Thyroid and blood thyrocalcitonin concentrations and C-cell abundance in two strains of rats at different ages

Influence of ovariectomy and estradiol treatment on calcium homeostasis during aging in rats

Study was carried out an Wistar female rats to evaluate the consequences of ovariectomy and 17 beta-estradiol substitutive treatment during aging on bone. Ca metabolism and calciotropic hormones. Three groups of fifteen rats, mature, old and senescent (4-, 10-, and 28 month-old) female were fed a diet (6 g/100 g BW/day) containing 0.9% Ca and 0.8% Pi, Within each group, 10 rats were surgically ovariectomized (OVX). From day 1 until day 60 after OVX, they were subcutaneously injected with either 17 beta-estradiol (E: 10 micrograms/kg BW/48 h; n = 5) or with solvent alone (OVX; n = 5). Five other rats were sham operated (SH) and received solvent alone. Animals were put in balance 1 day per week to determine Ca and Pi intestinal apparent absorption and urinary pyridinium cross-links excretion was measured by HPLC. All rats were killed by exsanguination 60 days after OVX. Plasma was collected for measurement of intact parathyroid hormone (PTH), calcitonin (CT), insulin-like growth factor-1 (IGF-1), Ca and Pi. The success of OVX was confirmed at necropsy by observation of marked atrophy of the uterine horns. The right femur was collected, cleaned from adjacent tissue and used for mineral analysis. Despite correct matching for feeding, BW was significantly larger in 6 and 12 month-old OVX rats. OVX and 17 beta-estradiol had no significant effect upon plasma Ca, Pi and CT concentrations. Aging is associated with increased circulating PTH levels (pg/ml) (SH-6 months: 50.8 +/- 12.6; 12 months: 219.1 +/- 34.9; 30 months: 158.7 +/- 23.5; P < 0.05). Urinary and fecal Ca and Pi excretion in senescent animals were higher than in adult or old rats, thus resulting in a drastic fall in both intestinal apparent absorption and retention of Ca and Pi in 30 month-old animals. In each group, urinary pyridinium cross-links excretion and plasma osteocalcin concentration were higher in the OVX animals than in the controls, consistent with increased bone turnover in the estrogen deficient state. Both biochemical turnover markers were reduced in the estrogen-treated groups. In the same way, OVX increased and estrogen decreased the plasma IGF-1 levels. We conclude that 17 beta-estradiol prevents high turnover-induced osteopenia even in 30 month-old rats.

Postnatal variations in the number and size of C-cells in the rat thyroid gland

The heterogeneous distribution of thyroid C-cells has until now hindered an objective evaluation of changes caused by age or experimental stimuli. To overcome this, a rigorous methodology has been designed to detect variations in shape, size, and number of C-cells throughout development. Using this methodology, we have demonstrated that C-cells do not significantly alter their shape with age. However, their volume increases gradually from 472 microns3 in newborn rats to 1653 microns3 in 120-day-old animals. Over the same time period, the mean number of C-cells within the thyroid gland increased 9-fold (from 1.6 x 10(4) to 1.5 x 10(5), and the number of C-cells per unit area decreased (from 6.15 x 10(4)/mm3 to 2.6 x 10(4)/mm3). We conclude that there are marked variations in size, total number, and number of C-cells per unit area in the rat thyroid gland after birth.

Effect of ipriflavone on bone mineral density and calcium-related factors in elderly females

The effects of ipriflavone (7-isopropoxy-3-phenyl-4H-1-benzopyran-4-one) on bone mineral density (BMD) of the 3rd lumbar vertebra and on calcium (Ca)-related factors, including serum calcitonin (CT) levels before and after rapid calcium infusion (4 mg/kg for 5 minutes), were studied in 11 elderly female subjects (80 +/- 2 years of age, mean +/- SE). Ipriflavone (IP) administration (600 mg/day, 7 months) resulted in inhibition of BMD loss in 7 patients (responders, mean change of BMD value 2.2 +/- 2.3%), whereas 4 patients showed a loss of BMD (nonresponders, mean change of BMD value -13.1 +/- 2.6%) compared with pretreatment values. The responder group showed a significant increase in mean pretreatment serum CT levels (from 20 +/- 2 pg/ml to 42 +/- 7 pg/ml, P < 0.05) after treatment with IP, and a significant decrease in the mean basal serum level of corrected Ca (from 9.6 +/- 0.2 mg/dl to 8.7 +/- 0.1 mg/dl, P < 0.01) after treatment with IP; nonresponders did not show these changes. For responders, both the percentage of change and the maximal value of serum CT in response to Ca infusion were maintained at rather high levels, both before and after IP treatment; nonresponders showed almost no response to a stimulation test for CT. These findings suggest that IP inhibits bone loss in elderly female subjects possibly through the mechanism of increasing CT secretion.

The aging thyroid. I. A description of lesions and an analysis of their age and sex distribution

Two types of follicular change in the thyroid are described. The first represents an involutional change in which colloid cysts (macrofollicles) are often found. The second represents a hyperplastic-dysplastic (microfollicular) lesion. Two types of change in calcitonin (C) cells are also described, one of which may represent an involutional process, although this is not certain. The second is a hyperplastic (micronodular) lesion, but without evidence of dysplasia. An infiltration of lymphocytes is also commonly encountered. Only about 15% of cases after age 60 are free of the follicular and lymphoid lesions. Both the macro- and microfollicular lesions show a statistically significant increase with age, as do the lymphoid lesion and its derivative Hashimoto's thyroiditis. C cell micronodules also appear to increase with age, but there are too few such cases for a reliable statistical analysis. An analysis of combinations of the follicular and lymphoid lesions show a particularly frequent association of the microfollicular and lymphoid lesions. Evidence is presented suggesting that many microfollicular lesions may represent clones of mutated cells, and that the lymphocytes may be targeted to these microfollicles. Lymphocytes were rarely found in association with C cell micronodules. Within individual thyroids there is considerable variation in the proportion of each lesion when combinations are present. Thus with advancing age there is an increasing heterogeneity of thyroid structure that may confound attempts to correlate structural and physiological changes with age.

Age associated increase of C cell follicles in guinea pig thyroid glands

The effect of aging on the formation of C cell follicles was examined in the thyroid gland of guinea pigs at various ages ranging from 1 to 29 months. The C cell follicles were demonstrated with the immunoperoxidase methods by using anticalcitonin and antisomatostatin antisera and with PAS reaction. They were already detected in 1-month-old guinea pigs but in low number. Thyroid glands from 1- to 14-month-old animals contained only a small number of C cell follicles and did not reveal the age-related increase. In aged guinea pigs (20- to 29-month-old), a dramatic increase of C cell follicles was found, about 13 times as high as the number of other age groups. The C cell follicles through all age groups were present in large clusters of C cells. In the aged guinea pigs, nodular large aggregates of C cells regarded as C cell hyperplasia occurred and numerous C cell follicles were formed in the large cell aggregates. Thus, the conspicuous increase of C cell follicles in aged animals was associated with a proliferative abnormality of C cells. The C cells forming follicles showed moderate to weak immunoreactivity for calcitonin, whereas they showed very intense immunoreactivity for somatostatin. In addition, the colloidlike and flocculent materials stored in the follicular lumina, which were consistently PAS-positive, were weakly immunoreactive to somatostatin but nonreactive to calcitonin.

Number and size of rat thyroid C cells: no effect of pinealectomy

A method for the estimation of the size and total number of calcitonin-containing cells (C cells) in the rat thyroid gland has been devised. The total area, the number of C cells per unit area, and the areal fraction of C cells were determined for the C cell region using step serial sections. From these data it was estimated that from 0.3 X 10(6) to 1.0 X 10(6) C cells were evenly divided between the two thyroid lobes. Approximately 150 micron3 of cytoplasm were associated with each of these cells. In comparison with sham-operated rats, pinealectomy had little effect on the number of C cells. In an experiment terminated in the summer, there was a statistically insignificant decrease 6 weeks postsurgery; no effect was seen at 12 weeks. On the other hand, a slight increase in the number of C cells was seen in January, 12 weeks postsurgery. The volume of cytoplasm per cell was not altered by pinealectomy.

The effect of calcitonin in vitro on tooth germs in protein-energy malnourished rats

The effect of calcitonin on the development of incisor and molar tooth germs was studied in normal and nutritionally deprived newborn rats. Calcitonin affected the calcium uptake of nutritionally deprived molar tooth germs in the early postnatal period; this interaction was not seen in the later postnatal period, however.