Abstract
Quantitative transmission electron microscope methods were used to determine the response of functionally inactive avian medullary bone osteoclasts to parathyroid hormone (PTH). Egg-lying Japanese quail were used during a period of the egg cycle when medullary bone was not being resorbed for egg shell calcification and when medullary bone osteoclasts were functionally inactive. Ruffled borders adjacent to bone surfaces were rarely, if ever, found on these cells. 20 min after the administration of PTH, over 70% of the osteoclast profiles had ruffled borders adjacent to bone surfaces. These ruffled borders were bounded by filamentous-rich "clear zones" and resembled ruffled borders found on functionally active cells. There was also a marked increase in plasma calcium levels after PTH administration. This study demonstrates that PTH stimulates the de novo generation of ruffled borders on osteoclasts in vivo and suggests that osteoclasts may be involved in the acute regulation of calcium metabolism by exogenous PTH.
Highlights
Quantitative transmission electron microscope methods were used to determine the response of functionally inactive avian medullary bone osteoclasts to parathyroid hormone (PTH)
20 min after PTH administration, there is a marked increase in plasma calcium levels (Table I)
Medullary bone osteodasts are round in shape and largely removed from bone surfaces except for a small filamentous zone that remains attached to the bone surface [9]
Summary
Quantitative transmission electron microscope methods were used to determine the response of functionally inactive avian medullary bone osteoclasts to parathyroid hormone (PTH). This study demonstrates that PTH stimulates the de novo generation of ruffled borders on osteoclasts in vivo and suggests that osteoclasts may be involved in the acute regulation of calcium metabolism by exogenous PTH. FFFI increases osteoclast populations in vivo [14], stimulates osteoclast activity in vitro [5], and accelerates the rate of skeletal remodeling [4]. These effects are usually noted long after changes in plasma calcium levels, leading to the belief that osteoclasts are not rapidly responsive to PTH arid not involved in acute regulation of calcium metabolism. This report demonstrates that the cell surface of functionally inactive osteoclasts is rapidly activated after PTH administration
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