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).

Evidence of a toxic effect of ethanol on bone in rats

Tibiae from rats treated chronically for 12 days with enough ethanol to induce physical dependence were found to have an increased incidence of fracture during dissection and cleaning (7 of 12 or 58%) compared to control animals (1 of 12 or 8%). The site of the fractures, the proximal end of the tibia, showed an increased opacity to X-rays, and the dried bones were distinctly darker in appearance than similarly prepared control bones. The effects noted in our study suggest that the rat model could be useful for the study of the mechanisms by which alcohol affects bone growth, remodeling, and strength. These studies might shed new light on the pathogenesis of increased bone fragility in alcoholics.

Age-associated C-cell hyperplasia in the human thyroid

C cells in 26 normal human thyroids from forensic autopsies were identified by immunoperoxidase staining for calcitonin. C-cell concentrations and total C-cell numbers were determined with the use of morphometric techniques. There was great variation in C-cell density within a given gland and among individuals, although C cells tended to concentrate about one third of the way down the vertical axis of the lateral lobes. Densities of 1-2000 cells/cu mm were found in the third and later decades. In addition there was a statistically significant (P less than 0.01) positive Spearman correlation between total C-cell numbers and age in males. C-cell hyperplasia appears to be an age-related phenomenon that may have physiologic significance and must be taken into consideration in evaluation of thyroid glands for the diagnosis of premalignant lesions of C cells.

C-cell nodules in adult human thyroid. A common autopsy finding

This study was designed to examine the morphologic features and distribution of calcitonin-producing cells (C-cells) in normal adults and in a general autopsy population. Random or serial sections from thyroid glands in forensic and general autopsies were examined by an immunoperoxidase stain for calcitonin to identify C-cells. Six glands out of 30 cases contained large C-cell nodules (85-343 C-cell nuclei per nodule). Five of the nodules were in patients over 50 years of age. C-cell nodules in thyroid sections may represent age-related hyperplasia or a normal variation of ontogeny. This study underscores the importance of serially sectioning the thyroid to evaluate nodular C-cell hyperplasia in preneoplastic or nonneoplastic functional disorders.

Calcitonin-like immunoreactivity in rat and human pituitary glands: histochemical, in vitro, and in vivo studies

This study was designed to determine whether pituitary glands contain an immunoreactive material which reacts with antisera to calcitonin (CT) and, if so, whether secretion of the material could be demonstrated. Testing 15 antisera to rat and human CT and using an immunoperoxidase method, we found 2 antisera to human CT which stained rat pituitaries and several which stained human pituitaries. Essentially all cells in the rat intermediate lobe and scattered cells in the rat and human anterior lobes showed staining, and staining was not entirely abolished by prior adsorption of antisera with rat or human CT. The 2 antisera which stained rat pituitaries showed cross-reactivity with several synthetic human CT fragments (1-18, 11-23 and 22-32) but not with ACTH-(1-39), ACTH-(1-24), beta-endorphin, alpha- or beta MSH, or bovine lipotropin. Crude extracts of pituitaries from 2 strains of young rats showed CT-like immunoreactivity which could be measured easily by RIA (0.2-0.3 ng/gland). In vivo, an antiserum which stained pituitaries and 1 which did not were compared using young rats made hypercalcemic (15-20 mg/dl) with iv Ca. In rats with thyroids, both antisera showed an increase in serum CT of more than 15-fold whether the pituitary was present or absent. In thyroidectomized rats, serum CT remained undetectable (less than 50 to 100 pg/ml) during hypercalcemia even if the pituitary was present. In vitro, rat pituitaries in a serum-free medium did not release measurable amounts of immunoreactive CT-like material even when medium contained high Ca (2.5 mM), high K (25 mM), or TRH (10(-6) M). Therefore, the findings agree with other reports of a CT-like material in the pituitary, but no secretion of the material could be demonstrated. We hypothesize that the material is not authentic CT but is, rather a related peptide sequence probably contained in the 31 K precursor protein of ACTH-beta-lipotropin.

Sex difference in serum calcitonin level in rats as related to feeding, fasting, and age

Serum calcitonin (CT) was measured in male and female Fischer fasted and fed rats from 1-24 months of age. Previous findings by ourselves and others that serum CT rises with advancing age and is higher in females than in males were confirmed and extended. The effects of feeding were examined with the use of three different protocols, overnight fasting then feeding for 1 h, feeding ad libitum, and feeding rats for 2 h after they had been on a fixed feeding schedule for 4 weeks. At 1 month of age serum CT was too low to measure in either sex, fed or fasted. From 2-24 months of age, feeding increased serum immunoreactive CT much more in females than in males. The increase in serum CT was accompanied by a slight decrease in serum calcium. We concluded that the release of CT in rats after eating is sex related.

Hypercalcitoninemia associated with return of serum calcium concentration toward normal in chronically parathyroidectomized rats

In chronically parathyroidectomized male Fischer and Holtzman rats, we found a progressive rise in the levels of serum immunoreactive calcitonin (CT) despite hypocalcemia. The rise was preceded by an increase in the thyroidal CT concentration (determined by RIA) and hyperplasia of C cells (determined by the immunoperoxidase bridge technique). In association with the rise in serum CT, we also observed a return of serum Ca toward normal levels, which the evidence suggests was not due to compensatory regeneration of parathyroid remnants after incomplete parathyroidectomy. It also is unlikely that ectopic parathyroid tissue was responsible for the return of serum Ca toward normal. Since the increase in serum CT after parathyroidectomy coincided with the return of serum Ca toward normal, we postulate that a gradual rise in serum Ca in chronically parathyroidectomized rats might stimulate the "CT-saturated" thyroid glands to release CT, thus leading to a progressive increase in serum CT. Alternatively, it is possible that the increase in serum CT after parathyroidectomy may be due in part simply to nonspecific leakage of CT from the "CT-saturated" thyroid glands.

Identification of C-cells in normal and goitrous rat thyroid tissues using antiserum to rat thyrocalcitonin and the immunoperoxidase bridge technique

Application of the immunoperoxidase bridge technique to the light microscopic localization of C-cells in rat thyroid tissue is described. Guinea pig antisera to rat thyrocalcitonin (TCT) were produced by the injection of highly purified rat TCT (100-300 MRC U/mg) emulsified in complete Freund's adjuvant. A 1:1000 dilution of the antiserum used in this study gave a strong positive reaction with rat C-cells, and 1 ml of undiluted antiserum provided sufficient material for staining approximately 5000 slides. The substitution of nonimmune guinea pig serum for the anti-rat TCT serum or the prior absorption of anti-rat TCT serum with increasing amounts of highly purified rat TCT both eliminated the staining of thyroid C-cells. Likewise, no staining was observed in tissue sections from rat parathyroid, ovary, pituitary gland, and skeletal muscle. Antiserum to synthetic human TCT also could be used to identify rat thyroid C-cells. The method revealed abundant C-cells in goiters from rats fed a low-iodine diet for more than 1 year. This finding was supported by electron microscopic evaluation of goitrous tissue and by the detection, by radioimmunoassay, of TCT in thyroid tissue and in peripheral blood from goitrous rats.

Effects of ethanol on chicks in 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. Results in vitro were as follows: 1) 5 to 30 mul 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 metabolism in 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 ethanol in vivo may at least partially result from ethanol-stimulated bone mineral deposition.