An ultrastructural study of postprandial changes in bone lining cells of lead-injected thyroidectomized and thyroid-intact rats.

Abstract

This report is an electron microscopic study demonstrating intracellular differences in endosteal bone lining cells in tissue removed from thyroid-intact (TI) and thyroidectomized (TX) rats. Rats with functional parathyroid gland transplants, many of which were thyroidectomized, were trained to a 0900 h feeding schedule. Some of the TX rats (TX + CT) were injected postprandially with calcitonin (80 pg/g body weight). One hour before sacrifice all rats were injected with lead acetate (20 mg/kg body weight). Sections of the diaphysealmetaphyseal junction of the tibia were prepared for morphological examination using two procedures designed for the study of nondecalcified bone tissue. The following results were obtained: (a) Following pyroantimonate fixation, the electron-dense precipitate in sections obtained from TI and TX + CT rats was arranged in a distinct intracellular organization within bone lining cells. Following an anhydrous tissue preparation (in ethylene glycol), the mitochondria of these cells contained distinct electron-lucent areas. A similar result was found in tissue from TI rats regardless of the relationship of the time of sacrifice to the last feeding. (b) In TX rats, the major difference in the appearance of these bone lining cells was in tissue removed 4 h following a calcium-containing meal. The electron-dense precipitate (resulting from pyroantimonate fixation) was diffusely distributed throughout the lining cells rather than organized. The mitochondria of the cells (anhydrous procedure) contained distinct electrondense areas. These marked differences in tissues from TX rats were transient. With time following feeding, the histological appearance of these cells returned to that seen in cells from TI rats and TX rats injected postprandially with calcitonin. These results, utilizing the unique reaction of lead with bone cells, demonstrate an additional calcitonin-dependent response of rats to oral intake of calcium. They support the concept that endosteal bone tissue contains target cells for calcitonin and that this hormone has a role in postprandial conservation and storage of calcium.