648
I L S E
L A S N I T Z K I
day of cultivation. Addition of P T H after 3 days growth in normal
medium did not restore the normal number of osteoclasts and in such
cultures bone resorption was absent. It seemed, therefore, that the
hormone is necessary for the survival and formation of osteoclasts,
which in their turn seem indispensable for the hormone to become fully
effective.
B . C H A N G E S I N E N Z Y M E
A C T I V I T Y
It is now generally accepted that parathormone influences carbohydrate metabolism in bone (Neumann and Neumann, 1958). Histochemical techniques (Lowry, Roberts and Lewis, 1956; Lowry,
Roberts and Chang, 1956) have shown, among other things, the presence of lactic dehydrogenase, glucose-6-phosphate dehydrogenase and
alkaline phosphatase in cartilage (Kuhlmann, 1960) and that of acid
and alkaline phosphatase, esterase, succinic dehydrogenase and cytochrome oxidase in bone tissue from mature animals (Burstone, 1959a,
b, 1960a, b ; Lipp, 1959). Walker (1961) demonstrated, also by a
histochemical method, the presence of dehydrogenases of the hexose
monophosphate shunt, the citric acid cycle, and glycolysis in osteoblasts and osteoclasts of bones from newly born rats. He postulates a
mechanism of hormone action by which the Krebs cycle in the osteoblasts is modified by an activation of the glutamate to oxalacetate
pathway, a change which promotes their conversion into osteoclasts.
Biochemical studies have shown that parathormone inhibits succinic
dehydrogenase (Laskin and Engel, 1956) and isocitric dehydrogenase
(Hekkelmann, 1961) in bone cells of meta- and diaphysis.
Herrmann-Erlee (1962) studied by histochemical means the localization of dehydrogenases of the hexose monophosphate shunt, of
glycolysis, the citric acid cycle, the cytochrome system and others
involved in fat metabolism and protein synthesis as well as acid and
alkaline phosphatases in radii from mouse embryos cultured for short
periods and the effect of parathormone on these enzymes. The distribution and amount of enzymes varied greatly in the different components of the control rudiments. The perichondrium, connective tissue,
and osteoblasts of the metaphysis displayed a high activity of all enzymes investigated while the cells of the epiphyseal cartilage and disc
showed little or no activity. In the cells of the proliferating zone the
amount of most enzymes was intermediate between that seen in the two
first groups. There was some enzyme activity in the osteoclasts but lactic
and glutamic dehydrogenases and alkaline phosphatase were completely
absent. In explants treated for 1 day with 1 i.u./ml medium of P T H
glucose-6-phosphate dehydrogenase, isocitric and lactic dehydrogenase,
I L S E
L A S N I T Z K I
day of cultivation. Addition of P T H after 3 days growth in normal
medium did not restore the normal number of osteoclasts and in such
cultures bone resorption was absent. It seemed, therefore, that the
hormone is necessary for the survival and formation of osteoclasts,
which in their turn seem indispensable for the hormone to become fully
effective.
B . C H A N G E S I N E N Z Y M E
A C T I V I T Y
It is now generally accepted that parathormone influences carbohydrate metabolism in bone (Neumann and Neumann, 1958). Histochemical techniques (Lowry, Roberts and Lewis, 1956; Lowry,
Roberts and Chang, 1956) have shown, among other things, the presence of lactic dehydrogenase, glucose-6-phosphate dehydrogenase and
alkaline phosphatase in cartilage (Kuhlmann, 1960) and that of acid
and alkaline phosphatase, esterase, succinic dehydrogenase and cytochrome oxidase in bone tissue from mature animals (Burstone, 1959a,
b, 1960a, b ; Lipp, 1959). Walker (1961) demonstrated, also by a
histochemical method, the presence of dehydrogenases of the hexose
monophosphate shunt, the citric acid cycle, and glycolysis in osteoblasts and osteoclasts of bones from newly born rats. He postulates a
mechanism of hormone action by which the Krebs cycle in the osteoblasts is modified by an activation of the glutamate to oxalacetate
pathway, a change which promotes their conversion into osteoclasts.
Biochemical studies have shown that parathormone inhibits succinic
dehydrogenase (Laskin and Engel, 1956) and isocitric dehydrogenase
(Hekkelmann, 1961) in bone cells of meta- and diaphysis.
Herrmann-Erlee (1962) studied by histochemical means the localization of dehydrogenases of the hexose monophosphate shunt, of
glycolysis, the citric acid cycle, the cytochrome system and others
involved in fat metabolism and protein synthesis as well as acid and
alkaline phosphatases in radii from mouse embryos cultured for short
periods and the effect of parathormone on these enzymes. The distribution and amount of enzymes varied greatly in the different components of the control rudiments. The perichondrium, connective tissue,
and osteoblasts of the metaphysis displayed a high activity of all enzymes investigated while the cells of the epiphyseal cartilage and disc
showed little or no activity. In the cells of the proliferating zone the
amount of most enzymes was intermediate between that seen in the two
first groups. There was some enzyme activity in the osteoclasts but lactic
and glutamic dehydrogenases and alkaline phosphatase were completely
absent. In explants treated for 1 day with 1 i.u./ml medium of P T H
glucose-6-phosphate dehydrogenase, isocitric and lactic dehydrogenase,