An Investigation Into the Parathyroid Origin of Calcitonin

SUMMARYThe fetal plasma magnesium concentration exceeds that of the mother but the difference is small compared to that of ionized calcium concentration. Although not fully independent of changes in maternal magnesaemia, fetal magnesaemia showed a high degree of autonomy during both hypermagnesaemic and hypomagnesaemic changes induced in the ewe. As with calcium, the placental gradient is reversed after fetal thyroparathyroidectomy (TXPTX) with thyroxine replacement. During perfusion in situ of the placenta from such TXPTX fetuses isolated from the fetus itself, a stable positive placental gradient of magnesium concentration could be re-established between the perfusing blood and the maternal circulation. As with calcium, this gradient could be increased by fetal calf parathyroid extract, parathyroid hormone-related protein (PTHrP 1-141), PTHrP (1-84) but not by PTHrP (1-34). It was concluded that a mid-molecule portion of PTHrP can stimulate a putative placental pump which is responsible for the gradients of both calcium ions and magnesium across the ovine placenta.

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“…All Keynes & Duncan (1966). This involved the removal of both superior parathyroid glands and both thyroid lobes.…”

Section: Animalsmentioning

confidence: 99%

Fetal magnesium homeostasis in the sheep

Barri¹,

Abbas²,

Pickard³

et al. 1990

Experimental Physiology

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“…The existence of calcitonin was soon confirmed by Kumar, Foster & Maclntyre (1963). Certain early experiments sug¬ gested a parathyroid origin for the hormone (Copp & Henze, 1964;Care, Keynes & Duncan, 1966) and calcitonin has been extracted from the parathyroid glands of dogs and rabbits Maclntyre, 1969). However, it soon became apparent that in mammals the hormone was produced and stored in cells in the thyroid gland.…”

Section: Nomenclaturementioning

confidence: 99%

Endocrine Control of Calcium Homeostasis

Copp¹

1969

Journal of Endocrinology

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Two endocrine glands of branchial origin are involved in regulation of calcium metabolism\p=m-\the parathyroids which secrete parathormone (parathyroid hormone) in response to hypocalcaemia, and the ultimobranchial glands which release calcitonin (thyrocalcitonin) during hypercalcaemia. The ultimobranchial glands are distinct organs in most vertebrates but in mammals the cells become embedded in the internal parathyroid and thyroid where they constitute the parafollicular 'C' cells. Calcitonin can be extracted from mammalian thyroid (hence the alternative name, thyrocalcitonin) but it is present in much higher concentrations in the ultimobranchial glands of lower vertebrates. In mammals, both hormones appear to act primarily on bone resorption and calcium mobilization from the skeleton, which is stimulated by parathormone and inhibited by calcitonin. Secretion or release of both hormones is determined by the level of calcium in the blood, and the two constitute a dual endocrine control comparable to that of insulin and glucagon in regulation of blood glucose. The ultimobranchials are the older glands phylogenetically for they are found in sharks and bony fishes, while the parathyroids appear first in amphibians.

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“…The preparation described by Care, Keynes & Duncan (1966) has been used successfully in the demonstration of the effects of changes in calcium, magnesium and strontium concentrations on the secretion of PTH in goats and sheep (Care, Sherwood, Potts & Aurbach, 1966; Buckle, Care, Cooper & Gitelman, 1968). Later, Mayer (1975), Mayer, Habener & Potts (1976) and Mayer & Hurst (1978) estimated the secretion rate of PTH in calves and by a similar technique demonstrated a non-linear relationship between secretion of PTH and plasma concentrations of calcium.…”

Section: Introductionmentioning

confidence: 99%

A Permanent Preparation Allowing Measurements of Secretion of Parathyroid Hormone in Conscious Goats

HOVE

1981

Journal of Endocrinology

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A preparation for estimations of rates of secretion of parathyroid hormone (PTH) in conscious goats is described. The procedure involved surgical isolation of a thyroid with its indwelling parathyroid gland, leaving the blood supply intact. Permanent access to the arterial and venous supplies of the preparation was secured by exteriorization of the jugular vein and carotid artery in skin-covered loops. The remaining parathyroids were removed leaving the isolated parathyroid gland as the only source of the hormone. For the seven goats operated on, the preparation has worked satisfactorily from the start in five and also in the remaining two after a reoperation to cut an accessory venous drainage. The loops have been catheterized repeatedly for extended periods of time and the preparation has proved useful for periods of up to 3 years. Secretion of PTH was measured in one goat at two consecutive parturitions. In late pregnancy, secretion rates of 0.7-0.9 ng/kg per min were observed when the dietary calcium intake was adequate. In the first weeks of lactation, secretion increased to 1.2-1.5 ng/kg per min when the intake of calcium was adequate and to 2.0-2.2 ng/kg per min when calcium intake was inadequate. Reductions in calcium intake led to increased rates of secretion of PTH both during pregnancy and during lactation. The results indicate that the preparation may be useful in the study of changes in PTH secretion both acutely and in connection with long-term studies of dietary adaptations of the calcium metabolism.

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An Investigation Into the Parathyroid Origin of Calcitonin

Cited by 21 publications

References 9 publications

Fetal magnesium homeostasis in the sheep

Fetal magnesium homeostasis in the sheep

Endocrine Control of Calcium Homeostasis

A Permanent Preparation Allowing Measurements of Secretion of Parathyroid Hormone in Conscious Goats

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