Food-restricted Males Research Articles

Sex-specific resilience of neocortex to food restriction.

Mammals have evolved sex-specific adaptations to reduce energy usage in times of food scarcity. These adaptations are well described for peripheral tissue, though much less is known about how the energy-expensive brain adapts to food restriction, and how such adaptations differ across the sexes. Here, we examined how food restriction impacts energy usage and function in the primary visual cortex (V1) of adult male and female mice. Molecular analysis and RNA sequencing in V1 revealed that in males, but not in females, food restriction significantly modulated canonical, energy-regulating pathways, including pathways associated waith AMP-activated protein kinase, peroxisome proliferator-activated receptor alpha, mammalian target of rapamycin, and oxidative phosphorylation. Moreover, we found that in contrast to males, food restriction in females did not significantly affect V1 ATP usage or visual coding precision (assessed by orientation selectivity). Decreased serum leptin is known to be necessary for triggering energy-saving changes in V1 during food restriction. Consistent with this, we found significantly decreased serum leptin in food-restricted males but no significant change in food-restricted females. Collectively, our findings demonstrate that cortical function and energy usage in female mice are more resilient to food restriction than in males. The neocortex, therefore, contributes to sex-specific, energy-saving adaptations in response to food restriction.

Sex-specific resilience of neocortex to food restriction

Mammals have evolved sex-specific adaptations to reduce energy usage in times of food scarcity. These adaptations are well described for peripheral tissue, though much less is known about how the energy-expensive brain adapts to food restriction, and how such adaptations differ across the sexes. Here, we examined how food restriction impacts energy usage and function in the primary visual cortex (V1) of adult male and female mice. Molecular analysis and RNA sequencing in V1 revealed that in males, but not in females, food restriction significantly modulated canonical, energy-regulating pathways, including pathways associated waith AMP-activated protein kinase, peroxisome proliferator-activated receptor alpha, mammalian target of rapamycin, and oxidative phosphorylation. Moreover, we found that in contrast to males, food restriction in females did not significantly affect V1 ATP usage or visual coding precision (assessed by orientation selectivity). Decreased serum leptin is known to be necessary for triggering energy-saving changes in V1 during food restriction. Consistent with this, we found significantly decreased serum leptin in food-restricted males but no significant change in food-restricted females. Collectively, our findings demonstrate that cortical function and energy usage in female mice are more resilient to food restriction than in males. The neocortex, therefore, contributes to sex-specific, energy-saving adaptations in response to food restriction.

Sex differences in effort-related decision-making: role of dopamine D2 receptor antagonism.

Depressed individuals demonstrate debilitating symptoms, including depressed mood, anhedonia, and effort-related deficits. Effort-related decision-making can be measured through providing subjects with a choice between high effort/reward and low effort/reward options, which is a dopamine (DA)-dependent behavior. While previous research has shown sex differences in depression rates, this has not been examined within operant-based effort-related decision-making tasks nor has DA been shown to underlie this behavior in female rats. The current study investigated sex differences in an effort-related decision-making task prior to and following administration of the DA D2 receptor antagonist haloperidol (HAL). Adult rats were food restricted or fed freely and trained in an effort-related progressive ratio choice task. After stable responding, HAL was administered acutely (0.05-0.2 mg/kg) prior to testing. Results indicate a significant effect of sex on training variables, with males having a greater number of lever presses, higher ratios, and longer active lever times. Pretreatment with HAL significantly reduced the same measures in both sexes for the high-valued reward, while increasing chow consumption in the food restricted males. Food restricted rats showed a greater number of total lever presses and achieved higher ratios; however, the effect in male food restricted rats was greatest. These data suggest that, although there are sex differences in training, HAL decreases behavior across sexes, demonstrating that the D2 mechanism is similar in both sexes. These findings provide a better understanding of motivational dysfunction in both sexes and potential treatment targets for depression.

Maternal modulation of paternal effects on offspring development.

The paternal transmission of environmentally induced phenotypes across generations has been reported to occur following a number of qualitatively different exposures and appear to be driven, at least in part, by epigenetic factors that are inherited via the sperm. However, previous studies of paternal germline transmission have not addressed the role of mothers in the propagation of paternal effects to offspring. We hypothesized that paternal exposure to nutritional restriction would impact male mate quality and subsequent maternal reproductive investment with consequences for the transmission of paternal germline effects. In the current report, using embryo transfer in mice, we demonstrate that sperm factors in adult food restricted males can influence growth rate, hypothalamic gene expression and behaviour in female offspring. However, under natural mating conditions females mated with food restricted males show increased pre- and postnatal care, and phenotypic outcomes observed during embryo transfer conditions are absent or reversed. We demonstrate that these compensatory changes in maternal investment are associated with a reduced mate preference for food restricted males and elevated gene expression within the maternal hypothalamus. Therefore, paternal experience can influence offspring development via germline inheritance, but mothers can serve as a modulating factor in determining the impact of paternal influences on offspring development.

The influence of food restriction and photoperiod on reproduction in male spiny mice (Acomys spinosissimus): Evidence for terminal investment?

Photoperiod and food availability often interact in the regulation of reproductive development in seasonal environments. We tested the effects of a 10% food restriction and short- (SD) and long-day (LD) photoperiods on reproductive preparedness of male spiny mice (Acomys spinosissimus) from South Africa. Males were either fed ad libitum or a 10% restricted diet and on both food regimes, they were exposed to either a 14 h light:10 h dark (LD) or 10 h light:14 h dark (SD) photoperiod. Testes size, seminiferous tubule diameter and faecal androgen metabolite (fAM) concentrations were larger in food restricted males subjected to LD than in any of the other groups. SD photoperiods did not suppress reproductive development, despite earlier findings, which may be explained by “spontaneous” recrudescence due to prolonged exposure to SD. The increased development of the gonads and higher fAM concentrations observed in food restricted LD males may indicate a terminal investment strategy in male spiny mice with males investing more into reproduction in the face of reduced future survival.

Dynamic resource allocation between pre- and postcopulatory episodes of sexual selection determines competitive fertilization success.

In polyandrous mating systems, male reproductive success depends on both mate-acquisition traits (precopulatory) and sperm competitive abilities (postcopulatory). Empirical data on the interaction between these traits are inconsistent; revealing positive, negative or no relationships. It is generally expected that the investment in pre- and postcopulatory traits is mediated by environmental conditions. To test how dietary resource availability affects sexual ornamentation, sperm quality and their interrelationship in three-spined sticklebacks (Gasterosteus aculeatus), full-sibling groups were raised under three conditions differing in food quantity and/or quality (i.e. carotenoid content): (i) high-quantity/high-quality, (ii) high-quantity/low-quality or (iii) low-quantity/low-quality. After 1 year of feeding, food-restricted males developed a more intense breeding coloration and faster sperm compared with their well-fed brothers, indicating that they allocated relatively more in pre- and postcopulatory traits. Moreover, they outcompeted their well-fed, carotenoid-supplemented brothers in sperm competition trials with equal numbers of competing sperm, suggesting that food-restricted males maximize their present reproductive success. This may result in reduced future reproductive opportunities as food-restricted males suffered from a higher mortality, had an overall reduced body size, and sperm number available for fertilization. In accordance with theory, a trade-off between the investment in pre- and postcopulatory traits was observed in food-restricted males, whereas well-fed males were able to allocate to both traits resulting in a significantly positive relationship.

Role of orexin/hypocretin in conditioned sucrose-seeking in female rats

The orexin/hypocretin system has recently been implicated in reward-seeking, especially for highly salient food and drug rewards. Given that eating disorders affect women more than men, we reasoned that the orexin system may be strongly engaged in female rats, and during periods of food restriction as we recently reported in male rats. Therefore, the present study examined the involvement of the orexin system in operant responding for sucrose, and in cue-induced reinstatement of extinguished sucrose-seeking, in ad libitum fed vs. food-restricted female subjects. Female Sprague Dawley rats were trained to self-administer sucrose pellets, and we determined the effects of pretreatment with the OxR1 receptor antagonist SB 334867 (SB; 10–30 mg/kg) on fixed ratio (FR) sucrose self-administration, and on cue-induced reinstatement of extinguished sucrose-seeking. SB decreased sucrose self-administration in food-restricted but not in ad libitum-fed females. SB did not alter active lever responding during cue-induced reinstatement of sucrose-seeking in either feeding group. These results confirm our previous results in male rats that signaling at the OxR1 receptor is involved in the sucrose reinforcement and self-administration in food-restricted subjects. However, the finding that SB is ineffective at attenuating cue-induced reinstatement in females, but was effective in food-restricted males, leads us to conclude that food seeking induced by conditioned stimuli engages the orexin system differentially in males and females.

Prenatal Food Restriction Induces a Hypothalamic-Pituitary-Adrenocortical Axis-associated Neuroendocrine Metabolic Programmed Alteration in Adult Offspring Rats

Intrauterine growth restriction produces susceptibility to adult metabolic syndrome, which may be caused by the permanent alteration of the hypothalamic-pituitary-adrenocortical (HPA) axis. We aimed to verify that HPA axis-associated neuroendocrine metabolic programming is altered in food-restricted (FR) offspring. Maternal rats were fed a restricted diet from gestational day 11 until full-term delivery, all pups were fed a high-fat diet after weaning and exposed to unpredictable chronic stress (UCS) during postnatal weeks 17-20. Serum levels of adrenocorticotrophic hormone and corticosterone in adult offspring of the prenatal FR group were lower than the control (CN) rats before UCS but increased significantly after UCS. Serum glucose levels in the FR group were normal before UCS but increased after UCS. Serum insulin levels were significantly decreased in FR males but showed a slight increase in FR females before UCS; however, insulin levels decreased significantly in the FR male and female rats after UCS. Before UCS, serum lipid levels were higher in the FR males but were normal in the FR females; after UCS, FR males had a slight decrease and FR females had an increasing trend in serum lipids levels. Lipid droplets in the hypothalamus, pituitary gland, and livers of the FR group indicated steatosis. These results suggest that prenatal food restriction alters HPA axis-associated neuroendocrine metabolism in adult offspring fed a high-fat diet, which may originate from the intrauterine programming and increase the susceptibility to adult metabolic diseases.

Long-day photoperiod interacts with vasopressin and food restriction to modulate reproductive status, and vasopressin receptor expression of male Golden spiny mice

We tested the effects of photoperiod, water and food availability on body mass, reproductive status and arginine vasopressin receptor 1A (Avpr1a) mRNA expression in males of desert-adapted golden spiny mice, Acomys russatus. In Experiment 1, males were acclimated to short-day (SD; 8 h:16 h light:dark) or long-day (LD; 16 h:8 h light:dark) photoperiods with either saline (control) or vasopressin treatment for 3 weeks. The results of this experiment revealed that under control conditions, SD mice increased body mass by ~5% while LD mice decreased it by ~4%. SD photoperiod had no effect on reproductive status and leptin levels, whereas LD males increased testes mass and serum testosterone, but the photoperiod had no effect on leptin levels. Vasopressin administration decreased LD-induced reproductive enhancement. Because no consistent effect of SD treatment was found on reproductive status, Experiment 2 was carried out only on LD-acclimated males kept under 75% food restriction (decrease from ad libitum) with saline or leptin treatment. Body mass, testes mass, serum testosterone, leptin concentrations and Avpr1a mRNA expression were measured. Food restriction remarkably decreased body mass, with a more potent effect in leptin-treated males, showing enhanced reproductive status and a significant increase in serum leptin compared with controls. Avpr1a expression was significantly upregulated in LD, vasopressin-treated and food-restricted males, with higher levels in the hypothalamus compared with the testes. We conclude that in A. russatus, LD photoperiod interacts with water and food availability to advance reproductive responses. Avpr1a is suggested to integrate nutritional and osmotic signals to optimize reproduction by modulating reproductive and energetic neuroendocrine axes at the central level. The interaction between photoperiod and other environmental cues is of an adaptive value to desert-adapted small rodents for timing reproduction in unpredictable ecosystems such as extreme deserts.

Food restriction promotes signaling effort in response to social challenge in a short-lived electric fish

Vertebrates exposed to stressful conditions release glucocorticoids to sustain energy expenditure. In most species elevated glucocorticoids inhibit reproduction. However individuals with limited remaining reproductive opportunities cannot afford to forgo reproduction and should resist glucocorticoid-mediated inhibition of reproductive behavior. The electric fish Brachyhypopomus gauderio has a single breeding season in its lifetime, thus we expect males to resist glucocorticoid-mediated inhibition of their sexual advertisement signals. We studied stress resistance in male B. gauderio (i) by examining the effect of exogenous cortisol administration on the signal waveform and (ii) by investigating the effect of food limitation on androgen and cortisol levels, the amplitude of the electric signal waveform, the responsiveness of the electric signal waveform to social challenge, and the amount of feeding activity. Exogenous cortisol administration did reduce signal amplitude and pulse duration, but endogenous cortisol levels did not rise with food limitation or social challenge. Despite food limitation, males responded to social challenges by further increasing androgen levels and enhancing the amplitude and duration of their electric signal waveforms. Food-restricted males increased androgen levels and signal pulse duration more than males fed ad libitum. Socially challenged fish increased food consumption, probably to compensate for their elevated energy expenditure. Previous studies showed that socially challenged males of this species simultaneously elevate testosterone and cortisol in proportion to signal amplitude. Thus, B. gauderio appears to protect its cortisol-sensitive electric advertisement signal by increasing food intake, limiting cortisol release, and offsetting signal reduction from cortisol with signal-enhancing androgens.

Developmental stress has sex-specific effects on nestling growth and adult metabolic rates but no effect on adult body size or body composition in song sparrows

Variation in the prenatal and postnatal environments can have long-term effects on adult phenotype. In humans and other animals, exposure to stressors can lead to long-term changes in physiology. These changes may predispose individuals to disease, especially disorders involving energy metabolism. In addition, by permanently altering metabolic rates and energy requirements, such effects could have important fitness consequences. We determined the effects of early-life food restriction and corticosterone (CORT) treatment on growth and adult body size, body composition (assessed via quantitative magnetic resonance) and metabolic rates in the song sparrow, Melospiza melodia. Nestlings were hand-raised in captivity from 3 days of age. Treatments (ad libitum food, food restriction or CORT treatment) lasted from day 7 to day 60. Both experimental treatments had sex-specific effects on growth. In the nestling period, CORT-treated males weighed more than controls, whereas CORT-treated females weighed less than controls. Food-restricted males weighed the same as controls, whereas food-restricted females weighed less than controls. Both experimental treatments also had sex-specific effects on standard metabolic rate (SMR). Females exposed to food restriction or CORT treatment during development had higher SMRs in adulthood than control females, but neither stressor affected SMR in males. There were no effects of either treatment on adult body size, body composition (lean or fat mass) or peak metabolic rate. Therefore, early-life stress may have sex-specific programming effects on metabolic rates and energy expenditure in song sparrows. In addition, both treatments affected nestling growth in a manner that exaggerated the typical sex difference in nestling mass, which could provide male nestlings with a competitive advantage over their sisters when developing in a poor-quality environment.

Effects of chronic food restriction and treatments with leptin or ghrelin on different reproductive parameters of male rats

The existence of a close relationship between energy status and reproductive function is well-documented, especially in females, but its underlying mechanisms remain to be fully unfolded. This study aimed to examine the effects of restriction of daily calorie intake, as well as chronic treatments with the metabolic hormones leptin and ghrelin, on the secretion of different reproductive hormones, namely pituitary gonadotropins and prolactin, as well as testosterone, in male rats. Restriction (50%) in daily food intake for 20 days significantly reduced body weight as well as plasma PRL and T levels, without affecting basal LH and FSH concentrations and testicular weight. Chronic administration of leptin to rats fed ad libitum increased plasma PRL levels and decreased circulating T, while it did not alter other hormonal parameters under analysis. In contrast, in rats subjected to 50% calorie restriction, leptin administration increased plasma T levels and reduced testis weight. Conversely, ghrelin failed to induce major hormonal changes but tended to increase testicular weight in fed animals, while repeated ghrelin injections in food-restricted males dramatically decreased plasma LH and T concentrations and reduced testis weight. In sum, we document herein the isolated and combined effects of metabolic stress (50% food restriction) and leptin or ghrelin treatments on several reproductive hormones in adult male rats. Overall, our results further stress the impact and complex way of action of different metabolic cues, such as energy status and key hormones, in reproductive function also in the male.

Gender-specific programmed hepatic lipid dysregulation in intrauterine growth-restricted offspring

Intrauterine growth restriction demonstrates increased risk of adult metabolic syndrome. The associated hyperlipidemia results from obesity or programmed metabolic abnormalities. Because lipid homeostasis is regulated by the liver, we hypothesized that hepatic structure and lipid content in intrauterine growth restriction would reflect a primary lipid dysfunction. From 10 days to term gestation, control pregnant rats received ad libitum diet; study rats were 25% food-restricted (FR). All dams received ad libitum diet throughout lactation. At 3 weeks of age, hepatic lobule size and lipid profile of the pups were determined. At 3 weeks of age, body and liver weights of the pups were comparable with controls, although with reduced hepatic lobule size. FR males had increased hepatic triglyceride and cholesterol content with elevated sterol regulatory element-binding protein-1c, fatty acid synthase, and lipoprotein lipase expression; FR females exhibited decreased hepatic cholesterol levels. Plasma lipid levels were unchanged in FR males and females. Developmental programming results in sex-dependent altered lipid metabolism with increased risk in males.

The effect of past condition on a multicomponent sexual signal.

Sexual-selection theory predicts that multiple signals may reveal male condition at different stages of life, thus allowing females to make a more reliable assessment of male quality. While the effect of current condition on signal design is well established, few studies have experimentally investigated the effects of past condition. We therefore manipulated the nutritional condition of male nymph field crickets Gryllus campestris and assessed the enduring effects on multiple components of the adult calling song. Food-restricted males had longer nymphal development times and smaller adult body sizes than nymphs with ad libitum food access. Nymphal feeding conditions specifically affected the allometric relationship between body size and harp size, as food-restricted males developed comparatively small harps, leading to a calling song of higher carrier frequency than that produced by similar-sized control males. Other calling-song components, notably chirp rate and chirp intensity, were not affected by the nymphal food treatment, exposing carrier frequency as the key component indicating past condition. In a previous study we established chirp rate as the sole indicator of current condition. The combined results represent experimental evidence of a multicomponent sexual signal that provides distinct information on male condition during different stages of life.

Decreased galanin mRNA levels in growth hormone-releasing hormone neurons after perinatally induced growth retardation.

Intrauterine growth retardation (IUGR) is associated with persistent postnatal growth retardation accompanied by dysfunction of the hypothalamic components of the growth hormone (GH) axis. At the adult stage, this is reflected by increased somatostatin (SS) and decreased neuropeptide Y (NPY) mRNA levels, whereas the GH-releasing hormone (GHRH) mRNA levels are normal and the output of GH remains unchanged. To extend our insight into the hypothalamic control of GH secretion in growth retarded rats, we determined galanin (GAL) mRNA levels at the adult stage of perinatally malnourished (i.e. IUGR and early postnatally food restricted) rats. Analyses included comparison of GAL mRNA levels in GHRH neurons in perinatally malnourished adult rats using a semi-quantitative double labeling in situ hybridization technique. We report that IUGR is accompanied by a 60% decrease in GAL mRNA levels in all GHRH neurons in the male IUGR group whereas a tendency towards a decrease was observed in the male early postnatally food restricted (FR) group. These effects became more pronounced when the analysis was restricted to GHRH neurons coexpressing GAL mRNA i.e. decreased GAL mRNA levels were seen in both male and female IUGR rats and in FR males. These data show that GAL mRNA levels in GHRH neurons are persistently decreased after perinatal malnutrition. Taking these results together with our previous data on SS, NPY and GHRH mRNA levels, we can conclude that IUGR leads to a reprogramming of the hypothalamic regulation of GH secretion.

Effects of psychosocial stress or food restriction on body mass and blood cellular immunity in laboratory rats

AbstractImmunological changes were studied in socially stressed loser rats and in rats restricted of food or water. Seven days of chronic social confrontation resulted in a significant loss of body mass as well as in marked alterations of blood cellular immunity in loser rats. Loser males showed increased numbers of granulocytes, reduced numbers of CD4 T cells, CD8 T cells, and B cells, as well as a lowered proliferative response of lymphocytes to concanavalin A. To test the possibility of whether the immunological change in loser males is a direct effect of altered nutritional state, non‐confronted males were restricted of food (−90 per cent) for 7 days to mimic the weight loss of loser males. While losers and food restricted males lost a similar 15 per cent of their initial body mass, their immunological outcome largely differed: food or water restriction had little immunological impact, except on granulocytes (reduced numbers). Obviously, social stress alters granulocyte numbers in a different direction than under food or water restriction. Together the data indicate that modulation of blood cellular immunity in loser males is unlikely to be caused by altered nutritional state during socially stressful confrontations. Copyright © 2001 John Wiley & Sons, Ltd.

Effects of Oxytocin Treatment in Early Life on Body Weight and Corticosterone in Adult Offspring from ad libitum-Fed and Food-Restricted Rats

The aims of this study were: (1) to assess the effects of maternal undernutrition during pregnancy on adult offspring with regard to growth, body composition and plasma levels of glucose, insulin and corticosterone, and (2) to investigate whether oxytocin treatment early in life could ameliorate the adverse effects of food restriction in utero. Pups from ad libitum-fed and food-restricted (60% of ad libitum intake during pregnancy) rats were injected subcutaneously once a day with oxytocin or saline on days 1–14 after birth. At adult age (62 days), male offspring from food-restricted dams had lower body weight, less adipose tissue, lower plasma glucose but higher corticosterone levels, compared to offspring from ad libitum-fed dams. However, oxytocin-treated food-restricted males had higher body weight, higher glucose and lower corticosterone levels compared to their saline-treated counterparts. In conclusion, oxytocin treatment early in life seems to ameliorate some of the adverse effects of food restriction in utero.

Testicular regression in response to food restriction and short photoperiod in white-footed mice (Peromyscus leucopus) is mediated by apoptosis.

Short day lengths or reduced food availability are salient cues for small mammals that breed seasonally. Photoperiod-mediated gonadal regression in white-footed mice (Peromyscus leucopus) is a slow, orderly process that involves testicular apoptosis. Testicular regression in response to restricted caloric intake is relatively rapid, and it is generally reversed quickly by ad libitum (ad lib) feeding. To determine the contribution of apoptotic cell death during food restriction, and to examine possible interactions with photoperiod, mice housed in long (16L:8D) or short (8L:16D) photoperiods were fed either ad lib or 70% of their average ad lib intake. Testes were removed at 2, 4, 6, or 8 wk of experimental treatment. Apoptotic activity was determined by in situ TUNEL labeling and assessment of DNA laddering. Significant (P < 0.05) gonadal regression in response to short days was first detected at 8 weeks in mice fed ad lib. Food-restricted, long-day mice also showed significant testicular regression at 8 wk. Combined exposure to short day lengths and food restriction resulted in significant testicular regression at 6 wk (P < 0.05). TUNEL labeling was slightly, though significantly, elevated in germ cells at 2 and 4 wk in long-day food-restricted mice (P < 0.05). TUNEL labeling was also elevated in short-day food-restricted males at these early times but then increased nearly 5-fold at 6 and 8 wk in these mice (P < 0.001). DNA laddering confirmed elevated apoptosis. Overall apoptotic activity negatively correlated with paired testis mass, plasma testosterone, and spermatogenic index measurements in both ad lib and food-restricted males. Few histological markers of necrotic cell death were observed in any group. Taken together, these results suggest that testicular regression in response to limited caloric intake or short days is mediated by apoptosis.

Survival, body weight, and spontaneous neoplasms in ad Libitum-fed and food-restricted Fischer-344 rats.

Ad libitum-fed (AL) and food-restricted (FR) Fischer-344 male and female rats were monitored for survival, body weight, and spontaneous neoplasms. Mean and maximal lifespans for each group were inversely related to mean body weights. AL males were the shortest lived (mean lifespan 101 wk) followed by AL females (118 wk), FR males (125 wk), and FR females (132 wk). Gross and microscopic examinations were performed on 851 rats from cross-sectional and longevity components of the study. In FR groups, the incidence of mammary gland fibroadenomas, testicular interstitial cell tumors, and pituitary neoplasms was decreased while the latency of these neoplasms was increased. In longevity components, most FR groups had a higher incidence of leukemia than AL cohorts, but all FR groups had a higher mean age at death for the rats with leukemia. Higher leukemia rate in the FR groups was thought to be a result of their extended mean lifespan.

Alterations in Hepatic Microsomal Mixed-Function Oxidase System during Different Levels of Food Restriction in Adult Male and Female Rats

Wistar strain adult male and female rats were given 25, 50 and 75% less food than an ad libitum-fed group of rats for 45 d and the effects of food restriction on hepatic drug metabolizing enzymes, microsomal electron transport components, NADPH-dependent lipid peroxidation and glutathione-S-transferase activities were studied. Compared to ad libitum-fed controls, the cytochrome P-450 levels were higher in food restricted male rats, while they were lower in food restricted females. The activities of NADPH cytochrome c reductase were lower in food restricted females than in ad libitum-fed controls. The activities of drug metabolizing enzymes, aminopyrine N-demethylase and acetanilide hydroxylase were higher in food restricted males, whereas in food restricted females these activities were lower than in respective groups fed ad libitum. Microsomal, NADPH-dependent lipid peroxidation was higher in 25 and 50% food restricted females while in 50 and 75% food restricted males it was lower than in ad libitum controls of the same sex. The cytosolic glutathione-S-transferase activities were lower in food restricted rats of both the sexes than in the same sexed controls. Another group of male and female rats were given 75% less food than the ad libitum-fed rats and refed for 3 d prior to killing. Here also, the effects of restriction were different between sexes. It is concluded that hepatic microsomal mixed-function oxidase system (MFOS) is altered due to feed restriction and food restriction followed by refeeding, in a sex-related manner.