Feeding-induced hypocalcaemia. Preliminary studies in sheep

The effect of feeding on calcium metabolism was studied in sheep. When crushed oats or pelleted concentrate was added to the diet of hay-fed sheep, there was a profound decrease in serum calcium. Serum calcium fell in spite of an increased daily intake of calcium.

Factors affecting the hypocalcaemic response to protamine

The hypocalcaemic response to protamine, as a measure of bone resorption rate, was studied in cattle and sheep. Three groups of calves were studied (1–3 days, 2–3 weeks and 4 months old). The oldest calves showed the greatest response, indicating a more rapid skeletal turnover in these animals, probably related to a higher growing rate. A group of cows was tested at 2 occasions, near parturition and 2–3 weeks after parturition. The decrease in plasma calcium was small near parturition, while a profound drop was obtained 2–3 weeks post partum, which supports earlier findings that bone resorption is more or less blocked in parturient cows. Young pregnant ewes showed the same degree of hypocalcaemia as adult pregnant ewes but the recovery was more rapid in the young animals. Young rams were given protamine before and after diethylstilboestrol treatment. No differences in calcium response were obtained. Varying plasma phosphate responses were obtained. A pronounced hyperphosphataemia was found in the adult pregnant ewes. Diethylstilboestrol caused hypermagnesaemia in the rams.

Studies on pentagastrin-induced hypocalcaemia in lactating cows

During recent years it has been evident that a number of gastrointestinal hormones are potent calcitonin secretagogues, and it has been suggested that a gastrointestinal-thyroid C cell system exists as a part of post prandial calcium homeostasis. In the present study the hypocalcaemic effect of pentagastrin, a synthetic peptide with gastrin effects, was studied in lactating cows. Intravenous infusion of pentagastrin caused marked hypocalcaemia and hypophosphataemia in the cows. Thyroidectomy completely abolished the hypocalcaemic and hypophosphataemic effects of the peptide. The results thus suggested that the effects of the peptide were due to release of endogenous calcitonin.

Further studies on theophylline-induced hypocalcaemia in sheep

The effects of various doses of theophylline on the plasma levels of calcium, inorganic phosphorus and magnesium were studied in sheep. The dose of 0.25 mg/kg/min. during 40 min. produced a hypocalcaemia, which was abolished by thyroidectomy. At a higher dose, 1.0 mg/kg/min., thyroidectomy reduced, but did not block, the hypocalcaemic effect of theophylline. Young sheep showed a greater calcium response than did adult ewes. The decrease in plasma calcium was in no case accompanied by hypophosphataemia. Plasma magnesium decreased in all groups after 1.0 mg/kg/min. and was not influenced by thyroidectomy. Theophylline increased the urinary excretion of calcium and magnesium. It is concluded that theophylline-induced hypocalcaemia in sheep is in part a result of increased calcitonin secretion but that also other mechanisms must be involved, e. g. a direct effect of theophylline on bone.

Lipid mobilization in parturient cows

The blood levels of calcium, inorganic phosphorus, magnesium, glucose and NEFA were studied in cows at the time around partus. Eight of 16 cows developed hypocalcaemic paresis. Besides hypocalcaemia the paretic cows showed lower levels of inorganic phosphorus and higher levels of glucose and NEFA than non-paretic cows 24 hrs. post partum. It is known that lipolysis is associated with uptake of calcium in adipose tissue. The calcium content in perirenal adipose tissue was however lower in paretic cows than in non-paretic parturient cows and lactating cows slaughtered 3–5 months after calving. The calcium content in omental adipose tissue was about the same in all 3 groups. Despite increased lipolysis the calcium content in adipose tissue is thus not increased in cows suffering from parturient paresis.

Some acute metabolic effects of parathyroid hormone in sheep

PERSSON, J. and J. LUTHMAN: Some acute metabolic effects of parathyroid hormone in sheep. Acta vet. scand. 1974, 15, 381–397. — It is now well established that calcium ions play a key role in the activation of many different cell systems. Parathyroid hormone (PTH) causes a shift of calcium into bone cells, and lipolytic hormones have little or no effect in calcium-free media. In the present investigation sheep were used to study the acute effects of intravenous injection of bovine PTH on mineral and lipid metabolism. A significant initial hypocalcaemia was found in all groups of animals. The subsequent rise in plasma calcium was most pronounced in rams. Thyroid-ectomized animals showed a greater calcium response than did intacts. PTH was found to have a strong lipolytic effect, comparable to that of catecholamines, and a slight hyperglycaemic effect. The rise in plasma NEFA was blocked by nicotinic acid, while the hyper-glycaemia was potentiated. Hypophosphataemia was obtained in young rams but not in young ewes, and in elder ewes a slight increase in the plasma phosphate level was found. Plasma magnesium decreased in all groups after PTH injection, while PTH + nicotinic acid caused a rise in magnesium concentration. The results are discussed in the view of current knowledge of mineral and lipid metabolism.

parathyroid hormone; hypocalcaemia; lipolysis; sheep.

The effects of insulin, glucose and catecholamines on some blood minerals in sheep

Intravenous injection of insulin, 0.5 i.u./kg, was followed by a decrease in plasma magnesium. It is earlier known that insulin sometimes lowers the blood magnesium level, and the mechanism behind this effect is said to be an increased tissue uptake of magnesium. Glucose infusion did not change plasma magnesium, whereas norepinephrine and epinephrine caused a slight reduction. Insulin at the dose of 1 i.u./kg reduced plasma calcium in intact sheep. In thyroidectomized sheep the same dose caused a rise in plasma calcium. It is suggested that insulin caused hypercalcaemia in the thyroidectomized sheep by increasing the rate of bone resorption, and that the decrease in plasma calcium observed in the intact sheep was due to release of calcitonin to such an extent that the bone resorbing effect of insulin was blocked. Insulin also lowered plasma inorganic phosphorus in the thyroidectomized sheep.

The hypocalcemic response to protamine as a measure of bone resorption

The heparin antagonist protamine inhibits bone resorption. In the present study protamine was given i.v. at a dose of 10 mg/kg to goats and sheep in various stages of pregnancy and lactation. It is known that bone resorption increases as pregnancy progresses. In sheep maximum in bone resportion is reached at early lactation. The hypocalcemic response to protamine followed a similar course. The slightest decrease in serum calcium was obtained during early pregnancy and the greatest during late pregnancy and early lactation. Protamine increased serum inorganic phosphorus. The increase was most pronounced during early pregnancy. Protamine did not significantly change serum magnesium.

Five lactating ewes were given 25000 i.u./kg of vitamin D3. Serum calcium increased and the hypocalcemic response to protamine was greater after vitamin D3 administration than before.

The results showed that the hypocalcemic response to protamine can be used as an indicator of the role of bone resorption in calcium homeostasis in various physiological situations.