Unveiling the nongenomic actions of thyroid hormones in adult mammalian brain: The legacy of Mary B. Dratman.

A comprehensive review was conducted to compile the contributions of Mary B. Dratman and studies by other researchers in the field of nongenomic actions of thyroid hormones in adult mammalian brain. Dratman and her collaborators authored roughly half of the papers in this area. It has been almost fifty years since Dratman introduced the novel concept of thyroid hormones as neurotransmitters for the first time. The characterization of unique brain-region specific accumulation of thyroid hormones within the nerve terminals in adult mammals was a remarkable contribution by Dratman. It suggested a neurotransmitter- or neuromodulator-like role of thyroid hormone and/or its derivative, 3-iodothyronamine within adrenergic systems in adult mammalian brain. Several studies by other researchers using synaptosomes as a model system, have contributed to the concept of direct nongenomic actions of thyroid hormones at synaptic regions by establishing that thyroid hormones or their derivatives can bind to synaptosomal membranes, alter membrane functions including enzymatic activities and ion transport, elicit Ca2+/NO-dependent signaling pathways and induce substrate-protein phosphorylation. Such findings can help to explain the physiological and pathophysiological roles of thyroid hormone in psychobehavioral control in adult mammalian brain. However, the exact mode of nongenomic actions of thyroid hormones at nerve terminals in adult mammalian brain awaits further study.

Nongenomic roles of thyroid hormones and their derivatives in adult brain: are these compounds putative neurotransmitters?

We review the evidence regarding the nongenomic (or non-canonical) actions of thyroid hormones (thyronines) and their derivatives (including thyronamines and thyroacetic acids) in the adult brain. The paper seeks to evaluate these compounds for consideration as candidate neurotransmitters. Neurotransmitters are defined by their (a) presence in the neural tissue, (b) release from neural tissue or cell, (c) binding to high-affinity and saturable recognition sites, (d) triggering of a specific effector mechanism and (e) inactivation mechanism. Thyronines and thyronamines are concentrated in brain tissue and show distinctive patterns of distribution within the brain. Nerve terminals accumulate a large amount of thyroid hormones in mature brain, suggesting a synaptic function. However, surprisingly little is known about the potential release of thyroid hormones at synapses. There are specific binding sites for thyroid hormones in nerve-terminal fractions (synaptosomes). A notable cell-membrane binding site for thyroid hormones is integrin αvß3. Furthermore, thyronines bind specifically to other defined neurotransmitter receptors, including GABAergic, catecholaminergic, glutamatergic, serotonergic and cholinergic systems. Here, the thyronines tend to bind to sites other than the primary sites and have allosteric effects. Thyronamines also bind to specific membrane receptors, including the trace amine associated receptors (TAARs), especially TAAR1. The thyronines and thyronamines activate specific effector mechanisms that are short in latency and often occur in subcellular fractions lacking nuclei, suggesting nongenomic actions. Some of the effector mechanisms for thyronines include effects on protein phosphorylation, Na+/K+ ATPase, and behavioral measures such as sleep regulation and measures of memory retention. Thyronamines promptly regulate body temperature. Lastly, there are numerous inactivation mechanisms for the hormones, including decarboxylation, deiodination, oxidative deamination, glucuronidation, sulfation and acetylation. Therefore, at the current state of the research field, thyroid hormones and their derivatives satisfy most, but not all, of the criteria for definition as neurotransmitters.

The many faces of thyroxine.

Hönes et al. have recently shown that in vivo interference with the apparatus of the nuclear receptor-mediated, gene-driven mechanism of triiodothyronine (T3) actions fails to eliminate all actions of T3. However, the investigators conducting that study provided little information regarding the mechanisms that might be responsible for conferring those implied gene-independent effects. Dratman has long ago suggested a system wherein such gene-free mechanisms might operate. Therefore, since news of that discovery was originally published in 1974, it seems appropriate to describe the progress made since then. We propose that thyroxine and triiodothyronine have many different structural properties that may confer a series of different capabilities on their functions. These conform with our proposal that a series of catecholamine analogs and their conversion to iodothyronamines, allows them to perform many of the functions that previously were attributed to nuclear receptors regulating gene expression. The actions of deiodinases and the differential distribution of iodine substituents are among the critical factors that allow catecholamine analogs to change their effects into ones that either activate their targets or block them. They do this by using two different deiodinases to vary the position of an iodide ion on the diphenylether backbones of thyroxine metabolites. A panoply of these structural features imparts major unique functional properties on the behavior of vertebrates in general and possibly on Homo sapiens in particular.

L-3,3',5-triiodothyronine and pregnenolone sulfate inhibit Torpedo nicotinic acetylcholine receptors.

The nicotinic acetylcholine receptor (nAChR) is an excitatory pentameric ligand-gated ion channel (pLGIC), homologous to the inhibitory γ-aminobutyric acid (GABA) type A receptor targeted by pharmaceuticals and endogenous sedatives. Activation of the GABAA receptor by the neurosteroid allopregnanolone can be inhibited competitively by thyroid hormone (L-3,3',5-triiodothyronine, or T3), but modulation of nAChR by T3 or neurosteroids has not been investigated. Here we show that allopregnanolone inhibits the nAChR from Torpedo californica at micromolar concentrations, as do T3 and the anionic neurosteroid pregnenolone sulfate (PS). We test for the role of protein and ligand charge in mediated receptor inhibition by varying pH in a narrow range around physiological pH. We find that both T3 and PS become less potent with increasing pH, with remarkably similar trends in IC50 when T3 is neutral at pH < 7.3. After deprotonation of T3 (but no additional deprotonation of PS) at pH 7.3, T3 loses potency more slowly with increasing pH than PS. We interpret this result as indicating the negative charge is not required for inhibition but does increase activity. Finally, we show that both T3 and PS affect nAChR channel desensitization, which may implicate a binding site homologous to one that was recently indicated for accelerated desensitization of the GABAA receptor by PS.

Dynamics of high frequency brain activity.

Evidence suggests that electroencephalographic (EEG) activity extends far beyond the traditional frequency range. Much of the prior study of >120 Hz EEG is in epileptic brains. In the current work, we measured EEG activity in the range of 200 to 2000 Hz, in the brains of healthy, spontaneously behaving rats. Both arrhythmic (1/f-type) and rhythmic (band) activities were identified and their properties shown to depend on EEG-defined stage of sleep/wakefulness. The inverse power law exponent of 1/f-type noise is shown to decrease from 3.08 in REM and 2.58 in NonREM to a value of 1.99 in the Waking state. Such a trend represents a transition from long- to short-term memory processes when examined in terms of the corresponding Hurst index. In addition, treating the 1/f-type activity as baseline noise reveals the presence of two, newly identified, high frequency EEG bands. The first band (ψ) is centered between 260-280 Hz; the second, and stronger, band is a broad peak in the 400-500 Hz range (termed ω). Both of these peaks display lognormal distributions. The functional significance of these frequency bands is supported by the variation in the strength of the peaks with EEG-defined sleep/wakefulness.

A stochastic mechanism for signal propagation in the brain: Force of rapid random fluctuations in membrane potentials of individual neurons.

There are two functionally important factors in signal propagation in a brain structural network: the very first synaptic delay-a time delay about 1ms-from the moment when signals originate to the moment when observation on the signal propagation can begin; and rapid random fluctuations in membrane potentials of every individual neuron in the network at a timescale of microseconds. We provide a stochastic analysis of signal propagation in a general setting. The analysis shows that the two factors together result in a stochastic mechanism for the signal propagation as described below. A brain structural network is not a rigid circuit rather a very flexible framework that guides signals to propagate but does not guarantee success of the signal propagation. In such a framework, with the very first synaptic delay, rapid random fluctuations in every individual neuron in the network cause an "alter-and-concentrate effect" that almost surely forces signals to successfully propagate. By the stochastic mechanism we provide analytic evidence for the existence of a force behind signal propagation in a brain structural network caused by rapid random fluctuations in every individual neuron in the network at a timescale of microseconds with a time delay of 1ms.

Interactions of L-3,5,3'-Triiodothyronine [corrected], Allopregnanolone, and Ivermectin with the GABAA Receptor: Evidence for Overlapping Intersubunit Binding Modes.

Structural mechanisms of modulation of γ-aminobutyric acid (GABA) type A receptors by neurosteroids and hormones remain unclear. The thyroid hormone L-3,5,3'-triiodothyronine (T3) inhibits GABAA receptors at micromolar concentrations and has common features with neurosteroids such as allopregnanolone (ALLOP). Here we use functional experiments on α2ß1γ2 GABAA receptors expressed in Xenopus oocytes to detect competitive interactions between T3 and an agonist (ivermectin, IVM) with a crystallographically determined binding site at subunit interfaces in the transmembrane domain of a homologous receptor (glutamate-gated chloride channel, GluCl). T3 and ALLOP also show competitive effects, supporting the presence of both a T3 and ALLOP binding site at one or more subunit interfaces. Molecular dynamics (MD) simulations over 200 ns are used to investigate the dynamics and energetics of T3 in the identified intersubunit sites. In these simulations, T3 molecules occupying all intersubunit sites (with the exception of the α-ß interface) display numerous energetically favorable conformations with multiple hydrogen bonding partners, including previously implicated polar/acidic sidechains and a structurally conserved deformation in the M1 backbone.

Mechanisms of L-triiodothyronine-induced inhibition of synaptosomal na(+)-k(+)-ATPase activity in young adult rat brain cerebral cortex.

The role of thyroid hormones (TH) in the normal functioning of adult mammalian brain is unclear. Our studies have identified synaptosomal Na(+)-K(+)-ATPase as a TH-responsive physiological parameter in adult rat cerebral cortex. L-triiodothyronine (T3) and L-thyroxine (T4) both inhibited Na(+)-K(+)-ATPase activity (but not Mg(2+)-ATPase activity) in similar dose-dependent fashions, while other metabolites of TH were less effective. Although both T3 and the ß -adrenergic agonist isoproterenol inhibited Na(+)-K(+)-ATPase activity in cerebrocortical synaptosomes in similar ways, the ß -adrenergic receptor blocker propranolol did not counteract the effect of T3. Instead, propranolol further inhibited Na(+)-K(+)-ATPase activity in a dose-dependent manner, suggesting that the effect of T3 on synaptosomal Na(+)-K(+)-ATPase activity was independent of ß -adrenergic receptor activation. The effect of T3 on synaptosomal Na(+)-K(+)-ATPase activity was inhibited by the α2-adrenergic agonist clonidine and by glutamate. Notably, both clonidine and glutamate activate Gi-proteins of the membrane second messenger system, suggesting a potential mechanism for the inhibition of the effects of TH. In this paper, we provide support for a nongenomic mechanism of action of TH in a neuronal membrane-related energy-linked process for signal transduction in the adult condition.

Effects of acute microinjections of the thyroid hormone derivative 3-iodothyronamine to the preoptic region of adult male rats on sleep, thermoregulation and motor activity.

The decarboxylated thyroid hormone derivative 3-iodothyronamine (T1AM) has been reported as having behavioral and physiological consequences distinct from those of thyroid hormones. Here, we investigate the effects of T1AM on EEG-defined sleep after acute administration to the preoptic region of adult male rats. Our laboratory recently demonstrated a decrease in EEG-defined sleep after administration of 3,3',5-triiodo-l-thyronine (T3) to the same brain region. After injection of T1AM or vehicle solution, EEG, EMG, activity, and core body temperature were recorded for 24h. Sleep parameters were determined from EEG and EMG data. Earlier investigations found contrasting systemic effects of T3 and T1AM, such as decreased heart rate and body temperature after intraperitoneal T1AM injection. However, nREM sleep was decreased in the present study after injections of 1 or 3 µg T1AM, but not after 0.3 or 10 µg, closely mimicking the previously reported effects of T3 administration to the preoptic region. The biphasic dose-response observed after either T1AM or T3 administration seems to indicate shared mechanisms and/or functions of sleep regulation in the preoptic region. Consistent with systemic administration of T1AM, however, microinjection of T1AM decreased body temperature. The current study is the first to show modulation of sleep by T1AM, and suggests that T1AM and T3 have both shared and independent effects in the adult mammalian brain.

Effects of acute microinjections of thyroid hormone to the preoptic region of hypothyroid adult male rats on sleep, motor activity and body temperature.

Thyroid hormones induce short-latency nongenomic effects in adult brain tissue, suggesting that their acute administration would affect brain activity in intact animals. The influence on EEG-defined sleep of acute restoration of l-3,3'5-triiodothyronine (T3) to a sleep-regulatory brain region, the preoptic region, was examined in hypothyroid rats. Sleep parameters were monitored for 48 h weekly: for 24 h immediately following a control microinjection and for an additional 24h after a second microinjection including a T3 dose to the preoptic region or lateral ventricle. Male albino rats were implanted with EEG and EMG electrodes, abdominal temperature/activity transponders and unilateral lateral ventricle cannulae or bilateral preoptic region cannulae, and were given 0.02% n-propythiouracil (PTU) in their drinking water for 4 weeks. For histologically-confirmed bilateral preoptic region cannula placements (N=7), effects of T3 (especially a 3 µg dose) were apparent within 10h of injection as decreases in REM, NREM and total sleep and increases in waking and activity. Minimal effects of lateral ventricle T3 microinjection were demonstrated (N=5). Significant effects due to the time of day on the experimental measures were seen in both lateral ventricle and preoptic region groups, but these effects did not interact with the effect of administered hormone dose. These effects of T3 microinjection to the preoptic region were demonstrated after acute injections and within hours of injection rather than after chronic administration over days.

Effects of acute microinjections of thyroid hormone to the preoptic region of euthyroid adult male rats on sleep and motor activity.

In adult brain tissue, thyroid hormones are known to have multiple effects which are not mediated by chronic influences of the hormones on heterodimeric thyroid hormone nuclear receptors. Previous work has shown that acute microinjections of l-triiodothyronine (T3) to the preoptic region significantly influence EEG-defined sleep in hypothyroid rats. The current study examined the effects of similar microinjections in euthyroid rats. In 7 rats with histologically confirmed microinjection sites bilaterally placed in the preoptic region, slow-wave sleep time was significantly decreased, but REM and waking were increased as compared to vehicle-injected controls. The EEG-defined parameters were significantly influenced by the microinjections in a biphasic dose-response relationship; the lowest (0.3µg) and highest (10µg) doses tested were without significant effect while intermediate doses (1 and 3µg) induced significant differences from controls. There were significant diurnal variations in the measures, yet no significant interactions between the effect of hormone and time of day were demonstrated. Core body temperature was not significantly altered in the current study. The demonstration of effects of T3 within hours instead of days is consistent with a rapid mechanism of action such as a direct influence on neurotransmission. Since the T3-mediated effects were robust in the current work, euthyroid rats retain thyroid hormone sensitivity which would be needed if sleep-regulatory mechanisms in the preoptic region are continuously modulated by the hormones. This article is part of a Special Issue entitled LInked: BRES-D-12-01552 & BRES-D-12-01363R2.

Non-genomic effect of L-triiodothyronine on calmodulin-dependent synaptosomal protein phosphorylation in adult rat cerebral cortex.

The present study was undertaken to examine calmodulin-dependent effect of thyroid hormones (THs) on synaptosomal protein phosphorylation in mature rat brain. Effect of L-triiodothyronine (L-T3) on in vitro protein phosphorylation was measured in a hypotonic lysate of synaptosomes prepared from adult male rat cerebral cortex, incubated in presence and absence of calcium ion (Ca2+) and calmodulin. L-T3 significantly enhanced incorporation of 32P into synaptosomal proteins as compared to basal level of phosphorylation in the presence of Ca2+ and calmodulin. Under these conditions, increase in protein phosphorylation was 47, 74 and 52% for 10 nM, 100 nM and 1 microM L-T3, respectively. Chelation of Ca2+ using ethylene glycol-bis (2-aminoethylether)-N, N, N', N'-tetraacetic acid (EGTA) inhibited the effects of Ca2+/calmodulin on TH-stimulated protein phosphorylation levels. This study suggests that a high proportion of L-T3-stimulated protein phosphorylation involves Ca2+/calmodulin-dependent pathways in adult rat cerebrocortical synaptosomes.

Extracellular noise-induced stochastic synchronization in heterogeneous quorum sensing network.

Quorum sensing is a bacterial mechanism used to synchronize the coordinated response of a microbial population. Because quorum sensing in Gram-negative bacteria depends on release and detection of a diffusible signaling molecule (autoinducer) among a multicellular group, it is considered a simple form of cell-cell communication for the purposes of mathematical analysis. Stochastic equation systems have provided a common approach to model biochemical or biophysical processes. Recently, the effect of noise to synchronize a specific homogeneous quorum sensing network was successfully modeled using a stochastic equation system with fixed parameters. The question remains of how to model quorum sensing networks in a general setting. To address this question, we first set a stochastic equation system as a general model for a heterogeneous quorum sensing network. Then, using two relevant biophysical characteristics of Gram-negative bacteria (the permeability of the cell membrane to the autoinducer and the symmetry of autoinducer diffusion) we construct the solution of the stochastic equation system at an abstract level. The solution indicates that stable synchronization of a quorum sensing network is robustly induced by an environment with a heterogenous distribution of extracellular and intracellular noise. The synchronization is independent of the initial state of the system and is solely the result of the connectivity of the cell network established through the effects of extracellular noise.

The mechanism for stochastic resonance enhancement of mammalian auditory information processing.

BACKGROUND: In a mammalian auditory system, when intrinsic noise is added to a subthreshold signal, not only can the resulting noisy signal be detected, but also the information carried by the signal can be completely recovered. Such a phenomenon is called stochastic resonance (SR). Current analysis of SR commonly employs the energies of the subthreshold signal and intrinsic noise. However, it is difficult to explain SR when the energy addition of the signal and noise is not enough to lift the subthreshold signal over the threshold. Therefore, information modulation has been hypothesized to play a role in some forms of SR in sensory systems. Information modulation, however, seems an unlikely mechanism for mammalian audition, since it requires significant a priori knowledge of the characteristics of the signal. RESULTS: We propose that the analysis of SR cannot rely solely on the energies of a subthreshold signal and intrinsic noise or on information modulation. We note that a mammalian auditory system expends energy in the processing of a noisy signal. A part of the expended energy may therefore deposit into the recovered signal, lifting it over threshold. We propose a model that in a rigorous mathematical manner expresses this new theoretical viewpoint on SR in the mammalian auditory system and provide a physiological rationale for the model. CONCLUSION: Our result indicates that the mammalian auditory system may be more active than previously described in the literature. As previously recognized, when intrinsic noise is used to generate a noisy signal, the energy carried by the noise is added to the original subthreshold signal. Furthermore, our model predicts that the system itself should deposit additional energy into the recovered signal. The additional energy is used in the processing of the noisy signal to recover the original subthreshold signal.

Effects of dietary caffeine and alcohol on liver carbohydrate and fat metabolism in rats.

BACKGROUND: The effects of caffeine on fatty liver induced by high-fat (low-carbohydrate) diets were examined in the presence or absence of alcohol consumption by rats. MATERIAL/METHODS: For periods ranging from two to twelve weeks, male Long-Evans rats were given alcohol-free or alcohol-containing liquid diets balanced for energy content, but varying in fat and carbohydrate. In addition, several of the groups were given 0.05% caffeine as a constituent of the liquid diet. At the end of the experiments, trunk blood was collected for blood glucose and plasma leptin, epididymal fat pads were weighed, and liver was taken for analysis of glycogen, glucose, and fat. RESULTS: Ethanol-containing diets increased liver fat and depleted liver glycogen and glucose as compared to the corresponding ethanol-free diets, but these effects were less severe in rats given high-carbohydrate diets as compared to those maintained on the high-fat diet. The inclusion of 0.05% caffeine in the diet increased the motor activity of animals with access to a running wheel, yet had no protective effect against ethanol-induced depletion of liver glucose and induction of fatty liver. In fact, caffeine appears to exacerbate the effect of ethanol to deplete liver glycogen, decrease epididymal fat pad weight and lower serum leptin. CONCLUSIONS: Since liver glycogen stores can be depleted by treatments such as caffeine which do not exacerbate ethanol-related liver fat accumulation, the depletion of liver glycogen following chronic ethanol is not the single causal determinant of the resulting fatty liver. Other aspects of carbohydrate metabolism, including accumulations of endogenous regulatory intermediates or ethanol-derived compounds, might be more directly influenced by chronic alcohol ingestion.

Influence of oxygenated fuel additives and their metabolites on gamma-aminobutyric acidA (GABAA) receptor function in rat brain synaptoneurosomes.

Experimental and occupational inhalational exposure to oxygenate fuel additives in reformulated gasoline has been reported to induce neurological symptoms (e.g., headache, nausea, dizziness). We reported previously that the ether additives (methyl-t-butyl ether (MTBE), t-amyl-methyl ether (TAME) and ethyl-t-butyl ether (ETBE)) and their metabolites (t-amyl alcohol (TAA), t-butyl alcohol (TBA) and ethanol) alter the binding of [3H]t-butylbicycloorthobenzoate ([3H]TBOB), a ligand for the gamma-aminobutyric acidA (GABAA) receptor in rat brain membrane preparations. To more directly assess the effects of the ethers and their alcohol precursors on GABAA receptor function, the uptake of 36Cl- was measured in synaptoneurosomes, a preparation of closed membrane sacs comprised of pre- and postsynaptic membranes from adult rat cerebral cortex. Each of the compounds caused a concentration-dependent enhancement of muscimol-stimulated uptake of 36CI-, which diminished with further increasing concentrations. The potency of the enhancement by the compounds was in the rank order: MTBE = TAME > TAA = ETBE > TBA > ethanol. The half-maximally effective concentration (EC50) for the facilitation of muscimol-stimulated 36Cl- uptake ranged from 0.06 to 3 mM, and that for the higher-dose inhibitory effect (IC50) ranged from 3 to 50 mM. The facilitatory concentrations of the compounds are in the range of the blood concentrations reported in experimental animals after exposures known to induce CNS effects such as ataxia. The results suggest a potential role of the GABAA receptor in some of the reported neurotoxic effects of gasoline additives.

Inhibition of the activity of the native gamma-aminobutyric acid A receptor by metabolites of thyroid hormones: correlations with molecular modeling studies.

To characterize the direct effects of thyroid hormones on native gamma-aminobutyric acid(A) (GABA(A)) receptors, rapid (5 s) actions of a series of iodothyronines on muscimol-stimulated uptake of (36)Cl(-) were investigated in synaptoneurosomes prepared from rat brain. The results were correlated with molecular modeling of the active compounds. Dose-response curves for muscimol in the presence of 3,3', 5-L-triiodothyronine (L-T3) indicated a noncompetitive inhibition of muscimol-stimulated (36)Cl(-) uptake by the thyroid hormone. Synaptoneurosomes prepared from cerebellum were less sensitive to L-T3 than those from cerebral cortex, in terms of the potency of the hormone. The overall efficacy approached complete inhibition for both brain regions. Muscimol-stimulated (36)Cl(-) uptake was inhibited differentially by iodothyronine derivatives. One group of compounds with IC(50) values of 18-30 microM included L-thyroxine (L-T4), D-thyroxine (D-T4), 3,3', 5,5'-tetraiodothyroacetic acid (Tetrac), and 3,3', 5-triiodothyroacetic acid (Triac). A second group with values of 75-100 microM included 3,3', 5'-l-triiodothyronine (reverse T3; r-T3), 3,3'-diiodo-L-thyronine (3,3'-l-T2) and 3,5-diiodo-L-thyronine (3,5-D-T2). A final group of inactive compounds with IC(50) values greater than 100 microM included 3',5'-diiodo-L-thyronine (3',5'-l-T2), 3-iodo-L-thyronine (L-T1), 3'-iodo-L-thyronine (3'-L-T1), and L-thyronine (L-T0). Molecular modeling of the active iodothyronines using the Gaussian03 series of programs indicated close correspondences with models of the GABA-inhibitory neurosteroid pregnenolone sulfate (PREGS), suggesting common mechanisms of action at the GABA(A) receptor.

Liver fat and plasma ethanol are sharply lower in rats fed ethanol in conjunction with high carbohydrate compared with high fat diets.

The effects of high fat and high carbohydrate diets on alcohol metabolism were studied on blood alcohol and liver fat concentration. In Experiment 1, rats consumed an alcohol-containing liquid diet. Blood was collected for ethanol, glucose and lactate analyses and livers were excised for lipid determination. Blood ethanol and liver fat were lower when rats consumed the high carbohydrate diet. Glucose concentrations were lower in rats fed the high fat diet compared with those fed the high carbohydrate diet when ethanol was consumed. In Experiment 2, rats consumed a high fat, ethanol-containing diet for 13 d. Half of the rats were switched to a high carbohydrate, ethanol-containing diet for an additional 11 d. The same analyses were carried out as for Experiment 1. Switching the high fat-fed rats to the high carbohydrate diet reversed the high blood ethanol and high liver fat values, even though the rats consumed significantly more alcohol with the high carbohydrate diet. In Experiment 3 the same high fat and high carbohydrate diets without ethanol were consumed for 2 wk, at which time ethanol was administered acutely, intraperitoneally, at 2 g/kg. Blood was analyzed for ethanol, glucose and lactate 30, 60 and 120 min after injection. Rats fed the high carbohydrate diet had lower blood ethanol but higher lactate at 120 min compared with those fed the high fat diet. The results suggest that the rate of ethanol elimination is slower in rats fed high fat than in those fed high carbohydrate diets, resulting in elevated blood ethanol and liver fat levels for the former.