Effect of gonadectomy on taste preference for glucose solutions in rats.

Mature male and female rats maintained on an ad lib diet were given a choice between tap water and glucose solutions of different concentrations (1, 5 and 12 percent). Both sexes exhibited a definite preference for the 12 percent glucose solution, but the females drank significantly more than males. Gonadectomy produced neither quantitative nor qualitative changes in the choice made by male rats. On the contrary, gonadectomized females showed a depression of the 12 percent glucose solution intake and an increase in the 5 percent glucose solution intake, resulting in a decrease of the total fluid intake. A comparison of ovariectomized and intact female rats in regard to the self-selection of tap water and a 5 percent glucose solution confirmed the stimulatory effect of ovariectomy on the 5 percent glucose solution intake. When a choice between tap water and 12 percent glucose solution was permitted the ovariectomized rats showed a weaker positive response to the sweet solution than the intact female rats.     

Sex differences in the taste preference for a salt solution in the rat

A two-bottle free choice method was employed to investigate the water and 3% NaCl solution intake in rats of both sexes from the age of 30 days to adulthood. No sex difference was observed until the period of sexual maturation was reached. From that time on females drank more of the salt solution than males; the sex difference was apparent also in the NaCl concentration in total fluids consumed. These sexual differences existed also in adult rats which had been gonadectomised at the age of 10 days. After the free choice experiment was completed, the total RNA content in cells of hypothalamus and hippocampus of adult males and diestrous females was investigated. In females no effect of increased salt intake was seen. In males increased salt intake was associated with increased RNA content in all cells investigated. The role of the hypothalamus in sexual differentiation of salt intake is discussed.     

Effects of wheel running on food intake and weight gain of male and female rats

Adult male and female rats were housed in a sedentary condition or given free access to a running wheel for 50 days. Running wheel activity of female rats was higher than that of males throughout the experiment. Food intake, of both male and female rats that could take exercise increased, and the rate of increase of females was greater than that of males. In both males and females there was a positive correlation between food intake and running wheel activity. These findings suggest that the sex difference in the rate of increase in food intake elicited by wheel running is at least partly explained by the sex difference in running wheel activity. Although food intake increased as a function of running wheel activity, the weight gains of both sexes were slower than those of sedentary rats. In both sexes this slower weight gain was mainly due to less accumulation of fat.     

Sex differences in the effects of voluntary activity on sucrose-induced obesity

Sedentary, adult rats of both sexes fed Purina chow and a 32% sucrose solution overate, gained excess weight and had higher Lee Indexes of obesity than control animals fed only Purina chow. The magnitude of these effects was similar in the males and females. Animals of both sexes fed the sucrose diet showed a slower rate of weight loss during food deprivation than the chow controls. Access to an activity wheel led to a reduction in caloric intake and the elimination of obesity in male rats. In the chow fed male rats activity led to a smaller, transient suppression in caloric intake and a slightly lower level of body weight than the sedentary chow controls. Access to activity did not affect body weight in the female rats in either dietary condition. Rather, both active groups of female rats appeared to compensate for the energy cost of voluntary activity by a small increase in food consumption. Long-term exposure to activity was associated with more rapid weight loss during food deprivation in both males and females. These data reveal that high levels of activity and obesity can co-exist when normal female rats are fed a palatable diet but that activity eliminates this form of obesity in the male rat.     

Effects of insulin on food intake and plasma glucose level in fat-fed diabetic rats

Schedules of insulin treatment which reliably increased eating in fat-fed diabetic rats were studied for their effect on plasma glucose concentrations. An inverse correlation between intake and plasma glucose was observed in fat-fed diabetics given long-term treatment with protamine-zinc insulin (PZI); however changes in glucose did not account for the differential effect of insulin on food intakes in normal controls or normal and diabetic rats fed a low-fat food. A single injection of 1 U PZI which increased eating in fat-fed diabetics but not normal controls 17–23 hr later did not reduce glucose concentrations from hyperglycemic levels in diabetics during the same time period. Injections of regular insulin increased eating in fat-fed diabetic and normal rats in a comparable fashion, but did not reduce plasma glucose in diabetics as low as in normal animals. The results show that the effect of exogenously administered insulin on food intake in fat-fed diabetics is largely unrelated to changes in circulating glucose levels and suggest that metabolic consequences of insulin treatment other than hypoglycemia may underlie the effect of the hormone on feeding in these animals.     

Longitudinal study of solute excretion and glomerular ultrastructure in an experimental model of aging rats free of kidney disease

Because experimental studies of kidney aging are frequently complicated by the presence of renal disease, we set out to define a model minimizing renal pathology and thus revealing basic aging phenomena. Male and female Wistar/Lou rats were conceived, born, and bred to 42 months in a specific pathogen-free husbandry. They had free access to water and to a protein diet containing 2% fish and 15% vegetable proteins. The mean survival ages of this colony were 39 months for females and 35 months for males. Body weight, 24-hour food and water intake, urinary volume, and solute excretion were measured every 6 months in a group of 12 males and 12 females. Throughout the study, the mean body weight remained close to 180 gm in females and 320 gm in males. Despite this size difference, absolute daily food intake was similar in the two sexes and almost constant over the studied period. Age-related changes in proteinuria and phosphate excretion were greater in males than in females. Decreased urine osmolality and increased urinary volume, on the other hand, were more pronounced in old females than in males. Renal loss of calcium was noticed in both sexes and glucosuria remained discrete. Kidneys examined at 12, 24, and 36 months in both sexes and also at 42 months in females were free of major pathology such as pronounced glomerulosclerosis, tubular nephrosis, tubular cast, or hydronephrosis. In the oldest animals a few foci of interstitial inflammation occasionally were seen. The sole significant morphologic change was a regular but moderate thickening of the glomerular basement membrane, which roughly doubled its size from 12 to 36 months. Morphometric studies failed to demonstrate an increase in mesangial matrix or mesangial cellularity. No changes in foot processes, slit diaphragms, or endothelial fenestrae were seen with increasing age. These observations indicate that basic age-related changes in kidney structure and function of rats fed ad libitum can be reduced to a few parameters provided that adequate strains, diet, and husbandry conditions are selected for experimentation.     

Effects of gustation and gastric loading on rapid calorie metering in rats

On gustation/intubation of nutritive sucrose or glucose solution, both ad lib and meal-time rats reduced their subsequent 1 hr calorie intake via stock diet. But gustation/intubation of calorically-inert water had no effect on 1 hr calorie intake of either group of rats. In contrast, on tasting calorically-inert but sweet saccharin, the 1 hr intake of meal-time rats was reduced, though not the intake of ad lib rats. However, on intubation of saccharin solution no reduction in 1 hr intake was shown by either meal-time or ad lib rats. Quinine also showed differential effects on calorie intake. On intubation, but not on gustation of quinine, both ad lib and meal-time rats evidenced increase in their 1 hr calorie intake. Daily (24 hr) calorie intake via stock diet of ad lib rats, in contrast to 1 hr intake was unaffected by gustation/intubation of any test solution, including nutritive sucrose and glucose. Meal-time rats daily (3 hr) intake, on the other hand, was similar to 1 hr calorie intake following test solution treatment. It was reduced on gustation/intubation of calorically-rich solution as well as on tasting the sweet, but calorically-inert saccharin. Taste/intubation of quinine did not cause any change in daily calorie intake of either ad lib or meal-time rats.     

Response to chronic insulin administration: effect of area postrema ablation

The effects of daily administration of protamine zinc insulin (PZI) on plasma insulin and glucose levels and on food intake and body weight of rats with lesions of the area postrema and adjacent caudal-medial portions of the nucleus of the solitary tract (APX rats) were examined. Prior to insulin treatment, APX rats weighted less and had lower plasma immunoreactive insulin (IRI) levels than nonlesioned controls but did not differ from controls in plasma glucose levels. Five daily injections of 5 U/kg PZI raised plasma IRI and lowered plasma glucose levels similarly for both lesioned and nonlesioned rats. When injected with increasing doses of PZI over a 30-day period, both lesioned and nonlesioned rats showed increases of food intake and rate of weight gain in response to 8 U/kg PZI. These data indicate that APX does not affect either physiological or behavioral responses to chronic peripheral insulin administration.     

Food intake,body composition and blood lipids following treadmill exercise in male and female rats

Body weight gain, food intake, body composition and blood lipids of male and female Osborne Mendel rats were compared on the same exercise treadmill program. To mimic their nocturnal habits, rats were exercised daily at the beginning of the 12 hour dark cycle and food intake was measured for both light and dark cycles. After a 10 day treadmill adaptation period, the duration of exercise was successively increased over a 12 day period until 60 min/day at 21.3 meters/min was reached. Relative to their respective controls, exercised male rats showed a reduction in body weight and light cycle food intake while female runners showed no change in body weight or food intake. Exercise resulted in a decrease in percent body fat in both males and females while only male runners increased percent protein. Both males and females reduced serum triglycerides while serum cholesterol was reduced only in the males. The short term exercise program produced highly significant changes in the males while the females were more resistant to the same exercise regimen.     

Sex and sodium intake in the rat.

Female rats drink more 3% NaCl solution than do males, both when they need sodium (need-induced sodium intake or sodium appetite) and when they do not (need-free sodium intake). The sexual dimorphism of sodium intake is a secondary sexual characteristic because after castration at 1 day of age male rats drank 3% NaCl in adulthood in a manner similar to that of females in both the need-free and need-induced state, and females given long-term, neonatal testosterone drank low, malelike volumes of 3% NaCl on a daily need-free basis, but their response to sodium depletion was unchanged. This sexual dimorphism of sodium intake seems to be governed by testosterone that has been converted in the brain to estrogen because treatment of Day 1 castrated females with a nonaromatizable androgen, dihydrotestosterone, did not change either their need-free or their need-induced 3% NaCl intake. Castration in adulthood of male and female rats did not change their sodium consumption. However, when castrated adults received testosterone, need-free intakes of NaCl were suppressed in both sexes, but the suppression of 3% NaCl intake occurred only while the steroid was present. Exogenous testosterone also lowered the need-induced sodium intake of adult castrated females. Thus, in castrated adults, need-free intake was actively suppressed by exogenous testosterone in both sexes, whereas need-induced intake of NaCl was suppressed only in females. These data indicate that sodium intake in the rat is a sexually dimorphic behavior that is organized neonatally and can be actively suppressed in adulthood by testosterone.     

Comparison of androgenic effects on food intake and body weight in adult rats

In order to investigate the interrelationships between sex hormones, food intake, and body weight, three androgens (testosterone propionate (TP), dihydrotestosterone (DHT), and androstenedione (ANDR)) were administered to separate groups of gonadectomized adult rats of both sexes. In males TP increased body weight to the greatest degree, while the effects of DHT, a non-aromatizable androgen, and ANDR were approximately equal to each other. The relationship between each androgen and food intake partly paralleled that of body weight. In females, however, DHT exerted a stronger effect on body weight than TP, and ANDR produced no significant increases: food intake was stimulated by both TP and DHT. As others have indicated, aromatization of testosterone to estrogen then is not critical to the effect of androgens on either food intake or body weight. Furthermore, the fact that increases in body weight are not always accompanied by concomitant changes in food intake suggests that gonadal hormones may exert their effects on body weight primarily through various metabolic processes, not simply through changes in food intake.     

Interaction of TRH and CCK in the satiation of alcohol intake

Thyrotropin-releasing hormone (TRH) and cholecystokinin octapeptide (CCK) are endogenous neuropeptides known to inhibit intake of alcohol. Although both peptides are released by alcohol consumption and are hypothesized to satiate alcohol intake, their interaction has not been examined. We deprived ad-lib-fed male (n=6) and female (n=4) Wistar rats of water for 23 h and then gave them 30 min access to 5% w/v ethanol, followed by 30 min access to water. After adaptation to this schedule, rats were randomly assigned to receive intraperitoneal injections of either saline+saline, CCK (4 microg/kg)+saline, saline+TRH (10 mg/kg) or CCK+TRH immediately before alcohol access. Analyses of variance revealed a significant (P<.05) effect of CCK, and a significant interaction of CCK and TRH in control of ethanol consumption. CCK reliably reduced alcohol intake, and TRH blocked this satiation effect of CCK, increasing intake by 88.8% and 34.6% in males and females, respectively. TRH increased water intake in females, and CCK blocked this effect of TRH. Results indicate an infra-dose-additive interaction of CCK and TRH in satiation of alcohol intake, which may reflect a natural, endogenous neuropeptide interaction in the regulation of caloric intake.     

Creatine kinase isoenzyme profiles after exercise in the rat: sex-linked differences in leakage of CK-MM

Changes in creatine kinase (CK) activity and CK isoenzyme profiles in plasma after exercise were studied in rats in order to establish the source of the exercise-induced rise in CK activity. Male and female rats ran on a treadmill for 2 h and blood samples, taken before and after exercise, were assayed for total CK, CK isoenzymes and aminoaspartate transaminase (AST) activity. These enzymes were also assayed in homogenates of liver and several muscles. We found that the isoenzyme composition of liver, plasma and muscle did not differ between the sexes. However, the exercise-induced CK and AST responses did differ: CK and AST increased after exercise in males (101% and 15% resp.), but much less in females (47% and 1%). Although the isoenzyme profiles in rest did not differ, significant differences were observed after running: in males CK-MM inereased with 678%, but females only showed a 114% increase. In contrast, CK-BB showed a small increase that was about the same for both sexes (males 41%, females 35%). We conclude that both males and females show a small and similar increase in CK-BB activity after exercise, and that a large release of CK-MM from skeletal muscle, observed only in males, accounts for sex-linked differences reported earlier.     

Biomechanical changes in long limb bones of HAN-Wistar rats during postnatal development

Summary From a total of 648 male and 638 female HAN-Wistar rats the bones of 12 males and 12 females were examined at seven week intervals from the 35th to the 1129th day after birth. Biomechanical properties of the femora, tibiae and humeri were defined in a bending test using a tension testing machine. Load deflection diagrams in bending were produced, and the values of maximum bending load, bending breaking load, maximum deflection and ultimate deflection were correlated to age, body weight and bone length. The mean values of weight, bone length and biomechanical data are significantly higher in male rats. In both sexes biomechanical properties show a clear dependence on age. Up to the age of 330 days the tibia is more flexible than the femur or humerus. Values of partial correlation coefficients demonstrate that weight exerts more influence on the biomechanical properties of bones than age or bone length. With increasing weight, the loading capacity of bones rises in both sexes.This study was supported by the Deutsche Forschungsgemeinschaft     

Neonatal food restriction permanently alters rat body dimensions and energy intake

Neonatal food restriction (FR) in rats, by means of increased litter size, has been used as a model for developmental programming by several investigators. However, the results reported have been inconsistent and difficult to compare between studies. In the present study, we aim to characterize the effects of this model throughout life in both sexes of one particular strain. On the second day of life, Wistar rat pups were randomly assigned to a litter of 10 (control) or 20 (FR). All litters had an equal number of males and females, and pups were weaned on day 25. Body dimensions and food intake were measured regularly until the age of one year. Serum leptin levels were determined in four subsets of different ages. FR acutely reduced growth in all body dimensions and serum leptin levels. Despite catch-up after weaning, all these parameters remained reduced throughout life. Male and female FR rats had a significantly reduced absolute energy intake throughout life. Male FR rats had significantly higher energy intake adjusted for body weight immediately after weaning. During catch-up growth, both FR males and females showed significantly enhanced feed efficiency. These results suggest that neonatal food restriction programmed both male and female Wistar rats to remain small and lean in adult life, with a lower food intake. Low neonatal leptin levels may play a mechanistic role in this process.     

Sex differences in self-grooming of rats: effects of gonadal hormones and context

When prepubescent males and females were placed alone in a novel cage, males were found to groom their genitals, but not other body regions, more than females. This sex difference was present in untreated and in testosterone-treated gonadectomized rats as well as in intact rats. Neither the presence of gonads nor testosterone treatment affected grooming in this context. However, when similarly treated rats of the same age were observed in groups in the home cage, no sex difference in genital grooming of intact or gonadectomized rats was found. Testosterone significantly increased nongenital grooming in both sexes and genital grooming in males. Thus, both the presence of sex differences and the effects of testosterone on self-grooming depend on the behavioral context.     

Papillary plasma flow in rats

Papillary plasma flow (PPF) was measured by the albumin accumulation technique in Wistar rats. PPF was significantly lower in male (293 +/- 5 microliter X min-1 X g-1) than in female (499 +/- 17) rats. Castration in male rats increased PPF; testosterone administration in gonadectomized rats returned PPF to control. Acute indomethacin administration equalized PPF in both sexes to low values close to those found in normal males (320 +/- 5 in males, 326 +/- 17 in females). Conversely, captopril administration equalized PPF in both sexes by raising PPF in males (505 +/- 21) without significant change in females (526 +/- 88). Dehydration decreased PPF slightly in males (255 +/- 28) but more markedly in females (349 +/- 11). This decrease was prevented by captopril administration (520 +/- 34 and 609 +/- 61 in males and females, respectively). In captopril-treated male rats, angiotensin II (AII) was continuously infused by osmotic minipumps at a rate of 5 micrograms/h. This did not restore PPF (405 +/- 12) to basal values. In contrast, AII infusion together with indomethacin administration completely restored PPF (322 +/- 22) in captopril-treated rats whereas indomethacin alone did not normalize PPF (425 +/- 18). We suggest that male sex hormones and AII decrease PPF, and account for the low PPF measured in male rats. Vasodilator PGs are involved in the high PPF found in female rats. The vasodilator action of captopril on papillary circulation is explained by both decreased AII formation and increased PG synthesis.     

Age-related changes in cortical porosity of the midshaft of the human femur

Complete cross-sections from the femoral midshaft of 180 individuals of known height and weight, aged 21–97 y, from a modern Australian population were examined using automatic video image analysis to quantify total subperiosteal porosity (TSPP). More specifically, the aim was to investigate whether age changes were similar in both sexes in (1) total subperiosteal area (TSPA), cortical area (CA) and medullary area (MA), (2) intracortical porosity (ICP), and (3) the respective contributions to TSPP made by MA and intracortical void area (ICVA). Our findings indicated that both sexes showed a significantly greater height normalised TSPA in the 70s as compared with the 20s. Males had consistently larger bones with a greater height normalised CA. In both sexes CA showed a tendency to increase till the 7th decade and then to decline, more so in females. MA approximately trebled in females and doubled in males over the age range studied. Although ICP also increased, from 4–6% in young adults to over 9% in the elderly, it showed a significant difference between the sexes only in the 3rd decade, being greater in males at this stage. By contrast, TSPP became significantly greater in females (from that recorded in the 3rd decade) by the time they reached the 50s, while in males this did not occur till the 80s. It increased from ∼25% in young adults of both sexes to ∼50% in females and ∼37% in males in their 80s. However, in the elderly there was great variability in both sexes in the appearance of bones from individuals of similar chronological age. Some bones differed little from those in younger subjects, others showed greatly increased ICP, still others displayed reduced cortical widths with low ICP. The femoral midshaft resembles other skeletal sites in that age changes in TSPP are more marked in females than males.     

The effects of chronic corticosterone on hippocampal astrocyte numbers: a comparison of male and female Wistar rats

Chronic stress an/or glucocorticoid administration produces atrophy of hippocampal neurons. However, evidence of the impact of glucocorticoids on glial cells, especially in both males and females, is limited. In the present study, we investigated the total percentage body weight, hippocampal volume and hippocampal astrocyte numbers following chronic corticosterone treatment in male and female Wistar rats. Males had greater left and right hippocampal volumes overall, but no effect on hippocampal volume was seen after corticosterone treatment. Total body weight was dose-dependently lower in both sexes, but the decrease was more prominent in male rats. Corticosterone treatment dose-dependently increased astrocyte numbers in the CA1 region, but not in the lateral and medial CA3 hippocampal regions. This increase was similar in both male and female rats. The astrogliosis observed following chronic corticosterone may have implications for extrasynaptic communication and neuron-glia interactions and is similar to changes in the astrocytic population observed in aged rats.     

Voluntary lactose ingestion in gerbils, rats, mice, and golden hamsters.

Over a period of 20 days, adult male gerbils, rats, mice, and hamsters were allowed to choose between tap water and a sugar solution (either sucrose, glucose, or lactose) presented in increasing concentrations (maximum concentration = 24% weight/volume). Rats, mice, and hamsters preferred both glucose and sucrose solutions to water across a wide range of concentrations; gerbils preferred sucrose solutions at concentrations of 8% and above, but preferences for glucose solutions were not significant. Gerbils, mice, and rats did not prefer lactose solutions to water at any concentration, and actually preferred water at higher lactose concentrations; in contrast, hamsters preferred lactose solutions to water at concentrations of 4% and above, and never preferred water to lactose solutions. As solution concentrations increased, all species consumed increasing amounts of glucose and sucrose (i.e., solute). The lactose intake of gerbils, rats, and mice tended to remain quite low even as solution concentration increased; in contrast, the lactose intake of hamsters was substantially greater than that of other species and increased to a maximum of 1.95 g/100 g body weight/day at the 24% concentration. These results indicate that gerbils and mice, like rats, have a low preference for lactose and consume very little of this disaccharide, and confirm that golden hamsters are exceptional in demonstrating both a preference for lactose solutions and an apparent tolerance to the effects of ingestion of substantial amounts of lactose.