Influence of Daytime LED Light Exposure on Circadian Regulatory Dynamics of Metabolism and Physiology in Mice

Light is a potent biologic force that profoundly influences circadian, neuroendocrine, and neurobehavioral regulation in animals. Previously we examined the effects of light-phase exposure of rats to white light-emitting diodes (LED), which emit more light in the blue-appearing portion of the visible spectrum (465 to 485 nm) than do broad-spectrum cool white fluorescent (CWF) light, on the nighttime melatonin amplitude and circadian regulation of metabolism and physiology. In the current studies, we tested the hypothesis that exposure to blue-enriched LED light at day (bLAD), compared with CWF, promotes the circadian regulation of neuroendocrine, metabolic, and physiologic parameters that are associated with optimizing homeostatic regulation of health and wellbeing in 3 mouse strains commonly used in biomedical research (C3H [melatonin-producing], C57BL/6, and BALB/c [melatonin-non-producing]). Compared with male and female mice housed for 12 wk under 12:12-h light:dark (LD) cycles in CWF light, C3H mice in bLAD evinced 6-fold higher peak plasma melatonin levels at the middark phase; in addition, high melatonin levels were prolonged 2 to 3 h into the light phase. C57BL/6 and BALB/c strains did not produce nighttime pineal melatonin. Body growth rates; dietary and water intakes; circadian rhythms of arterial blood corticosterone, insulin, leptin, glucose, and lactic acid; pO₂ and pCO₂; fatty acids; and metabolic indicators (cAMP, DNA, tissue DNA 3H-thymidine incorporation, fat content) in major organ systems were significantly lower and activation of major metabolic signaling pathways (mTOR, GSK3β, and SIRT1) in skeletal muscle and liver were higher only in C3H mice in bLAD compared with CWF. These data show that exposure of C3H mice to bLAD compared with CWF has a marked positive effect on the circadian regulation of neuroendocrine, metabolic, and physiologic parameters associated with the promotion of animal health and wellbeing that may influence scientific outcomes. The absence of enhancement in amelatonic strains suggests hyperproduction of nighttime melatonin may be a key component of the physiology.

Interstrain differences in susceptibility to non-alcoholic steatohepatitis

BACKGROUND AND AIM

The pathophysiological mechanisms leading to the development of non-alcoholic steatohepatitis (NASH) remain unclear. There are differences in the susceptibility to NASH between the different species and sexes. The investigation of the precise mechanism of interstrain differences may provide new means by which the pathophysiological mechanisms of NASH may be understood.

METHODS

C57BL/6N and C3H/HeN mice were administered a methionine- and choline-deficient (MCD) diet to establish a dietary model of NASH.

RESULTS

An elevation of the serum alanine aminotransferase and increased infiltration of inflammatory cells were predominant in C57BL/6N mice at 8 weeks. The increase in the steatosis and lipid contents in the liver was greater in C57BL/6N mice than in C3H/HeN mice. The indices of lipid peroxidation demonstrated by F2-isoprostanes or 8-hydroxy-2'-deoxyguanosine also increased in the livers of C57BL/6N mice. Furthermore, Sirius red staining revealed an increase in the degree of fibrosis in C57BL/6N mice given the MCD diet. As a result, the C57BL/6N strain had a higher susceptibility to NASH than the C3H/HeN mice. The carnitine palmitoyltransferase 1A (in beta-oxidation) mRNA and mitochondrial 3-hydroxy-3-methylglutaryl-CoA synthase 2 (in ketogenesis) mRNA were downregulated in the C57BL/6N mice in comparison with C3H/HeN mice. There were no differences in the expression of microsomal triglyceride transfer protein or sterol regulatory element binding protein 1 between the C57BL/6N and C3H/HeN mice.

CONCLUSION

There were interstrain differences in susceptibility to NASH observed in a rodent dietary model. Further evaluations of the precise molecular mechanism of this interstrain difference may provide some indications of the pathophysiological mechanisms of NASH in humans.

Protection against murine leukemia virus-induced spongiform myeloencephalopathy in mice overexpressing Bcl-2 but not in mice deficient for interleukin-6, inducible nitric oxide synthetase, ICE, Fas, Fas ligand, or TNF-R1 genes

Some murine leukemia viruses (MuLVs), among them Cas-Br-E and ts-1 MuLVs, are neurovirulent, inducing spongiform myeloencephalopathy and hind limb paralysis in susceptible mice. It has been shown that the env gene of these viruses harbors the determinant of neurovirulence. It appears that neuronal loss occurs by an indirect mechanism, since the target motor neurons have not been found to be infected. However, the pathogenesis of the disease remains unclear. Several lymphokines, cytokines, and other cellular effectors have been found to be aberrantly expressed in the brains of infected mice, but whether these are required for the development of the neurodegenerative lesions is not known. In an effort to identify the specific effectors which are indeed required for the initiation and/or development of spongiform myeloencephalopathy, we inoculated gene-deficient (knockout [KO]) mice with ts-1 MuLV. We show here that interleukin-6 (IL-6), inducible nitric oxide synthetase (iNOS), ICE, Fas, Fas ligand (FasL), and TNF-R1 KO mice still develop signs of disease. However, transgenic mice overexpressing Bcl-2 in neurons (NSE/Bcl-2) were largely protected from hind limb paralysis and had less-severe spongiform lesions. These results indicate that motor neuron death occurs in this disease at least in part by a Bcl-2-inhibitable pathway not requiring the ICE, iNOS, Fas/FasL, TNF-R1, and IL-6 gene products.

Circadian rhythms of dopamine in mouse retina: the role of melatonin

Both dopamine and melatonin are important for the regulation of retinal rhythmicity, and substantial evidence suggests that these two substances are mutually inhibitory factors that act as chemical analogs of day and night. A circadian oscillator in the mammalian retina regulates melatonin synthesis. Here we show a circadian rhythm of retinal dopamine content in the mouse retina, and examine the role of melatonin in its control. Using high-performance liquid chromatography (HPLC), we measured levels of dopamine and its two major metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA), in retinas of C3H+/+ mice (which make melatonin) and C57BL/6J mice that are genetically incapable of melatonin synthesis. In a light/dark cycle both strains of mice exhibited daily rhythms of retinal dopamine, DOPAC, and HVA content. However, after 10 days in constant darkness (DD), a circadian rhythm in dopamine levels was present in C3H, but not in C57 mice. C57 mice given ten daily injections of melatonin in DD exhibited a robust circadian rhythm of retinal dopamine content whereas no such rhythm was present in saline-injected controls. Our results demonstrate that (1) a circadian clock generates rhythms of dopamine content in the C3H mouse retina, (2) mice lacking melatonin also lack circadian rhythms of dopamine content, and (3) dopamine rhythms can be generated in these mice by cyclic administration of exogenous melatonin. Our results also indicate that circadian rhythms of retinal dopamine depend upon the rhythmic presence of melatonin, but that cyclic light can drive dopamine rhythms in the absence of melatonin.

Developmental expression of monoamine oxidases A and B in the central and peripheral nervous systems of the mouse

Monoamine oxidases A (MAOA) and B (MAOB) are key players in the inactivation pathway of biogenic amines. Their cellular localization has been well established in the mature brain, but nothing is known concerning the localization of both enzymes during development. We have combined in situ hybridization and histochemistry to localize MAOA and MAOB in the developing nervous system of mice. Our observations can be summarized as five key features. (1) MAOA is tightly linked to catecholaminergic traits. MAOA is expressed in all noradrenergic and adrenergic neurons early on, and in several dopaminergic cell groups such as the substantia nigra. MAOA is also expressed in all the neurons that display a transient tyrosine hydroxylase expression in the brainstem and the amygdala and in neurons with transient dopamine-beta-hydroxylase expression in the cranial sensory ganglia. (2) MAOA and MAOB are coexpressed in the serotoninergic neurons of the raphe from E12 to P7. During postnatal life, MAOA expression declines, whereas MAOB expression remains stable. (3) MAOA is transiently expressed in the cholinergic motor nuclei of the hindbrain, and MAOB is expressed in the forebrain cholinergic neurons. (4) MAOA- and MAOB-expressing neurons are also detected in structures that do not contain aminergic neurons, such as the thalamus, hippocampus, and claustrum. (5) Starting at birth, MAOB expression is found in a variety of nonneuronal cells, the choroid plexus, the ependyma, and astrocytes. These localizations are of importance for understanding the effects of monoaminergic transmission during development.

Alpha7-nicotinic receptor expression and the anatomical organization of hippocampal interneurons

C3H and DBA/2 mice differ in their hippocampal inhibitory function, as measured by the inhibitory gating of pyramidal neuron response to repeated auditory stimulation. This functional difference appears to be related to differences in expression of the alpha7 nicotinic cholinergic receptor, which may be generally expressed by interneurons. This study examines the relationship between genetic variation in alpha7 receptor subunit expression and GABAergic interneuron distribution in various regions and layers of the hippocampus in the two mouse strains. Subpopulations of hippocampal interneurons in both mouse strains were found to bind [(125)I]alpha-bungarotoxin. However, the distribution of the [(125)I]alpha-bungarotoxin-positive hippocampal interneurons was significantly different between C3H and DBA/2 mice. In region CA1, and to a lesser extent in region CA3, DBA/2 mice had increased numbers of [(125)I]alpha-bungarotoxin-positive neurons in stratum lacunosum-moleculare and decreased numbers in stratum oriens. Similar differences in GABAergic neuron distribution were observed in region CA1 in the two strains. C3H/DBA/2 F1 animals were backcrossed to the C3H parental strain for six generations, with selection for either the DBA/2 or C3H allelic variant of the alpha7 receptor gene. The distribution of [(125)I]alpha-bungarotoxin labeling closely resembled the DBA/2 parental phenotype in animals retaining the DBA/2 allele of the alpha7 gene. These data suggest that the alpha7 receptor gene locus may influence the anatomical organization of at least a subset of hippocampal interneurons by an as yet unidentified mechanism. This difference in interneuron anatomy may also contribute to functional differences in inhibitory sensory gating between the two strains.

Jejunal function and plasma amino acid concentrations in the segmental trisomic Ts65Dn mouse

Mice trisomic for the distal portion of MMU 16 (Ts65Dn) were examined for differences in jejunal function and plasma amino acids as compared to diploid controls. Eighteen control and 19 Ts65Dn mice were compared for whole-body and intestinal O2 consumption, jejunal glucose uptake, and plasma amino acid concentrations. Ts65Dn mice consumed less (P < 0.02) O2 per gram of fasted body weight. No significant differences were found in either active or passive glucose uptake. Oxygen consumption by jejunal tissue was not different between Ts65Dn and control mice. The apparent energetic efficiency of jejunal active glucose uptake (eta mol ATP expended/eta mol glucose uptake) was significantly higher (115.6 vs. 80.8; P < 0.05) in Ts65Dn mice. Histomorphometric analysis of jejunal mucosa showed that Ts65Dn mice had shorter villus height (P < 0.04) and decreased planar villus circumference (P = 0.05). No differences were found in total jejunal protein (microgram/g) or DNA (mg/g) concentrations. Significantly higher concentrations of plasma tyrosine, phenylalanine, valine, leucine, isoleucine, and citrulline (P < 0.05) were found in Ts65Dn mice. Lower plasma concentrations of hydroxyproline were detected in Ts65Dn mice (P < 0.05). These data suggest that Ts65Dn mice have anomalies in digestive function and amino acid metabolism as compared to normal, diploid controls.

Differential sensitivity to lithium's reversal of amphetamine-induced open-field activity in two inbred strains of mice

To determine whether genetic differences could contribute to the pharmacological sensitivity of lithium chloride (LiCl) to reverse amphetamine-associated changes in behavior C57BL/6nCrlBR and C3H/HenCrlBR male mice were tested for the ability of an acute dose of LiCl to reverse the locomotor enhancing effects of an acute dose of amphetamine. A series of experiments were conducted that compared dose response of LiCl, chamber lighting conditions, and chamber shape on amphetamine-induced activity in two strains of mice with different genetic backgrounds. Acute amphetamine (3 mg/kg) increased locomotor activity in C57BL/6nCrlBR mice and LiCl (1-4 mEq/kg) blocked this effect. LiCl-induced changes in baseline activity seen at high doses of LiCl were not seen for the low doses. The dark condition reduced time resting but chamber shape did not appear to alter results. In C3H/HenCrlBR mice, amphetamine did not significantly increase levels of activity but did decrease rearing behavior which suggests that genetic difference between C57BL/6nCrlBR and C3H/HenCrlBR mice may contribute to sensitivity to amphetamine. In sum, the ability of LiCl to reverse amphetamine-induced changes in locomotor activity in C57BL/6nCrlBR mice may provide a useful model to study genetic and pharmacological aspects of psychiatric illnesses such as bipolar disorder.

Response of C2C12 mouse and turkey skeletal muscle cells to the beta-adrenergic agonist ractopamine

The effects of ractopamine (RAC) and ractopamine stereoisomers (RR, RS, SR, and SS) on cyclic AMP (cAMP) production, total protein, and DNA concentrations in mouse skeletal muscle cells (C2C12) were evaluated. The RAC (10 microM) caused an approximately 30% increase in cell number, protein, and DNA concentrations in myoblasts after 48 h; no differences were found in myotubes. The RAC-stimulated increase of these variables in myoblasts was blocked by the presence of equimolar concentrations of propranolol. At a later passage, myoblasts failed to exhibit an increase in cell number, protein, or DNA upon exposure to RAC. Both myoblasts and myotubes increased cAMP production in response to 10 microM RAC. The RAC isomers ranked RR >> SR > RS approximately SS in ability to stimulate cAMP production, with essentially no response to SS. The SR produced about 50% of the RR response. Coincubation of propranolol (10 microM) and RAC (10 microM) prevented RAC-stimulated cAMP production in myotubes but not in myoblasts (approximately 35% of cAMP produced by RAC alone). Turkey satellite cells (derived from biceps femoris of 12-wk-old toms) produced essentially no increased cAMP when exposed to 10 microM RAC stereoisomers. Stability of RAC was evaluated under laboratory storage and culture conditions. The RAC was stable for more than 4 mo when stored in deuterated DMSO (>98% purity) at room temperature or in aqueous solutions at -80 degrees C, as determined from sequential nuclear magnetic resonance studies. Radiolabeled RAC was incubated for 72 h in the presence of serum-containing medium, with or without C2C12 cells. Ninety-eight percent of the parent compound found in the medium at time zero was present in the medium as parent at the end of 72 h. The cellular cAMP response to RAC through beta-adrenergic receptors seems to be stereospecific. If the state of myoblasts and myotubes in vitro reflects the in vivo state, then the ractopamine effect in vivo on cellular processes (including cell division and protein and DNA accumulation) may be independent of beta-adrenergic receptors in muscle.

PSP expression in murine lacrimal glands and function as a bacteria binding protein in exocrine secretions

Nonobese diabetic (NOD) mice, an animal model for type I autoimmune diabetes and autoimmune sialoadenitis, abnormally express parotid secretory protein (PSP) in the submandibular glands (Robinson, C. P., H. Yamamoto, A. B. Peck, and M. G. Humphreys-Beher. Clin. Immunol. Immunopathol. 79: 50-59, 1996). To evaluate possible PSP gene dysregulation in the NOD mouse, we have examined a number of organs and tissues for PSP mRNA transcripts and protein expression. Results indicate that PSP is produced in the lacrimal glands of NOD mice as well as most laboratory mouse strains. Although purified salivary PSP from C3H/HeJ or BALB/c mice fails to affect amylase enzyme activity in in vitro assays, PSP bound to whole bacteria in a Zn2+-dependent manner. Additionally, radiolabeled protein bound to specific bacterial membrane proteins using a ligand binding assay. PSP gene transcription, but not protein production, was observed in the heart and pancreas from NOD mice, indicating abnormal transcription of the PSP gene. Sequence analysis of PSP cDNA from NOD mice revealed numerous base differences (compared with the published PSP sequence) capable of leading to significant amino acid substitutions, suggestive of strain-specific differences for the protein in mice. Together these results suggest that there exists in the NOD mouse a dysregulation of PSP transcription in various tissues. However, except for C3H/HeJ mice, PSP appears as a normal product of the lacrimal glands where, as in saliva, it may function as a nonimmune antimicrobial agent in the protection of tissue surfaces exposed to the external environment.

Genetic differences of lipid metabolism in macrophages from C57BL/6J and C3H/HeN mice

Cholesterol metabolism in macrophages from atherosclerosis-prone C57BL/6J mice was compared with that in macrophages from atherosclerosis-resistant C3H/HeN mice. Plasma total cholesterol levels of both types of mice were significantly increased, but HDL cholesterol level was increased only in C3H/HeN mice when a high-cholesterol diet (1% cholesterol) was fed for 5 weeks. After incubation of macrophages from male and female mice on the high-cholesterol diet with beta-VLDL for 24 hours, cholesterol content in macrophages from C57BL/6J was approximately 1.5- to 2.0-fold higher than in those from C3H/HeN mice. [3H]Cholesterol oleate-beta-VLDL incorporation into macrophages from C57BL/6J mice on the high-cholesterol diet was greater than incorporation into those from C3H/HeN mice. The release of [3H]cholesterol from macrophages from C57BL/6J mice on the high-cholesterol diet was one seventh that from macrophages from C57BL/6J mice on the basal diet or that from macrophages from C3H/HeN mice on the basal or high-cholesterol diet. Acid cholesterol esterase activity was almost the same in macrophages from any group. Acyl CoA:cholesterol acyltransferase activity in macrophages from C57BL/6J mice on the high-cholesterol diet increased compared with that from macrophages from C57BL/6J mice on the normal diet. Neutral cholesterol esterase activity in macrophages from C57BL/6J mice was about half of that in macrophages from C3H/HeN mice independent of the type of diet. There were no sex differences in these metabolisms. Considered with our previous data, these results suggested that a high-cholesterol diet may cause metabolic changes to accumulate cholesterol ester in macrophages from C57BL/6J mice in accordance with genetic abnormalities.

Apoptosis in C3H/10T1/2 mouse embryonic cells: evidence for internucleosomal DNA modification in the absence of double-strand cleavage

Apoptosis in embryonic C3H/10T1/2 (clone 8) cells is marked by specific changes in morphology and DNA fragmentation that differ from those found in apoptotic thymocytes. These results demonstrate that ultrastructural changes within the nucleus associated with endonucleolytic degradation are linked with structural degradation at higher levels of chromatin organization. Strand modifications within the internucleosomal linker region are shown to involve alkaline-sensitive sites that appear to be sensitive to S1 endonuclease. Our results suggest that apoptosis is not dependent upon internucleosomal cleavage and may reveal the penultimate step and the nature of the metabolic cascade that leads to cell death.

Effects of pituitary hormones on the cell-specific expression of the KAP gene

The expression of kidney androgen-regulated protein (KAP) gene in mouse kidney is regulated in a multihormonal fashion. As determined by in situ hybridization analysis, epithelial cells of proximal convoluted tubules of cortical nephrons express KAP mRNA in response to androgenic stimulation while similar cells in the juxtamedullary S3 segment of the tubules express KAP mRNA under estrogenic and pituitary hormonal control. In situ hybridization analysis of kidney sections using hypophysectomized (hypox) mice resulted in a total absence of KAP mRNA suggesting the participation of a pituitary hormone(s) in the constitutive expression of KAP mRNA in S3 cells. Treatment of hypox mice with steroid hormones showed that androgens restored the ability of cortical tubule cells to synthesize KAP mRNA. Estrogen treatment, on the other hand, partially induced KAP gene expression only in S3 cells. These results indicated that the androgenic response of the gene is independent of pituitary function, while expression in S3 cells, although partially induced by the direct action of estrogens, is primarily regulated by a pituitary factor. In order to elucidate which hormone(s) is responsible for KAP gene expression in S3 cells, individual pituitary hormones were administered to hypox normal animals and to strains of mice genetically deficient in certain pituitary hormones. Surgically treated C57BL/6 female and male mice were implanted for 7 days with osmotic pumps containing individual pituitary hormones, after which the kidneys were analyzed by in situ hybridization. Mice injected with growth hormone (GH), corticotropin (ACTH), prolactin (PRL), or vehicle failed to express KAP mRNA. Mice treated with thyrotropin (TSH), follitropin (FSH), and lutropin (LH) exhibited high levels of KAP mRNA in S3 cells of females as well as in the renal cortex of male animals. Expression in the cortex in response to LH and FSH may be due to their gonadotropic effect on testosterone production. Similarly, contamination of TSH samples with small amounts of the gonadotropins may explain the cortical response to TSH. TSH produced the strongest response in S3 cells suggesting that it is responsible for the permissive effect of the pituitary on KAP gene expression. This conclusion was supported by studies performed with the dwarf mouse (dw/dw) which lacks PRL, GH, and TSH due to a mutation in the pit-1 gene. In situ hybridization analysis of dwarf mice kidney sections showed a complete lack of KAP gene expression. The possible participation of GH and PRL was eliminated on the basis of the hormone replacement studies.(ABSTRACT TRUNCATED AT 400 WORDS)

T Cell maturation stage-linked heterogeneity of the glycosylphosphatidylinositol membrane anchor of Thy-1

We showed that some of Thy-1 molecules on murine thymocytes are resistant to phosphatidylinositol-specific phospholipase C (PI-PLC) derived from Bacillus thuringiensis. Both immature thymocytes with low CD3 expression and mature thymic T lymphocytes with high CD3 expression carried the PI-PLC-resistant Thy-1, and the PI-PLC-sensitivity of Thy-1 extensively varied among thymocyte subpopulations. In contrast, the same PI-PLC fully hydrolysed the anchor of Thy-1 on peripheral T lymphocytes. When the latter cells were activated with mitogen in vitro, however, some Thy-1 on them became resistant to PI-PLC. We then found that virtually all Thy-1 molecules on thymocytes became sensitive to PI-PLC when they were treated with hydroxylamine that should cleave ester-linked lipids. The result ruled out the possibility that the PI-PLC-resistant Thy-1 had a transmembranous peptide sequence, and suggested the presence of an additional fatty acyl group on the inositol ring of the Thy-1 anchor. In addition, the molecular size of the PI-PLC-resistant membrane-bound Thy-1 was only marginally larger than that of the PI-PLC-sensitive solubilized Thy-1 in detergent-partitioning SDS-PAGE analysis.

The influence of different light intensities on pineal melatonin content in the retinal degenerate C3H mouse and the normal CBA mouse

The sensitivity of light-induced suppression of pineal melatonin content was compared between C3H mice with hereditary retinal degeneration and CBA mice with normal retinas. At 2 h before lights on of light-dark (LD) cycles, when pineal melatonin content is the highest in both strains, groups of mice were exposed to different intensities of white fluorescent light (100, 0.14, 0.017 lux in both strains and 0.0021 and 0.00026 lux in CBA mice). For each intensity, pineals were collected just before and 5, 15 and 30 min after exposure to light. In C3H mice, the threshold of light intensity to suppress pineal melatonin content was between 0.14 and 0.017 lux, whereas that in CBA mice was between 0.0021 and 0.00026 lux. These results suggest that both rods and cones mediate photic information to the pineal gland in mice.

Elimination and tissue distribution of the monosaccharide lipid A precursor, lipid X, in mice and sheep

Lipid X (2,3-diacylglucosamine 1-phosphate) is a novel monosaccharide precursor of lipid A (the active moiety of gram-negative endotoxin) and has been found to be protective against endotoxin administered to mice and sheep and against life-threatening gram-negative infections in mice. Because of the need to design optimal dosing regimens in experimental models of ovine and murine septicemia, the pharmacokinetic profile of lipid X was investigated in sheep and in two strains of mice by using 32P-labeled lipid X. In sheep, peak whole blood lipid X levels after a bolus injection of 100 micrograms of lipid X per kg were 900 ng/ml. An initial rapid distribution phase of 7.98 +/- 0.1 min was observed, followed by a prolonged elimination phase of 3.0 +/- 0.5 h; the area under the curve from time zero to infinity was 428 +/- 27 ng.h/ml. The serum half-lives of lipid X were slightly shorter than whole blood half-lives, suggesting that lipid X associates with cellular elements. Metabolites of lipid X could not be detected in serum over a 4-h period. Lipid X appears to accumulate mainly in the liver, and the tissue distribution of lipid X resembles that of lipopolysaccharide. The elimination rate of lipid X in mice was approximately four times as rapid as that seen in sheep. Lipid X pharmacokinetics in lipopolysaccharide-sensitive DBA/2J mice were virtually identical with those seen in endotoxin-resistant C3H/HeJ mice. The pharmacokinetics described here should greatly aid in the design and interpretation of animal studies investigating the therapeutic applications of lipid X in gram-negative septicemia.

Dose-response analysis of nicotine tolerance and receptor changes in two inbred mouse strains

Mice of two inbred strains, DBA and C3H, were infused i.v. with saline, or 2, 4 or 6 mg/kg/hr of nicotine for 10 days. Two hours after termination of infusion the mice were challenged with one of several nicotine doses and the effects on respiration rate, Y-maze activity and rears, acoustic startle response, heart rate and body temperature were measured. Saline-infused C3H mice were less responsive than were DBA mice for all these tests with the exception of the acoustic startle response test. Nicotine-treated DBA mice developed a dose-related tolerance for most measures, whereas C3H mice did not appear to develop tolerance to any measure until the infusion dose reached 4 mg/kg/hr. The two mouse strains did not differ in the number of [3H] nicotine binding sites in six brain regions, and chronic nicotine treatment elicited similar changes in the binding of this ligand in the two strains. C3H mice had greater concentrations of alpha-[125I] BTX binding in hippocampus, midbrain and hypothalamus than did DBA mice. Chronic nicotine treatment resulted in an identical increase in bungarotoxin binding in the two mouse strains such that the initial strain differences were maintained. These results indicate that a threshold in drug response must be surpassed before a mouse develops tolerance to nicotine. In addition, mechanisms other than differences in receptor numbers must be invoked to explain differences in response to nicotine.

Ethionine carcinogenesis in CD-1, BALB/c and C3H mice

In two separate in vivo studies, ethionine was evaluated for carcinogenic activity in mice. In the first study, DL-ethionine was fed in a chow diet at 0 (controls), 0.1 (low dose, LD) and 0.25% (high dose, HD) concentrations to the following groups of mice (30 animals/group): Swiss Webster CD-1 females, BALB/c males, and C3H/HeN males and females. Because of severe toxicity, BALB/c females were fed 0.05% (LD) and 0.1% (HD) ethionine. The Swiss and BALB/c mice were maintained on their respective diets for up to 105 weeks before killing whereas the C3H mice were killed at 68 weeks because of the high spontaneous incidence of liver tumors in this strain. The percentages of animals at risk (surviving the time to the first liver tumor recorded in each sex and strain) that bore liver tumors were as follows: Swiss female control, 0% (0/29), Swiss female LD, 87% (20/23); Swiss female HD, 89% (16/18); C3H male controls, 35% (8/23); C3H male LD, 55% (16/29); C3H male HD, 58% (15/26); C3H female controls, 5% (1/20); C3H female LD, 60% (12/20); C3H female HD, 92% (12/13); BALB/c male controls, 4% (1/23); BALB/c male LD, 8% (2/24); BALB/c male HD, 31% (5/16); BALB/c female controls, 0% (0/30); BALB/c female LD, 52% (14/27); and BALB/c female HD, 92% (12/13). The female mice were more responsive than the males in developing liver tumors. The results of the feeding study are compared with those obtained in a second study in which C3H female mice were intubated with 0, 150 or 500 mg DL-ethionine/kg body wt three times per week for 30 weeks and killed at 2 years. Only the LD mice showed a significantly increased incidence of liver tumors (20/39) as compared to controls (12/41) or HD mice (7/37) in the latter study. The hepatic levels of the major ethionine metabolite and methylase inhibitor, S-adenosylethionine (AdoEt), as well as of the endogenous methyl group donor, S-adenosylmethionine (AdoMet) were determined in Swiss female mice fed either 0.1 or 0.3% in the diet for 1-6 weeks. Hepatic AdoEt levels ranged from 37 to 80 micrograms/g liver in the LD animals and from 61 to 203 micrograms/g liver in the HD group; levels of the endogenous metabolite AdoMet correspondingly dropped to 65% of the normal levels. The present results (i) extend to different strains and to both sexes previous observations demonstrating the hepatocarcinogenic activity of ethionine in mice; and (ii) indicate that as in the rat such activity may be exerted through the formation of AdoEt.

Oxygen consumption in mice (I strain) after feeding

To determine if excess heat production can account for the lower fat accumulation in I strain mice, oxygen consumption, a measure of energy expenditure, was measured in I mice and C57BL mice (a control strain) to determine basal metabolic rate (BMR) and resting metabolic rate (RMR) and response to food consumption and acute cold exposure. Oxygen consumption was higher in the I strain than in the C57BL mice only after the dark cycle (feeding period). No difference between I and C57BL mice in spontaneous activity was found during the dark or light cycle. Body temperature was also not different in I and C57BL mice. Oxygen consumption in response to norepinephrine was similar in the two strains. These results indicate oxygen consumption is greater in I than C57BL mice only in response to feeding. Differences in glucose utilization by I and C57BL mice, including a lower glucose tolerance curve, greater deposition of glucose to muscle glycogen and lactate production in I mice also indicate differences in nutrient processing. Higher oxygen consumption after feeding in I mice than in C57BL mice indicates inefficient food utilization and accounts for their lower ability to store energy as fat.

Strain differences in the production of mouse interferon

Studies were conducted to compare the interferon (IFN) production of four strains of mice when injected with Newcastle disease virus (NDV), polyinosinic-polycytidylic acid (poly I. C), lipopolysaccharide (LPS) or purified protein derivative (PPD). When injected with NDV, C57BL/6 and DDD mice generated higher levels of IFN than BALB/c and C3H/He mice. Upon injection with poly I. C or LPS, C57BL/6 and C3H/He mice produced higher levels of IFN than BALB/c and DDD mice. Differences in IFN production were also observed among BCG-sensitized mice of all four strains upon injection with PPD, C57BL/6 mice engendered the highest levels of IFN, while the C3H/He and DDD mice were intermediate in their response, with the BALB/c mice producing the least amount of IFN.

Strain dependent rate of Li+ elimination associated with toxic effects of lethal doses of lithium chloride in mice

Strain differences in response to the administration of two lethal doses (700 and 900; mg/kg) of lithium chloride were studied in eight week old males from six genetic strains of mice. Two parameters were considered; (a) toxicity (time to death) and (b) hypothermia. Lithium distribution in the body (blood, seven tissues, excreta and urine) were evaluated for each strain following IP injection of 200 mg/kg dose of LiCl. The strain differences were significant for toxicity. The order of susceptibility of the strains was 129/ReJ greater than S.W. greater than C3H/S greater than DBA/2 = Balb/c greater than C57/6J with a 15-fold difference between the most susceptible and the least susceptible strain at the 900 mg/kg dose. Strain differences for hypothermic response at both doses were not significant. Significant strain differences were also observed for lithium distribution in different parts of the body, excreta and urine. The concentration of Li+ found in urine and excreta was positively correlated with resistance (time to death at 900 mg/kg LiCl) to the toxic effect of lithium. The lithium concentration in blood, muscle and lung on the other hand reflected a negative correlation with toxicity. The susceptibility of a strain could be characterized by its inherent lithium excretory ability, particularly through urine. It may suggest an involvement of membrane transport mechanisms in determining toxicity to lithium compounds.

Steroid-hormone-binding proteins in normal and neoplastic mammary tissues from C3H mice fed diethylstilbestrol

Mammary tumors develop earlier and in greater numbers in C3H mice fed diets containing up to 1000 ppb diethylstilbestrol or 5000 ppb estradiol-17 beta. We have analyzed the steroid-hormone-binding proteins in cytosols of normal target tissues and in neoplastic mammary tissues of control and estrogen-fed mice to determine whether the capacity for hormone response was altered by dietary estrogens. Using estradiol-17 beta as a ligand, estrogen-binding proteins were measured with Kd = 10(-11)-10(-10) M and sedimentation constants of 8 and 4 S. The binding capacity (per mg cytosol protein) of uterus exceeded that of normal mammary gland 10-20-fold, while mammary tumors only contained half the binding capacity of virgin mammary gland. Binding proteins for the glucocorticoid, triamcinolone acetonide, exhibited a sedimentation constant of 7-8 S and Kd = 10(-9)-10(-8) M. The glucocorticoid binding capacity of mammary tumors exceeded that of virgin mammary gland. Binding proteins for progestins were measured using the synthetic ligand R5020. Mammary gland contained progestin-binding proteins with 4 S sedimentation constants and Kd = 10(-9)-10(-8) M. Not all mammary tumors contained progestin-binding proteins, and the binding capacities varied considerably among those that did. The molecular characteristics of the steroid receptors in tumors were the same as those found in normal target tissues. There was nothing to suggest that dietary estrogens altered the characteristics of the three steroid-binding proteins.

Comparative study of hepatic microsomal and cytosolic enzyme activities in three murine strains

A comparative study on hepatic microsomal p-nitroanisole-O-demethylase, aminopyrine-N-demethylase, NADPH-cytochrome c reductase and cytosolic glutathione (GSH) S-transferase was performed in both sexes of C3Hf, C57BL/6J and DBA/2 mice. In control and phenobarbital (PB)-induced mice similarities in hepatic microsomal activities were found with slight variations among strains and sexes. The Ah locus nonresponsive DBA/2 mice showed uninduced microsomal activities after beta-naphthoflavone (BNF), as expected; the other two strains were induced by BNF to a similar extent. Differences in cytosolic GSH S-transferase were detected among strains and sexes; C57BL/6J mice showed the highest basal and induced levels. The males of all the three strains examined were found to have higher GSH S-transferase activity than females.

Hepatic metallothionein synthesis in neonatal Mottled-Brindled mutant mice

Mottled-brindled mutant mice did not display the elevated hepatic metallothionein synthesis normally observed in 2- to 6-day-old wild-type mice. This difference between normal and mutant mice was not due to a decreased ability to synthesize metallothionein in the liver, since hepatic metallothionein synthesis was inducible in response to copper, cadmium, zinc, or hydrocortisone administration to neonatal mutant mice. Hydrocortisone treatment resulted in increased metallothionein synthesis in liver of mutant mice but had no ameliorative effect on the mottled-brindled disease.

Luteinizing hormone receptors and testosterone production in whole testes and purified Leydig cells from the mouse: differences among inbred strains

Testicular and Leydig cell function were studied in four inbred strains of mice. Significant strain-related differences were found in the number of LH receptors and in the production of testosterone in vitro in response to increasing concentrations of human CG (hCG) by both decapsulated testes and isolated Leydig cells. Maximal testicular testosterone production was similar in the C57BL/10J and C57BL/6J strains and considerably less in the DBA/2J (DBA) and C3H/HeJ strains, which were similar. However, the number of testicular LH receptors was less in C57BL/6J mice than in all three other strains. The pattern of maximal testosterone production by isolated Leydig cells among the four strains was similar to that observed for whole testes, whereas the number of LH receptors per 10(6) Leydig cells was least for Leydig cells from the DBA strain. When the number of Leydig cells per testis was estimated by dividing the number of testicular LH receptors by the number of LH receptors in 10(6) Leydig cells, it was apparent that testes from DBA mice contain approximately twice as many Leydig cells as those from the other strains. Differences in maximal testicular testosterone production appear to be reflected in differences in maximal testosterone production by isolated Leydig cells from each strain. However, there were no differences in testicular sensitivity to hCG but there were differences in Leydig cell sensitivity to hCG among the four strains. Furthermore, the existence of strain-related differences in well defined functional characteristics of Leydig cells offers the opportunity to study the genetic as well as physiological mechanisms involved in the regulation of Leydig cell function in normal individuals.

Differences in liver ganglioside patterns in various inbred strains of mice

The ganglioside patterns in the liver of different inbred and hybrid strains of mice were investigated. The inbred strains were Balb/cAnNCr1BR, C57BL/6NCr1BR, DBA/2NCr1BR. C3H/HeNCr1BR; the hybrid strain was the Swiss albino. The following major gangliosides were found to be present in mouse liver: GM3-NeuAc; GM3-NeuGl, GM2 [a mixture of one species carrying N-acetylneuraminic acid (NeuAc) and one carrying N-glycollylneuraminic acid (NeuGl)], GM1 and GD1a-(NeuAc,NeuGl). The qualitative and quantitative patterns of liver gangliosides were markedly different in the various inbred strains of mice; in Balb/cAnNCr1BR strain, ganglioside GM2 was preponderant (99.2% of total ganglioside content); in C57BL/6NCr1BR, the major ganglioside was GM2 (90.4%), followed by GM3-NeuAc (5.6%) and GM3-NeuGl (4.0%); in DBA/2NCr1BR, GM2 accounted for 77.1%, GD1a-(NeuAc,NeuGl) 18.9% and GM1 3.1% of gangliosides; in C3H/HeNCr1BR, GM2 constituted 50.6%, GM1 22.8% and GD1a-(NeuAc,NeuGl) 22.1%. In the hybrid Swiss albino mice, liver ganglioside composition markedly varied from one animal to another, GM3-NeuGl, GM2 and GD1a-(NeuAc,NeuGl) being the predominant gangliosides in the various cases.

Certain mouse strains are deficient in a kidney brush-border metallo-endopeptidase activity

Preparations of microvilli from kidneys of BALB/c mice contain an alkaline metallo-endopeptidase, meprin (metallo-endopeptidase from renal tissue). Certain genealogically related inbred mice are markedly deficient in meprin activity. The meprin-deficient strains (CBA/J and C3H/HeJ) exhibit normal levels of other brush-border enzymes: alkaline phosphatase, aminopeptidase M and another proteinase, a phosphoramidon-sensitive neutral endopeptidase. Meprin deficiency cannot be attributed to a shift in pH optimum and is unlikely to be due to the presence of endogenous inhibitors.

Effects of methylcholanthrene and benzanthracene on blastogenesis and aryl hydrocarbon hydroxylase induction in splenic lymphocytes from three inbred strains of mice

The effects of polycyclic aromatic hydrocarbons (PAH) such as benzanthracene (BA) and methylcholanthrene (MCA) on 3H-thymidine incorporation and aryl hydrocarbon hydroxylase (AHH) induction were assayed in mitogen-activated and non-activated splenic lymphocyte cultures derived from three strains of mice (C57BL, C3H and DBA/2). Results of three separate experiments on blastogenesis and the substrate induction of AHH were statistically significant. In mitogen-activated and non-activated lymphocytes from C57BL and C3H mice (AHH responsive strains) the percentage of blastogenesis induced by BA or MCA was higher than in lymphocytes from the non-responsive strain (DBA/2). On the basis of the PAH concentrations used MCA and BA were similar as inducers of blastogenesis and of AHH activity. AHH induction was measurable only in mitogen-activated lymphocytes and showed a non-linear relation to blastogenesis. In responsive strains, 10 microM oF BA or 1.5 microM of MCA induced AHH 2-5 fold, while in non-responsive mice induced AHH was very close to the basal level. This difference between the level of induction of lymphoblast formation and AHH in responsive and non-responsive strains of mice may be related to different subpopulations of lymphocytes in spleen or other lymphatic organs.

Swift increase in alcohol metabolism (SIAM) in the mouse: comparison of the effect of short-term ethanol treatment on ethanol elimination in four inbred strains

Ethanol metabolism increases 2 to 3 hr after the administration of ethanol. This phenomenon, called the swift increase in alcohol metabolism, has been compared in four inbred strains of mice (DBA/2J, C3H/HeJ, AKR/J and C57BL/6J). Basal rates of ethanol elimination were determined in individual mice after an i.p. injection of ethanol (2 g/kg). Little variability in this basal rate of ethanol elimination was observed within each strain. Mice were then exposed to ethanol vapor (20--22 mg/l) and rates of ethanol elimination were determined every 2 hr for 8 hr. By 2 to 3 hr, the rates of ethanol elimination initially increased 2- to 3-fold and then declined toward basal rates over the 8-hr interval in all strains studied. In another experiment, the dose of ethanol was varied to produce blood ethanol levels ranging from 50 to 250 mg/100 ml in both basal- and ethanol vapor-treated mice. Ethanol elimination increased greater than 1.5-fold in all four strains studied when basal rates were compared to rates observed after 4 hr of vapor treatment at the same blood ethanol level; however, the dose at which the maximal increase occurred differed among the strains. DBA/2J mice exhibited a maximal increase in the rate of ethanol elimination when ethanol concentrations were in the range of 30 to 50 mg/100 ml; the increase was smaller as the dose was increased. In contrast, AKR/J and C57BL/6J mice required 100 to 150 mg/100 ml of ethanol to activate the swift increase in alcohol metabolism effect. These data indicate clearly that the swift increase in alcohol metabolism effect is a common phenomenon and that dose and time relations differ in various inbred strains of mice.

Effects of genetically different strains of mice on the microsomal activation of 2-aminofluorene

Five strains of mice were examined for microsomal cytochrome P450 (Cyt P450) activity and ability of the microsomal preparation to activate 2-aminofluorene (2-AF) to its mutagenic form. Each strain was assayed under normal and induced conditions. Group A strains known to be easily induced to carcinogenesis by chemicals (C57BL/6J and BALB/cJ) showed higher levels of Cyt P450 and increased mutagenesis activity of the metabolized 2-AF than Group B strains which are known to be high spontaneous tumor producers (CE/J, A/HeJ, C3H/HeJ). Induction of the hepatic microsomes with Aroclor 1254 increased the difference between the two groups.

DNA methylation and methylase levels in normal and malignant mouse hepatic tissues

The status of DNA methylation, as measured by the 5-methylcytosine content of nuclear DNA, was examined in normal livers and in chemically induced or spontaneous primary hepatocellular carcinoma (PHC) arising in three strains of mice. The DNA from spontaneous tumors of genetic origin in C3H mice and also from acetylaminofluorene, chlordane, or 3'-methyl-4-dimethylaminoazobenzene-induced tumors in C57Bl and B6C3 mice was undermethylated compared to the levels in background and normal liver samples. The DNA methylase activities from normal liver, background liver, and PHC were assayed in C3H mice to determine whether the observed genomic undermethylation is related to a dysfunction of this enzyme and were compared to the rates of DNA synthesis in these tissues. Since DNA methylase levels from tumor nuclei were elevated compared to background, it is concluded that the undermethylation found in the tumor genomes of this system is not due to inactivation nor a significant deficiency of the activity of this enzyme relative to the demand in tumors for methylation of de novo synthesized DNA.

Induction of gamma-glutamyl transpeptidase activity by dietary phenobarbital in "spontaneous" hepatic tumors of C3H mice

Biochemical features of spontaneous hepatic tumors in C3H mice were studied histochemically in comparison with those of neoplastic lesions developed in animals fed dietary phenobarbital (PB) continuously or treated with diethylnitrosamine (DEN) during 11 approximately 14 weeks of age. All 42 spontaneous hepatic tumors that developed in control mice by 74 weeks of age were completely negative for gamma-glutamyl transpeptidase (gamma-GTPase) activity. Dietary phenobarbital enhanced hepatic tumorigenesis remarkably, and 32 out of 43 tumors found at 70 weeks showed multifocal gamma-GTPase activity. DEN induced gamma-GTPase-positive islands of hepatocytes, but 12 out of 13 tumors larger than 5 mm in diameter that developed by 60 weeks were gamma-GTPase-negative. The phenomenon of induction of gamma-GTPase activity by PB in "spontaneous" hepatic tumors appears to be important both for elucidating the mechanism of promotion by PB and also for analyzing multisteps of carcinogenesis.

X-ray-induced production of granulocyte-macrophage colony-stimulating factor (GM-CSF) by mouse spleen cells in culture

Spleen cells were collected from normal mice and cultured in a medium containing 20% calf serum. Addition of lipopolysaccharide (LPS) in the culture significantly increased the production of granulocyte-macrophage colony-stimulating factor (GM-CSF), and a maximum induction was attained in 5 days. Irradiation of the spleen cells with 300 to 3,000R X-rays also enhanced the production of GM-CSF, but there was a latent period of about 5 days before the factor appeared in the culture medium. The observed difference between LPS and X-rays in the timing of inducing GM-CSF production in the spleen cell culture was consistent with the difference in timing of the increase of spleen cell proliferation observed in animals after the administration of LPS or during recovery from damages by X-irradiation. It was observed furthermore that the X-ray-induced GM-CSF differed from the LPS-induced GM-CSF in its molecular properties; the X-ray-induced factor was represented by an acidic (pI = 3.0) 70,000-dalton species, while the LPS-induced factor was much smaller in size (M.W. 20,000) and less acidic (pI = 5.4). These results suggest that different mechanisms of GM-CSF production operate in the spleen in response to either LPS or X-rays.

A bactericidal activity of microsomal preparations

Exposure of suspension of Salmonella typhimurium tester strains TA1535, TA1537 and TA98 to mouse hepatic post-mitochondrial supernatants (S9) resulted in appreciable loss of bacterial viability. This lethal activity was destroyed by heating at 56 degrees C for 30 min. The toxic component of the S9 has not been identified.

A decrease in guanylate cyclase activity in some tissues of C3H/HeJ mice with retinal dystrophy

Guanylate cyclase activity was assayed in homogenates, in particulate and soluble fractions from retina, cerebellum, cerebral cortex and adrenal gland of adult C3H/HeJ mice with a dystrophic retinopathy. In comparison to control mice (DBA/1J), in C3H/HeJ strain a significant decrease in guanylate cyclase activity occurred in homogenates from retina, cerebellum and adrenal gland. In particular a significant decrease was found in particulate fraction of retina, in the soluble fraction of cerebral cortex and cerebellum and in both fractions of the adrenal gland. In contrast to the retina and cerebellum where guanylate cyclase activity in homogenates was found significantly decreased both in the male and female, in the cerebral cortex guanylate cyclase decreased in both sexes although in female this was more marked.

Developmental expression of murine HPRT. I. Activities, heat stabilities, and electrophoretic mobilities in adult tissues

Total and specific activity of the enzyme hypoxanthine phosphoribosyltransferase (HPRT) varied widely among six tissues from C3H/f mice; the highest levels of activity were in brain. More striking were thermostability differences in tissue enzymes. Although brain, spleen, and kidney HPRT retained 65% basal activity after 15 min at 85 C, heart, liver, and erythrocyte HPRT retained only 20-30% initial activity. Kidney HPRT behaved as monospecific heat-stable enzyme (K-denatauration=0.022/min, and liver enzyme behaved as monospecific heat-labile enzyme (K-denaturation=0.061/min), while other tissues appeared to contain both forms of the enzyme. Multiple electrophoretic activity bands were present in all tissues; no activity band was restricted to a single tissue. The data presented here are consistent with the hypothesis that the distinct tissue properties of HPRT result from posttranslational modification of the product of a single genetic locus which is expressed in all tissues.

Genetic differences inthe te of histidase synthesis in inbred mice

Inbred strains of mice fall into two groups with respect to their liver histidase activity levels, high strains having approximately twice as much activity as low strains. Analysis of the F1, F2, and backcross progeny of the mating of a high activity strain (C57BL/6J) and a low activity strain (C3H/HeJ) indicates that the difference between the strains is determined by a single genetic locus with two alleles exhibiting additive inheritance. No differences with respect to various physical and kinetic parameters were found in studies of partially purified histidase from both strains. Quantitation of the amount of enzyme present by immunotitration showed that the amount of enzyme antigen is proportional to the level of enzyme activity in the two strains. Measurements of the relative rates of histidase synthesis by combined radiochemical and immunological techniques showed that the relative rate of synthesis was closely correlated with the amount of enzyme present. Rates of enzyme degradation in the two strains, measured by recovery of activity after irreversible inhibition with nitromethane, were the same.

Characterization of major milk proteins from BALB/c and C3H mice

Milk proteins from BALB/c and C3H mice were characterized with respect to their electrophoretic migration in polyacrylamide gels under alkaline and acid conditions. The major casein and whey proteins from each strain migrated similarly under the conditions employed. Phosphoproteins were identified by staining with "Stains-all" and by changes in electrophoretic mobility and staining induced by prior treatment with phosphatase. Sialic acid-rich glycoproteins were identified by staining with periodic acid-Schiff and with "Stains-all" by prior treatment with neuraminidase to identify sialic acid as the acidic portion of the molecule. The two major whey proteins were characterized further by their migration in sodium dodecyl sulfate gels. One protein had the same mobility as mouse serum albumin. The other protein migrated with a mobility similar to that of bovine alpha-lactalbumin. The identity of the former protein was confirmed by its reaction with goat anti-mouse serum albumin in an immunodiffusion procedure, and the latter protein by its B protein activity in the lactose synthetase assay.

Aryl hydrocarbon hydroxylase in liver nuclei of C3H/He and DBA/2 mice

Aryl hydrocarbon hydroxylase activity in liver nuclei from C3H/He mice is apparently increased by the administration of 3-methylcholanthrene, but the enzyme activity from the DBA/2 mice is not. On the other hand, by treatment of the mice with phenobarbital sodium, the increased activity in liver nuclei was observed in both strains of mice. There are approximately the same levels of the apparent Km for benzo[alpha]pyrene in liver nuclei from both strains of mice even after treatment with 3-methylcholanthrene, but different Km values for NADPH and NADH are observed between the constitutive and induced enzyme, showing 0.032 and 0.091 mM for NADPH, and 0.303 and 1.67 mM for NADH, respectively. Both 5, 6- and 7, 8-benzoflavones enhance the activity in the constitutive enzyme, but inhibit it in the induced enzyme non-competitively. Nicotinamide inhibits both enzyme activities in liver nuclei. Cyclohexene oxide and 1, 1, 1-trichloropropane oxide enhance the activity in the induced enzyme, but not in the constitutive enzyme in liver nuclei. The differences in the properties between the contitutive and induced enzymes and between the enzymes in microsomes and in nuclei from mouse liver were discussed briefly.

Cyclic guanosine monophosphate: elevation in degenerating photoreceptor cells of the C3H mouse retina

As a result of an early deficiency in cyclic nucleotide phosphodiesterase activity, guanosine 3',5'-monophosphate accumulates in retinal photoreceptor cells before they begin to degenerate. It is suggested that degeneration of the photoreceptor cells is related to an imbalance in their metabolism or function which is caused by the elevated levels of cyclic guanosine monophosphate.