20
Ν. G. PON
in extracts of epididymal fat pads (133). This and other experiments
with homogenates of fat pads from fasted rats led to the conclusion that
the activation of the dehydrogenases following ingestion of a sudden load
of carbohydrate results in the synthesis of the enzymes, not in the activation of inactive preformed enzymes.
Experiments with adipose tissues of normal and obese mice, in the
presence and absence of insulin and/or growth hormone, gave essentially
the same results as those with rats (134). On the other hand, adipose
tissue of tumor-bearing mice has a relatively depressed pentose phosphate cycle activity (135). One final note; the interscapular brown fat of
the rat also seems to contain pentose phosphate cycle enzymes, as shown
by experiments with homogenates and variously labeled glucose in the
presence and absence of DPN
+ , ATP, and TPN
+
(136).
3. Adrenals
Glock and McLean have shown that adrenal cortex contains a high
level of the oxidative enzymes of the pentose phosphate cycle (137).
They have also demonstrated that the adrenal medulla contains much
less of these enzymes, which was confirmed by the work of Kelley et al.
(138). Other investigators have gone further by showing that both dehydrogenases are localized within the adrenal cortex, with maximum levels
in the zona fasciculata (an inner zone of the cortex) (139). In vivo
administration of ACTH causes the glucose-6-phosphate and 6-phosphogluconate dehydrogenases to shift toward the medulla, to a section between the fasciculata and the reticularis. The latter enzyme, however,
is activated throughout the cortex. In contrast to these studies are those of
glucose-6-phosphate dehydrogenase in the glomerulosa, the subcapsular
region nearest the periphery of the adrenal cortex (140, 141). In tissues
from sodium-depleted rats (fed a salt-poor diet), the normally narrow
zone widens and the dehydrogenase level increases markedly. The high
enzymatic activity is concentrated in the peripheral glomerulosa, the
inner portion becoming relatively poor in dehydrogenase activity. The
conclusion is that the glomerulosa are composed of two types of cells
that respond to sodium-depletion. Glucose phosphate dehydrogenase
may be required for energy production and TPNH formation, possibly
for synthesis of aldosterone, since the dehydrogenase activity is highest
in the region where lipid concentration is lowest.
As in the case of adipose tissues, a variety of conditions can affect the
pentose phosphate cycle activity in the adrenal glands. Thus dehydroepiandrosterone, when added in vitro to a homogenate of adrenals in the
presence of glucose and TPN
+ , has two effects. If the TPN
+ level is not
limiting, the hormone decreases the formation of C0 2 and the production
Ν. G. PON
in extracts of epididymal fat pads (133). This and other experiments
with homogenates of fat pads from fasted rats led to the conclusion that
the activation of the dehydrogenases following ingestion of a sudden load
of carbohydrate results in the synthesis of the enzymes, not in the activation of inactive preformed enzymes.
Experiments with adipose tissues of normal and obese mice, in the
presence and absence of insulin and/or growth hormone, gave essentially
the same results as those with rats (134). On the other hand, adipose
tissue of tumor-bearing mice has a relatively depressed pentose phosphate cycle activity (135). One final note; the interscapular brown fat of
the rat also seems to contain pentose phosphate cycle enzymes, as shown
by experiments with homogenates and variously labeled glucose in the
presence and absence of DPN
+ , ATP, and TPN
+
(136).
3. Adrenals
Glock and McLean have shown that adrenal cortex contains a high
level of the oxidative enzymes of the pentose phosphate cycle (137).
They have also demonstrated that the adrenal medulla contains much
less of these enzymes, which was confirmed by the work of Kelley et al.
(138). Other investigators have gone further by showing that both dehydrogenases are localized within the adrenal cortex, with maximum levels
in the zona fasciculata (an inner zone of the cortex) (139). In vivo
administration of ACTH causes the glucose-6-phosphate and 6-phosphogluconate dehydrogenases to shift toward the medulla, to a section between the fasciculata and the reticularis. The latter enzyme, however,
is activated throughout the cortex. In contrast to these studies are those of
glucose-6-phosphate dehydrogenase in the glomerulosa, the subcapsular
region nearest the periphery of the adrenal cortex (140, 141). In tissues
from sodium-depleted rats (fed a salt-poor diet), the normally narrow
zone widens and the dehydrogenase level increases markedly. The high
enzymatic activity is concentrated in the peripheral glomerulosa, the
inner portion becoming relatively poor in dehydrogenase activity. The
conclusion is that the glomerulosa are composed of two types of cells
that respond to sodium-depletion. Glucose phosphate dehydrogenase
may be required for energy production and TPNH formation, possibly
for synthesis of aldosterone, since the dehydrogenase activity is highest
in the region where lipid concentration is lowest.
As in the case of adipose tissues, a variety of conditions can affect the
pentose phosphate cycle activity in the adrenal glands. Thus dehydroepiandrosterone, when added in vitro to a homogenate of adrenals in the
presence of glucose and TPN
+ , has two effects. If the TPN
+ level is not
limiting, the hormone decreases the formation of C0 2 and the production