chrysemys picta, Pseudemys scripta, and Graptemys pseudogeographica were studied. The turtles have two pairs of parathyroid glands which are composed of cell cords of typical endocrine appearance and follicles often containing PAS-positive material. The histological structure of the glands does not appear to vary seasonally, even during the reproductive period. Serum calcium concentrations of normal C. picta and P. scripta averaged 2.40 ± 0.06 m m/l, while the mean phosphate value of normal animals was 0.93 ± 0.04 m m/l. Parathyroidectomy was not followed by significant change in these levels, even after 8 weeks. Bladder urine showed wide fluctuations in calcium and phosphate concentrations. After parathyroidectomy there was no significant difference in urine calcium levels. Hyperphosphaturia occurred in sham-operated control animals, but this was not seen in parathyroidectomized animals. Following parathyroidectomy, calcium concentrations in fibulae of C. picta were not significantly changed. Injection of 100 or 200 units of mammalian parathyroid extract (Lilly) into intact or parathyroidectomized C. picta resulted in a striking increase in urine phosphate levels ( p=<0.05–<0.01 from days 3–6 after injection). Smaller but consistent increases in serum and urine calcium concentrations were seen after the injection of 100 or 200 units of parathyroid extract. No changes occurred in serum phosphate values with the doses administered. Injection of parathyroid extract (189–378 units) did not affect calcium levels in fibulae, as measured by wet-ash analysis. Marrow cavities of femurs of hatchling G. pseudogeographica contained many osteoclasts, and these showed a consistent though not statistically significant increase in number after parathyroid extract injection. Large numbers of osteoclasts could also be found in femurs of older animals, but only in areas where the marrow cavities were lined with uncalcified cartilage. Several possible hypotheses are discussed to account for the lack of effect of parathyroidectomy on serum calcium concentrations in the turtles.