D. Harold Copp

Direct Humoral Control of Parathyroid Function in the Dog.

Summary Direct humoral control of parathyroid function has been demonstrated in dogs in which the isolated thyroid-parathyroid glands were perfused with high calcium or low calcium blood. The latter appears to release parathyroid hormone or a substance with identical action. The resulting rise in systemic blood calcium does not depend on a fall in the inorganic phosphate of blood. These experiments indicate a “feedback” mechanism involving the parathyroids which is sufficiently sensitive and fast-acting to account for the acute homeostatic control of blood calcium.

Studies on the regulation and characterization of plasma stanniocalcin in rainbow trout

Stanniocalcin (STC) is a hormone that is synthesized and secreted by the corpuscles of stannius (CS), endocrine glands that are unique to the bony fishes. The hormone inhibits Ca2+ transport from the aquatic environment into the bloodstream by way of the gills. Previous in vitro studies by our laboratory have shown that STC secretion is positively regulated by Ca2+ in a time- and dose-dependent fashion. In this report, we have examined circulating levels of STC in free-swimming, cannulated rainbow trout and how hormone levels are affected by surgical stress and intra-arterial infusions of mono and divalent cations. In addition, the plasma hormone has been concentrated by immunoaffinity chromatography and characterized by Western blot analysis. The results suggest that the in vivo response of the CS is extremely rapid and Ca(2+)-specific and that STC circulates in multiple molecular weight forms.

Molecular cloning and cDNA sequence analysis of coho salmon stanniocalcin

Stanniocalcin (STC) (formerly known as both teleocalcin and hypocalcin) is an anti-hypercalcemic, glycoprotein hormone that is produced by the corpuscles of Stannius (CS), endocrine glands that are confined to bony fishes. The hormone has a unique amino acid sequence and exists as a disulfide-linked homodimer in the native state. In previous studies, we have described the purification and characterization of two salmon STCs, and examined the regulation of hormone secretion in response to calcium using both in vitro and in vivo model systems. This report describes the molecular cloning and cDNA sequence analysis of a coho salmon STC messenger RNA (mRNA) from a salmon CS lambda gt10 cDNA library. The STC mRNA in salmon is approximately 2 kilobases in length and encodes a primary translation product of 256 amino acids. The first 33 residues comprise the prepro region of the hormone, whereas the remaining 223 residues make up the mature form of the hormone. One N-linked, glycosylation consensus sequence was identified in the protein coding region as well as an odd number of half cysteine residues, the latter of which would allow for interchain bonding or dimerization of monomeric subunits. In addition, three sites were identified in the mature protein core of STC (two dibasic, one tribasic) that may be acted upon by endopeptidases to produce truncated forms of the hormone. In support of this latter possibility, Western blot analysis revealed multiple molecular weight forms of sTC within salmon glands.

Comparative biochemistry and physiology of teleocalcin from sockeye and coho salmon

This is a comparative study of the glycoprotein hormone, teleocalcin, from the corpuscles of Stannius of sockeye (Oncorhynchus nerka) and coho (O. kisutch) salmon. Coho teleocalcin was purified by the same procedures used previously to obtain sockeye teleocalcin and was obtained in a comparable yield. Both salmon teleocalcins had the same molecular weight as estimated by sodium dodecyl sulfate-electrophoresis and both appeared to have the structure of disulfide-linked oligomers. The two hormones were similar on the basis of amino acid and carbohydrate composition and shared 95% homology in the first 40 residues on the N-terminal. The salmon teleocalcins also shared 80% homology with the predicted 1-40 N-terminal sequence from Australian eels (Anguilla australis). Both teleocalcins had potent inhibitory effects on gill calcium uptake in intact rainbow trout (Salmo gairdneri). However, these effects were observed only at the peak in the calcium uptake cycle that is displayed by this species. In North American eels (A. rostrata), the acute administration of both teleocalcins caused significant inhibition of gill calcium uptake without any concomitant changes in plasma calcium levels or other plasma electrolytes. In 4- and 7-day stanniectomy (STX) eels, the acute administration of coho teleocalcin significantly reduced or completely abolished the accelerated gill calcium transport that occurs postoperatively, with no concomitant changes in plasma electrolytes or post-STX hypercalcemia. These experiments provide further evidence that teleocalcin is a regulator of gill calcium transport and has no acute hypocalcemic effects in fish.

The gill calcium transport cycle in rainbow trout is correlated with plasma levels of bioactive, not immunoreactive, stanniocalcin

Stanniocalcin (STC) is an inhibitor of gill Ca2+ transport that is produced by the corpuscles of Stannius, endocrine glands in bony fish. In young rainbow trout (Oncorhynchus mykiss), there are cyclical changes in the rate of gill Ca2+ transport, with alternating phases of accelerated and reduced uptake every 14 days. Previous studies by our laboratory have established that the responsiveness of young trout to the inhibitory effects of exogenous STC is dependent on this cycle. Trout are highly responsive to STC at peaks of Ca2+ uptake and unresponsive at nadirs, which has led us to suggest that the gill Ca2+ transport cycle may be regulated by a reciprocal cycle in the levels of plasma STC. In this report, we have further characterized the gill Ca2+ transport cycle in salmonids and investigated the role of STC in its regulation. Our results showed that the cycle is synchronous and is likely a characteristic feature in all salmonids but that it varies in amplitude between species. Surprisingly, we observed no correlation between circulating levels of radioimmunoassayable STC and the rate of gill Ca2+ transport in trout. To address this apparent contradiction, trout fry were passively immunized with STC antiserum to determine if there were variable amounts of bioactive STC in the circulation, at times when trout were either more or less sensitive to exogenous STC. We observed that during the times when trout were responsive to STC treatment (i.e., cycle peaks), passive immunization had no effect on the rate of gill Ca2+ transport in fish from the same population, indicating that there were low levels of bioactive STC in the circulation.(ABSTRACT TRUNCATED AT 250 WORDS)

The homeostatic function of bone as a mineral reservoir

Abstract The skeleton contains more than 99 per cent of the calcium, 80 to 90 per cent of the phosphate, and two thirds of the sodium in the body and provides an essential reservoir for the homeostatic control of the level of these elements in blood. The minute crystals of bone salt have a theoretical surface area of 100 to 200 acres, and studies with radioactive isotopes have indicated that approximately 10 to 15 per cent of the calcium and phosphate present is readily exchangeable in vitro. In the living animal, only 0.2 to 0.5 per cent of the calcium is exchangeable, but this plays an important role in regulating the level of plasma calcium, for it acts as a “buffer” to prevent wide fluctuations in blood level. In fact, the bone resembles an ion-exchange column, contributing to the stability of the blood levels, and, along with the kidneys, is an important factor in ionic homeostasis. Like the kidneys, bone has a tremendous blood flow relative to its metabolic needs, and this blood flow is sharply reduced by the action of epinephrine. The skeleton also plays an important part in long-range mineral control. Excess calcium and phosphate may be stored in bone; when the diet does not contain adequate amounts of calcium or phosphate, these elements may be mobilized to maintain the essential level in soft tissues, with a resulting loss of bone mineral and the development of osteopenia or rickets. It is of interest that in this process the teeth are largely spared.

An Indirect Method of Bone Blood-Flow Measurement Based on the Bone Clearance of a Circulating Bone-Seeking Radioisotope

1. A simple, reliable, and useful indirect method of measuring bone blood flow in animals is described, based on the clearance of a circulating bone-seeking radioisotope. This method is based on an adaptation of the Fick principle. It was originally proposed by Frederickson, Honour, and Copp in 1955. The present authors have amplified the method by developing the standardized techniques, by testing the validity, by studying the possible sources of errors, the advantages and limitations, and by applying the methood to a number of quantitative studies. 2. Bone clearance of the isotope is defined as the volume of blood cleared of the isotope by bone and is obtained by dividing the bone uptake by the average isotope concentration in one milliliter of arterial blood integrated over the first five minutes after injection. The rate of blood flow is expressed as milliliters of blood per minute per 100 grams wet bone (including marrow). 3. The method gives a useful measure of, at best, about 75 per cent of the actual blood flow of bone, and can be applied to a wide variety of studies. 4. A few examples are given. The rates of blood flow of various bones in the rabbit and dog were remarkably similar with an average of about ten milliliters per minute per 100 grams of wet bone including the marrow. The rates of the entire skeletal blood flow in the two species were estimated as about 5 to 10 per cent of the resting cardiac output. 5. One of the major limitations of the method at present is that it is not applicable to man without modification. However, it should be possible to modify the technique so that it could be applied in man at the time of bone biopsy, amputation, or other surgery on bone.

Calcitonin—A new hormone from the parathyroid which lowers blood calcium

Abstract Until recently, it was thought that the parathyroid glands secreted a single hormone (parathormone) which raised the blood calcium. A year ago, in the course of studies on the effect of various plasma calcium levels on parathyroid function, we discovered that perfusion of the isolated glands with high-calcium blood resulted in the release of a previously unsuspected hormone which actively lowered the blood calcium level. We have named this hormone “calcitonin” because it is concerned with maintaining the normal level or “tone” of calcium in body fluids. It is fast and short-acting, the maximum fall in plasma calcium occurring within 20 to 30 minutes following a single injection, after which the level returns to normal within an hour. There is accumulating evidence that the parathyroid glands play an active role in controlling hypercalcemia. If the parathyroid glands are removed after infusion of parathyroid extract, or after EDTA-induced hypocalcemia which stimulates endogenous parathormone production, there is a prompt rise in plasma calcium which does not occur if the glands are left intact. A rise in plasma calcium also occurs if parathyroidectomy is performed during calcium infusion.

PARATHYROID CONTROL OF HYPERCALCEMIA DUE TO INJECTION OF PARATHYROID EXTRACT IN THE RAT.

Summary and conclusions Following subcutaneous injection of 85 u parathyroid extract/100 g into young rats, the rise in plasma calcium 6 hours later was 3–6 times as great when the parathyroids were removed as in the control rats with intact glands. The smaller response in the latter was attributed to a controlling effect of the parathyroids on hypercalcemia through liberation of the hypocalcemic hormone, calcitonin.

Calcium regulation in birds

Abstract The level of calcium ions in the body fluids of birds is regulated with great precision in spite of a lightweight skeleton and an enormous turnover of calcium which occurs in the egg-laying cycle. High intestinal absorption is particularly important in this cycle, and may be 30–100× that occurring in man. As in mammals, birds produce the two calcium-regulating hormones—parathormone from the parathyroids, and calcitonin from the ultimobranchial glands. Parathyroidectomy lowers plasma calcium and may cause tetanic convulsions. There is little evidence that ultimobranchialectomy seriously affects the skeleton or the egg-laying cycle.