Radioimmunoassay of human calcitonin using labeled [Asu1, 7]-human calcitonin analogue

Secretion of calcitonin from the thyroid gland increases in aged rats

Age-related changes in the secretion rate of immunoreactive calcitonin against antiserum for human calcitonin (iCT) from the thyroid gland were investigated in adult (4-5 months old) and aged (24-29 months old) male Wistar rats anesthetized with 1.0-1.2% halothane. The secretion rate of iCT was calculated by measuring the concentration of iCT using a radioimmunoassay method in both the thyroid venous blood plasma and the systemic arterial blood plasma, as well as measuring the thyroid blood plasma flow. The secretion rate of iCT was 0.271 +/- 0.063 ng.kg-1.min-1 in the adult and 1.248 +/- 0.147 ng.kg-1.min-1 in the aged rats, indicating a significant increase in secretion in the aged rats. The concentration of iCT in the systemic arterial blood plasma was 0.091 +/- 0.013 ng/ml in the adult and 0.480 +/- 0.026 ng/ml in the aged rats. The age-related increase in the secretion rate of iCT from the thyroid gland seems to result in an increase in iCT concentration in the systemic arterial blood plasma. Furthermore, the content of iCT in the thyroid gland was also increased in the aged rats. Therefore, it is suggested that both the synthesis and secretion of iCT in the thyroid gland are increased in aged rats.

1,25(OH)2D and 24,25(OH)2D production in the developing kidney

To clarify the state of vitamin D production by the developing kidney, firstly, we measured serum levels of 1,25(OH)2D and 24,25(OH)2D in humans of different ages (pregnant and nonpregnant women, adult males, children and newborn infants) and secondly, we measured 1 alpha- and 24-hydroxylase activity in the kidney mitochondria of rats at different ages. The mean serum levels of 1,25(OH)2D in pregnant women, cord blood and newborns were significantly higher than those in children and nonpregnant women and adult males. In newborns, the level increased with gestational age. Synthesis of 1,25(OH)2D was, at least in part, under the control of the fetus and newborn, rather then being solely a reflection of the conditions prevailing in the mother. The 1 alpha-hydroxylase activity in mitochondria was highest in the 1- to 2-month-old rats, and it decreased gradually thereafter. The change in 1 alpha-hydroxylase activity with age was due to a change in the Vmax of the system.

Phorbol ester stimulates calcitonin secretion synergistically with A23187, and additively with dibutyryl cyclic AMP in a rat C-cell line

The mechanism of action of 12-O-tetradecanoyl phorbol-13-acetate (TPA) on calcitonin secretion was studied in a rat C-cell line, rMTC 6-23. TPA stimulated calcitonin secretion at the concentration of 16nM. This effect was synergistically enhanced with calcium ionophore, A23187. Synthetic diacylglycerol, 1-oleoyl-2-acetyl-glycerol (OAG), also showed a synergism with A23187 on calcitonin secretion. When dibutyryl cyclic AMP was added with TPA, an additive effect was obtained. These data suggest that C-kinase might be a possible regulator of calcitonin secretion in addition to the cyclic AMP-mediated pathway.

Effect of calcium channel agonist Bay K 8644 on calcitonin secretion from a rat C-cell line

Bay K 8644, a novel dihydropyridine, stimulates calcitonin secretion in a dose-dependent manner from a rat medullary thyroid carcinoma cell line, rMTC 6-23, and causes an increase in cytosolic free calcium concentration, as measured by quin-2. These effects are competitively inhibited by nifedipine, and completely abolished in the absence of extracellular calcium. These data suggest that calcium influx via voltage-dependent calcium channels plays a crucial role in the regulation of cytosolic free calcium concentration and calcitonin secretion.

Comparison of renal responses to synthetic human PTH(1-34) administration in normal young and elderly male subjects

A parathyroid hormone (PTH) loading test with synthetic human PTH(1-34) was performed in 7 young and 6 elderly normal males. The elderly subjects had significantly higher mean basal levels of serum PTH than the young subjects (0.262 +/- 0.035(SE) vs 0.097 +/- 0.012 ng Eq/ml, P less than 0.001). When human PTH(1-34) at a dose of 100 U was administered to these subjects, the mean increases in urinary excretions of adenosine cyclic 3',5'-monophosphate(cAMP) and inorganic phosphorus (Pi), expressed as increases in absolute amounts per unit time, were significantly lower in the elderly subjects. (3.65 +/- 1.02 vs 7.41 +/- 1.05 mumol/h, P less than 0.05 for cAMP and 14.7 +/- 6.3 vs 41.8 +/- 8.6 mg/2h, P less than 0.05 for Pi) and an inverse correlation was found between the serum PTH levels and the increases in urinary cAMP excretion (mumol/hr; r = -0.63, P less than 0.05). However, when corrected for the glomerular filtration rate (GFR) and the units of PTH administered per kg body weight, the increases were not significantly different in the two groups (elderly 52.1 +/- 7.5 vs young 60.0 +/- 19.2 nmol . kg/100 ml GFR . U . h for cAMP and 0.315 +/- 0.061 vs 0.186 +/- 0.044 mg . kg/100 ml GFR . U . 2 h respectively for Pi).(ABSTRACT TRUNCATED AT 250 WORDS)

Relation of doubling time of plasma calcitonin levels to prognosis and recurrence of medullary thyroid carcinoma

Plasma calcitonin (CT) levels were measured serially in 54 patients surgically treated for medullary thyroid carcinoma. Patients with postoperative basal CT levels higher than 1 ng/ml measured within 1 month after surgery had a higher recurrence rate than those with lower CT levels (p less than 0.002). Patients with postoperative basal CT levels higher than 2 ng/ml had a lower survival rate than those with lower CT levels (p less than 0.01). However, preoperative basal CT levels had no significant correlation with life expectancy or recurrence during the present observation period. Serial measurements in 23 patients with elevated postoperative CT levels showed exponential increases in basal CT levels in 19 patients (p less than 0.05 in nine patients, 0.05 less than p less than 0.1 in four patients) and slight decreases in four (p less than 0.05 in one patient). Doubling time of CT levels calculated from the regression line in each patient showed the highest correlation with 3-year survival, recurrence within 5 years, and time interval between surgery and clinical recurrence of the tumor, allowing quantitative prediction of the prognosis.

Serum calcium regulating hormones in the perinatal period

To clarify perinatal vitamin D metabolism, we measured 25-hydroxyvitamin D (25OHD), 24,25-dihydroxyvitamin D [24,25(OH)2D], 1,25-dihydroxyvitamin D [1,25(OH)2D], calcium (Ca), phosphorus (P), parathyroid hormone (PTH), and human calcitonin (CT) in paired maternal, cord, and infant serum. Cord serum 25OHD was significantly lower than the maternal level, and cord serum 24,25(OH)2D was also significantly below the maternal concentrations. Maternal, cord, and infant serum 1,25(OH)2D, on the other hand, was significantly higher than the normal adult level. The serum PTH was low, but the CT concentration was high in the cord. Cord serum Ca and P levels were significantly higher than maternal. The reason for the elevated circulating 1,25(OH)2D level in the perinatal period is uncertain, and we speculate that the possible factors are gonadal steroids, placental lactogen, prolactin, and CT. In addition, serum 24,25(OH)2D and 1,25(OH)2D concentrations are under some control by the fetus.

The effect of oestrogens on human calcitonin secretion after calcium infusion in elderly female subjects

The effect of oestrogen administration (4-6 weeks) on the response of human calcitonin (hCT) secretion to 5 min calcium infusions was studied in ten elderly women. There was no significant difference in mean basal plasma hCT levels before and after oestrogen administration. However, the mean increment in plasma hCT in response to calcium infusion (delta hCT) increased significantly (P < 0.001) from 21.9 +/- 6.6 (mean +/- SE) before treatment, to 79.6 +/- 15.5 ng/l after oestrogen administration. Mean serum calcium levels decreased significantly (P < 0.001) from 2.42 +/- 0.06 before to 2.19 +/- 0.07 mmol/l after oestrogen treatment. Mean plasma immunoreactive PTH (iPTH) levels increased significantly (P < 0.05) from 521 +/- 41 before to 696 +/- 96 ng/l after oestrogen treatment. To exclude out the possibility that the decreased serum calcium level itself might have influenced delta hCT, 1 alpha-hydroxycholecalciferol (1 alpha-OH-D3) was administered with oestrogens. While this resulted in a slight increase in serum calcium level, there was no significant difference in delta hCT in response to calcium infusion following oestrogen treatment alone, and after combination therapy of oestrogen and 1 alpha-OH-D3. The primary action of administered oestrogen may be in stimulating hCT secretion which results in a decrease in plasma calcium concentration and an increase in plasma iPTH level.