16. A C T I O N S OF H O R M O N E S
649
DPN and TPN-diaphorase and alkaline phosphatase were considerably
reduced in the epiphyseal disc, the proliferating zone, osteoblasts and
perichondrium, while succinic, glutamic and glycerophosphate dehydrogenases were only slightly inhibited or remained unchanged.
Although these findings are based on semi-quantitative estimations,
they agree well with in vivo results by Kuhlmann (1960) who by biochemical methods demonstrated a reduction of lactic and glucosesphosphate dehydrogenases and alkaline phosphatases in femurs of
newly born dogs treated with the hormone. The presence of glutamic
dehydrogenase in the osteoclasts on which Walker's hypothesis (1961)
of the conversion of osteoblasts into osteoclasts is based could, however,
not be confirmed by Herrmann-Erlee.
Thus parathormone induces severe changes both in parietal bone
and in limb-bone rudiments. This effect is produced at the cellular
level and in the parietal bone is closely bound up with the presence of
osteoclasts. However, the hormone does not, as previously thought,
evoke a new formation of these elements but seems necessary for the
survival, activity and increase of the osteoclasts present in the bone
before explantation. The exact nature of their function is not known
and it is not clear whether they are directly responsible for the lysis of
the bone or whether they act as scavengers after the hormone has
directly affected the bone matrix (Vol.2, Chapter 5). The thinning of the
peripheral region of parietal bone and the changes in the cartilage
matrix in limb-bone rudiments which are brought about without the
"help" of osteoclasts makes the second explanation more likely. The
reduction of enzymes shortly after treatment, i.e. before the morphological changes had manifested themselves, suggest that the effect on
the bone is caused by an alteration of metabolic pattern, in particular
that of carbohydrate metabolism, by the hormone.
I X . C O N C L U S I O N S
The studies on the effects of hormones on cells and organs in vitro
indicate that most of the hormones examined affect cells and tissues
directly. They may have a general effect and, like insulin, enhance
proliferation in cell cultures and organized tissues alike or, like the
anterior pituitary and sex hormones, influence their target organs in a
specific manner by promoting the differentiation of specialized structures and functions.
Hormone-dependent target tissues retain this characteristic in vitro
only if grown as organ cultures, while cell cultures derived from them
lose the hormone sensitivity of the parent tissue.
Y*
649
DPN and TPN-diaphorase and alkaline phosphatase were considerably
reduced in the epiphyseal disc, the proliferating zone, osteoblasts and
perichondrium, while succinic, glutamic and glycerophosphate dehydrogenases were only slightly inhibited or remained unchanged.
Although these findings are based on semi-quantitative estimations,
they agree well with in vivo results by Kuhlmann (1960) who by biochemical methods demonstrated a reduction of lactic and glucosesphosphate dehydrogenases and alkaline phosphatases in femurs of
newly born dogs treated with the hormone. The presence of glutamic
dehydrogenase in the osteoclasts on which Walker's hypothesis (1961)
of the conversion of osteoblasts into osteoclasts is based could, however,
not be confirmed by Herrmann-Erlee.
Thus parathormone induces severe changes both in parietal bone
and in limb-bone rudiments. This effect is produced at the cellular
level and in the parietal bone is closely bound up with the presence of
osteoclasts. However, the hormone does not, as previously thought,
evoke a new formation of these elements but seems necessary for the
survival, activity and increase of the osteoclasts present in the bone
before explantation. The exact nature of their function is not known
and it is not clear whether they are directly responsible for the lysis of
the bone or whether they act as scavengers after the hormone has
directly affected the bone matrix (Vol.2, Chapter 5). The thinning of the
peripheral region of parietal bone and the changes in the cartilage
matrix in limb-bone rudiments which are brought about without the
"help" of osteoclasts makes the second explanation more likely. The
reduction of enzymes shortly after treatment, i.e. before the morphological changes had manifested themselves, suggest that the effect on
the bone is caused by an alteration of metabolic pattern, in particular
that of carbohydrate metabolism, by the hormone.
I X . C O N C L U S I O N S
The studies on the effects of hormones on cells and organs in vitro
indicate that most of the hormones examined affect cells and tissues
directly. They may have a general effect and, like insulin, enhance
proliferation in cell cultures and organized tissues alike or, like the
anterior pituitary and sex hormones, influence their target organs in a
specific manner by promoting the differentiation of specialized structures and functions.
Hormone-dependent target tissues retain this characteristic in vitro
only if grown as organ cultures, while cell cultures derived from them
lose the hormone sensitivity of the parent tissue.
Y*