Food restriction increases life span of hypertensive animals

Food restriction was used to increase the life span of normotensive (WKY) and Spontaneously Hypertensive Rats (SHR). When SHR's were maintained on 40% of an otherwise typical lab rat diet, their mean life spans increased from 18 months to over 30 months. The mean life times of normotensive rats which were similarly food restricted were expanded from 24 months to over 32 months. Histological examination of heart, adrenals, kidneys and brain showed that freely fed hypertensive rats died of end-organ damage associated with high blood pressure. In contrast, deaths of food restricted hypertensive rats appeared due to changes associated with old age, rather than specific lesions due to hypertension. Thus, food restriction allows a genetically hypertensive animal to reach a normal life span and to die of age-related rather than hypertension-related events.     

Dietary resistant starch increases hypothalamic POMC expression in rats

Resistant starch (RS) is fermentable dietary fiber. Inclusion of RS in the diet causes decreased body fat accumulation and altered gut hormone profile. This study investigates the effect of feeding RS on the neuropeptide messenger RNA (mRNA) expressions in the arcuate nucleus (ARC) of the hypothalamus and whether vagal afferent nerves are involved. The rats were injected intraperitoneally with capsaicin to destroy unmyelinated small vagal afferent nerve fibers. The cholecystokinin (CCK) food suppression test was performed to validate the effectiveness of the capsaicin treatment. Then, capsaicin-treated rats and vehicle-treated rats were subdivided into a control diet or a RS diet group, and fed the corresponding diet for 65 days. At the end of study, body fat, food intake, plasma peptide YY (PYY) and glucagon-like peptide 1 (GLP-1), and hypothalamic pro-opiomelanocortin (POMC), neuropeptide Y (NPY), agouti-related peptide (AgRP) gene expressions were measured. RS-fed rats had decreased body fat, increased POMC expression in the hypothalamic ARC, and elevated plasma PYY and GLP-1 in both the capsaicin and vehicle-treated rats. Hypothalamic NPY and AgRP gene expressions were not changed by RS or capsaicin. Therefore, destruction of the capsaicin-sensitive afferent nerves did not alter the response to RS in rats. These findings suggest that dietary RS might reduce body fat through increasing the hypothalamic POMC expression and vagal afferent nerves are not involved in this process. This is the first study to show that dietary RS can alter hypothalamic POMC expression.     

Food restriction and refeeding in growing rats.

1. The interrelationship between food intake, body weight and oxygen consumption was analysed at 25 degrees C in growing rats. 3. The experiment was divided into two phases lasting four weeks each. During the first phase the animals were subjected to energy restriction and during the second phase they were allowed ad lib energy intake. Four groups of rats were studied: Control with ad lib food intake and three restricted groups R4, R5, and R6 which received during the first phase 4, 5, and 6 g per day of stock diet in a single meal. 3. The results showed a decrease in body weight and oxygen consumption during the restriction period and a recovering of the latter during the refeeding period, without body weight recovering. 4. It is concluded that an energy conservation mechanism is present during food restriction and for some time after refeeding.     

Dexamethasone treatment increases neuropeptide Y levels in rat hypothalamic neurones

Immunoreactive glucocorticoid receptors (GR) have previously been demonstrated in neuropeptide Y (NPY) neurones of the rat hypothalamus. To determine whether NPY synthesis is influenced by glucocorticoids, the effect of dexamethasone (DEX) on the levels of immunoreactive NPY in rat hypothalamic neurones was investigated in vivo and in vitro. Daily injections of DEX (0.1 mg/day) for 5 days increased the NPY content of the mediobasal hypothalamus in female rats by 117% (p less than 0.002). Primary cultures of hypothalamic neurones were also sensitive to the effect of glucocorticoids. Intracellular NPY levels were significantly increased (p less than 0.001) compared to control values by 151%, 222% and 268% when cultures were maintained in a defined serum free medium containing DEX 10(-9), 10(-8) and 10(-7) M respectively.     

Energy restriction with protein restriction increases basal metabolism and meal-induced thermogenesis in rats

We previously observed an increased sympathetic nervous system (SNS) activity that was partly responsible for a defect in the insulin secretion response to glucose after postweaning protein-energy restriction (PER) in female rats. These results, together with other data on low-protein feeding, suggested that a low protein-to-energy ratio (P/E) in the diet could stimulate energy expenditure (EE), but direct measurements of EE have never been reported under conditions of PER. The goal of the present study was thus to quantify the changes induced by PER to body composition, the various parameters of EE, and plasma triiodothyronine levels. PER induced severe growth retardation, but the subcutaneous white and interscapular brown adipose tissue masses were preserved. Basal metabolism, meal-induced thermogenesis, and triiodothyronine levels were increased, but substrate utilization by the working muscles was unaffected. Meal-induced thermogenesis was increased by spontaneous activity in PER rats only. These results suggest that rats adapt to a low P/E in the diet by burning part of their excess nonprotein energy and storing the remaining excess in subcutaneous adipose tissue.     

Differential contribution of hypothalamic MAPK activity to anxiety-like behaviour in virgin and lactating rats

The c-Raf - MEK1/2 - ERK1/2 mitogen-activated protein kinase (MAPK) intracellular signalling cascade in neurons plays important roles in the control of a variety of behaviours, including social behaviours and anxiety. These roles partially overlap with those described for oxytocin (OXT), and it has been shown that OXT activates the MAPK pathway in the hypothalamus (of male), and hippocampus (of female) rats. Here, by combining behavioural (light/dark box) and biochemical analyses (western blotting), we tested two hypotheses: (i) that OXT is anxiolytic within the hypothalamus of females, and (ii) that this effect, as well as that of lactation-associated anxiolysis, depends on the recruitment of the MAPK pathway. We found that, when injected bilaterally into the hypothalamic paraventricular nucleus (PVN), OXT decreased anxiety-like behaviour in virgins, and that this effect depended on phosphorylation of MEK1/2. MAPK pathway activation in lactation was evident by high phosphorylated (p) MEK1/2 levels, and nuclear translocation of ERK1. The high pMEK1/2 levels were necessary for the anxiolytic phenotype typically observed during lactation. Interestingly, exogenous OXT in lactating rats reduced pMEK1/2 levels without a concomitant effect on anxiety, indicating that OXT receptor activation can lead to recruitment of additional intracellular pathways to modulate MEK activity. Still other pathways could include MEK, but without subsequent activation of ERK, as we did not observe any increase in OXT-induced ERK phosphorylation. Together the results demonstrate that the MAPK pathway, especially MEK1/2, is critically involved in the regulation of anxiety-like behaviour in female rats.     

Food restriction prevents the loss of isosafrole inducible cytochrome P-450 mRNA and enzyme levels in aging rats

The influence of food restriction (FR) on the drug-inducible capacity of liver microsomal cytochrome P-450s IA1, IA2 and IIB1 and IIB2 was studied in 20-month-old male Fischer-344 rats. ELISA and Western Blotting revealed that the induction of the cytochrome P-450-IA1/IA2 and P-450-IIB1/IIB2 enzymes was considerably higher in the liver microsomes of FR rats than in their ad libitum (AL) fed counterparts. In order to determine whether the higher P-450 enzyme levels in FR rats were a reflection of an increased synthesis rate or a stabilization of these enzymes, hybridization studies were performed with a cDNA probe for P-450-IIB1/IIB2. These studies show markedly higher levels of P-450-IIB1/IIB2 mRNAs in the livers of FR rats as compared to AL animals. These results suggest that it is possible to prevent the age-dependent loss of drug-induced cytochrome P-450s by 40% dietary restriction which suggest FR may improve the drug-metabolizing capacity during aging.     

Circadian rhythm in hypothalamic leptin receptor (Ob-Rb) mRNA expressions and cerebrospinal fluid and circulating glucose and leptin levels in lactating rats

In lactating animals, the food consumption increases several-fold for milk supply to the pups. The present study was conducted to clarify the relationship between the hyperphagia during lactation and hypothalamic leptin receptor (Ob-Rb) mRNA expression, cerebrospinal fluid (CSF) and circulating leptin and glucose levels. Food intakes significantly higher in lactation than in non-lactation at all time points (3 points: light phase, 4 points: dark phase) of the day. However, the expression of the hypothalamic Ob-Rb mRNA showed similar circadian rhythms in both the non-lactation and lactation, with only slight differences between the two groups. CSF leptin and glucose levels were constant throughout the day in both non-lactation and lactation, and there was almost no difference between the two groups at each time point. Circulating leptin and glucose levels showed circadian rhythms only in the non-lactating period, and were lower in lactation than in non-lactation, especially in the dark phase. In conclusion, the present study provides evidence that Ob-Rb mRNA expression fluctuates in the lactation period as well as in the non-lactation period, suggesting that the expression profile of whole hypothalamic Ob-Rb may not contribute to the difference in food consumption between lactation and non-lactation, and that chronic decrease in blood glucose levels may be associated with the increase in food consumption during lactation.     

Inhibitory response in neurosecretory cells of the hypothalamic supraoptic nucleus to subiculum stimulation in lactating rats

The effects of subiculum stimulation were investigated in 80 antidromically identified hypothalamic supraoptic neurons in lactating rats. Inhibition manifesting as suppression of antidromic action potentials (or of their somatodendritic component) was revealed in 26% of cells, induced by applying conditioned and test stimuli to the subiculum and neurohypophysial stalk. In some instances inhibition arose following a latency of 5–25 msec after each subicular stimulus and lasted only briefly; it set in gradually in other cases, leading to stable long-term changes in the excitability of neurosecretory cells. No activation was produced by this stimulation. It is deduced that subicular inhibitory inputs follow different patterns, thus reflecting morphological organizational aspects of synaptic inhibitory inputs to neurosecretory cells.A. A. Ukhtomskii, Institute of Physiology, A. A. Zhdanov State University, Leningrad. Translated from Neirofiziologiya, Vol. 20, No. 4, pp. 431–437, July–August, 1988.     

Maternal obesity increases hypothalamic leptin receptor expression and sensitivity in juvenile obesity-prone rats

In rats selectively bred to develop diet-induced obesity (DIO) or to be diet-resistant (DR), DIO maternal obesity selectively enhances the development of obesity and insulin resistance in their adult offspring. We postulated that the interaction between genetic predisposition and factors in the maternal environment alter the development of hypothalamic peptide systems involved in energy homeostasis regulation. Maternal obesity in the current studies led to increased body and fat pad weights and higher leptin and insulin levels in postnatal day 16 offspring of both DIO and DR dams. However, by 6 wk of age, most of these intergroup differences disappeared and offspring of obese DIO dams had unexpected increases in arcuate nucleus leptin receptor mRNA, peripheral insulin sensitivity, diet- and leptin-induced brown adipose temperature increase and 24-h anorectic response compared with offspring of lean DIO, but not lean DR dams. On the other hand, while offspring of obese DIO dams did have the highest ventromedial nucleus melanocortin-4 receptor expression, their anorectic and brown adipose thermogenic responses to the melanocortin agonist, Melanotan II (MTII), did not differ from those of offspring of lean DR or DIO dams. Thus, during their rapid growth phase, juvenile offspring of obese DIO dams have alterations in their hypothalamic systems regulating energy homeostasis, which ameliorates their genetic and perinatally determined predisposition toward leptin resistance. Because they later go onto become more obese, it is possible that interventions during this time period might prevent the subsequent development of obesity.     

Food restriction suppresses muscle growth and augments osteopenia in ovariectomized rats.

We examined effects of 4 wk of food restriction on ovariectomy-related changes in muscle, bone, and plasma insulin-like growth factor I (IGF-I). Female Sprague-Dawley rats (7 mo old) were assigned to freely eating groups: sham-operated (Sham), ovariectomized (Ovx-AL), and estrogen (estradiol)-replaced Ovx (Ovx+E(2)). Ovx rats were also pair fed with Sham (Ovx-PF) or weight matched with Sham by food restriction (Ovx-FR). Ovx-AL and Ovx-PF rats had similar estrogen status and body weight; therefore, the groups were combined (group: Ovx). After treatment, body weight was approximately 10% greater in Ovx than in Sham rats (P < 0.05), and muscle weight-to-body weight ratios were comparable among all groups. Bone mineral contents of whole tibiae in Ovx-FR and Ovx were approximately 15% (P < 0.05) and approximately 6% lower than in Sham rats (P < 0.05), respectively. Plasma IGF-I was approximately 30% higher in Ovx than in Sham (P < 0.05) but was similar between Sham and Ovx-FR. IGF-I was highly correlated with body weight and muscle mass. Within non-estrogen-replaced Ovx rats, IGF-I explained approximately 19% of variance in bone mineral content after accounting for variance attributable to body weight. Findings suggest that estrogen acts indirectly on skeletal muscle and bone in rats through regulation of body growth by factors such as IGF-I.     

Protein restriction to pregnant rats increases the plasma levels of angiotensin II and expression of angiotensin II receptors in uterine arteries

Whether gestational protein restriction affects the renin-angiotensin system (RAS) in uterine artery remains unknown. In this study, we hypothesized that gestational protein restriction alters the expression of RAS components in uterine artery. In study one, time-scheduled pregnant Sprague Dawley rats were fed a normal or low-protein (LP) diet from Day 3 of pregnancy until they were killed at Days 19 and 22. The uterine arteries were collected and used for gene expression of Ace, Ace2, Agtr1a, Agtr1b, Agtr2, Esr1, and Esr2 by quantitative real-time PCR and/or Western blotting. LP increased plasma levels of angiotensin II in pregnant rats. In the uterine artery, the expressions of Agtr1a, Agtr1b, and Esr1 were increased by LP at Days 19 and 22 of pregnancy, whereas the abundance of AGTR1 and AGTR2 was increased by LP at Day 19 of pregnancy. The expression of Ace2 was not detectable in rat uterine artery. In study two, virgin female rats were ovariectomized and implanted with either 17beta-estradiol (E2), progesterone (P4), both E2 and P4, or placebo pellets until they were killed 7 days later. In rat uterine artery, E2 and P4 reduced the expression of Agtr1a, and E2 increased the expression of Agtr1b and Agtr2, but neither E2 nor P4 regulated the expression of Ace. These results indicate that gestational protein restriction induces an increase in Agtr1 expression in uterine artery, and thus may exacerbate the vasoconstriction to elevated angiotensin II present in maternal circulation, and that female sex hormones also play a role in this process.     

Dietary zinc restriction in rats alters antioxidant status and increases plasma F2 isoprostanes

Approximately 12% of Americans do not consume the estimated average requirement for zinc and could be at risk for zinc deficiency. Since zinc has proposed antioxidant function, inadequate zinc consumption may lead to an enhanced susceptibility to oxidative stress through several mechanisms, including altered antioxidant defenses. In this study, we hypothesized that dietary zinc restriction would result in lower antioxidant status and increased oxidative damage. We fed weanling Sprague-Dawley rats (n=12 per group) a zinc-adequate (50 mg/kg of zinc) diet, a zinc-deficient (<0.05 mg/kg of zinc) diet or a pair-fed diet for 3 weeks and then assessed their antioxidant status and oxidative stress parameters. Rats were zinc deficient as indicated by a significant (P<.05) reduction in body weight (49%) and 19% lower (P<.05) hepatic zinc (20.6+/-2.1 mg/kg) as compared with zinc-adequate rats (24.6+/-2.2 mg/kg). Zinc deficiency resulted in elevated (P<.05) plasma F(2) isoprostanes. Zinc deficiency-mediated oxidative stress was accompanied by a 20% decrease (P<.05) in the ferritin-reducing ability of plasma assay and a 50% reduction in plasma uric acid (P<.05). No significant change in plasma ascorbic acid or in plasma alpha-tocopherol and gamma-tocopherol was observed. However, hepatic alpha-tocopherol and gamma-tocopherol concentrations were decreased by 38% and 27% (P<.05), respectively, as compared with those in zinc-adequate rats. Hepatic alpha-tocopherol transfer protein levels were unaltered (P>.05) by zinc deficiency, but cytochrome P450 (CYP) 4F2 protein levels were elevated (P<.05) as compared with those in zinc-adequate rats. Collectively, zinc deficiency increased oxidative stress, which may be partially explained by increased CYP activity and reductions in hepatic alpha-tocopherol and gamma-tocopherol and in plasma uric acid.     

Long-term obesity levels in female OLETF rats following time-specific post-weaning food restriction

Obesity and the metabolic syndrome represent serious health threats affecting increasing numbers of individuals, with females being more affected than males and with growing incidence among children and adolescents. In the present study, we used the OLETF rat model of early-onset obesity to examine the influence of different timing of food restriction on long-term obesity levels in females. Food restriction took place at different time windows: from weaning until postnatal day (PND) 45 (early); from weaning until PND90 (chronic); or from PND45 until PND70 (late). Follow-up continued until PND90. During and after the termination of the diet-restriction period, we focused on peripheral adiposity-related measures such as fat pad weight (brown, retroperitoneal and inguinal); inguinal adipocyte size and number; and leptin, oxytocin and glucose levels. We also examined body weight, feeding efficiency, spontaneous intake after release from diet-restriction, and plasma creatinine levels and estrous cycle characteristics as a result of the chronic diet. The results suggest that while food restriction produced significant weight and adiposity loss, OLETF females presented poor weight loss retention after the early and late short-term diets. The estrous cycle structure and time of first estrous of the OLETF rats were normalized by chronic food restriction. Females responded to early food restriction in a different manner than males did in previous studies, further emphasizing the importance of sex-appropriate approaches in the investigation and treatment of the pathologies related to obesity and the metabolic syndrome.     

Long-term obesity levels in female OLETF rats following time-specific post-weaning food restriction

Obesity and the metabolic syndrome represent serious health threats affecting increasing numbers of individuals, with females being more affected than males and with growing incidence among children and adolescents. In the present study, we used the OLETF rat model of early-onset obesity to examine the influence of different timing of food restriction on long-term obesity levels in females. Food restriction took place at different time windows: from weaning until postnatal day (PND) 45 (early); from weaning until PND90 (chronic); or from PND45 until PND70 (late). Follow-up continued until PND90. During and after the termination of the diet-restriction period, we focused on peripheral adiposity-related measures such as fat pad weight (brown, retroperitoneal and inguinal); inguinal adipocyte size and number; and leptin, oxytocin and glucose levels. We also examined body weight, feeding efficiency, spontaneous intake after release from diet-restriction, and plasma creatinine levels and estrous cycle characteristics as a result of the chronic diet. The results suggest that while food restriction produced significant weight and adiposity loss, OLETF females presented poor weight loss retention after the early and late short-term diets. The estrous cycle structure and time of first estrous of the OLETF rats were normalized by chronic food restriction. Females responded to early food restriction in a different manner than males did in previous studies, further emphasizing the importance of sex-appropriate approaches in the investigation and treatment of the pathologies related to obesity and the metabolic syndrome.     

Dentin hypersensitivity induces anxiety and increases corticosterone serum levels in rats

Aims

Investigate the relationships between experimentally induced dentin hypersensitivity (DH) with behavioral, endocrine and dentin erosion data.

Methods

Male Wistar rats divided into four groups, two controls and two experimental, received tap water or isotonic solution (Gatorade®, lemon, pH 2.7) for 30 or 45 days. The DH test was performed by a cold water stimulus on molars. A score (0–3) was given to the rats' pain response. Anxiety was evaluated by the elevated plus maze model and by serum corticosterone levels. The dentin erosion was observed by scanning electron microscopy (SEM). Anatomopathological studies were performed on the stomach, adrenal, kidney, and liver.

Results

Relative to control groups, experimental rats showed: 1) increased hypersensitivity scores (control group, 0; experimental groups, 2 (limits 0.5–3) on the 30th day and 2 (limits 1–3) on the 45th day); 2) reduced percentage of time and entries in the open arms and in serum corticosterone levels; 3) totally exposed dentinal tubules on the 30th day in SEM analysis of the teeth; and 4) no alterations in the anatomopathological and histological evaluations.

Conclusions

The treatment with isotonic solution for 30 days was able to induce DH after erosive challenge and severe DH was observed after isotonic solution treatment for 45 days. The pain induced by cold stimuli was consistent with the grade of DH. The close relationships between dental erosion, response to pain, serum levels of corticosterone and the EPM behavior responses reveal the effects of DH at several levels.