Nancy B. Clark

Influence of estrogens upon serum calcium, phosphate and proteins concentrations of fresh-water turtles

Abstract 1. 1. Concentrations of total calcium, inorganic phosphate and total protein were measured in serum of normal fresh-water turtles, Chrysemys picta , caught in local Connecticut pondsd from April to July. Hypercalcemis, hyperphosphatemia and hyperproteinemia occurred in females during May and June, the time of egg-production and egg-laying, presumably in response to increased secretion of endogenous estrogens. 2. 2. Single doses of estradiol benzoate ranging from 20 μg to 750 μg induced significantly higher concentrations of these fractions of serum calcium, phosphate and protein in both sexes of non-breeing C. picta and Pseudemys scripta . 3. 3. The elevated values of calcium, phosphate and protein in sera of normal females during the breeding season exceeded those induced in non-breeding animals by a dose of 20 μg estradiol benzoate.

Ultrastructure of the Stannius corpuscles of the killifish, Fundulus heteroclitus, and its relation to calcium regulation☆☆☆

The ultrastructure of the corpuscles of Stannius of the euryhaline killifish Fundulus heteroclitus adapted to freshwater, seawater, and artificial calcium-deficient seawater is presented. The Stannius corpuscles of fish kept in calcium-deficient seawater appear inactive and show an accumulation of secretory granules and a relatively inactive Golgi complex. In contrast, the corpuscles of fish kept in seawater show depletion of secretory granules, hyperactivity of the Golgi complex, and dilation of the endoplasmic reticulum, indicating a response to the demand for a calcium-lowering factor in the high calcium environment. These changes are related to the difference in calcium levels of the environment and probably not to the differences in total osmotic concentration. The presence of rough endoplasmic reticulum indicates that the product of the gland may be proteinaceous.

Aspects of Calcium Regulation in Embryonic Lepidosaurians and Chelonians and a Review of Calcium Regulation in Embryonic Archosaurians

Embryos of oviparous and viviparous lepidosaurians, chelonians, and archosaurians must maintain calcium homeostasis while mobilizing large quantities of calcium from the yolk, eggshell, or maternal circulation. The same calcium-regulating hormones that control the calcium status of adults are assumed to control the calcium status of embryos as well, but the target organs for calcium regulation may be different in embryos and adults. The yolk sac, which mediates the uptake of calcium from the yolk (and the deposition of calcium into yolk in archosaurians), the chorioallantois, which mediates the release of calcium from the eggshell and the transport of shell calcium to the vasculature in oviparous species, and the chorioallantoic placenta, which mediates the maternal-fetal transfer of calcium in viviparous species, are potential targets for calcium-regulating hormones (calcitonin, parathyroid hormone, calcitriol) during embryogenesis. However, the role of these hormones in mediating the calcium status of embryos has been examined only in avian species, and the most detailed information available in this regard is for calcitriol (the vitamin D hormone). The presence of receptors for calcitriol in the yolk sac and chorioallantoic membranes of avian species and the extreme calcium deficiency of vitamin-D-deficient embryos indicate that calcitriol plays an important role in regulating calcium metabolism during avian embryogenesis. A source of parathyroid hormone also is required for normal development, but the target organ(s)for this hormone have not been identified. The role of calcitonin in calcium regulation by embryonic birds is poorly understood, and the potential for hormonal control of calcium homeostasis in embryonic reptiles has not been examined.

Avian medullary bone in organ culture: effects of vitamin D metabolites on collagen synthesis.

SummaryA new organ culture system for the study of bone metabolism has been developed using chicken medullary bone. The presence of viable bone cells in culture was demonstrated by histological and histochemical techniques. Incorporation of3H-proline into collagenase-digestible protein (CDP) and noncollagen protein (NCP) was determined using purified bacterial collagenase. Collagen accounted for approximately 10–15% of the total protein labeled. The addition of 1,25-dihydroxycholecalciferol (1,25 (OH)2D3) resulted in a dose-dependent inhibition of3H-proline incorporation into CDP at doses from 10−10M to 10−7M, with maximal suppression reaching 30% of control. The effect was specific for collagen, since3H-proline incorporation into NCP was unaffected. Hydroxyproline analysis of bone explants and culture medium revealed a 1,25(OH)2D3-induced decrease in the3H-hydroxyproline content of the system (bone + medium), suggesting that the effect of 1,25(OH)2D3 is due to inhibition of collagen synthesis rather than enhanced collagen degradation, impaiored incorporation of collagen into bone matrix, or bone resorption Medullary bone collagen synthesis was not affected by 24,25(OH)2D3, either alone or in combination with 1,25(OH)2D3. Structure-activity studies of vitamin D metabolites showed that 1,25(OH)2D3 and 1,24,25(OH)3D3 were the most potent metabolites tested, followed by 1-alpha(OH)D3. 25(OH)D3 and 24,25(OH)2D3 had no effect at concentrations as high as 10−7M. These results indicate a possible role for vitamin D in the regulation of medullary bone formation during the reproductive cycle of the egg-laying hen, and suggest the potential utility of medullary bone as anin vitro model for the study of bone formation

The role of parathyroid hormone on renal excretion of calcium and phosphate in the Japanese quail

Abstract Renal excretion patterns were investigated in male Japanese quail, Coturnix coturnix japonica, after administration of avian saline, parathyroid extract (PTE), or after parathyroidectomy (PTX). Consistent long-term effects of parathyroid hormone were on excretion of phosphate, which increased significantly by 40 min after hormone administration and remained at high levels for approximately an hour. Phosphate secretion occurred in response to the hormonal stimulus. Serum calcium values also increased significantly for the first 2 hr after hormone injection. PTX quail had consistently lower GFR (CIn), which correlated with decreased inulin U P ratios and decreased amounts of sodium reabsorption by the renal tubules (TNa). PTX also resulted in decreased tubular reabsorption of calcium (Tca) but in this case the fractional excretion of calcium ( C Ca C In , which corrects for changes in GFR) was elevated. Thus the lack of hormone resulted in a significant increase in urinary calcium loss. This correlated with a steady development of hypocalcemia after PTX. Tubular reabsorption of phosphate (TPO4) increased and fractional excretion of phosphate ( C PO 4 C In ) gradually decreased following PTX leading to significantly lower phosphate excretion values by 3 hr after PTX.

Ultrastructure and histochemistry of the ultimobranchial body of fresh-water turtles

SummaryThe ultimobranchial body of fresh-water turtles,Pseudemys scripta andChrysemys picta, ultrastructurally and histochemically resembles the gland of other vertebrate groups and the homologous thyroid parafollicular cells of mammals. Characteristic features of all of these tissues are secretory granules measuring approximately 150–250 mμ, a distended endoplasmic reticulum, prominent Golgi regions and large numbers of free ribosomes. Unusual features of the turtle ultimobranchial body are an abundance of large cytoplasmic bodies measuring 800–1000 mμ and a dense, homogenous material within the lumina of the ultimobranchial follicles. The large cytoplasmic bodies usually occur near the luminal portion of the cells and are of similar electron density to the luminal contents, suggesting a possible functional relationship of these two glandular components.

Ultrastructure of the parathyroid gland of fresh-water turtles

The parathyroid glands of fresh‐water turtles (Pseudemys scripta and Chrysemys picta) are composed of cords of cells in which dark and light variants of chief cells and occasional oxyphil cells can be distinguished. Cytoplasmic granules measuring about 0.3–0.4 μm and all the cellular organelles associated with protein and carbohydrate synthesis can be seen in both dark and light chief cells; the cytoplasm of oxyphils is packed with mitochondria which obscure other organelles. An unusual feature of the dark chief cells is the presence of crystalline‐like material within parallel arrays of cisternae of rough endoplasmic reticulum. A similar crystalline‐like structure is seen occasionally within some cytoplasmic granules.

Calcium regulation in reptiles

Abstract It is clear from the few studies which have been done that the parathyroid gland is essential for normal calcium and phosphate homeostasis in reptiles. More studies are needed of different species and groups of reptiles, and of the effect of parathyroid hormone upon bone and kidney of these animals. The explanation for the seeming lack of importance of the parathyroid gland in turtle calcium regulation may lie in the large stores of calcium and phosphate in the bony shells of these animals. Experiments to test this hypothesis are yet to be done. The involvement of the ultimobranchial body in calcium metabolism in reptiles is at present a very tenuous hypothesis. Clearly further studies are necessary to determine the function of this gland, which appears ultrastructurally to be an active secretory organ.

Effect of parathyroidectomy in the lizard, Anolis carolinensis

Abstract Anolis carolinensis is the first species of lizard possessing four parathyroid glands in which parathyroid structure and function have been studied. The histology of the gland, similar to that of other reptiles, is composed of cell cords and of cells arranged in follicular patterns. The follicles sometimes contain a secretion which stains positively with PAS. Parathyroidectomy resulted in tetanic convulsions and paralysis in Anolis within 1–2 days after the operation. The attacks were induced when the animals ran or did any sort of mild exercise, were of about a 30-second duration, and could be reinduced after approximately 1 hour. With one exception, removal of three glands or less did not produce tetany.

Calcium regulation in the embryonic chick: I. Effect of parathyroidectomy and ultimobranchialectomy during late embryogenesis

Abstract Parathyroidectomy (PTX), ultimobranchialectomy (UBX), both operations (PTX-UBX), or sham surgery was performed on chick embryos at 18 days of incubation. Blood samples were taken from 1 to 20 hr after the operations and analyzed for calcium and phosphate concentrations. Serum calcium values decreased approximately 10% in PTX animals 5 hr after surgery and remained at this level for the duration of the experiment. Calcium values of the PTX-UBX group dropped significantly below those of shams 7 hr after the operation; these values continued to drop and stabilized at approximately 25% below control by 15 hr. UBX and sham-operated animals had no significant change in serum calcium values. Serum phosphate values rose following PTX and were significantly higher than control at 5, 7, and 10 hr post-PTX before returning to normal. The serum phosphate values of the PTX-UBX group were significantly higher than control 10 hr after the operation. Neither UBX nor the sham operation significantly altered serum phosphate values. Removal of parathyroid tissue thus results in a gradual decline in serum calcium and a rise in serum phosphate concentrations in 18-day chick embryos. The more striking drop in serum calcium seen in the PTX-UBX group is attributed to the loss of accessory parathyroid tissue within ultimobranchial glands. These experiments indicate that the parathyroid gland does play a role in maintenance of plasma calcium and phosphate values in chicks during late embryogenesis.