Weanling ventromedial hypothalamic syndrome. bone geometry and biomechanics

The effect of growth-retarding, obesifying lesions in the ventromedial hypothalamic nucleus (VMN) on bone geometry and biomechanics was investigated in male weanling rats. The animals received bilateral, symmetrical, electrolytic lesions (VMNL rats) shortly after weanling (age 27 days); sham-operated rats served as controls (SCON). The rats were maintained for 42 postoperative days and then terminated. Body weight, nose-tail length, food intake, carcass water, and lean body mass were all significantly (p < 0.001) reduced in the VMNL group compared to SCON rats. Carcass fat, lipogenic efficiency (carcass fat % laid down/mean food intake) (both p < 0.001) and epididymal fat pad weight (p < 0.01) were significantly increased in VMNL versus SCON. Femur length, anteroposterior diameter (both p < 0.001), and mediolateral femur diameter (p < 0.01) were significantly reduced in VMNL versus SCON rats, but torque and angle of torque were comparable among the groups. VMNL rats femora also showed a significant greater maximum shear stress compared to the control animals. The reduced parameters in the VMNL rats are in good agreement with the previously demonstrated reduced plasma and pituitary growth hormone levels found in this hypothalamus preparation.

The lateral hypothalamic syndrome in the weanling rat: bone geometry and biomechanics

Male weanling Sprague-Dawley rats received bilateral electrolytic lesions in the lateral hypothalamic area (LHAL). One group of sham-operated controls was fed ad lib (CON-ADLIB), another was pair fed to the LHAL group (CON-PF). The experiment was terminated 1 month after surgery. At that time, LHAL rats were 49% and CON-PF rats were 41% lighter than CON-ADLIB. Carcass protein in LHAL rats was significantly reduced in LHAL: versus CON-ADLIB. Linear growth was significantly reduced by 18% in LHAL versus CON-ADLIB, as well as LHAL: versus CON-PF by 6%. Mean caloric intake was significantly reduced by 48% in LHAL versus CON-ADLIB, as was caloric efficiency (body weight gained per calories eaten) by 36%, as well as, in CON-PF versus CON-ADLIB by 20%. LHAL rats showed a significantly shorter (10%), narrower (15%) and thinner (25 %) cortex at midshaft of the femur. Resistance to torsional loads was reduced by 25% in both LHAL and CON-PF, but this did not reach statistical significance, in comparison to CON-ADLIB. There was no statistical significance among the groups in stiffness and maximal angular displacement. We conclude that the reduced bone geometrical and biomechanical properties in both LHAL rats and CON-PF versus CON-ADLIB are similar because both former groups of rats were greatly subcaloric. Thus, the changes here observed are not due to a specific neuroendocrine/autonomic lesion effect but may be attributable to the reduced food intake, i.e., nutritional factors.

Effect of dorsomedial hypothalamic nuclei knife cuts on ingestive behavior

Previous findings show that rats with electrolytic or excitotoxic lesions in the dorsomedial hypothalamic nucleus (DMN) are hypophagic and hypodipsic and have reduced ponderal and linear growth but normal body composition. DMN-lesioned (DMNL) rats also show altered ingestive responses to naloxone. The present study investigated the intrahypothalamic nerve pathways involved in these DMNL effects and the response of the pathways to deprivation challenges by placing knife cuts posterior (Post), lateral (Lat), ventral (Vent), dorsal, or anterior to the DMN or by administering sham operations. One major finding was that rats with Post or Vent were hypophagic (P < 0. 05) and had reduced body weight but responded normally to deprivation challenges. Post and Lat groups were hypodipsic (P < 0. 05), but plasma Na+, K+, and osmolality and 24-h post-water-deprivation drinking responses were similar in all groups. Naloxone did not suppress the intake of Post rats. It appears that the hypophagia and the reduced body weight after DMNL involve fibers entering or leaving the DMN from ventral and posterior directions, and they may be part of an opioid feeding system.

Reduced femoral geometry but normal biomechanics in the dorsomedial hypothalamic nucleus-lesioned rat

Bone geometry, structure, and biomechanical properties were investigated in a model of growth retardation, the dorsomedial hypothalamic nucleus-lesioned (DMNL) weanling rat. Male weanling Sprague-Dawley rats received bilateral electrolytic lesions in the dorsomedial hypothalamic nucleus (DMN) at age 27 days. Sham-operated rats served as controls. All rats were maintained postoperatively for 40 days. Upon sacrifice, DMNL rats weighed less (p < 0.01), were shorter (p < 0.01), and ate less (p < 0.01) when compared to controls, but their body composition was normal. The femora in DMNL were shorter (p < 0.01), had a smaller outer anteroposterior (AP) diameter (p < 0.04), polar moment of the area (p < 0.02), and maximal (p < 0.02) and minimal (p < 0.03) principal moment of the area when compared with sham-operated rats. Notably, mean torque at failure, torsional energy, stiffness, and maximal stress did not demonstrate statistically significant differences between the two groups. These data clearly show that despite the reduced size and bone growth, DMNL rats responded normally to the mechanical challenges applied to test bone biomechanical properties. The data, therefore, add to previous evidence and strengthen the hypothesis that DMNL rats are governed by an "organismic" set point.

The dorsomedial hypothalamic nucleus revisited: 1998 update

This article reviews data that have accumulated since the early 1970s on the role of the dorsomedial hypothalamic nucleus (DMN) in neuroendocrine and autonomic homeostasis. Both the ventromedial hypothalamic nucleus (VMN) and the lateral hypothalamic area (LHA) project to the DMN, which in turn projects to the paraventricular nucleus of the hypothalamus (PVN), thus placing the DMN at an important nodal point of neuroendocrine/autonomic circuitries. The DMN is composed of cells and fibers containing neuropeptide Y (NPY), and the nutritional status (starvation-refeeding) is reflected in NPY levels of both VMN and DMN in Sprague-Dawley, Zucker (fa/fa), and corpulent rats (cp/cp JCR:LA). The DMN is involved in the final common pathway of corticotrophin-releasing hormone (CRH) secretion by the PVN, sympathetic nervous system outflow to the adrenal gland, and brown adipose tissue (BAT) thermogenesis. The DMN is also part of a "fear circuitry" regulating cardiovascular responses to stress such as myocardial blood flow and the tachycardia associated with the defense reaction. This appears to be mediated by a gamma amino butyric acid (GABA) mechanism. Although exhibiting reduced ponderal and linear growth and hypophagia and hypodipsia, the rat with DMN lesions (DMNL rat) has normal body composition, anabolic hormone levels, and intermediary metabolism, and it responds normally to numerous endocrine, nutritional, intra- and extracellular thirst and body weight-regulatory challenges. The DMNL rat shows normal efficiency of food utilization, but shows an attenuated response to the feeding-stimulatory effect of insulin. The only other lesion-induced abnormalities are hyperprolactinemia and a disrupted circadian corticosterone rhythm. The hyperprolactinemia in DMNL rats appears to be related to an attenuation of dopamine (DA). Rats with DMNL are capable of mating and can bear offspring, but there is a dramatic effect on litter size and other litter parameters that only improves when one parent is a DMNL rat. Antiaging effects produced by DMNL are evident in the prevention of age-associated microalbuminuria and kidney lesions, as well as, in prevention of the age-related decline in circulating insulin-like growth factor I (IGF-I). Recent evidence suggests that DMN, together with the VMN and the arcuate nucleus (ARC) of the hypothalamus, may be part of the circuitry that is responsive to the feedback signal from adipose tissue by the hormone leptin. The above findings and others suggest that the DMN plays a diverse role in physiological regulatory processes.

Increased plasma IGF-1 levels but lack of changes in adipocyte glucose transport in weanling rats with dorsomedial hypothalamic nucleus lesions 1 year after lesion production

Experimental destruction of the dorsomedial hypothalamic nuclei (DMN) in weanling rats exerts an antiaging effect by preventing microalbuminuria and kidney lesions both 1 month and 1 year after lesion production. In the present study we report further on antiaging effects of DMN lesions (DMNL) by measuring glucose transport into adipocytes and plasma levels of insulin-like growth factors 1 and 2 (IGF-I, IGF-II). Male and female weanling Sprague-Dawley rats received bilateral electrolytic lesions in the DMN; sham-operated animals served as controls (SCON). The rats were maintained for 1 year and food intake was measured 3 weeks after surgery and 3 weeks prior to sacrifice. As expected, DMNL resulted in profound reductions of body weight and food intake, with male DMNL rats showing higher body weights and body weight gains than their female counterparts. The same was true of the respective SCON. In male DMNL rats, carcass fat in absolute terms was significantly reduced vs. SCON, but it was comparable among all groups when expressed in percent. Lean body mass (LBM), although significantly reduced in absolute terms in DMNL rats vs. SCON, was, however, significantly higher in male DMNL vs. SCON when expressed in percent, but not in females. LBM laid down per food energy taken in was higher in DMNL rats of both sexes than in their respective SCON. Efficiency of food utilization was normal in male DMNL vs. male SCON but was higher in female DMNL vs. SCON. Both male and female DMNL rats had significantly higher plasma IGF-1 concentrations than their respective SCON, and male DMNL rats had higher values than female DMNL rats. Plasma concentrations of IGF-II were significantly higher in DMNL vs. SCON, but only in females. Under both basal and insulin-stimulated conditions, DMNL rats had normal 3-0-methylglucose flux in adipocytes from epididymal fat pads vs. SCON. However, DMNL and SCON responded similarly to the stimulating effect of insulin. Although one-year-old rats may not be considered "aged", we do consider the observed lack of a drop in plasma IGF-I levels that occurs with aging as an "anti-aging" effect of DMN lesions.

Aging and the hypothalamus: research perspectives

There are several hypothalamic theories of aging, none of which has been validated. An approach to validation is to search for consequences of anatomic ablations of hypothalamic regions that are functional hallmarks of aging, or consequences of ablation that postpone the appearance of hallmarks of aging or extend longevity. Ablation of the hypothalamic ventromedial nucleus (VMN) in the weanling rat is associated with subsequent increased body fat, glucose intolerance, hyperlipidemia, and decreased renal function. Each of these consequences is characteristic of aging in humans and in several animal models of aging. Ablation of the hypothalamic dorsomedial nucleus (DMN) in the weanling rat leads to a symmetrically smaller animal with normal glucose and lipid metabolism, decreased body fat for size, and reduced risk of decreased renal function and circulating IGF-I levels. These are findings consistent with calorie restriction models in rodents that significantly extend life span. This review compares outcomes of lesions in the VMN, DMN, and lateral hypothalamic area (LHA) for relevance to aging. To establish a relationship between these anatomic areas of the hypothalamus and aging, it is concluded that the VMN, DMN, and LHA lesions should be examined for impact on longevity and compared with data obtained from simultaneously studied intact ad-lib-fed and 40% calorie-restricted animals. Lesioned animals also should be rigorously studied for neurotransmitters (e.g., neuropeptide Y, beta-endorphin, serotonin, corticotropin-releasing factor, and galanin), and for behavioral changes consistent with aging, for accumulation of specific tissue lipofuscin and amyloid that are associated with normal aging and for other age-dependent findings, such as incidence of tumors and cataract.

The lateral hypothalamic area revisited: ingestive behavior

This article discusses the role of the lateral hypothalamic area (LHA) in feeding and drinking and draws on data obtained from lesion and stimulation studies and neurochemical and electrophysiological manipulations of the area. The LHA is involved in catecholaminergic and serotonergic feeding systems and plays a role in circadian feeding, sex differences in feeding and spontaneous activity. This article discusses the LHA regarding dietary self-selection, responses to high-protein diets, amino acid imbalances, liquid and cafeteria diets, placentophagia, "stress eating," finickiness, diet texture, consistency and taste, aversion learning, olfaction and the effects of post-operative period manipulations by hormonal and other means. Glucose-sensitive neurons have been identified in the LHA and their manipulation by insulin and 2-deoxy-D-glucose is discussed. The effects on feeding of numerous transmitters, hormones and appetite depressants are described, as is the role of the LHA in salivation, lacrimation, gastric motility and secretion, and sensorimotor deficits. The LHA is also illuminated as regards temperature and feeding, circumventricular organs and thirst and electrolyte dynamics. A discussion of its role in the ischymetric hypothesis as an integrative Gestalt concept concludes the review.

In vitro [U-14C]glucose utilization by tissues of weanling rats with lateral hypothalamic area lesions one month after lesion production

The role of the lateral hypothalamic area (LHA) in intermediary metabolism was investigated by quantitation of [U-14C]glucose oxidation to 14CO2 and 14C incorporation into the glycogen and lipid fraction of the liver, epididymal fat pad, and diaphragm. Weanling male Sprague-Dawley rats received bilateral electrolytic lesions in the LHA (LHAL rats). Sham operated rats were either fed ad libitum (CON-ADLIB) or pair-gained to the LHAL rats (CON-PG). The experiment was terminated 1 month after lesion production. LHAL rats were significantly (SIG) lighter and shorter and ate less than CON-ADLIB; LHAL rats were also SIG shorter than CON-PG, pointing to a food intake-independent lesion effect. Both LHAL and CON-PG rats had SIG less percent carcass fat than CON-ADLIB, but there was no SIG difference between LHAL and CON-PG rats. Also, LHAL rats had a SIG higher percentage of carcass protein than both CON-ADLIB and CON-PG. Furthermore, LHAL rats incorporated SIG less glucose into liver glycogen than CON-ADLIB but SIG more into CON-PG, whereas CON-PG rats incorporated SIG less into liver glycogen than CON-ADLIB, again suggesting a food intake-independent effect. There was no difference among the groups in glucose oxidation and incorporation into lipids and glycogen in both diaphragm and epididymal fat pads and liver total lipid. However, livers of CON-PG metabolized SIG more [U-14C]glucose to CO2 than did livers of CON-ADLIB, suggesting a food intake-dependent effect. There was no difference between LHAL and CON-PG rats in this parameter.(ABSTRACT TRUNCATED AT 250 WORDS)

Somatic parameters, organ growth, and plasma substrates in weanling rats with lateral hypothalamic lesions one month postoperatively

Somatic and some metabolic aspects of the syndrome that follows bilateral destruction of the lateral hypothalamic area (LHA) have been studied primarily in mature rats. Fewer data are available for the weanling rat. Weanling Sprague-Dawley rats received small (10 mC) bilateral electrolytic lesions (LHAL). Sham-operated controls were pair-gained to LHAL rats (CON-PG) or fed ad lib (CON-ADLIB). All rats were killed 1 month after LHAL. Both LHAL and CON-PG weighed less, had less carcass fat, and were shorter than CON-ADLIB. Also, LHAL were somewhat, but significantly (SIGN), shorter than CON-PG. Rats with LHAL has less carcass protein than CON-ADLIB in percent but not in absolute terms. Liver, epididymal fat pads, diaphragm, kidneys adrenals, testes, spleen, and heart grew SIGN smaller in LHAL vs. CON-ADLIB, but in no instance was there a SIGN difference between LHAL and CON-PG. In body weight percentage, some of these differences (liver, kidneys, heart) were not SIGN. Both LHAL and CON-PG had larger adrenals than CON-ADLIB and both LHAL and CON-PG had SIGN less protein in their livers, epididymal fat pads, and diaphragm than CON-ADLIB. In organ weight percentage, however, LHAL rats had more protein in their livers and fat pads than CON-ADLIB and LHAL rats had less protein in fat pads than CON-PG in absolute but not in percent organ weight terms. Plasma glucose was similar in all groups, but LHAL had SIGN lower triglycerides and total cholesterol than CON-ADLIB.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential response of glucose utilization by three rat muscle tissues to dietary fatty acid composition

Rats were fed a semisynthetic diet containing 14% of either beef fat, safflower oil, or menhaden oil plus 2% corn oil for 7 weeks, and three tissues, diaphragm, heart, and skeletal muscle, were examined for fatty acid composition in their phospholipids and triglycerides. In addition, the lipid concentrations in these tissues were examined. The in vitro oxidation and incorporation of glucose into lipids of these tissues were also examined. Skeletal muscle showed the greatest change in phospholipid composition with diet. All tissues were responsive to changes in diet in regards to the triglyceride fraction. Dietary alteration of tissue phospholipid composition did not alter lipid concentration in these tissues. However, in diaphragm tissue, rats fed the beef fat diet had lower phospholipid and higher triglyceride synthesis compared with those fed either menhaden oil or safflower oil. In addition, triglyceride synthesis was higher in the diaphragm of animals fed the menhaden oil diet as compared with the safflower oil diet. Therefore, dietary fatty acid composition may play a role in the triglyceride and phospholipid metabolism of rat diaphragm.

Hormone and somatic changes in rats pair-fed to growth retarded dorsomedial hypothalamic nuclei-lesioned rats

Rats with dorsomedial hypothalamic nuclei lesions (DMNL) are hypophagic and have reduced linear and ponderal growth, but have normal body composition and anabolic hormone concentrations. Previous studies have shown rats pair-fed to levels consumed (70-80% of ad lib) by DMNL rats, using a meal-feeding paradigm, have abnormal body composition and hormone concentrations. Whether the noted changes were due to restriction per se or method of food presentation was uncertain. In the present study, one group of sham-operated rats was pair fed (SHPF) by a computer-operated system that presented 45 mg food pellets in the exact amount and pattern as their DMNL yoked partner; another sham-operated group was ad lib fed (SHAD). At the end of Experiment 1 (11 days) and Experiment 2 (3 weeks) blood was collected for hormone and metabolite analyses; body compositions were also determined. Unlike an earlier report, the DMNL and SHPF groups had normal percentage body fat. Percentage carcass protein was similar in all groups at 11 days, but slightly elevated in DMNL rats at 3 weeks. Also, in contrast to an earlier study, plasma-free fatty acid levels were comparable in DMNL and SHPF rats. Plasma insulin was normal in the DMNL and SHPF rats at 11 days, but was lowered (p < 0.05) in the SHPF group at 3 weeks. Plasma thyroxine was reduced (p < 0.01) in the SHPF group at 11 days but returned to normal by 3 weeks. Thyroxine and triiodothyronine levels were normal in the DMNL groups. Plasma corticosterone levels were similar in all groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of aging, diet, and sex on plasma glucose, fructosamine, and lipid concentrations in barrier-raised Fischer 344 rats

We studied the relationships of plasma glucose, fructosamine, triglycerides, and cholesterol as a function of age, gender, and diet in barrier-raised Fischer 344 rats aged 5 to 26 months, fed a diet either ad libitum or restricted to 60% of the ad libitum caloric intake. The complex relationships of these plasma levels to age, gender, and diet led to the development of a model with age, diet, and sex as covariates. Overall, fasting plasma glucose concentrations were reduced by approximately 25% in rats on the restricted diet, compared to ad libitum-fed animals. There was a significant age-dependent decline in glucose levels in male animals, whereas in females there was an increase in plasma glucose with aging. Plasma fructosamine levels in calorie-restricted animals, overall, were reduced by 7% compared to levels in animals fed ad libitum. There was a significant positive correlation between plasma glucose and fructosamine levels. Mean plasma triglyceride content was decreased by 50% in calorie-restricted rats compared to ad libitum-fed animals. A significant decrease in triglyceride levels with increasing age was seen in male animals, and an increase with aging in females. There was a significant positive correlation between plasma glucose and triglyceride levels. Plasma cholesterol levels in calorie-restricted animals were reduced by 7% compared to levels in ad libitum-fed animals. An increase of cholesterol concentration with aging was significant in both males and females. Analysis of the data showed that there were significant differences between male and female Fischer 344 rats in the response of plasma glucose and fructosamine to aging and calorie restriction. Changes of plasma triglyceride and cholesterol with aging and dietary calorie restriction were also different in males and females. Studies of the effect of aging on glycemia and blood lipid content should take into account the contributions of animal sex.

The effect of dorsomedial hypothalamic nucleus lesions on kidney function and structure after 1 and 12 months

According to the Dillman theory (17), aging results from a deterioration of metabolism that begins with an elevation of hypothalamic receptor thresholds for feedback signals from the periphery. Three hypothalamic areas are known to contain such receptors: the ventromedial and dorsomedial hypothalamic nuclei (DMN) and the lateral hypothalamic area. We have hypothesized that selective destruction of those hypothalamic areas might be followed by physiological changes associated with aging. Electrolytic bilateral DMN lesions were produced in male and female weanling rats. These rats were maintained for up to 13 months of age. Sham-operated rats served as controls. Food intake and body weight were monitored postoperatively and prior to sacrifice. Before sacrifice, tail blood and a 24-h urine samples were obtained. In accordance with previous findings, rats with DMN lesions showed dramatic reductions of ponderal growth and food intake but had normal body composition. Total protein and albumin excretion rates were significantly lower in rats with lesions. The fractional contribution of albumin to total urinary protein was also decreased in rats with lesions. Histological examination of the kidneys showed significantly less pathology in the kidneys of rats with DMN lesions; the severity of renal pathology was correlated directly with proteinuria. These changes were seen as early as 1 month after production of the lesion. The attenuation of age-related changes in kidney functions and structure in rats with lesions could be due to reduced food intake (dietary restriction is known to produce similar results), and/or a direct effect of the lesion.(ABSTRACT TRUNCATED AT 250 WORDS)

The lateral hypothalamic area revisited: neuroanatomy, body weight regulation, neuroendocrinology and metabolism

This article reviews findings that have accumulated since the original description of the syndrome that follows destruction of the lateral hypothalamic area (LHA). These data comprise the areas of neuroanatomy, body weight regulation, neuroendocrinology, neurochemistry, and intermediary metabolism. Neurons in the LHA are the largest in the hypothalamus, and are topographically well organized. The LHA belongs to the parasympathetic area of the hypothalamus, and connects with all major parts of the brain and the major hypothalamic nuclei. Rats with LHA lesions regulate their body weight set point in a primary manner and not because of destruction of a "feeding center". The lower body weight is not due to finickiness. In the early stages of the syndrome, catabolism and running activity are enhanced, and so is the activity of the sympathetic nervous system (SNS) as shown by increased norepinephrine excretion that normalizes one mo later. The LHA plays a role in the feedback control of body weight regulation different from ventromedial (VMN) and dorsomedial (DMN). Tissue preparations from the LHA promote glucose utilization and insulin release. Although it does not belong to the classical hypothysiotropic area of the hypothalamus, the LHA does affect neuroendocrine secretions. No plasma data on growth hormone are available following electrolytic lesions LHA but electrical stimulation fails to elicit GH secretion. Nevertheless, antiserum raised against the 1-37 fragment of human GHRF stains numerous perikarya in the dorsolateral LHA. The plasma circadian corticosterone rhythm is disrupted in LHA lesioned rats, but this is unlikely due to destruction of intrinsic oscillators. Stimulation studies show a profound role of the LHA in glucose metabolism (glycolysis, glycogenesis, gluconeogenesis), this mechanism being cholinergic. Its role in lipolysis appears not to be critical. In general, stimulation of the VMN elicits opposite effects. Lesion studies in rats show altered in vitro glucose carbon incorporation into several tissue fractions both a few days, and one mo after lesion production. Several of these changes may be due to the reduced food intake, others appear to be due to a "true" lesion effect.

Hypophagic rats with dorsomedial hypothalamic lesions produce lighter and smaller pups with a lower survival rate at weaning than offspring of sham-operated controls

Weanling and mature rats with dorsomedial hypothalamic nucleus lesions (DMNL rats) show reduced ponderal and linear growth and hypophagia and hypodipsia in the presence of normal body composition and anabolic hormone levels. The present study was conducted to assess their reproductive/parenting capacity and some offspring parameters. Four groups were used: DMNL mothers and fathers, DMNL mothers and control (SCON) fathers, SCON mothers and DMNL fathers, and SCON mothers and SCON fathers. The constituent rats of each group were bred to yield between 14 and 22 litters. The smallest litter size, litter weight, mean pup weight, percent of live-born and percent of weaned pups and greatest percentage of still-born pups were recorded when both parents were DMNL rats. The latter parents also cannibalized the majority of litters. The above parameters improved when only one parent was a DMNL rat, but this was still significantly below the offspring of SCON x SCON parents. The DMN is not part of the classical hypophysiotropic area (HTA), but earlier findings indicate hyperprolactinemia in DMNL rats. Therefore, the lesion-induced hypophagia during gestation and the postpartum neuroendocrine profile of the DMNL mothers may be the cause of the observed litter deficiencies and poor survival.

Calorie restriction decreases microalbuminuria associated with aging in barrier-raised Fischer 344 rats

Renal function as a sensitive biomarker of aging has been studied in specific pathogen-free (SPF) Fischer 344 rats (n = 211), and results are presented according to animal age (5, 8, 12, 18, 24 mo), sex, and diet (ad libitum vs. 40% calorie restriction). Plasma creatinine concentration, endogenous creatinine clearance, total protein excretion, and albumin excretion were measured. Kidney histology was evaluated by light microscopy. In both calorie-restricted and ad libitum-fed animals, kidney weight (KW) and body weight (BW) showed parallel changes with age. The KW-to-BW ratio was unaffected by age in all groups. There was no alteration in plasma creatinine concentration as a function of age or diet. In these SPF animals there was also no change in glomerular filtration rate with age. In animals fed ad libitum, albumin and protein excretion increased with age (females: 0.39 +/- 0.05 at 5 mo vs. 7.4 +/- 2.6 mg protein.24 h-1.g KW-1 at 24 mo; males: 4.1 +/- 0.6 at 5 mo vs. 15 +/- 3 mg protein.24 h-1.g KW-1 at 24 mo). The higher protein excretion rate in all males at 5 mo reflected the excretion of sex-dependent low-molecular-weight proteins that commenced with sexual maturation. Calorie restriction prevented the age-dependent increase in total protein excretion. Kidney histopathology was positively correlated with total protein and albumin excretion. Microalbuminuria preceded the development of lesions detectable by light microscopy. These observations support the concept that microalbuminuria in this model is a sensitive and early biomarker of nephropathy that can be monitored easily and noninvasively.

Metabolic and neuroendocrine indices one month after lateral hypothalamic area lesions

Mature male rats received bilateral electrolytic lateral hypothalamic area lesions (LHAL) or were sham-operated fed ad lib (CON-ADLIB) or sham-operated pair-fed/gained (CON-PF) to LHAL rats. One month later all rats were sacrificed. Rats with LHAL were hypophagic and had reduced body carcass fat, testes, livers, epididymal fat pads (PADS), diaphragms (DIA), and body weight compared to CON-ADLIB. In the liver, LHAL rats incorporated more C14-U-glucose carbon (GLUCINC) into lipid and glycogen than both CON groups, but GLUCINC was similar among CON groups. In PADS, LHAL rats oxidized more glucose carbon (GLUCOX) than CON-ADLIB but less than CON-PF/PG. The latter showed greater GLUCOX than CON-ADLIB. In DIA, LHAL and CON-PF/PG showed reduced GLUCINC into glycogen vs. CON-ADLIB. Plasma glucose was similar among groups, but insulin was lower in LHAL and CON-ADLIB than in CON-PF/PG. Rats with LHAL had lower plasma T3 concentrations than CON-ADLIB, but similar T3 levels compared to CON-PF/PG. Several of the metabolic changes in LHAL rats could be due to hypophagia; however, four out of nine metabolic indices, glucose carbon incorporation into liver lipid and glycogen and epididymal fat pad lipid and oxidation, were significantly different from CON-PF/PG, i.e., they were independent of food intake. Possibly then, they are due to a lesion effect other than on feeding mechanisms. Some aspects of metabolism that were previously found to be altered 48 h after LHAL were recovered, whereas others apparently were not.

Effects of caloric restriction and aging on erythrocyte membrane Ca(2+)-ATPase activity in specific pathogen-free Fischer 344 rats

Dietary caloric restriction extends life span in the Fischer 344 rat. The interaction of aging and caloric restriction was examined at the level of the plasma membrane transport-associated enzymes, Ca(2+)-adenosine triphosphatase (ATPase) and Na,K-ATPase, in the Fischer rat. Animals were in four age groups, ranging from 6.1 to 25.0 months, and were specific pathogen-free (SPF, barrier-raised). Results from male and female animals raised on an ad libitum diet were compared with those from rats that received 60% of the age-specific caloric intake of their ad lib littermates. The responses of erythrocyte membrane Ca(2+)-ATPase activity in vitro to thyroid hormone (L-thyroxine [T4]; 3,5,3'-triiodothyronine [T3]) and to purified calmodulin, a Ca(2+)-binding protein activator of Ca(2+)-ATPase, were measured. Erythrocyte membrane Na,K-ATPase was also compared in the two diet groups, as was plasma glucose. Plasma membrane Ca(2+)-ATPase activity in the absence of added thyroid hormone and calmodulin was significantly reduced in calorically restricted rats (-39%, P less than .001), compared with ad lib-fed animals, and the response was similar in the four age groups aged 6.1, 12.7, 17.0, and 25.0 months. In contrast, pooled (all ages) Ca(2+)-ATPase response in vitro to T4 and to T3 in calorically restricted animals was enhanced compared with the ad lib group (+62% and +58%, P less than .001, respectively). Calmodulin responsiveness of the enzyme was increased by 45% (P less than .001) in calorie-deprived animals, similar to the change in T4 and T3 responsiveness.(ABSTRACT TRUNCATED AT 250 WORDS)

Brown (BAT) and white (WAT) adipose tissue in high-fat junk food (HFJF) and chow-fed rats with dorsomedial hypothalamic lesions (DMNL rats)

Male weanling rats received dorsomedial hypothalamic nucleus lesions (DMNL) or sham operations and were fed for 173 postoperative days a high-fat diet and given a 32% sucrose solution as drinking fluid. This was supplemented with chocolate chip cookies, potato chips and marshmallows. Other DMNL and sham-operated controls were fed lab chow instead of the above high-fat junk food diet (HFJF) and given tap water instead of 32% sucrose solution. All animals were killed on postoperative day 174. Caloric intake per 100 g body weight was similar in all groups; however, the HFJF fed control and DMNL rats had significantly elevated carcass fat. Since HFJF-DMNL rats were not nearly as obese as the HFJF control animals, it appears that the DMNL offered some protection against the HFJF-diet-produced obesity. When their smaller body size is considered. DMN lesions had no effect on brown adipose tissue (BAT) mass in chow-fed or HFJF fed rats, whereas BAT size was significantly enlarged in HFJF-fed control animals. This suggests but does not prove that HFJF-fed controls, but not DMNL rats, may be using dietary-induced thermogenesis (DIT) to attenuate their obesity. We hypothesize that the HFJF-fed DMNL may not be enhancing DIT as reflected in normal BAT size, because they had not attained a degree of fatness to activate this system, or the DMN lesions impaired its activation. Both HFJF-fed groups showed reduced linear growth compared to their counterparts. The reason for stunting is uncertain, but may be related to their low plasma insulin concentrations.

Somatic, endocrine and metabolic changes in controls pair-fed for six weeks to rats with dorsomedial hypothalamic nucleus lesions (DMNL rats)

One group of weanling male Sprague-Dawley rats received lesions in the dorsomedial hypothalamic nuclei (DMNL rats), whereas two additional groups of rats were sham-operated (CON). One of these CON groups was allowed to feed ad lib (CON-ADLIB) while the other CON group was pair-fed for 6 weeks to the DMNL rats (CON-PF). Despite eating the same amount of food as DMNL rats. CON-PF animals had consistently lower body weights and also utilized food energy more poorly than DMNL rats. The CON-PF group also had smaller kidneys and less percent liver protein but more epididymal fat pad percent protein than DMNL rats. Whereas plasma glucose concentrations were comparable among the three groups, insulin levels were significantly higher, and free fatty acid levels lower in CON-PF than in DMNL rats. The CON-PF group incorporated less glucose-U-C14 carbon into liver glycogen but more of the tracer into liver lipid than the DMNL group. Glucose carbon was also incorporated more avidly into epididymal fat pad lipid by CON-PF than by DMNL rats. The data not only confirm previous findings in DMNL rats but in addition show that the neurologically intact rats fed the same amount of food that is eaten spontaneously by DMNL rats show somatic and metabolic alterations that suggest that they cannot cope with this low amount of substrate. The normalcy of the DMNL rats, compared to ad lib-fed sham-operated controls, in all metabolic parameters suggests that the low food intake is indeed "normal" for this preparation and may be the reflection of an "organismic" set point.

Metabolic-endocrine correlates of the lateral hypothalamic syndrome: the first 48 hours

Mature (224 g) male Sprague-Dawley rats received bilateral electrolytic (1 mA for 8 sec) lesions in the lateral hypothalamic area (LHAL) or sham operations (CON). One group of CON was allowed to eat ad lib (CON-ADLIB), a second CON group was pair-fed to the LHAL rats (CON-PF). Tap water was available ad lib. Two days after the operation/sham operation all rats were killed by decapitation. Body weight, body weight change, food intake, carcass fat, liver weight, epididymal fat pad weight, in vitro incorporation of U-C14-glucose into liver total lipid, glycogen and CO2 (oxidation) (DPM, DPM/mg protein) as well as oxidation in fat pad tissue, plasma glucose and insulin were significantly reduced in LHAL and CON-PF rats compared with CON-ADLIB. Glucose carbon incorporation into epididymal fat pad lipid and glycogen were normal in LHAL and CON-PF. Liver protein and plasma free fatty acids (FFA) were both higher in LHAL and CON-PF than in CON-ADLIB groups. Thus, many of the somatic and metabolic changes that appear in the first few days after lesion production are simply due to hypophagia. However, CON-PF rats also exhibited some significant differences from the LHAL group, i.e., their plasma glucose and incorporation of glucose carbon into liver glycogen (DPM) were significantly lower than in LHAL rats; alternatively, plasma FFA levels were higher in CON-PF than in LHAL rats. Also, liver weight/100 g body weight was lower and fat pad weight/100 g body weight was higher in CON-PF than in LHAL rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Failure to demonstrate an effect of dietary fatty acid composition on body weight, body composition and parameters of lipid metabolism in mature rats

The objectives of the present study were to examine the effects of dietary fatty acid composition on body composition and on several parameters of lipid metabolism in adipose tissue and to assess the ease of weight loss with restricted dietary intake. Rats were fed diets containing 14% fish oil, safflower oil or beef fat plus 2% corn oil. These diets were fed ad libitum for 4 wk (first phase). A number of the animals from each group were killed, and the others were fed 50% of their first-phase food intake for an additional 4 wk (second phase). The diets used in the second phase contained 3% of the above fats plus 2% corn oil. Food consumption, food efficiency and body weights were monitored. After the rats were killed, fatty acid composition of epididymal fat pads was examined. In addition, in vivo lipolysis and in vitro lipogenesis in epididymal fat pads were examined. The results indicate that dietary fatty acid composition had no effect on body weight, food consumption, in vivo lipolysis and in vitro lipogenesis in epididymal fat pads. In addition, although dietary fatty acid manipulation resulted in alteration in adipose tissue fatty acid composition, it had no effect on the rate of weight loss, body composition, in vivo lipolysis and in vitro lipogenesis in epididymal fat pads. It is concluded that dietary fatty acid composition does not play a role in body composition and in lipid metabolism in adipose tissue of mature rats.

Normal catch-up growth in rats severely food-restricted prior to lesions of the dorsomedial hypothalamic nucleus: the first 48 hours

Following a brief period of ad lib (AL) feeding, 45-day-old male Sprague-Dawley rats were either fed AL or food-restricted (REST) for 21 days to 50% of the intake of the AL rats. At this time, some AL and some REST rats received electrolytic lesions in the dorsomedial hypothalamic nuclei (DMNL), whereas other AL and REST rats were sham-operated (CON). Following this, all rats were refed (REF) AL and killed two days later. At this time, DMNL-REST + REF and DMNL-AL weighed as much as CON-REST + REF and CON-AL, whereas the body weight of the DMNL-AL group began to separate from the CON-AL group; carcass lipid and protein were normal among the groups. DMNL-AL laid down more % lipid and % protein/g food eaten than CON-AL; this was not the case in the REST + REF groups. DMNL-AL were hypophagic vs. CON-AL, but DMNL-REST + REF ate as much as CON-REST + REF. Compared to DMNL-AL, DMNL-REST + REF increased their food intake more than four-fold and also utilized food energy more efficiently than DMNL-AL rats. Epididymal fat pads and kidneys were smaller in REST + REF vs. AL groups, irrespective of brain manipulation. Plasma glucose and growth hormone were normal among the groups, but plasma insulin concentrations were higher in REST + REF DMNL and CON groups vs. DMNL-AL and CON-AL, respectively. Glucose incorporation into epididymal fat pad lipid and CO2 and liver lipid was elevated in REST-REF groups vs. respective AL groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Recovery of rats with dorsomedial hypothalamic nucleus lesions (DMNL rats) from body weight restriction: effect of duration of postoperative prerestriction period

The present study was performed to see whether somatic and underlying metabolic-adaptive responses of DMNL rats and sham-operated controls (CON) to body weight restriction and subsequent refeeding could be influenced by the duration of ad lib feeding between lesion production and start of restriction. In contrast to previous studies (42 and 55 days, respectively) this time was reduced to 25 days. Restriction was similar, i.e., 27 days. DMNL rats show the same adaptive capacity in most parameters as do restricted CON. However, this response was at a lower level of absolute body weight, appropriate, so it appears, for their DMNL-induced lower body weight. In some parameters different responses were noted, however, suggesting that the time of ad lib feeding following the DMNL does indeed affect adaptive responses. Notably, this is the case in both DMNL and CON commensurately. Linear growth was reduced by restriction in the present but not in the two previous studies. Food intake showed a pronounced "overshoot" on refeeding but did not previously. Efficiency of food utilization was normal in the present study but depressed previously. A rise in plasma free fatty acids was not evident but was so in previous experiments. We concluded that, although DMNL rats respond to food restriction and recovery like similarly-treated CON, the duration of the ad lib feeding before restriction and/or the absolute age of the animals at that time, do indeed affect some parameters. This may be related to the fact that different aspects of the DMNL syndrome declare themselves in a sequential rather than a simultaneous manner.

Further evidence for the existence of an "organismic" set point in rats with dorsomedial hypothalamic nucleus lesions (DMNL rats): normal catch-up growth

The present study was performed to assess the capacity of rats with dorsomedial hypothalamic nucleus lesions (DMNL rats) and sham-operated controls (CON) for catch-up growth following body weight (b.wt.) reduction prior to DMNL (and sham-lesion) production. Male SD rats (45 days, 157 +/- 1.3 g) were maintained for 11 days ad lib (ADLIB) after arrival and then divided into two groups. One group continued to feed ADLIB, the other group was fed half of the ration eaten by ADLIB rats for 32 days. At this point each group was divided into two subgroups. One subgroup received DMNL, the other subgroup consisted of CON. From then on all rats were fed ADLIB [except for one group of CON that was pair-fed to the ADLIB DMNL rats (PF-CON)] for 37 days (69th day of experiment) and then killed. DMNL rats lesioned at normal b.wt. (ADLIB DMNL) showed a precipitous drop in food intake, b.wt. and efficiency of food utilization (EFU). In striking contrast, rats that had received DMNL after b.wt. restriction (REST DMNL) and were then refed ADLIB showed a dramatic rise in food intake, b.wt., change in b.wt. and EFU, the latter being almost twice that of the ADLIB DMNL. Notably, the PF-CON weighed less than the ADLIB CON and utilized food poorer than ADLIB CON, REST CON and ADLIB DMNL. Liver weight (both absolute and relative (per kg 3/4 b.wt.) was reduced in DMNL irrespective of dietary treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Pair-feeding of sham-operated controls to rats with dorsomedial hypothalamic lesions: new evidence for an 'organismic' set point

Weanling male Sprague-Dawley rats received electrolytic lesions in the dorsomedial hypothalamic nuclei (DMNL rats) and sham operations, respectively, and were maintained on lab chow ad libitum for 23 days (Expt. 1) and 55 days (Expt. 2). Following this period, one group of sham-operated controls was pair-fed to the DMNL rats, which were hypophagic compared to a second sham-operated group that was fed ad libitum. This period lasted 27 days (Expt. 1) and 24 days (Expt. 2). Although pair-fed controls were heavier than DMNL rats, they showed normal food utilization (EFU) in Expt. 1 and reduced EFU in Expt. 2. Pair-fed controls also had decreased carcass fat, hypoglycemia, hypoinsulinemia, hypotriglyceridemia and enhanced in vitro epididymal fat pad glucose oxidation when compared to DMNL rats. These data suggest that pair-fed controls cannot cope as efficiently with the reduced influx of substrate as do DMNL rats. Evidently, the reduced amount of food that DMNL rats spontaneously eat is adequate for their reduced body size, whereas this is not the case in the pair-fed controls. This is taken as evidence for a harmonious readjustment by DMN lesions of both body size and food intake and the underlying homeostatic processes and supports our concept of an 'organismic' set point that has been released by the DMN lesions.

Failure to demonstrate disruption of ultradian growth hormone rhythm and insulin secretion by dorsomedial hypothalamic nucleus lesions that cause reduced body weight, linear growth and food intake

Weanling male rats received bilateral electrolytic lesions in the dorsomedial hypothalamic nuclei (DMNL rats); sham-operated animals served as controls. At the end of a 39-day postoperative period DMNL rats were lighter and shorter than controls and also exhibited significant hypophagia. Their efficiency of food utilization (weight gained for the amount of food eaten) was normal, however. Subsequent determination of plasma growth hormone (GH) and insulin (IRI) levels every 15 min for 6-h periods from freely moving chronically cannulated rats showed no differences in pulsatile patterns and peaks of GH nor in plasma IRI levels between DMNL rats and controls. There was also no significant difference between mean 6-H GH and IRI concentrations between the two groups. The reduced body weight, length and food intake are apparently unrelated to the normal GH and IRI secretory patterns. In conjunction with previous data indicating normal somatomedin activity and normal responses to various homeostatic challenges, the data make a strong case for the argument that DMNL rats are not "growth-retarded". Rather, they are normal animals that are "scaled-down" to a smaller size with maintenance of normal homeostatic capacity. This has been hypothesized to be due to the existence in these animals of an "organismic" set point.

Differential effect of common snack foods on caloric intake, growth and obesity in weanling male and female rats with hypothalamic obesity

In order to see whether weanling normophagic rats with hypothalamic obesity (VMNL rats) become hyperphagic and more obese than when fed lab chow, and to see in addition whether there is a possible sex difference in whatever response is found, male and female VMNL rats were fed lab chow for 14 days after lesion production and then, for the following 42 days, they received Hostess HoHos, potato chips, marshmallows and french fries in addition to lab chow. At termination, body weights were similar among the groups, but VMNL rats were fatter and shorter than controls. Also, female VMNL rats were fatter and shorter than male VMNL rats and layed down more fat per unit of food energy. Total caloric intake was greater in controls than in VMNL rats and in males than in females. However, the females showed a decrease in intake and the males an increase over time. Males ate more lab chow and french fries than females. Lab chow was the only food that VMNL rats ate more of than controls. The VMNL rats ate less french fries, HoHos and potato chips than controls, but similar amounts of marshmallows. There was no sex difference in macronutrient intake and per cent macronutrient intake. Moreover, controls ate as much carbohydrate and less per cent carbohydrate than VMNL rats, more fat than VMNL rats, but normal per cent fat and normal protein and per cent protein. Sex X lesion interactions indicated that female VMNL rats ate more per cent carbohydrate than female controls and male VMNL rats, ate more protein than male controls. The greater degree of obesity in the females despite the lower caloric intake may be due to enhanced food energy utilization. The data also show that weanling VMNL rats do not exhibit the great preference for palatable diets that have been reported for mature rats with ventromedial hypothalamic area lesions and that the only sex difference in intake is with french fries, which have neither the highest fat nor the highest carbohydrate content of the foods tested.

Body weight set point studies in weanling rats with dorsomedial hypothalamic lesions (DMNL rats)

In order to further characterize a previously postulated "organismic" set point, weanling DMNL and control (CON) rats were maintained on lab chow ad lib (AL) for 55 post-operative days. Subsequently, some DMNL and CON rats were food-restricted (REST) to 80% of the food intake of their AL-fed counterparts for 24 days. At this point, representative rats from each group were killed by decapitation and the remaining animals were re-fed AL and killed 7 and 22 days thereafter. At the end of REST, both DMNL and CON showed significant weight loss, which was greater in CON than in DMNL rats. After 7 days of refeeding, DMNL rats normalized their body weights but re-fed CON still weighed less than AL-fed CON 22 days after refeeding. Food intake in formerly REST groups overshot on refeeding for 7 days, but this was significant only in DMNL rats. Notably, during this time formerly REST-DMNL ate as much as AL-fed CON. Efficiency of food utilization was normal in DMNL during AL feeding and became reduced on REST as it did in REST-CON. Notably, on refeeding formerly REST-DMNL rats overshot that of AL-fed DMNL rats by the same magnitude as previously REST-CON overshot the values of AL-fed CON. After 22 days of refeeding, this overshoot was still evident in DMNL but not in CON. At the end of the REST period, plasma insulin and glucose were similar in AL-fed DMNL and AL-fed CON. They were significantly and comparably reduced in both REST-DMNL and REST-CON compared to the AL-fed DMNL and AL-fed CON. On refeeding these changes normalized within seven days. At the end of REST, plasma free fatty acid concentrations were higher in REST-DMNL and REST-CON than in AL-fed DMNL and AL-fed CON. After seven days of refeeding they normalized only in formerly REST-CON. Plasma glycerol and total protein were normal throughout all groups, as was carcass protein. Carcass fat was equivalently reduced in both DMNL and CON at the end of REST and normalized 7 days after refeeding. AL-DMNL had the same carcass fat as AL-CON and REST-DMNL had the same carcass fat as REST-CON. In conjunction with previously reported normal anabolic hormone levels the data suggest that DMNL rats are not growth-retarded but are merely scaled down in size without compromise of their homeostatic competence. We take this as strong evidence for the existence of an "organismic" set point.

Effect of palatable diet on growth, caloric intake and endocrine-metabolic profile in weanling rats with dorsomedial hypothalamic lesions

Weanling male Sprague-Dawley rats received bilateral electrolytic lesions in the dorsomedial hypothalamic nuclei (DMNL rats); sham-operated rats served as controls. All animals were fed lab chow for 15 postoperative days. At that time they were subdivided into two groups each. One DMNL and one control group continued to be fed lab chow until the termination of the experiment on postoperative day 116. A second DMNL and control group were fed a high-fat diet and 32% sucrose solution (HF/SS diet). All DMNL rats showed reduced body weight and linear growth, but the HF/SS diet depressed these parameters further below the levels of the chow-fed groups. Both DMNL and control rats fed HF/SS had more carcass fat, heavier epididymal fat pads, more carcass fat per calories eaten, higher plasma levels of glucose, glycerol and free fatty acids but lower insulin levels than chow-fed DMNL rats and controls. This occurred in the face of lower body weights and caloric intake. Neither growth hormone nor insulin showed lesion effects. Rats with DMNL exhibited the same inverse relationship between plasma insulin and free fatty acids as controls. The data indicate that DMNL rats respond to the HF/SS diet essentially like sham-operated controls, i.e., they develop dietary obesity. Although they do show some small deficits, their lipogenic capacity is actually significantly greater than that of HF/SS-diet fed controls.

Differential spontaneous and stimulated in vitro release of newly synthesized or stored rGH and rPRL by pituitaries from rats with hypothalamic lesions

These experiments were designed to examine which aspects of basal and responsive somatotroph and lactotroph synthesis and release behavior in vitro are functions of in vivo tonic hypothalamic environment. Although we cannot specifically define in vivo hypothalamic tone, we show that spontaneous rates of hormone synthesis and release in vitro, as well as release in response to a secretagogue, are influenced by altered in vivo hypothalamic tone. This work combines in vivo destruction of hypothalamic (ventromedial [VMN] or dorsomedial [DMN]) nuclei with in vitro double-label perifusion to track hormone synthesis and release of newly synthesized and stored hormone. We demonstrate that hormone synthesis rates are greater in DMN-lesioned (DMNL) or sham-operated (SHAM) animals than in VMN-lesioned (VMNL) animals and that DMNL and SHAM synthesis rates fall with time outside the hypothalamic environment. We show that basal release of newly synthesized rGH by DMNL tissue exceeds that of SHAM, while release from VMNL tissue is less than that of SHAM. Accidental placement of small bilateral lesions between and not impinging on either the DMN or VMN nuclei did not alter newly synthesized rGH release but accelerated newly synthesized rPRL release. Although basal fractional release of stored growth hormone and prolactin was the same for the three groups, potassium ion-induced release of stored hormone was similar in DMNL or SHAM tissue, but depressed in VMNL tissue. Thus, the creation of definable hypothalamic damage in a living animal produced specific modifications in in vitro pituitary synthetic/secretory behavior, presumably by reproducibly altering hypothalamic secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Meal patterns of rats with dorsomedial hypothalamic nuclei lesions or sham operations

Rats with bilateral dorsomedial hypothalamic electrolytic lesions (DMNL rats) are hypophagic, hypodipsic and have reduced linear and ponderal growth when compared to sham operated controls (SCON). Nevertheless, previous studies have shown that DMNL rats eat and drink adequate amounts for their size and have normal body composition. In the present study we investigated meal parameters: meal size, and frequency (both light and dark period), total intake and meal size per metabolic size (body weight 0.75). Compared to SCON, DMNL rats at twelve days post surgery weighed less, were shorter, but had a normal body composition as determined by the Lee Index, and were hypophagic (grams eaten/day). The animals were placed into individual, self-contained feeding modules and given powdered chow. After familiarization to the modules, meal parameters were recorded continuously by a computer for an eight day period. While dark phase meal frequency did not differ significantly between groups, the lesioned rats took more meals during the light period. Over the eight-day measurement period DMNL rats were hypophagic compared to SCON in absolute terms. However, when total intake and meal size were normalized to metabolic size, these two parameters did not differ significantly between groups. Upon refeeding, after a one-day fast, the initial meal size of the normally hypophagic DMNL rats exceeded that of SCON. Rats with DMNL have previously been shown to have deficits in some hypothesized short-term food intake control mechanism (e.g., cholecystokinin, glucose sensing). Thus overeating by the lesioned rats after a fast could possibly result from a specific short term control deficit.(ABSTRACT TRUNCATED AT 250 WORDS)

Failure to demonstrate early metabolic changes in weanling growth-retarded hypophagic rats with lesions in the dorsomedial hypothalamic nuclei

Experiment 1: Weanling male rats received bilateral electrolytic lesions in the dorsomedial hypothalamic nuclei (DMNL rats); sham-operated animals served as controls. Rats were killed four hours and three and seven days postoperatively (post-op). Plasma was obtained and epididymal fat pads, diaphragm and liver aliquots were harvested and the in vitro incorporation of U-14C-glucose into CO2, glycogen, lipid and saponifiable fatty acids (FAs) were measured. Body weight, carcass lipid and food intake were significantly lower in DMNL rats than in controls. The only significant lesion-induced metabolic changes were hypoglycemia and greater tracer incorporation into epididymal fat pad lipid and diaphragm glycogen. Both DMNL rats and controls showed similar time courses of tracer incorporation into epididymal CO2 and FAs, diaphragm lipid and liver CO2, glycogen, lipid and FAs. Lesioned rats also showed more pronounced decreases of tracer incorporation from day 0 to day 3 in epididymal glycogen and lipid and diaphragm CO2 and glycogen. These data make it appear unlikely that very early deficits in glucose metabolism are the cause of the growth retardation seen in long-term studies with DMNL rats. The data also demonstrate considerable locus specificity, since weanling rats with ventromedial hypothalamic lesions (VMNL rats) in similar short-term studies have shown dramatic alterations in the above parameters. Experiment 2: Weanling DMNL rats and sham-operated rats were injected via tail vein with tritiated water one hour post-op. One hour after the injection they were decapitated. There were no significant differences between DMNL rats and controls in mumoles tritiated water incorporated into total liver, grams liver tissue, mg liver glycogen and ml or mg plasma glucose.(ABSTRACT TRUNCATED AT 250 WORDS)

Ventromedial and dorsomedial hypothalamic syndromes in the weanling rat: is the "center" concept really outmoded?

This report juxtaposes findings from weanling rats with precise lesions in the ventromedial (VMNL rats) to data of weanling rats with lesions in the dorsomedial (DMNL) hypothalamic nuclei. Despite the proximity of the two nuclei their destruction produces opposite effects in most cases but similar responses in other parameters. Absolute and relative food intake are normal in VMNL rats yet they become obese in the face of normal body weight gains. DMNL rats show both reduced absolute food intake and body weight but normal relative food intake and body composition. Both VMNL and DMNL cause reduced linear growth and running wheel activity. DMNL rats defend their lower body weight set point against various challenges and maintain normal body composition. Organ growth in both absolute and relative terms is reduced in VMNL rats. In DMNL rats relative organ growth is normal. Pancreatic growth, protein/pancreas and content and concentrations of several pancreatic enzymes are normal in DMNL but reduced in VMNL rats. Mean 24-hour plasma growth hormone (GH) and corticosterone (B) levels are reduced and insulin levels are greatly elevated in VMNL rats; prolactin (PRL) levels are normal. In DMNL rats, GH, B, insulin and somatomedin activity are normal but PRL is elevated. Circadian rhythms of GH, insulin and triiodothyronine are normal in DMNL rats but B levels are disrupted, as they are in VMNL rats. Glucose incorporation and oxidation in adipose tissue of VMNL rats are enhanced in VMNL rats but normal in DMNL rats. Gluconeogenesis in VMNL rats is enhanced as early as 4 hours post-operatively; in DMNL rats it is normal at this time and several weeks thereafter. Basal lipolysis in epididymal fat pads is elevated in both VMNL and DMNL rats but epinephrine-stimulated lipolysis is elevated in VMNL and decreased in DMNL rats. Both VMNL and DMNL rats show normal basal and epinephrine-stimulated lipolysis in interscapular brown adipose tissue. Several hepatic enzymes are normal in DMNL and depressed in VMNL rats. The above data suggest that the DMN and its circuitry are part of an "organismic" set point system with a "true" body weight and no fat set point, as seems to be the case in the VMNL rat.

Plasma hormone levels in growth-retarded rats with dorsomedial hypothalamic lesions

Rats with lesions in the dorsomedial hypothalamic nuclei (DMNL rats) are hypophagic and growth-retarded. Since previous work had shown normal plasma growth hormone and insulin levels in DMNL rats we investigated the diurnal patterns of these and other hormones involved in growth. Trial 1: Rats received electrolytic DMNL or sham operations (SCON). The DMNL rats exhibited no differences from SCON rats in plasma triiodothyronine (T3), growth hormone (GH), insulin and somatomedin (SM) concentrations, Trial 2: kainic acid, a neurotoxin, was used for lesion production. Again, DMNL rats showed no deficiencies in plasma levels of T3, GH or insulin. Trial 3: In this experiment, diurnal hormone profiles were assessed. The GH profile and mean 24-hour secretion of both DMNL and SCON groups did not differ significantly. Both groups exhibited a diurnal release of T3, with the DMNL rats showing slightly higher levels. Plasma insulin rose after dark, i.e., at the onset of feeding, in SCON but not in DMNL rats; the later have a previously reported disrupted feeding rhythm. Glucose patterns were in keeping with insulin profiles. Controls showed a normal plasma corticosterone rhythm whereas DMNL rats had an altered pattern. The data suggest that deficiencies in the principal anabolic and growth-promoting hormones cannot be responsible for the retarded growth of DMNL rats.

Pancreatic and intestinal digestive enzymes in post-weanling rats with hypothalamic obesity

Male Sprague-Dawley rats received bilateral electrolytic lesions in the ventromedial hypothalamic nuclei (VMNL rats) at the age of 31 days; sham-lesioned rats served as controls. For 28 post-operative days all animals self-selected from three synthetic diets, each high in carbohydrate, fat and protein, respectively. Following this, half of the VMNL rats and half of the controls were switched to lab chow for 14 days. Body weights were comparable among the groups, but linear growth was greatly reduced and body fat (Lee Index) was elevated in VMNL rats, irrespective of diet. In the sham-lesioned controls, the synthetic diets reduced most parameters of exocrine pancreatic activity. In VMNL rats, in contrast, pancreatic parameters were unaffected by the synthetic diet. The data suggest that VMN lesions disinhibit the exocrine pancreas. In contrast, most parameters of intestinal activity were not influenced by VMN lesions.

Pancreatic growth and enzyme profiles in weanling rats with normophagic hypothalamic obesity

Weanling male rats with ventromedial hypothalamic lesions (VMNL rats) and sham-operated controls were killed 1, 2, 4, and 5 weeks postoperatively. The VMNL rats developed normophagic hypothalamic obesity in the presence of normal body weight and reduced linear growth. In both VMNL and control rats, pancreatic weight and protein content increased with time but were lower in the lesioned animals. Pancreatic DNA content was arrested in VMNL rats and remained so during the remainder of the experiment. The only significant enzyme changes (trypsinogen, amylase, and lipase) were evident in higher trypsinogen concentration in VMNL rats during 2 and 4 weeks after lesion production. In view of previous data on both hypophysectomized and VMNL rats and the known role of the ventromedial hypothalamic nucleus in neuroendocrine and neuroautonomic function, it is speculated that the changes observed here are in part due to disruption of neuroendocrine and in part due to disturbance of neuroautonomic control systems.

Normal pancreatic and intestinal enzymes in hypophagic growth-retarded rats that received dorsomedial hypothalamic lesions shortly after weaning

Male weanling Sprague-Dawley rats received bilateral electrolytic lesions in the dorsomedial hypothalamic nuclei (DMNL rats). Sham-operated rats served as controls. After being fed lab chow for two postoperative weeks, the animals were divided into four groups. One group of DMNL rats and controls received a high-caloric diet (high-fat diet, chocolate chip cookies, 32% sucrose solution, potato chips and marshmallows), whereas another group of DMNL rats and controls continued to receive lab chow. The experiment was terminated on the 185th postoperative day. In accordance with previous findings, DMNL rats, irrespective of diet, were lighter and shorter than controls. In addition, DMNL rats fed junk food were lighter than DMNL rats fed lab chow, and junk-fed controls weighed as much as chow-fed controls. Both DMNL rats and controls fed junk food were also shorter and showed higher carcass fat than their chow-fed counterparts. Also, DMNL rats fed junk food had less carcass fat than junk-fed sham-operated controls, whereas in accordance with previous findings, there was no difference between chow-fed DMNL rats and chow-fed sham-operated controls. Irrespective of diet, DMNL rats ate less calories than their respective sham-operated controls. Both absolute and percent pancreas weight and protein/pancreas were unaffected in DMNL rats but were reduced in both junk-fed groups in comparison with their chow-fed counterparts. Both concentrations and contents of pancreatic trypsinogen, amylase and lipase were unaffected in DMNL rats but total activities of all three enzymes were dramatically reduced in the junk-fed compared with the chow-fed DMNL rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in cell membrane Na,K-ATPase activity associated with induction of dietary obesity in the rat

The effect of diet-induced obesity on tissue Na, K-ATPase activity ("sodium pump") has been determined in the intact rat exposed to a cafeteria diet. Mature female Charles River rats showed significant increases in carcass lipid on this regimen (P less than 0.01), whereas male rats exposed to cafeteria diet and control male and female animals on laboratory chow showed no increase in carcass lipid over the 54 to 103 days that the animals were studied. In the female cafeteria-diet group, red blood cell membrane Na, K-ATPase activity and carcass lipid were highly correlated (r = 0.847, P less than 0.001). Significant trends in Na, K-ATPase activity as a function of carcass lipid did not occur in either kidney or liver crude membrane preparations from cafeteria-diet females. No correlation was seen in red cell, liver, or kidney membrane Na, K-ATPase with carcass lipid in male cafeteria-diet animals or in the control males and females. In this animal model of nongenetic obesity, changes in tissue Na, K-ATPase activity can be induced by dietary manipulation and are sex-specific and organ-specific.

Suppression of feeding by cholecystokinin but not bombesin is attenuated in dorsomedial hypothalamic nuclei lesioned rats

Rats with dorsomedial hypothalamic lesions (DMN-L) or sham operations were injected IP with saline or the satiety peptide cholecystokinin (CCK) at 3.0 and 6.0 micrograms/kg at the onset of the dark phase. Food consumption was then measured 15, 30 and 60 min later. Compared to saline baseline intake, CCK suppressed feeding during the first 30 min following injection in the sham operated group but not in the DMN-L group. Bombesin (BBS), another satiety peptide was also injected (4.0 and 8.0 micrograms/kg) into the two groups. BBS produced significant and comparable suppression of feeding in both DMN-L and sham operated rats. In a third trial a large dose of CCK (12.0 micrograms/kg) was injected into the two groups as described above. The CCK suppressed feeding for 60 min in the control group. CCK also attenuated feeding in the DMN-L group, but for only 30 min. However, even this suppression was reduced compared to the control group. The data suggest that the DMN may play a role in CCK induced satiety.

Paraventricular nucleus lesions in weanling female rats result in normophagia, normal body weight and composition, linear growth and normal levels of several plasma substrates

Female weanling rats received small (1 mAmp for 5 sec) electrolytic lesions in the paraventricular nuclei. Sham-operated rats served as controls. The rats were maintained for 42 days and body weight, linear growth, Lee Index, food intake and efficiency of food utilization were determined throughout the study. Plasma glucose, glycerol, free fatty acids, total protein and carcass fat and protein were determined at sacrifice. There was no significant difference between the lesioned and the sham-operated rats in any of the parameters measured. The findings are interpreted to mean that the PVN of the weanling rat is not functionally mature or alternatively, that there exists a sex difference in weanling rats in response to PVN lesions.

Naloxone suppression of food and water intake and cholecystokinin reduction of feeding is attenuated in weanling rats with dorsomedial hypothalamic lesions

In Experiment 1, sham operated (SCON) and dorsomedial hypothalamic nuclei (DMN) lesioned (L) rats were given saline or naloxone (0.1, 1.0 or 2.0 mg/kg) just prior to the onset of the dark cycle, lights out. Compared to saline injections, naloxone at all doses suppressed the cumulative food intake of the SCON during the second and third hr of measurement. Naloxone was without significant effect on the food intake of DMNL rats. Similar results were obtained in Experiment 2, except that naloxone at 2.0 mg/kg significantly suppressed the DMNL rats' food intake by the fourth hr of measurement. Cumulative water intake of both groups was significantly suppressed by naloxone in both experiments but its effects appeared to be attenuated in the DMNL group. In a preliminary trial cholecystokinin octapeptide (3.0 and 6.0 micrograms/kg) given at the onset of the dark cycle significantly suppressed the food intake of the SCON group but had no significant effect on the DMNL rats. The possibility exists that the reduced food intake and lower body weight of DMNL rats may partially result from damage to an opioid system. The data also tentatively suggest that DMN may play a role in cholecystokinin-induced satiety.

Brown adipose tissue metabolism in hypothalamic-obese rats

Studies were performed to evaluate the metabolic changes of brown adipose tissue (BAT) in rats with hypothalamic obesity (VMNL). In vitro 14C-palmitate oxidation and incorporation into triglycerides were similar in VMNL and control rats. However, protein and fatty acid content and incorporation of 14C-palmitate into phospholipid were significantly less in both hyperphagic and normophagic VMNL rats. In order to assess in vivo BAT lipogenesis, rats were injected with 3H2O. Plasma H2O incorporation into BAT lipids was significantly greater in VMNL rats. Likewise, BAT lipid content was higher in obese rats. In another experiment BAT was incubated with U-14C-glucose to evaluate glucose utilization by BAT. 14C-glucose was oxidized and incorporated into both lipids and glycogen more rapidly by obese than by normal rat BAT. Glycogen content was greater in VMNL rats. Tissues were also incubated with 1-14C-pyruvate and 2-14C pyruvate. Pyruvate incorporation into glyceride glycerol and oxidation of 2-14C pyruvate through the Krebs cycle were similar in both obese and control rats. However, the incorporation of pyruvate into glyceride fatty acids was increased in VMNL rats. The results indicate that both fatty acid and lipid synthesis are increased in BAT of obese rats whereas lactate production is decreased and Krebs cycle activity is normal. Some of these changes appear to be independent of the level of food intake.

Brown adipose tissue metabolism in cold-acclimated weanling rats with hypothalamic obesity

Certain aspects of intermediary metabolism of white (epididymal) and brown (interscapular) adipose tissue (BAT) were studied in cold-acclimated weanling rats with hypothalamic obesity. Groups of rats with ventromedial hypothalamic lesions (VMNL rats) and controls were maintained for four weeks at 6 degrees C and 22 degrees C, respectively. Sham-operated rats served as controls. Cold-acclimated VMNL rats showed greater percent BAT but normal percent epididymal fat pad weight, hypophagia, reduced body weight and body weight gains, hyperdipsia, hyperinsulinemia, normoglycemia and normal circulating fatty acid levels, higher carcass lipid and lower carcass protein. They also exhibited a higher rate of epididymal fat pad lipolysis than the controls, but the increment during cold adaptation was less in the VMNL rats compared with the 22 degrees C-maintained VMNL animals. In-vitro metabolism was determined in both the basal and the epinephrine-stimulated state. Basal-state 14C-palmitate oxidation, BAT fatty acid and lipid contents were increased in VMNL rats but protein content, incorporation into phospholipid and triglycerides, BAT lipolysis and glycolysis were normal in cold-acclimated VMNL rats. Epinephrine-stimulated BAT showed similar fatty acid content and palmitate oxidation and incorporation into triglycerides in VMNL and control rats. Epinephrine-stimulated BAT showed similar fatty acid content and palmitate oxidation and incorporation into triglycerides in VMNL and control rats, but the epinephrine-stimulated increase in lipolysis only in the cold-acclimated VMNL rats. Whereas at 22 degrees C BAT of VMNL rats showed decreased palmitate oxidation and no change of incorporation into phospholipid and triglyceride, during cold acclimation VMNL rats showed normal BAT metabolism and normal response to epinephrine, except for an increase in lipolysis. The data are in agreement with the observation that hypothalamic-obese mature rats have normal cold survival potential and allow us to extend this fact to the normophagic-obese-weanling rat.

Hypothalamus and brown fat: white and brown adipose tissue lipolysis in weanling rats with dorsomedial hypothalamic lesions

Weanling male Sprague-Dawley rats received bilateral electrolytic lesions in the dorsomedial hypothalamic nuclei (DMN); sham-operated animals served as controls. The animals were fed lab chow and given tap water ad libitum. Fourteen days after the hypothalamic operation they were weighed and measured to assess ponderal and linear growth gains and Lee Index and were sacrificed on the following day. Body weight, body weight gain over two weeks, nose-tail length and gain in nose-tail length, and food intake were all highly significantly reduced in DMNL rats in comparison with controls. Lee Index and efficiency of food utilization were normal, however. Epididymal fat pads weighed less in both absolute and relative (percentage body weight) terms than in controls. Basal lipolysis was increased and epinephrine-stimulated lipolysis was decreased in DMNL rats, as was the protein content of the epididymal fat pads. Lipid content was normal, however. Interscapular brown adipose tissue (BAT) was significantly lighter in DMNL rats than in controls in absolute terms, but all other parameters measured were normal, as were plasma glucose, glycerol, and free fatty acids. Comparison with results from rats that received ventromedial hypothalamic lesions shortly after weaning indicates a differential effect in most epididymal fat pad parameters but similarities to changes in BAT. These data add to previous demonstrations of normal responses to homeostatic challenges in the growth-retarded, hypophagic-hypodipsic rat with lesions in the dorsomedial hypothalamic nucleus.

Nutritional studies in the weanling rat with normophagic hypothalamic obesity

Weanling male hypothalamic-obese Sprague-Dawley rats (VMNL) and sham-operated controls (CON) fed stock diet for 2 weeks postoperatively ate similar amounts, but VMNL laid down more fat and less body weight per calories. Three equicaloric diets of different macronutrient (MN) content each were fed for 21 days. Diet selection: VMNL selected more carbohydrate (CHO) diet and protein diet but similar amounts of fat diet; total caloric intake was comparable. Percent diet selection showed the identical pattern. MN intake: VMNL ingested more percent CHO, less percent protein and similar percent fat as CON. Refeeding after 2-day fast: both groups selected similar amounts of diets, but VMNL ingested less protein. High protein diet along (9 days): both groups increased caloric intake over previous regimens, weight gain and caloric intake were similar, but Lee Index was higher in VMNL. Stock diet (32 days): VMNL showed normal body weight gains but higher Lee Index despite hypophagia. They utilized calories similarly for body weight gains but more poorly for fat deposition than CON. After death several key plasma substrates were similar in both groups but epididymal fat pads were heavier in VMNL.

Water regulation in weanling hypodipsic dorsomedial hypothalamic-lesioned rats

Weanling rats with dorsomedial hypothalamic nuclei lesions (DMN-L) are hypodipsic and hypophagic when compared to sham-operated rats. When tested for interdependence of food and water intake (WI) the DMN-L rats drank in the absence of food and ate in the absence of water. The data suggest DMN-L rats are not prandial drinkers. On testing for intracellular thirst (5.8 or 5.4% NaCl, 1 ml/100 g body wt), extracellular thirst [polyethylene glycol (PG), 25% wt/vol, 0.5 ml/35 g body wt], or a combination of both thirsts, the DMN-L rats responded as well or better than the control animals when the test data were expressed as a percentage of the rat's base-line WI. Both groups were more responsive to PG when tested in the light phase. When injected with angiotensin II (200 micrograms/100 g body wt) both groups responded similarly. Therefore, whereas the DMN-L rats were hypodipsic in comparison to controls, they respond as well or better than control animals when classical thirst testing procedures are utilized. It is suggested that DMN-L may have "reset" WI similarly to the previously proposed reset for body weight and food intake.