1. PENTOSE PHOSPHATE CYCLE
25
respective positions, but, in the case of the thyroxine studies, the
activities of glucose-6-phosphate and 6-phosphogluconate dehydrogenases
were assayed.
Of interest is the action of epinephrine on the thyroid system. Apparently, the epinephrine in the incubation mixture turns pink, a finding
which suggested to the workers that adrenochrome is formed
(181).
Accordingly, adrenochrome was tested and found to stimulate the
oxidation of glucose in even lesser amounts than epinephrine. Thus
epinephrine may act after its conversion to adrenochrome. Both these
compounds catalytically accelerate the oxidation of TPNH and DPNH
by a thyroid mitochondrial-microsomal preparation. The conclusion is
that a rise in the TPN
+ level seems to be responsible for the increased
oxidation of glucose-l-C
14
, although the reason for the increase of
glucose-6-C
14
oxidation remains obscure. These observations are consistent with the findings of experiments with in vitro addition of serotonin
(182), thyroid-stimulating hormone (183), and the artificial electron
acceptor Synkavite (176) to slices of thyroid gland. In all cases, the level
of TPN
+ seems to be rate limiting.
Thyroxine, administered in vitro (178), increased the activity of the
dehydrogenases of the pentose phosphate cycle. However, the response
of these enzymes to thyroxine does not occur in the fasted rat.
Propylthiouracil is a drug that affects the uptake of radioactive iodine
and of oxygen as well as the formation of diiodotyrosine by thyroid
slices. Its effect on the oxidation of glucose is concentration dependent,
a small dose (10~
8 Μ) inhibiting slightly the oxidation of C-l while
augmenting that of C-6, whereas a large dose (ΙΟ
-3 Μ) significantly
decreasing the oxidation of both carbons (179).
Tremblay and Pearse have examined by histochemical techniques
slices of monkey (Macaca irus) and human parathyroids (184). They
found that oxyphile cells contain a high activity of DPNH and TPNH
diaphorases and dehydrogenases including those of succinate, ß-hydroxybutyrate, and gIucose-6-phosphate. The principal cells, on the other
hand, are weak in these enzymes. They concluded, therefore, that the
oxyphile cells, which are normally considered to be degenerate, are in
fact active secretory elements of the parathyroid glands. In connection
with glucose metabolism in this tissue, parathyroid adenoma slices gave
large C-l:C-6 ratios when incubated with the corresponding labeled
glucose (147).
Human, rabbit, and calf testes also gave very high C-l:C-6 ratios
of C0 2 from labeled glucose (147). In vitro treatment of these tissues
with follicle-stimulating hormone, luteinizing hormone, or chorionic
gonadotropin did not affect this ratio. Using cytochemical methods,
25
respective positions, but, in the case of the thyroxine studies, the
activities of glucose-6-phosphate and 6-phosphogluconate dehydrogenases
were assayed.
Of interest is the action of epinephrine on the thyroid system. Apparently, the epinephrine in the incubation mixture turns pink, a finding
which suggested to the workers that adrenochrome is formed
(181).
Accordingly, adrenochrome was tested and found to stimulate the
oxidation of glucose in even lesser amounts than epinephrine. Thus
epinephrine may act after its conversion to adrenochrome. Both these
compounds catalytically accelerate the oxidation of TPNH and DPNH
by a thyroid mitochondrial-microsomal preparation. The conclusion is
that a rise in the TPN
+ level seems to be responsible for the increased
oxidation of glucose-l-C
14
, although the reason for the increase of
glucose-6-C
14
oxidation remains obscure. These observations are consistent with the findings of experiments with in vitro addition of serotonin
(182), thyroid-stimulating hormone (183), and the artificial electron
acceptor Synkavite (176) to slices of thyroid gland. In all cases, the level
of TPN
+ seems to be rate limiting.
Thyroxine, administered in vitro (178), increased the activity of the
dehydrogenases of the pentose phosphate cycle. However, the response
of these enzymes to thyroxine does not occur in the fasted rat.
Propylthiouracil is a drug that affects the uptake of radioactive iodine
and of oxygen as well as the formation of diiodotyrosine by thyroid
slices. Its effect on the oxidation of glucose is concentration dependent,
a small dose (10~
8 Μ) inhibiting slightly the oxidation of C-l while
augmenting that of C-6, whereas a large dose (ΙΟ
-3 Μ) significantly
decreasing the oxidation of both carbons (179).
Tremblay and Pearse have examined by histochemical techniques
slices of monkey (Macaca irus) and human parathyroids (184). They
found that oxyphile cells contain a high activity of DPNH and TPNH
diaphorases and dehydrogenases including those of succinate, ß-hydroxybutyrate, and gIucose-6-phosphate. The principal cells, on the other
hand, are weak in these enzymes. They concluded, therefore, that the
oxyphile cells, which are normally considered to be degenerate, are in
fact active secretory elements of the parathyroid glands. In connection
with glucose metabolism in this tissue, parathyroid adenoma slices gave
large C-l:C-6 ratios when incubated with the corresponding labeled
glucose (147).
Human, rabbit, and calf testes also gave very high C-l:C-6 ratios
of C0 2 from labeled glucose (147). In vitro treatment of these tissues
with follicle-stimulating hormone, luteinizing hormone, or chorionic
gonadotropin did not affect this ratio. Using cytochemical methods,