Tai-Chan Peng

Interrelationships of bone ash and whole bone properties in the lactating and parous rat

SummarySeveral investigators have studied the mechanical properties of long bones of rats and have found that bone strength may be associated with bone mineral content. In this study we examined further the interrelationships of whole bone properties and bone ash weight of the rat femur. Using a 3-point bending test, the bones were evaluated during lactation and after one to three pregnancy— lactation periods—experiments in which bone ash was significantly reduced. A relationship was established between the time of lactation and the ash weight, stiffness, strength, and toughness but not the ductility. Using all of the experimental data, a highly significant relationship was observed between ash weight and stiffness. A similar significant correlation was revealed between bone ash and strength or toughness, although drawing individual lines for each experiment rather than a common line for all the experiments appeared more appropriate. Given the inherent inaccuracies in the material property measurements of bone, the results suggest that routine measurements of whole bone properties provide an important and sensitive way to evaluate bone quality and that these properties correlate significantly with the bone ash weight.

Secretion of calcitonin gene-related peptide from baby rat thyroid glands in vitro.

Abstract Thyroid glands from 8-day-old rat pups were incubated in serum-free medium for 6 hr. Both calcitonin (CT) and calcitonin gene-related peptide (CGRP) released into medium were measured by radioimmunoassay. In 6 separate experiments CGRP was easily detected in medium in ng/ml concentrations. In 4 of the 6 experiments, where CT release was stimulated by high medium [Ca], the concentration of CGRP in medium showed a positive, significant correlation with the medium CT concentration (r=0.41-0.69, p < .05-<.01). The results are in concert with reports describing the presence of CGRP in the C-cell, and they further show that CGRP, as Well as CT, Can be Secreted by C-Cell.

Acute lead-induced increase in serum calcium in the rat without increased secretion of calcitonin.

Summary An acute marked increase in total serum calcium was observed after a single iv injection of lead. The response was prompt, serum calcium rising above 20 mg/dl 60-90 min after doses ≥ 15 mg/kg. The hypercalcemia was due entirely to a rise in the non-dialyzable calcium fraction. In contrast, the ultrafilterable fraction which includes ionic calcium was actually diminished. This explains the absence of an increase in serum calcitonin despite severe hypercalcemia. A slight rise in total plasma proteins also was observed after lead injection but the significance of this observation remains to be determined. These acute effects of lead on calcium homeostasis are apparently different from its chronic effects since we have found, in a separate study, that rats exposed to lead for 1 year developed hyperplasia of C-cells and an increase in the levels of calcitonin in both the blood and the thyroid glands.

Serum calcitonin, calcium and thyroxine in young and old Zucker fatty rats (fa/fa)

We determined the serum levels of calcitonin (CT), calcium (Ca), and thyroxine (Ti) in lean (?/+) and fatty (fa/fa) male Zucker rats 10 weeks and 10-12 months of age. The most dramatic finding was a high level of serum CT (3.24 +/- 1.18 ng/ml) in young fatties whereas sera from young leans were all below the limit of assay detection (less than 0.120 ng/ml, p less than 0.01). Young fat rats also had elevated levels of both Ca (11.2 +/- 0.2 vs. 9.7 +/- 0.2 mg/dl, p less than 0.001) and Ti (6.7 +/- 0.48 vs. 4.72 +/- 0.28 micrograms/dl, p less than 0.01). In older animals the mean serum level of CT increased further in the fatties and became readily measurable in leans (5.67 +/- 1.94 vs. 1.49 +/- 0.55, p less than 0.01). Thyroid C-cells, identified immunohistochemically, were abundant in both leans and fatties at this age but were substantially more numerous in the fat rats (p less than 0.001). Calcium levels increased somewhat in the older leans, but still remained higher in the fat rats (p less than 0.05). Thyroxine values were essentially the same for old animals of both genotypes (5.07 +/- 0.61 vs. 5.54 +/- 0.88). Age effects were not significant for any measure in the fat animals, but in the leans there were significant age-related increases in CT (p less than 0.02) and serum Ca (p less than 0.05).

Effects of ethanol on chicksin vivo and on chick embryo tibiae in organ culture

Hypocalcemia previously reported in rats and dogs following oral administration of ethanol may have been caused by a movement of calcium from blood to bone. This present study was undertaken to determine whether ethanol also causes hypocalcemia in chicks and to investigate the direct effects of ethanol on mineral accretion, glucose metabolism and growth of embryonic chick tibiae in an organ culture system. A high dose of ethanol (6 g/kg body wt) produced hypocalcemia, hypermagnesemia and an elevated hematocrit in chicks. Resultsin vitro were as follows: 1) 5 to 30 μl ethanol/ml medium produced dose-related increases in bone mineral from 58–440%; 2) lactate production was inhibited at all ethanol levels; 3) increased mineral accretion did not occur in ethanol-treated tibiae when iodoacetate was in the medium, but did occur in mechanically disrupted bones exposed to ethanol; and 4) the ethanol response in bone was directly related to the medium phosphate concentration. The results lead to the following conclusions: 1) ethanol has a direct stimulatory effect on bone mineral accretion and an inhibitory effect on bone glucose metabolismin vitro; 2) viable bone cells and an adequate phosphate supply are necessary for the ethanol response, but tissue integrity is not; and 3) the hypocalcemic effect of ethanolin vivo may at least partially result from ethanol-stimulated bone mineral deposition.

Physiological Function of Thyrocalcitonin

This chapter discusses the biochemical methods to study physiological functions of thyrocalcitonin. Parathyroid hormone is virtually essential for life. If the source of the endogenous hormone, the parathyroid glands, is removed, the plasma calcium falls to a dangerously low level and if appropriate therapy is not administered the animal may die. It is apparent that parathyroid hormone must be secreted essentially continuously in order to protect against hypocalcemia. In contrast to parathyroidectomy, thyroidectomy does not result in any acute change in the blood calcium level in rats and other animals maintained in the fasting state. The hypocalcemia resulting from parathyroidectomy is not matched by hypercalcemia after thyroidectomy. The lower the plasma calcium, the less calcium is lost in the urine. Rats with intact thyroid glands excrete very little calcium, whereas thyroidectomized rats excrete a relatively tremendous amount—20 times as much. The most likely threat of hypercalcemia in healthy animals occurs during absorption of calcium from the diet. The normal thyroid gland responds quickly to the presence of calcium in the gastrointestinal tract by increasing the secretion of thyrocalcitonin that in turn prevents or restricts hypercalcemia by its action on bone.