MRC mU Research Articles

Expression of calcium-binding protein regucalcin mRNA in rat liver is stimulated by calcitonin: the hormonal effect is mediated through calcium.

The involvement of a hypocalcemic hormone calcitonin (CT) in the expression of hepatic Ca(2+)-binding protein regucalcin mRNA was investigated. The change of regucalcin mRNA levels was analyzed by Northern blotting using liver regucalcin complementary DNA (0.9 kb). A single oral administration of calcium chloride (100 mg Ca/100 g body weight) to rats induced a remarkable increase in the serum calcium concentration and a corresponding elevation of the liver calcium content during 120 min after the administration. Thyroparathyroidectomy (TPTX) did not cause a significant increase in the liver calcium content after calcium administration. Hepatic regucalcin mRNA level was markedly elevated by calcium administration; the level was about 180% of controls at 60 min after the administration. This increase was completely abolished by TPTX. A single subcutaneous administration of CT (synthetic eel CT; 25-100 MRC mU/100 g) to TPTX rats received oral administration of calcium (100 mg/100 g) produced a remarkable increase in hepatic regucalcin mRNA levels; the level was about 280% of controls with the dose of 25 MRC mU CT/100 g. The present finding suggests that the expression of hepatic mRNA is stimulated by CT, and that the hormonal effect is mediated through Ca2+ in rat liver.

Synthetic (Asu1,7) eel calcitonin increases phosphorus content in the hepatic bile of intact and nephrectomized rats.

The effect of synthetic [Asu1,7] eel calcitonin (CT) on phosphorus content in the hepatic bile was investigated in intact and nephrectomized rats. The subcutaneous administration of CT (80 MRC mU/100 g BW) produced a significant fall in the serum inorganic phosphorus concentration and a corresponding increase in the amount of phosphorus in the liver and kidney. These changes were observed even at the lowest dose of CT (40 MRC mU/100 g BW). The phosphorus contents in the spleen, heart, lungs and muscle were not significantly changed by CT administration. CT also provoked a marked elevation of phosphorus excretion into the bile. In nephrectomized rats, CT (80 MRC mU/100 g BW) caused a significant decrease in serum inorganic phosphorus concentration and a remarkable increase in liver phosphorus content. CT markedly increased phosphorus excretion into the bile of nephrectomized rats. These results support the theory that the hypophosphatemic effect of CT may be, at least partly, based on its action on liver in addition to kidney. This effect of CT on the liver may be the cause of increased excretion of phosphorus into the bile.

The effect of porcine calcitonin on plasma calcium in Channa punctatm Bloch

The effect of porcine calcitonin on the plasma calcium of the freshwater Indian murrel, Channa punctatus Bloch has been studied. An injection of 200 MRC mU of porcine calcitonin was given intraperitoneally, while control fish received the gelatin carrier. A significant hypocalcaemia was noted I h after calcitonin treatment (P < 0.001). The plasma calcium had returned to the normal level by the 6th h.

Effect of calcitonin on serum glucose concentration in rats.

Calcitonin (CT) administered subcutaneously to intact and thyroparathyroidectomized rats caused a significant decrease in the serum calcium, while the serum glucose concentration increased. The maximal response was obtained with 80 MRC mU/100 g body weight. The lowest dose of CT which produces a detectable effect was approximately 20 MRC mU. Glucagon (5 μg/100 g) caused a rapid elevation in the serum glucose, reaching a maximum level within 15 min, whereas CT caused a more gradual increase in the serum glucose, reaching a maximum after 60 min. Administration of CT to fasted rats caused a significant increase in the serum glucose. Liver glycogen levels were relatively decreased by CT administration. Administration of CT produced the accumulation of calcium in liver cells and significantly elevated glucose-6-phosphatase and phosphorylase activities in liver homogenate. These results suggest that a rise in the serum glucose concentration produced by CT may involve the production of glucose in the liver.

Thyrocalcitonin injection to rats increases the liver inorganic phosphate.

The mechanism of the hypophosphatemic effect of thyrocalcitonin (TCT) is uncertain and may involve removal of inorganic phosphate (P1) from the plasma by heretofore unidentified organs. Rats, 192 g. thyroparathyroidectomized 16-24 h earlier, received 100 MRC mU TCT or vehicle (V) SC and 100 muCi 32PO4 iv. One h later plasma and tissue samples were collected. Compared to rats which received V, TCT-treated rats had lower plasma P1 (-0.36 plus or minus 0.08 mumol/ml, P smaller than 0.001) and Ca, higher liver P1 (+0.66 plus or minus 0.19 mumol/g, P smaller than 0.01) and unchanged red blood cell and rectus abdominus P1. TCT had no significant effect on the amount of perchloric acid soluble phosphate in any of the tissues. TCT-treated rats had lower plasma 32P1 (cpm/ml) and higher liver 32P1 (cpm/g) with no significant changes in specific activity (SA). TCT caused a small decrease in muscle 32P1 SA. There were no significant changes in the 32P (cpm/g) or 32P SA of the acid soluble phosphate fraction of any of the tissues. The results suggest that a portion of the hypophosphatemic effect of TCT can be accounted for by the increased P1 level in the liver.

Effect of porcine, salmon and human calcitonin on urinary excretion of some electrolytes in sheep.

SUMMARY Purified porcine and salmon calcitonin and synthetic salmon and human calcitonin were infused at the rate of 20 MRC mu./kg/h over a 96 h period in intact male lambs. Every calcitonin preparation significantly increased the urinary excretion of inorganic phosphorus, sodium, potassium and calcium, while the urinary excretion of magnesium was always significantly inhibited. Similar significant effects were observed with purified porcine calcitonin in thyroparathyroidectomized lambs supplemented with thyroxine. Oxidation of calcitonin with performic acid completely abolished its effects on plasma calcium and on the kidney. It is concluded that, when used at physiological doses, in sheep calcitonin has an important effect on urinary excretion of inorganic phosphorus, sodium and magnesium.

Effect of graded levels of thyrocalcitonin upon thyroid secretion rate, endocrine glands, liver, kidney and spleen weights of female rats.

SummaryFifty mature female rats were divided into 5 groups of 10 animals each on the basis of equal thyroxine secretion rate (TSR). Twenty-eight days after the TSR was determined initially, groups III, IV and V were treated with 30, 60 and 90 MRC mU of thyrocalcitonin (TCT)/100 g body weight twice daily intraperitoneally. Groups I and II acted as normal and vehicle treated groups, respectively. The treatment was started 14 days prior to the start of the TSR estimation and continued until the TSR of the animals was estimated. The animals were then sacrificed and the following glands and organs were removed and weighed: ovaries, adrenals, pituitary, thyroid, uterus, liver, kidneys and spleen. Administration of 30 and 90 mU TCT/100 g body weight twice daily for at least 14 days caused a significant (p < .01) decrease in TSR, but the 60 mU dose of TCT did not. Significant (p < .05) increases in weights of the adrenals and liver were noticed in all the treated groups, whereas kidney weight changes were signifi...

Thyroidal content of thyrocalcitonin in lactating rats.

ABSTRACT Thyrocalcitonin (TCT) content of thyroid glands was determined by bioassay in Sprague-Dawley-Rolfsmeyer rats at 1, 5, 10, 15 and 20 days of lactation and found to be 476, 523, 762, 553 and 564 MRC mU per gland (5 rats on each day of lactation). A control group of normal virgin rats had 438 MRC mU per gland. These experiments indicate that at day 10 of lactation TCT content of the gland is significantly (P &lt; 0.05) higher than any other day. The possible explanation of TCT accumulation is that during lactation animals undergo a mild hypocalcaemia due to large amounts of calcium drain in milk. Hypocalcaemia and lack of hypercalcaemic stimulation of TCT secretion have been reported to cause TCT accumulation in the thyroid gland. Though gland content does not necessarily reflect secretory status of a hormone, it is possible that less TCT is discharged from the gland during the middle of lactation.

THE EFFECT OF LONG-TERM TREATMENT WITH CALCITONIN ON BONE, KIDNEY, AND INTESTINE IN YOUNG RATS

Young intact, parathyroidectomized, and thyroparathyroidectomized rats were treated for an month with injections of 130 MRC mU every eighth hours. No changes took place in the bone content of calcium, magnesium, or hydroxyproline, when the animals were compared with the corresponding control groups. This suggested that parathyroidectomized and thyroparathyroidectomized animals were rather insensitive to the hormone, while intact rats developed a secondary hyperparathyroidism during the treatment.

LATS inhibition by a soluble lipoprotein from human thyroid gland.

Extracts of human thyroids, prepared by methods designed to concentrate lipoproteins, demonstrated potent LATS-inhibiting activity; on the average 0.5 gEq/ml inhibited 6.8 MRC mU LATS /ml. Similar extracts from plasma, liver, spleen and kidney did not significantly inhibit LATS. Such a crude lipoprotein solution (CLS) from thyroid contained about 6 mg protein, 1 mg lipid and 0.4 mg thyroglobulin (Tg) per gEq wet thyroid tissue. CLS was fractionated on an agarose column and the 3 fractions so obtained were tested for LATS-inhibiting activity and analyzed by immunoelectrophoresis (IEP) using antisera against CLS, Tg and whole human serum (WHS). LATS-inhibiting activity was present only in the first fraction. This fraction demonstrated 3 protein bands in IEP against anti-CLS; one was identified as due to Tg, another migrated like albumin, and the third was an unidentified heavy band near the origin. The former 2 were also present in the later agarose column fractions which did not inhibit LATS. The heavy band near the origin seen exclusively in fraction I stained for both protein and lipid. These findings are consistent with, though not final proof of, the hypothesis that at least one of the materials in thyroid tissue reacting with LATS is a lipoprotein. It seems possible that this lipoprotein derives from the plasma membrane to which LATS binds in vivo.

Effect of calcitonin on vitamin A-induced changes in bone in the rat.

The specific effects of calcitonin on inhibition of bone resorption were studied. For this purpose, bone resorption was artificially increased by administration of vitamin A. Three groups of growing rats were studied. All were given daily subcutaneous injections of 8% gelatin in acetate buffer for 4 weeks. The first group were controls; the second and third groups were each given 2500 IU of vitamin A acetate sc thrice weekly. In addition to vitamin A, the third group received 100 MRC mU of porcine calcitonin daily in the gelatin buffer. Rats receiving vitamin A alone gained less weight. Both femoral length and area of cortical bone at the midshaft were less than those in controls. Histological studies showed that bone in the caudal vertebrae of vitamin A-treated animals had thinner cortices and less trabecular bone, calcified cartilage and growth cartilage. The number of nonhaversian (vascular) channels and the percentage of osteocytic cavities greater than 15 n in diameter were increased. These changes were partially or wholly prevented by calcitonin. We conclude that vitamin A inhibits bone growth and stimulates bone resorption. Calcitonin prevents both effects: its action can be maintained. (Endocrinology88: 129, 1971)

The effect on bone of long-term treatment of intact, parathyroidectomized and thyroparathyroidectomized rats with calcitonin.

ABSTRACT Intact, parathyroidectomized, and thyroparathyroidectomized young, male Wistar rats were treated with sc injections of 80 MRC mU of calcitonin twice daily for three weeks and compared with similar controls receiving the vehicle for calcitonin. The serum calcium responses to single injections of calcitonin on the 10th and the 21st experimental days were found to be identical in the calcitonin-treated animals and their corresponding controls. The results of calcium and magnesium determinations in the sternal manubria and in the left clavicles showed no evidence of an increased mineral deposition in the bones of calcitonin-treated rats, nor did isotope studies with 45Ca or survey X-rays and microdensitometer scannings of two caudal vertebrae. The results in the intact rats can be explained by an increased parathyroid function as a counteraction to calcitonin. Rats with no parathyroid glands will have a greatly reduced bone resorption and will therefore show a diminished response to calcitonin. This can explain the observation that mineral deposition in bone is not increased in thyroparathyroidectomized and parathyroidectomized rats after long-term treatment.

The effect of calcitonin on disuse atrophy of bone in the rat

In thirty female Sprague-Dawley rats the left hind leg was immobilized with plaster casts. According to treatment they were divided into the following groups: A) Control, no casts. B) No treatment. C) 50 MRC mU calcitonin (own preparation) in 5% gelatin subcutaneously per day. D) Vehicle alone subcutaneously. E) 50 MRC mU calcitonin (Ciba) in 5% gelatin subcutaneously per day. In addition, untreated rats without casts served as control (group A). After 6 weeks the femora and tibiae were X-rayed, weighed and examined histologically. The bones of the left and right legs did not differ in control group A. In groups B, C, D, and E a disuse osteoporosis had developed in the left legs (rarefication of trabecular bone volume of femur neck) which could not be seen in X-rays. Calcitonin treatment did not prevent the development of the bone atrophy. However, the pressure of the plaster casts had induced a periosteal apposition in some tibiae, and under calcitonin treatment the extent of this new formation in all femora and tibiae was markedly increased. The vehicle alone was ineffective. It can be concluded that whereas calcitonin is without effect on disuse osteoporosis, it probably favours new bone formation which is induced by other mechanisms.

Intrathyroidal thyrocalcitonin levels in neonatal and adult rats.

Intrathyroidal thyrocalcitonin levels were determined by bioassay in Sprague-Dawley rats 5, 15, 30, 60, 120 and 360 days of age. The thyrocalcitonin concentration, expressed as a per cent of the 60-day-old controls, was 11 % in the 5-day-old rat and 38 % at 15 days. The other age groups had intrathyroidal thyro-calcitonin concentrations that did not differ significantly from the 60-day-old animals. Fifteen-day-old rats, injected with 25,000 USP U of vitamin (D3 4 days previously, had a plasma calcium of 15.6 mg/100 ml and the thyroidal thyrocalcitonin level was only 19% of the vehicle-injected control. When 15-day-old rats were injected every 2 hr with 450 MRC mU of thyro-calcitonin for an 8-hr period, the plasma calcium level dropped to 6.1 mg/100 ml and the thyroidal thyrocalcitonin level increased slightly. Since the thyroidal content of thyrocalcitonin is reported to be inversely related to the rate of thyrocalcitonin secretion, these experiments would indicate that despite the low thyroidal thyrocalc...

Detection of thyrocalcitonin in rat serum by direct tissue culture bio-assay.

Sera obtained from rats with intact thyroids after a calcium stress inhibit bone resorption in tissue culture. The inhibitory activity in serum was equivalent to that of 1-2 MRC mU of thyrocalcitonin (TCT)/ml. It appeared with hypercalcemia and disappeared when serum calcium concentration fell. The active material could be extracted from the serum with oxycellulose and further isolated by column chromatography. Its behavior when subjected to extraction and Sephadex chromatography was identical with that of TCT extracted from rat thyroid glands. No TCT activity could be detected in the serum of rats not subjected to calcium stress either by direct assay or after oxycellulose extraction. This suggests that the activity is less than .05 MRC mU/ml in normal animals. (Endocrinology 86: 1231, 1970)

Plasma phosphate and the hypocalcemic response of intact, parathyroidectomized and nephrectomized rats to thyrocalcitonin.

The purpose of these experiments was to study the effect of the administration of rat thyrocalcitonin (RTCT) to intact, parathyroidectomized (PTX) and nephrectomized (Nephx) rats up to 24 hr after bilateral nephrectomy. The work was instigated because of our recent reports suggesting that, under various physiological conditions, there was a marked difference in the ΔCa:ΔPO4 produced by either TCT or ultimobranchial calcitonin administration. For these experiments all rats were injected with 25 MRC mU of a crude extract of RTCT. Comparative studies were made in both parathyroid intact and PTX animals before and at various intervals following nephrectomy. These studies indicated that the plasma phosphate drop following TCT was surprisingly constant both before and after nephrectomy, despite the rising plasma phosphates caused by kidney removal. The hypocalcemic effect of the hormone was enhanced, however, by the high phosphate level. In fact, the drop in plasma calcium level produced was proportional to sta...

Comparative effects of thyrotropin and long-acting thyroid stimulator on thyroidal intermediary metabolism: Relationship to pyridine nucleotide levels

Both thyrotropin (TSH) and the long-acting thyroid stimulator (LATS) of Graves' disease stimulate glucose oxidation and phospholipogenesis in sheep thyroid slices. TSH (0.2–0.5 USP U./ml.) effected a 22–39 per cent mean increase in 14CO 2 production from glucose-1- 14C while LATS (2–4 MRC mU./ml.) caused a 28–32 per cent mean increase in glucose oxidation. Lesser concentrations of both stimulators (TSH, 10–50 mU./ml.; LATS, 0.5–2 MRC mU./ml.) were required for significant augmentation of 32P incorporation into thyroidal phospholipids. Varying the incubation time from 1–6 hr. did not differentially alter TSH or LATS effects on 14CO 2 production or 32P incorporation in thyroid slices. Measurement of thyroidal pyridine nucleotides (PN) under these circumstances indicates little or no correlation between stimulator-induced changes in NAD NADH or NADPH NADP ratios on the one hand and augmentation of either glucose oxidation or phospholipogenesis on the other. Although dibutyryl cyclic 3′, 5′-adenosine monophosphate mimics the effects of TSH and LATS on thyroidal glucose oxidation and phospholipogenesis, the concomitant alterations seen in PN levels (increased NADH, NADPH) were entirely unlike those seen with either stimulator. These findings confirm the dissociation between changes in thyroidal PN and augmentation of intermediary metabolism within the gland.