Electron microscopic studies on the effect of long-term hypercalcemia on the thyroid parafollicular cell and the parathyroid cell of rats

Effect of maternal nicotine/thiocyanate exposure during gestational period upon pituitary, thyroid and parathyroid function/morphology of 1-month-old rat offspring

INTRODUCTION

Impact of in utero exposure to nicotine, on the structure of the thyroid-pituitary axis and the parathyroid glands have been examined in 1-month-old rats and compared with that of thiocyanate.

MATERIALS AND METHODS

Three pregnant female groups were used; control, nicotine and thiocyanate. Treatment started from gestation day (4-20) and the specimens were harvested from the male offspring of all groups at the age of 1 month and processed for light, electronmicroscopic and immunohistochemical examination. Total triiodothyronine (tT3), total thyroxine (tT4) and total thyrotropin (TSH) were quantitatively determined in serum.

RESULTS

Both nicotine and thiocyanate activated the thyroid follicular cells, with an increase in height (about 30 %) and a negative feedback on the pituitary thyrotrophs which revealed a reduction in the number of cytoplasmic secretory granules, particularly the thiocyanate group. However, in thiocyanate group there was signs of impaired secretory activity of the thyroid gland. The arbitrary area of parathyroid chief cells, increased (about 45 %) particularly in nicotine group, with signs of reduced activity and a positive feedback on the parafollicular cells which revealed hypertrophy, proliferation (25 %) and increased intensity of positive immunohistochemical reaction for calcitonin.

CONCLUSION

Nicotine impaired chief parathyroid cells activity and consequently activated parafollicular cells. Thiocyanate reduced pituitary thyrotrophs activity, whereas both nicotine and thiocyanate increased thyroid follicular cells activity. This impact of in utero exposure persisted for 1-month postnatal.

Electron-microscopic studies on the threshold value of calcium concentration for the release of storage granules and the acceleration of their degradation in the rat parathyroid gland

To determine both a threshold value of calcium concentration (CC) for the release of storage granules and that for the acceleration of degradation of these granules, the rat parathyroid glands were perfused in situ with HEPES-Ringer solutions containing different concentration of Ca2+ for 10 min. With perfusates containing 0.83-1.21 mM Ca2+ (equivalent to 8-11 mg/dl serum calcium), the number of type-I storage granules (large core) [NSG-I] and that of type-II storage granules (small core) [NSG-II] remained unchanged. With perfusates containing 0.83 mM Ca2+ (7.5 mg/dl) or less, however, both NSG-I and NSG-II decreased remarkably and the former was larger than the latter. On the contrary, with perfusates containing 1.27 mM Ca2+ (11.5 mg/dl) or more, NSG-II increased and the ratio of NSG-I to NSG-II was changed reversely. We concluded that a threshold value of CC required for the release of storage granules may be present between 0.88 and 0.83 mM Ca2+ (8 and 7.5 mg/dl) and that a threshold value of CC for accelerating the transformation of type-I granules into type-II, the degradation of storage granules, may be situated at about 1.27 mM Ca2+ (11.5 mg/dl). Additionally, it was suggested that both pro-secretory and storage granules are not only formed at the innermost Golgi cisterna but also at the trans-Golgi network.

Electron microscopic studies of the parathyroid gland of senile dogs

The parathyroid gland of healthy senile dogs aged 8.5 to 15 years was compared with that of mature control dogs by examination with the electron microscope. Preparations fixed by perfusion with glutaraldehyde showed the cytoplasmic matrix of most parenchymal cells to be uniformly dense. None of the cells were of the extremely light type and dark cells were much less frequently noted than in preparations fixed by immersion in glutaraldehyde or osmium tetroxide. Syncytial cells and so-called coloid follicles were more frequent in senile dogs than in control dogs. It was suggested that the content of the latter structures is not colloid but necrotic substance hiving origin from the parenchymal cells and that perhaps the occasional cells containing large, membrane-bound inclusions may be degenerating cells which ultimately produce this necrotic substance. Oxyphil cells and mitochondria-rich cells of another type were found in all senile dogs, but not in the controls. These cells, especially the mitochondria-rich cells, frequently contained bizarre mitochondria that were modified in shape, size and arrangement. The most striking feature of these mitochondria was the concentric arrangement of elongated mitochondria which seemed to consist of densely layered cup-shaped mitochondria. Such mitochondria were noted in all senile dogs aged ten years and over. The significance of mitochondrial ple-morphism in the parathyroid gland of senile dogs was discussed.