The role of the gonads and the hypophysis in the regulation of hydroxysteroid dehydrogenase activities in rat kidney.

With the exception of 3beta-hydroxy-steroid dehydrogenase all the hydroxysteroid dehydrogenases of adult male and female rat kidney show significant sex differences in their activities. Interference with the organisms endocrine balance (gonadectomy on day 25 of life, hypophysectomy on day 50, a combination of both these operations, administration of testosterone or oestradiol) demonstrates that the sexually differentiated enzyme activities may be classified as androgen or oestrogen dependent, the respective sex hormone acting either in an inductive or repressive manner. The criteria for androgen dependency (microsomal 3alpha- and 20beta-, cytoplasmic 17beta- and 20alpha- hydroxysteroid dehydrogenase) are the feminization of the enzyme activity in male animals after castration and the masculinization of the activity in male and female castrates as well as in normal female animals after administration of testosterone. This latter effect on normal females cannot be a testosterone mediated inhibition of ovarian function since ovariectomy has no effect. For 3alpha-, 20alpha-, and 20beta-hydroxysteroid dehydrogenase the effects of hypophysectomy parallel those of gonadectomy. However, after hypophysectomy the activity of 17beta-hydroxysteroid dehydrogenase falls significantly below the gonadectomized level. The androgen effect on 3alpha and 20beta-hydroxysteroid dehydrogenase is independent of the hypophysis, whereas that of 17beta- and 20alpha-hydroxysteroid dehydrogenase is mediated by the hypophysis.     

The metabolism of oxytocin during lactation in the rabbit

1. It has been suggested that changes in the concentration of hypothalamic enzymes inactivating oxytocin might be taken as an index of hormone production (Hooper, 1966). The present work describes the changes in enzyme concentration shortly after parturition and during lactation. 2. Two groups of animals were used; one consisted of lactating animals from which litters had been removed shortly after parturition. 3. Two fractions obtained from homogenized hypothalamus contained enzyme activity. In animals which had been suckled for 3 days the enzyme activity in the supernatant fraction was three times as great as that observed during pregnancy. Between the third and fifth days the activity reverted to pregnancy levels, and remained fairly constant for as long as the animals were suckled. 4. In animals whose litters were removed shortly after birth, the enzyme activity reverted to pregnancy levels by about the third day post partum, and by the sixth day non-pregnancy levels were reached. 5. The enzymes of a particulate fraction behaved somewhat differently; 6 hr. after parturition the enzyme activity was similar to that found in pregnant animals and there was no detectable activity by the tenth day in suckled animals. In non-suckled animals the enzyme activity decreased more rapidly, and non-detectable levels were reached by the fourth day post partum.     

Adrenal microsomal C19-steroid 5α-reductase activity in the Snell transplantable rat adrenocortical tumour 494 and the effect of oestradiol, testosterone propionate and adrenocorticotrophin in intact and gonadectomized rats

The C(19)-steroid 5alpha-reductase activity in the microsomal fraction of rat adrenal tissue under various hormonal treatments was examined. In intact control rats the activity is similar in both males and females, and after gonadectomy it is markedly increased. Treatment with oestradiol (150mug/day per animal for 7 days) or testosterone propionate (2mg/day per animal for 7 days) lowered the activity of 5alpha-reductase in castrated animals to approximately the values for intact animals in both sexes, and in intact animals the activity was also decreased by these treatments. The enzyme activity was also decreased by adrenocorticotrophin treatment but to a lesser extent than by the steroid hormones. The activity of the 5alpha-reductase enzyme in the Snell adrenocortical tumour 494 is very low when incubated as a whole homogenate, but the activity in microsomal material of the tumour was measured and unexpectedly found to be similar to that in intact controls.     

Ischemia-Induced Translocation of Ca2+/Calmodulin-Dependent Protein Kinase II: Potential Role in Neuronal Damage

The activities of Ca2+/calmodulin (CaM)-dependent, Ca2+/phospholipid-dependent, and cyclic AMP-dependent protein kinases (CaM-KII, PKC, and PKA, respectively) were determined in rat brains after global ischemia. Both CaM-KII and PKC activities were significantly depressed in both hippocampal and cerebral cortical regions of ischemic animals, whereas no change was detected in PKA activity. The loss of CaM-KII activity was more dramatic and more sustained than the loss of PKC activity and correlated with the duration of ischemia. These decreases in enzyme activity were found in both supernatant and pellet fractions from crude homogenates. When the supernatant and pellet were analyzed for the amount of CaM-KII 50-kDa protein, a significant decrease was detected in supernatant fractions that paralleled a gain in the amount of CaM-KII in the pellet. Thus, the loss of CaM-KII activity in the supernatant can be explained by translocation of the enzyme to the pellet. Whether inactivation of CaM-KII occurs during or after the enzyme translocates from the supernatant to the pellet is unknown. Our results indicate that loss in CaM-KII activity parallels neuronal damage associated with ischemia; down-regulation of CaM-KII activity coincided with translocation of the enzyme to the particulate fraction, and it is proposed that this may be, in fact, a mechanism for controlling excessive CaM-KII phosphorylation.     

Adentylate cyclase activity in myocardium of spontaneously hypertensive rat: effect of endogenous factors and solubilization

The isoproterenol- and glucagon-stimulated adenylate cyclase activities in the myocardial membranes of hypertensive rat were consistantly lower as compared with normal controls. Addition of cytosolic fraction (100,000 x$\text{g}$ supernatant) to the particulate preparation had an additive effect for glucagon and Gpp(NH)p stimulated enzyme activity and a synergistic effect for isoproterenol stimulation. Cytosolic fraction of normal control animals did not bring the adenylate cyclase activity in SHR equivalent to the control values. The basal and F^?-stimulated enzyme activity of solubilized adenylate cyclase was reduced by about 30% in SHR as compared with WKY, which could be due to a decrease in the actual amount of adenylate cyclase in the myocardium of SHR.     

The effects of serum oestrogen-binding components on the unbound oestradiol-17 beta fraction in the serum of developing female rats and on inhibition of [3H]oestradiol uptake by uterine tissue in vitro

Total oestradiol concentrations in the serum of young female rats were high and decreased after about 21 days of age. High affinity serum oestradiol-binding components (EBP), however, fell steadily from 5 to 23 days of age while the unbound oestradiol-17 beta fraction, which was low early in development, increased between 21 and 28 days of age. Injection (i.v.) of immature (EBP-rich) oestradiol-free serum into 21-day-old female rats led to a decrease in the unbound oestradiol fraction and an increase in serum FSH concentrations. Incubation of uterine tissue with [3H]oestradiol, with or without the addition of diethylstilboestrol (DES), showed the rate and degree of total and DES-suppressible uptake of [3H]oestradiol to be greatest from buffer, less from adult (EBP-poor) serum and negligible from immature (EBP-rich) serum; moreover, there was a positive correlation between the degree of uptake of [3H]oestradiol and the unbound fraction of [3H]oestradiol in the incubate. It is concluded that, at least in young rats, oestradiol activity depends more on the availability of free oestradiol than on its total plasma concentrations.     

The association of lysosomal enzymes with nuclei during enzyme induction in rat liver.

Male rats of the Holtzman strain were fasted for 3 days and refed a diet high in carbohydrate (68.9%). The induction of liver glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase was monitored for up to 48 h after refeeding. Induction occurred by 24 h, and by 48 h, 4.2- and 1.5-fold increases were observed for glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, respectively, compared with that of livers of pellet-fed rats. After refeeding, lysosomes increased in fragility as judged by an increased release of acid phosphatase activity during standard homogenization. Fragility was greatest 3 h after refeeding, but normal fragility was observed 24 h after refeeding. Nuclei were isolated from the liver samples before and after refeeding. Those isolated just before refeeding revealed small latent acid phosphatase activity (4–6%). However, after refeeding the carbohydrate-rich diet, a transient and significant (P < 0.01) increase in the latent activity occurred that was maximal (20%) at 1 h, returning to normal by 24 h. Cross-mixing the 800g nuclear pellet from livers of animals starved for 3 days with the 800g supernatant fraction from livers of animals refed the carbohydrate-containing diet did not alter the nuclear lysosomal-free (overt) or latent (detergent-released) enzyme activity. Similarly, mixing the 800g nuclear pellet from livers of animals refed for 1 h with the 800g supernatant fraction from livers of animals starved for 3 days, but not refed, did not change the nuclear lysosomalfree or latent enzyme activity. Purified nuclei, further washed in hypotonic buffer, lost acid phosphatase activity, but those isolated from livers of rats refed for 1 h retained 10% of the enzyme latency, whereas all latency was lost from those isolated from uninduced rats. A second lysosomal enzyme, β-galactosidase, became associated with the nuclei with the same temporal pattern as for acid phosphatase. However, no variation in nuclear content of cytosolic lactate dehydrogenase occurred as a result of feeding the high-carbohydrate diet to starved rats. When similarly starved rats were refed a diet high in lipid and carbohydrate-free, no induction of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase was observed. Lysosomes were not temporarily fragile and purified nuclei did not exhibit increased latency of acid phosphatase activity. Though the evidence presented does not establish a direct correlation between lysosome migration to nuclei as a required function in enzyme induction, the temporal and specific nature of the phenomenon support the hypothesis that liver lysosomal enzymes participate in early signals in the induction of enzymes of lipogenesis.     

Nature of the Cytoplasmic Factor(s) Modulating Adenylate Cyclase in the Developing Rat Brain

Abstract: Adenylate cyclase activity in the particulate fraction from rat brain was markedly enhanced by the cytoplasmic fraction, which itself contained negligible enzyme activity, indicating the presence of some stimulatory factor(s) in the supernatant. Activation of adenylate cyclase was dependent on the supernatant concentration up to 1 mgiml, but higher concentration of the supernatant did not produce further activation of the enzyme. The supernatant retained its stimulatory activity after boiling for 5 min, extensive dialysis, and phospholipase A and DNAase treatments, but was completely inactivated by digestion with trypsin. Ability of the supernatant to activate adenylate cyclase was low during fetal life, increased severalfold neonatally, and declined somewhat thereafter to an adult level. Adenylate cyclase in the particulate fraction from 2-day-old rat brain was also activated by GTP, calcium-dependent regulator (CDR) of cyclic AMP phosphodiesterase in the presence of 100 pM-Ca¹, and by NaF. The supernatant produced additive activation of the enzyme with NaF but not with GTP or CDR, suggesting a common site of action of the supernatant factor(s) and the latter two agents. DEAE-cellulose chromatography of the boiled supernatant resolved the heat-stable proteins into several peaks. Adenylate cyclase activator eluted in two distinct peaks, one of which also contained CDR activity. It is concluded that rat brain supernatant contains some factor in addition to CDR which activates particulate adenylate cyclase.     

Uptake of oestradiol by the rabbit hypothalamus. Specificity of binding by nuclei in vitro

The binding of [6,7-(3)H]oestradiol-17beta to subcellular fractions of the hypothalamus and the cerebellum of the rabbit was studied in vitro. Uptake of steroid was higher in hypothalamic nuclei than in cerebellar nuclei. Lower binding was observed in other fractions of both tissues. After dialysis of the fractions, hypothalamic nuclei retained a high percentage of oestradiol whereas cerebellar nuclei lost most of the bound steroid. Supernatant fractions of both tissues retained a significant proportion of label after dialysis and after gel filtration on Sephadex G-200. No specific binding was observed in these fractions when subjected to sucrose-density-gradient centrifugation. Purification of nuclei followed by incubation with labelled oestradiol in the absence of the supernatant fraction resulted in loss of binding of steroid by hypothalamic nuclei. Incubation of the purified hypothalamic nuclei with supernatant fraction maintained the binding specificity of hormone retention.     

Physiological changes in the activities of extramitochondrial acetyl-CoA hydrolase in the liver of rats under various metabolic conditions

Significant increase in the activity of an acetyl-CoA hydrolase (ATP-stimulated, ADP-inhibited enzyme) in the supernatant fraction of rat liver was observed after 44-68 h of starvation (about 2-fold), and in the early stage of diabetes (about 1.6-fold), but not in the chronic stage of diabetes. The increased enzymatic activity in starved rats returned to the control level within 20 h when the animals were given laboratory chow, but not when they were given fat-free diet with a high carbohydrate content, and the enzyme activity was increased by the latter diet containing 1% thyroid powder. A single intraperitoneal injection of 3,3'5-triiodo-L-thyronine or 3,3',5,5'-tetraiodo-L-thyronine resulted in twice the normal enzyme activity two days later, and conversely 7 days after thyroidectomy, the enzyme activity was about 60% of the control level. A single subcutaneous injection of alpha-(p-chlorophenoxy)isobutyric acid, a hypolipidemic drug, doubled the enzyme activity in euthyroid rats, but not in thyroidectomized rats. Of the various tissues tested besides the liver, only the kidney had detectable ATP-stimulated and ADP-inhibited enzyme activity (5% of the activity in liver cytosol). The kidney enzyme had similar kinetic and immunochemical properties to the liver enzyme. Changes in the enzyme activity in the liver in various states were closely related to the amount of enzyme present, judging from results obtained by enzyme-linked immunosorbent assay. The physiological role of this enzyme (which hydrolyzes acetyl-CoA to acetate and CoASH) may be in maintenance of the cytosolic acetyl-CoA concentration and CoASH pool for both fatty acid synthesis and oxidation.     

A study of some enzymes of glycerolipid biosynthesis in rat liver after subtotal hepatectomy

1. The accumulation of triglyceride in the liver remnant after subtotal hepatectomy (removal of 82% of the liver) exceeded that described for partial hepatectomy (removal of 70% of the liver). 2. Palmitoyl-CoA synthetase, glycerol phosphate acyltransferase and diglyceride acyltransferase activities were measured in the microsomal fraction, and phosphatidate phosphohydrolase activity was measured in the particle-free supernatant fraction, prepared from the liver remnant at various times after subtotal hepatectomy. 3. The only enzyme showing a significant change in specific activity was phosphatidate phosphohydrolase. The specific activity was approximately fivefold that of the control value at 6h after operation and threefold that of the control at 10, 16 and 24h after operation. A smaller increase in the specific activity of the enzyme in sham-operated animals occurred only at 6h after operation. 4. However, at this time the total phosphohydrolase activity of the remaining liver in the sham-operated rats was approximately threefold that in hepatectomized rats. 5. Injection of actinomycin D prevented the increase in activity of phosphatidate phosphohydrolase but did not prevent the accumulation of triglyceride.     

Early changes in the nucleoside diphosphate kinase activity of the rat brain and liver during whole body gamma irradiation in an absolutely lethal dose

Nucleoside diphosphatkinase activity in mitochondria and post-mitochondrial supernatant fraction from brain and liver tissues was shown to decrease sharply during the first 60 min after total-body gamma-irradiation of rats with an absolutely lethal dose (30 Gy). A significant increase in the enzyme activity was registered 3 and 24 h following irradiation. Changes in nucleoside diphosphatkinase activity were more pronounced in mitochondria (particularly in liver mitochondria) than in the supernatant fraction.     

Two forms of aspartate aminotransferase in rat liver and kidney mitochondria

1. Butan-1-ol solubilizes that portion of rat liver mitochondrial aspartate aminotransferase (EC 2.6.1.1) that cannot be solubilized by ultrasonics and other treatments. 2. A difference in electrophoretic mobilities, chromatographic behaviour and solubility characteristics between the enzymes solubilized by ultrasonic treatment and by butan-1-ol was observed, suggesting the occurrence of two forms of this enzyme in rat liver mitochondria. 3. Half the aspartate aminotransferase activity of rat kidney homogenate was present in a high-speed supernatant fraction, the remainder being in the mitochondria. 4. A considerable increase in aspartate aminotransferase activity was observed when kidney mitochondrial suspensions were treated with ultrasonics or detergents. 5. All the activity after maximum activation was recoverable in the supernatant after centrifugation at 105000g for 1hr. 6. The electrophoretic mobility of the kidney mitochondrial enzyme was cathodic and that of the supernatant enzyme anodic. 7. Cortisone administration increased the activities of both mitochondrial and supernatant aspartate aminotransferases of liver, but only that of the supernatant enzyme of kidney.     

Postnatal development of peroxisomal and mitochondrial enzymes in rat liver.

Subcellular organellles from livers of rats three days prenatal to 50 weeks postnatal were separated on sucrose gradients. The peroxisomes had a constant density of 1.243 g/ml throughout the life of the animal. The density of the mitochondria changed from about 1.236 g/ml at birth to a constant value of 1.200 g/ml after two weeks. The peroxisomal and mitochondrial fatty acid beta-oxidation and the peroxisomal and supernatant activities of catalase and glycerol-3-phosphate dehydrogenase were measured at each age, as well as the peroxisomal core enzyme, urate oxidase, and the mitochondrial matrix enzyme, glutamate dehydrogenase. All of these activities were very low or undetectable before birth. Mitochondrial glutamate dehydrogenase and peroxisomal urate oxidase reached maximal activities per g of liver at two and five weeks of age, respectively. Fatty acid beta-oxidation in both peroxisomes and mitochondria and peroxisomal glycerol-3-phosphate dehydrogenase exhibited maximum activities per g of liver between one and two weeks of age before weaning and then decreased to steady state levels in the adult. Peroxisomal beta-oxidation accounted for at least 10% of the total beta-oxidation activity in the young rat liver, but became 30% of the total in the liver of the adult female and 20% in the adult male due to a decrease in mitochondrial beta-oxidation after two weeks of age. The greatest change in beta-oxidation was in the mitochondrial fraction rather than in the peroxisomes. At two weeks of age, four times as much beta-oxidation activity was in the mitochondria as in the peroxisomal fraction. Peroxisomal glycerol-3-phosphate dehydrogenase activity accounted for 5% to 7% of the total activity in animals younger than one week, but only 1% to 2% in animals older than one week. Up to three weeks of age, 85% to 90% of the liver catalase was recovered in the peroxisomes. The activity of peroxisomal catalase per g of rat liver remained constant after three weeks of age, but the total activity of catalase further increased 2.5- to 3-fold, and all of the increased activity was in the supernatant fraction.     

Effect of gonadal steroids on hypothalamus and anterior pituitary endo-oligopeptidase B (proline-endopeptidase) activity in castrated female rats

In the present study we investigated the possible participation of endo-oligopeptidase B (poline-endopeptidase) in the control of gonadotrophin secretion through the control of LH-RH inactivation. This enzyme selectively hydrolyzes the Pro9-Gly10-NH2 peptide bond of LH-RH, thereby inactivating this substance. The enzyme activity was evaluated using a specific colorimetric substrate, i.e., Z-Gly-Pro-SM. Female adult Wistar rats were submitted to castration, experimental situations that are known to produce changes in gonadotrophin secretion. Hypothalamic and pituitary endo-oligopeptidase B activity was shown to be present predominantly in the soluble fraction of the enzyme preparations. The results also indicated that endo-oligopeptidase B activity adult female rat pituitary decreased after castration and increased after administration of estradiol and progesterone to castrated animals. The present results lead us to suggest that anterior pituitary endo-oligopeptidase B may be related to the control gonadotrophin secretion in female rats.     

The hypophysis in the regulation of androgen and oestrogen dependent enzyme activities of steroid hormone metabolism in rat liver cytosol.

In order to determine whether the gonadal and hypophyseal modes of regulation recently reported for the microsomal enzymes of hepatic steroid metabolism are also valid for cytoplasmic enzymes, three enzymes whose activities exhibit sex differences (male:female activity ratio shown in brackets), 5beta-reductase(1.7:1), 20alpha-hydroxysteroid dehydrogenase(5 : 1) and 17beta-hydroxysteroid dehydrogenase (4:1), as well as one enzyme whose activity shows no sex difference, 3beta-hydroxy-delta5-steroid dehydrogenase, were investigated after various interferences with the endocrine balance (gonadectomy, hypophysectomy, combination of both operations, administration of testosterone or oestradiol). From the results of this and a previous study the following statements can be made about the endocrine control of hepatic enzyme activities. Those enzymes whose activities show sex differences are either androgen or oestrogen dependent; the sex hormone acts in either an inductive or repressive manner. 1) Criteria for androgen dependency are the feminization of enzyme activity after testectomy or inhibition of testicular function by administration of oestradiol; masculinization of the enzyme activity after administration of testosterone to male or female castrates. Using these criteria the following enzymes investigated in this laboratory fall into this category: all microsomal enzymes which show sex differences in their activity (3alpha-, 3beta-, delta4-3beta, 20-hydroxysteroid dehydrogenase; cortisone alpha-reductase; steroid hydroxylases and 16alpha-hydroxylase) as well as the cytoplasmic 20alpha-hydroxysteroid dehydrogenase. Apart from the single exception of 20alpha-hydroxy-steroid dehydrogenase the presence of the hypophysis is obligatory for the androgen to be effective. The hypophysis does not only work in a permissive manner, but participates in establishing the sex specific activity levels in a manner which is antagonistic to the androgen action. 2) Criteria for oestrogen dependency are that the female animal reacts to gonadectomy, as well as to the inhibition of ovarian function after testosterone administration, by a masculinization of the enzyme activities. After administration of oestradiol, but not gonadectomy, the male animal exhibits typical female activity. Using these criteria the cytoplasmic 5beta-reductase and 17beta-hydroxysteroid dehydrogenase are oestrogen dependent. The repressive oestrogen effect observed on 17beta-hydroxysteroid dehydrogenase is antagonistic to hypophyseal action, whereas in the case of 5beta-reductase it is synergistic. 3) The activities of cytoplasmic 3beta-hydroxy-delta5-steroid dehydrogenase and microsomal 7alpha-hydroxylase show no sex differences and are not influenced by any interference with the endocrine balance.     

Activation of rat parotid low Km cyclic AMP phosphodiesterase by isoproterenol

Approximately 94% of rat parotid cyclic AMP phosphodiesterase activity measured at a substrate concentration of 0.1 microM cyclic AMP was found in the 100,000 X g supernatant while the remaining enzyme activity was in the particulate fraction. Incubation of parotid slices with 10 microM isoproterenol resulted in approximately 40% activation of the cyclic AMP phosphodiesterase activity of the 100,000 X g supernatant. The enzyme activity in the particulate fraction was unaffected. The activation resulted from an increase in the value of the Vmax while the apparent Km (0.51 microM) was unaffected. The concentration of isoproterenol required to give half-maximal activation was 0.34 microM. The activation was rapid, became significant after 2 min and reached maximum after 30 min incubation of the parotid slices with isoproterenol. The activation of the enzyme activity by isoproterenol could be blocked by propanolol but was unaffected by cycloheximide. Dibutyryl-cyclic AMP was also effective while phenylephrine and carbamylcholine were ineffective in increasing the activity of the enzyme.     

Cytoplasmic changes in level and distribution of glucose-6-phosphatase activities from rat liver during diethylnitrosamine-induced carcinogenesis.

Glucose-6-phosphatase (EC 3.1.3.9) activities were determined in isolated microsomes, cytoplasmic smooth and rough membranes, ribosomes and free cytosol from rat liver undergoing carcinogenesis by diethylnitrosamine (DENA) and compared with cytoplasmic fractions isolated in parallel from healthy animals from the same age.With continuous administration of a low dose of DENA (2.6 mg/kg rat per day for 20 weeks in the drinking water) livers of carcinogen treated rats became heavier than the control livers but the body weight decreased. About 70% of total glucose-6-phosphatase activity could be detected in the microsomal fraction. While there was no significant difference in this activity in both animal groups up to the 4th week, glucose-6-phosphatase of cancerous liver showed a distinct decrease of activity compared with normal liver.During cancer induction this enzyme became more soluble, confirmed by the observation that it was detached from firmer structures of cytoplasm as rough membranes and polysomes and translocated to smooth membranes and the soluble cytoplasmic fraction successively. The corresponding increase in glucose-6-phosphatase activity in the 105 000 g supernatant appears to be due to the loss of enzyme activity in a distinct cytoplasmic membrane fraction. These data strongly suggest that in parallel with alteration of cytoplasmic membrane structures during carcinogen feeding glucose-6-phosphatase is detached from heavier components of the cytoplasm while total activity decreased. Possible mechanisms of these findings are discussed.     

On the synthesis and degradation of the multiple forms of catalase in mouse liver: effects of aminotriazole and p-chlorophenoxyisobutric acid ethyl ester

Aspects of the synthesis and degradation of the multiple forms of catalase in mouse liver have been investigated. The kinetics of return of catalase after aminotriazole inhibition indicated a product-precursor relationship between the granular and supernatant pools of the enzyme, and electrophoretic resolution of the individual heteromorphs of catalase during this treatment served to substantiate this relationship and indicated, in addition, that aminotriazole-inhibited catalase may be partially reactivated in the cytosol. Changes in the activity of mouse liver and kidney catalases after the administration of chlorophenoxyisobutyric acid ethyl ester (CPIB) were also monitored. After an initial decline in activity, a rapid increase to an elevated steady state occurred, with an approximately threefold increase in the liver and twofold increase in the kidney. Subcellular fractionation of the livers of CPIB-treated mice showed a massive initial increase in the supernatant pool of catalase, accompanied by a steady decrease in the activity of the peroxisomal pools. Activity increased in the peroxisomal pools at later stages of treatment, but even after a new CPIB-induced steady state was achieved, the supernatant pool of catalase remained grossly elevated. Electrophoresis of the individual heteromorphs of catalase in the supernatant after CPIB treatment showed a predominance of the most cathodal migrating forms, and turnover studies demonstrated that catalase in CPIB-treated animals exhibited a substantially lowered rate of degradation by comparison with normal animals. These results have been discussed in relation to the intracellular sequestration and turnover characteristics of catalase.     

The effect of stress on the activity of hepatic tryptophan pyrrolase, of tyrosine aminotransferase in various organs and on the level of tryptophan in the liver and plasma of rats.

In rats subjected to 400 revolutions in Noble-Collip drums, hepatic tryptophan pyrrolase activity increases and plasma tryptophan level decreases. After bilateral adrenalectomy, the alterations of plasma tryptophan are even more pronounced and liver tryptophan increases in contrast to tryptophan pyrrolase activity which remains unchanged after injury. The possible significance of the posttraumatic increase of tryptophan pyrrolase in intact animals for brain serotonin metabolism and hepatic gluconeogenesis is underlined. The activity of tyrosine aminotransferase in liver, brain, adrenal, kidney and muscle tissue of rats was determined with special reference to the possible effect of the before-mentioned stress procedure. Organ homogenates were centrifuged at 15000 x g and both supernatants and pellets were investigated for enzyme activity with the exception of the liver, where only the supernatant fraction was used. Tyrosine aminotransferase activity in the liver supernatant considerably exceeded the corresponding values in both supernatant and pellet of the remaining organs, in which a prevalence of the mitochondrial enzyme was obvious. In contrast to the clear-cut increase of the hepatic enzyme during stress, essentially no changes were noted in the brain, the adrenals, kidney or muscle under similar conditions...