Effects of seasonality and fasting on the plasma leptin and thyroxin levels of the raccoon dog (Nyctereutes procyonoides) and the blue fox (Alopex lagopus)

Plasma leptin and thyroxin concentrations of eleven raccoon dogs and eleven blue foxes were monitored for 6 months. Half of the animals were placed on a 3-week fast in November. Leptin levels were low in summer, but in October they rose significantly. In November, leptin concentrations decreased rapidly within a week although the body mass of the animals remained stable. There were no significant differences between experimental groups for raccoon dogs, but in blue foxes the fasting group had lower leptin levels than the control group. High thyroxin levels in summer decreased as autumn progressed, but thyroxin concentrations of the fasting groups increased at the end of the fast. Leptin levels of the raccoon dog and the blue fox are not determined only by the fat reserves of the animals, but they seem to reflect the autumnal deposition of fat at the onset of winter. Blue foxes have metabolic rates of active animals during the winter and higher leptin levels in December than raccoon dogs. The superficially hibernating raccoon dogs have low leptin levels after the onset of winter perhaps as an adaptation to fasting. J. Exp. Zool. 289:109-118, 2001.     

Year round plasma leptin and androgen concentrations in a tropical bat

The detailed reproductive patterns and their associated endocrine characteristics have been documented only for a few species of bats. The objective of this study was to examine seasonal changes in plasma concentrations of leptin and compare it with the changes in body mass, circulating concentrations of testosterone, androstenedione and its correlation with prolonged survival of sperm during winter dormancy in the male sheath-tailed batTaphozous longimanus Hardwicke, 1825. Six bats were captured every month for three consecutive years during 2002 to 2005 from Varanasi, a subtropical part of India. The changes in the body mass were positively correlated with circulating concentration of leptin. Leptin concentration reached a peak (14 ng/ml) in November coinciding with peak body mass. Leptin levels declined during other months of the year except for a rise in March and August. Plasma leptin was positively correlated with androstenedione concentration, but did not show significant correlation with testosterone level. We noticed a significant increase in testosterone secretionin vitro in response to leutinizing hormone (LH) stimulation. However, we did not notice any increase in testosterone or androstenedione secretionin vitro in response to leptin stimulation. Plasma leptin concentration did not show any correlation with testis mass in this study. The higher concentration of testosterone and androstenedione may be responsible for the prolonged survival of sperm in the epididymidies and higher levels of leptin in November may be responsible for maintaining reproductive function during winter dormancy. We suggest that inT. longimanus, higher leptin concentrations in November may be responsible for the gonadal recrudescence and reproductive response during winter dormancy is modified by energy availability and by changing leptin concentrations during this period.     

Leptin immunoexpression and innervation in rat interscapular brown adipose tissue of cold-acclimated rats: the effects of L-arginine and L-NAME

The aim of the present study was to explore the effect of nitric oxide on leptin immunoexpression and innervation in interscapular brown adipose tissue (IBAT) of room- and cold- acclimated rats. Animals acclimated both to room-temperature (22 +/- 1 degrees C) and cold (4 +/- 1 degrees C) were treated with L-arginine, a substrate for nitric oxide synthases (NOSs), or N?-nitro-L-arginine methyl ester (L-NAME), an inhibitor of NOSs, for 45 days. Leptin expression and localization in brown adipocytes was studied by immunohistochemistry, and innervation stained by the Bodian method. Strong leptin immunopositivity was observed in brown adipocytes cytoplasm of all room-acclimated groups, but nuclear leptin positivity was found only in L-NAME treated rats. In cold-acclimated control and L-NAME treated rats leptin immunopositivity was absent, while L-arginine treatment reversed the cold-induced suppression of leptin expression. Comparing to control, L-arginine, and even more L-NAME, at 22 +/- 1 degrees C induced greater innervation. In conclusion, L-arginine treatment changes leptin expression pattern on cold in rat IBAT.     

Lower serum leptin concentrations in rugby players in comparison with healthy non-sporting subjects--relationships to anthropometric and biochemical parameters

Leptin is a protein hormone synthesized by adipocytes. Its serum concentrations reflect the total body fat content. Serum leptin concentrations are significantly higher in obese than in lean people and in women than in men. However little information about the influence of physical activity on serum leptin concentrations is available. We have compared the body weight, the body mass index (BMI), the body fat content (measured by caliper as skinfold thickness) and the serum concentrations of leptin, triglycerides, total, high density and low density lipoprotein (LDL) cholesterol in 14 top rugby players and 10 healthy controls. We found that serum leptin, total and LDL cholesterol concentrations were significantly lower in the rugby players group than in the control subjects. The body weight and BMI were significantly higher in the rugby players, while the body fat content was only slightly (non-significantly) higher in the control group. The serum leptin concentrations in both groups positively correlated with the BMI and body fat content and also with LDL concentrations in the control group. The serum leptin concentrations in the rugby players were lower than in the non-sporting subjects despite a similar body fat content in both groups. We would therefore suggest the possibility that regular hard physical training decreases serum leptin concentrations not only by the decrease of total body fat content, but also by a separate mechanism, which is not directly dependent on the changes in the amount of body adipose tissue.     

Seasonality and fasting effect in raccoon dog Nyctereutes procyonoides serum leptin levels determined by canine leptin-specific enzyme-linked immunosorbent assay

Leptin is an adipocyte-derived peptide hormone that acts on the brain and regulates food intake and energy balance. Several previous reports have suggested that overwintering raccoon dogs Nyctereutes procyonoides are able to control their adiposity efficiently, but the contribution of leptin to weight regulation in these animals remains unclear. To study the seasonality of overwintering raccoon dogs as well as the effects of fasting on them, serum leptin levels were investigated using a newly established canine leptin-specific enzyme-linked immunosorbent assay (ELISA) kit. Of the nine animals studied, five were fed and four were fasted (deprived of food for 2 months in winter). Blood samples and body fat weights were monitored once a month throughout the experimental period (July 2007-March 2008). Leptin concentrations obtained by ELISA were significantly higher than and had a positive correlation with those obtained by previously used multispecies radioimmunoassay (RIA) kits. Moreover, ELISA showed a clearer correlation between the body fat weight and leptin levels compared with RIA, suggesting the efficacy of canine leptin-specific ELISA kit for leptin estimation in raccoon dogs. Autumnal fattening was observed in both groups of animals, but the wintertime loss of adipose tissue was more obvious in the fasted group. Serum leptin concentrations determined by ELISA showed seasonal changes without significant differences between the fed and fasted animals. Therefore, high levels of leptin may be responsible for the suppression of feeding behavior in raccoon dogs before winter.     

Seasonal weight regulation of the raccoon dog (Nyctereutes procyonoides): interactions between melatonin,leptin, ghrelin,and growth hormone

The raccoon dog (Nyctereutes procyonoides, Canidae, Carnivora) is a middle-sized omnivore with excessive autumnal fattening and winter sleep. We studied seasonal weight regulation of the species by following the plasma leptin, ghrelin, and growth hormone (GH) levels of farm-bred raccoon dogs (n = 32) for 6 months. In August, half of the raccoon dogs received continuous-release melatonin implants, and in November, half of the animals of both the sham-operated and melatonin-treated groups were fasted for 2 months. In the autumn, the plasma leptin and GH levels were low, but the ghrelin levels were relatively high and correlated positively with energy intake. This represents the period of energy storage. Leptin and GH levels peaked simultaneously in late October, and melatonin advanced the peaks by 1 week. Thereafter, the levels rapidly declined, representing the transition period from autumnal anabolism to wintertime catabolism. In the winter, the leptin and GH levels rose to high levels, but the ghrelin-leptin ratio was very low. This is the period of winter sleep, with fat accumulated in the autumn as the principal metabolic fuel. In the winter, leptin, ghrelin, and GH may work in synergy to increase lipolysis. GH may also induce winter sleep to the raccoon dog. Fasting had no effect on the hormone levels, unlike in humans and rodents. Instead of the amount of fat in the body, the main regulators of the levels of these hormones in the raccoon dog are presumably seasonal rhythms entrained by melatonin.     

Correlation between birth weight, leptin, zinc and copper levels in maternal and cord blood

Leptin and zinc are involved in the regulation of appetite. Copper is a trace element regulating the functions of several cuproenzymes that are essential for life. To evaluate the relationship between zinc and copper status and the leptin system in humans, we examined whether leptin concentrations in the mother and the newborn correlate with the weight of mother, placenta and newborn. A total of 88 pregnant women at 38-42 weeks' gestation were studied. All infants were categorized as small for gestational age (SGA) (n = 16), average for gestational age (AGA) (n = 59) or large for gestational age (LGA) (n = 13). Leptin, zinc, and copper levels were measured in maternal and cord serum at birth. Maternal BMI and placental weight of the LGA groups were significantly higher than those of the SGA and AGA groups. Cord and maternal leptin levels of the SGA groups were significantly lower than those of the AGA and LGA groups. Maternal serum leptin levels were positively correlated with BMI and maternal zinc levels in all groups. Cord serum leptin levels of all groups were positively correlated with birth weight and placental weight. Birth weight was negatively correlated with maternal and cord copper level of all groups. Umbilical leptin concentrations of SGA newborns correlated with leptin concentrations of their mothers. In all pregnancies, birth weight increases in association with increase in cord leptin level. Our results suggest that maternal zinc but not copper level has an effect on maternal serum leptin levels. The increase in copper level in both maternal and cord blood may contribute to restriction in fetal growth.     

Seasonal changes in plasma leptin concentration related to antler cycle in Iberian red deer stags

The aim of this study is to describe the leptin cycle in male Iberian red deer (Cervus elaphus hispanicus) and relate it to antler and testosterone cycles. An additional aim is to assess the relationship between the plasma leptin concentration during antlers’ growth and their final size. Therefore, blood from 21 Iberian red deer males was sampled monthly to analyse leptin and testosterone. At the same time the deer were weighed and their body condition was assessed. The length of antlers was measured every 2 weeks and, after casting, their final length and perimeters were taken. Leptin showed a seasonal cycle, with a peak in June that decreased as testosterone increased. Low values were observed in autumn, winter and early spring. The relationship observed between leptin and body mass or body condition score was different in spring, when plasma testosterone concentration is low, than in autumn, when testosterone increases. Leptin peak amplitude was positively related to final antler size. In conclusion, the relationship between leptin and body mass and body condition score changes through the year, possibly due to the influence of androgens and photoperiod. There was a positive relationship between plasma concentration of leptin during antler growth and final antler length.     

Percent Body Fat and Lean Mass Explain the Gender Difference in Leptin: Analysis and Interpretation of Leptin in Hispanic and Non‐Hispanic White Adults

Objective: To reassess the relationship between body fat and fasting leptin concentrations comparing plasma vs. serum assessments of leptin; ratios vs. regression adjustment for body composition; fat and lean mass vs. percent body fat; and gender‐, ethnic‐, and age‐related variations. Research Methods and Procedures: Subjects included 766 adults from the nondiabetic cohort of the San Luis Valley Diabetes Study examined at follow up (1997 to 1998). Body composition was determined by dual energy X‐ray absorptiometry. Leptin concentrations were determined after an overnight fast. Results: Fasting serum and plasma assessments of leptin were correlated with percent body fat to the same degree. Women had significantly higher serum leptin concentrations than men when leptin concentrations were divided by body mass index, fat mass in kilograms or percent body fat. The methodological problem inherent in interpreting these ratio measures is pictorially demonstrated. In regression analysis, fat mass alone did not explain the gender difference. However, lean body mass was inversely related to leptin concentrations (p < 0.0001) and explained 71% of the gender difference at a given fat mass. Percent body fat explained all of the gender difference in leptin concentrations in both Hispanics and non‐Hispanic whites. Similar to findings about gender differences, ethnic‐ and age‐related variations in the leptin‐body fat association were minimized when percent body fat was employed as the body fat measure. Discussion: Regression analysis and percent body fat measured with dual energy X‐ray absorptiometry are recommended when assessing the relationship between leptin and body fat. Gender differences in leptin concentrations were accounted for by percent body fat in free living (no diet control), Hispanic and non‐Hispanic white adults.     

The concentration dependent biphasic effect of leptin on endogenous cholesterol synthesis in human monocytes

In human monocytes 100 ng/mL leptin increased both statin-inhibitable free radical and cholesterol production in vitro. In our recent study, we aimed to elucidate the concentration dependence of observed leptin-effect. Following leptin stimulation cholesterol synthesis was measured in the presence of inhibitors to determine affected signal pathways. Leptin at low (10-100 ng/mL) concentrations increased [(14)C]acetate incorporation, whereas at 250 ng/mL and higher concentrations it suppressed cholesterol synthesis. HMG CoA reductase, phosphatidyl-3-kinase (PI3K) and mitogen activated protein kinase (MAPK) were involved in mediating leptin effects at low concentrations, whereas the cholesterol synthesis suppression was abolished by inhibitors of protein kinase C (PKC) and PI3K.     

Plasma leptin suppression by arginine vasopressin in normal women and men

Leptin inhibits appetite by activating several neuroendocrine systems, including the hypothalamo-pituitary-adrenal cortical (HPA) axis. In turn, elevated glucocorticoids can increase circulating leptin. We therefore measured plasma leptin in 12 normal women and eight normal men administered low-dose physostigmine (PHYSO) and arginine vasopressin (AVP) to stimulate the HPA axis. The subjects underwent four test sessions 5-7 days apart: PHYSO (8 microg/kg IV), AVP (0.08 U/kg IM), PHYSO + AVP, and saline control. Serial blood samples were taken before and after pharmacologic challenge and analyzed for leptin, adrenocorticotropin (ACTH)1-39, cortisol, and AVP. Estradiol and testosterone also were measured at each test session. PHYSO and AVP produced no side effects in about half the subjects and predominantly mild side effects in the other half, with no significant female-male differences. Correlations between side effects (absent or present) after PHYSO or AVP and the corresponding leptin responses were nonsignificant. Baseline plasma leptin concentrations were significantly higher in the women than in the men (p < 0.003). Leptin concentrations following PHYSO remained unchanged from baseline, indicating that the short-lived ACTH and cortisol increases produced by PHYSO did not affect leptin secretion. In contrast, AVP administration, while also increasing ACTH and cortisol, suppressed leptin, to a significantly greater degree in the women than in the men (p = 0.01). This significant suppression of leptin by AVP has not been previously described; physiologically, it may be part of a negative feedback regulatory system between central leptin and its activation of the HPA axis, by inhibition of leptin production or acceleration of its clearance.     

Leptin, but not immune function, is linked to reproductive responsiveness to photoperiod

Energetic demands are high while energy availability is minimum during winter. To cope with this energetic bottleneck, animals exhibit numerous energy-conserving adaptations during winter, including changes in immune and reproductive functions. A majority of individual rodents within a population inhibits reproductive function (responders) as winter approaches. A substantial proportion of small rodents within a species, however, fails to inhibit reproduction (nonresponders) during winter in the field or in the laboratory when maintained in winter-simulated day lengths. In contrast, immune function is bolstered by short day lengths in some species. The specific mechanisms that link reproductive and immune functions remain unspecified. Leptin is a hormone produced by adipose tissue, and several studies suggest that leptin modulates reproductive and immune functions. The present study sought to determine if photoperiodic alterations in reproductive function and leptin concentrations are linked to photoperiod-modulated changes in immune function. Siberian hamsters (Phodopus sungorus) were housed in either long (LD 16:8) or short (LD 8:16) day lengths for 9 wk. After 9 wk, blood samples were collected during the middle of the light and dark phase to assess leptin concentrations. One week later, animals were injected with keyhole limpet hemocyanin to evaluate humoral immunity. Body mass, body fat content, and serum leptin concentrations were correlated with reproductive responsiveness to photoperiod; short-day animals with regressed gonads exhibited a reduction in these measures, whereas short-day nonresponders resembled long-day animals. In contrast, immune function was influenced by photoperiod but not reproductive status. Taken together, these data suggest that humoral immune function in Siberian hamsters is independent of photoperiod-mediated changes in leptin concentrations.     

Elevated leptin concentrations in pregnancy and lactation: possible role as a modulator of substrate utilization.

Energy needs are increased during pregnancy and lactation. These increased energy needs may be met through partitioning of nutrients for energy utilization which is under hormonal control. The objective of the present studies was to determine if changes in plasma leptin occurred during pregnancy and lactation and if the changes were related to prolactin. Plasma leptin and prolactin were measured longitudinally in 9 women through pregnancy and lactation. In a second study, leptin and prolactin were measured 4 days and 28 days postpartum in 21 lactating women. Mean plasma leptin during the three trimesters of pregnancy was significantly higher (29.3+/-2.8 ng/ml) when compared to mean leptin during the three time periods of lactation (19.3+/-3.2 ng/ml) and control groups (9.8+/-1.4 ng/ml). Plasma leptin was elevated early in pregnancy and remained elevated throughout pregnancy. In the second study, the mean plasma leptin in the lactating women was significantly higher 4 days postpartum (17.3+/-3.7 ng/ml) and 28 days postpartum (19.2+/-3.9 ng/ml) when compared to controls (11.6+/-1.2 ng/ml). Prolactin in the control subjects (24+/-4 ng/ml) was significantly lower than in the pregnant (202+/-16 ng/ml) and lactating (108+/-26 ng/ml) groups. Similar observations were made in the second study (controls 20+/-2 ng/ml; lactation 28 days 159+/-21 ng/ml). Leptin during lactation was lower than in pregnancy but higher than control subjects. Regression analysis suggested that BMI and prolactin can be used as predictors of leptin in pregnancy and lactation. The increase in leptin and prolactin early in pregnancy suggests an association between the two hormones. Results of the present studies and research done by other investigators presents a strong role for leptin during pregnancy and lactation. Leptin is regulated by factors other than adiposity especially in reproductive women leading to our hypothesis that there are leptin and prolactin mediated effects on substrates used for energy utilization during pregnancy and lactation.     

Leptin mRNA expression in the rat mammary gland at different activation stages

Leptin is expressed in various tissues, suggesting that this protein is effective not only at the central nervous system level, but also peripherically. Recent studies have shown leptin production by other tissues, including the placenta, stomach, and mammary tissues, but there is no information available concerning expression levels of leptin in the rat mammary gland at different activation stages. We used semi-quantitative RT-PCR to investigate leptin mRNA expression levels in the rat mammary gland at different activity stages. Rat mammary gland samples were collected from virgin females and on days 6, 12, 18 of pregnancy and of lactation (six rats per group). The expression levels of leptin mRNA were measured by semi-quantitative RT-PCR, with β-actin as an internal control. Leptin mRNA was highly expressed in virgin rat mammary glands (leptin(IOD)/β-actin(IOD) = 1.60). It decreased gradually during pregnancy, being lowest at 18 days of pregnancy, when the levels were significantly lower than in virgin mammary tissue. Leptin mRNA increased slightly during lactation, but the difference was not significant. By day 18 of lactation, expression levels of leptin mRNA reached the same values as in virgin mammary tissue (leptin(IOD)/β-actin(IOD) = 1.65). Based on these results, we suggest that leptin has an important regulation role in rat mammary gland activation.     

Changes in serum leptin, insulin, androstenedione and luteinizing hormone during ovarian cycle in the bat, Taphozous longimanus

Detailed reproductive pattern and associated endocrine characteristics have been documented in only a few species of order Chiroptera. The aim of the present study was to examine the changes in body weight, serum insulin, leptin, androstenedione and luteinizing hormone (LH) concentrations during annual ovarian cycle in the sheath-tailed bat, Taphozous longimanus. Bats were sampled over three years. Leptin, a satiety hormone produced primarily by adipose tissue, provides information to feeding center of the brain about nutritional status, fat mass, appetite and energy expenditure. The circulating concentration of leptin begins to increase from October and attains a peak in December. The peak serum leptin concentration coincides with body weight in November before winter dormancy in December. The serum leptin levels dissociate from body weight during December. The other peaks of serum leptin levels coincide with late stages of the two successive pregnancies. The serum insulin concentration begins to increase from September and attains a peak during December. The insulin concentration remains low from January to August. The circulating androstenedione concentration begins to increase in October, reaching a peak in December. This increase in androstenedione concentration correlated with the period of heavy accumulation of abdominal fat and increase in body weight. There was a sharp decline in androstenedione concentration and body weight in January. The serum LH shows peaks, in November, coinciding with the peaked body weight, the other peaks in January and May, coinciding with ovulation for the two successive pregnancies. The high leptin and insulin levels might be responsible for the maintenance of reproductive response and gonadal function during adverse environmental condition in the winter, while high androstenedione, and associated body weight along with LH might be responsible for maintaining basal gonadal function. We conclude that high leptin, androstenedione and insulin serve, as signal for the reproductive functions in that sufficient body fat are available to meet the caloric demands and maintain normal function during adverse winter conditions.     

Reproduction in high body condition mares with high versus low leptin concentrations

Previous results from our laboratory indicated that a majority of mares with high body condition scores (BCS) displayed estrous cycles or had considerable follicular activity during the winter. Among these high BCS mares, about 35% of them exhibited a persistent hyperleptinemia and hyperinsulinemia. The current experiment was designed to compare the reproductive characteristics of high BCS mares with hyperleptinemia to those with normal (low) plasma concentrations of leptin during the winter and the first estrous cycle (or the first full cycle encountered for those already cycling). Light horse mares with high BCS (6-8.5) were assigned to groups based on leptin concentrations (8/group): low (<5 ng/mL) and high (>10 ng/mL). Beginning 7 January, mares were assessed every 3d for follicular activity and then daily once a follicle >25 mm was detected. Mares were subsequently monitored through their first and second ovulations. Leptin concentrations remained higher (P<0.001) in mares in the high leptin group over the duration of the experiment. Also, high leptin mares had greater (P<0.0001) insulin response to glucose infusion and a faster (P<0.05) rate of glucose clearance. One mare with high leptin and three mares with low leptin had progesterone concentrations indicative of the presence of a corpus luteum at the onset of the experiment. Plasma concentrations of LH, FSH, and progesterone did not differ between groups (P>0.1) during the first estrous cycle occurring after 7 January. Date of first ovulation after 7 January and interovulatory interval were similar (P>0.1) for the two groups, as were estimates of follicular numbers on the ovaries (small, medium, and large; P>0.1). It is concluded that the perturbations in leptin and insulin secretion observed in some high BCS mares are not associated with alterations in ovarian activity or the estrous cycle during winter and into the period of vernal transition.     

Effects of living at two ambient temperatures on 24-h blood pressure and neuroendocrine function among obese and non-obese humans: a pilot study

The effects of environmental temperature on blood pressure and hormones in obese subjects in Japan were compared in two seasons: summer vs winter. Five obese (BMI, 32?±?5 kg/m²) and five non-obese (BMI, 23 ±3 kg/m²) men participated in this experiment at latitude 35°10′ N and longitude 136°57.9′ E. The average environmental temperature was 29?±?1 °C in summer and 3?±?1 °C in winter. Blood samples were analyzed for leptin, ghrelin, catecholamines, thyroid stimulating hormone (TSH), free thyroxine (fT₄), free triiodothyronine (fT₃), total cholesterol, triglycerides, insulin and glucose. Blood pressure was measured over the course of 24 h in summer and winter. A Japanese version of the Profile of Mood States (POMS) questionnaire was also administered each season. Systolic and diastolic blood pressures in obese men were significantly higher in winter (lower environmental temperatures) than in summer (higher environmental temperatures). Noradrenaline and dopamine concentrations were also significantly higher at lower environmental temperatures in obese subjects, but ghrelin, TSH, fT₃, fT₄, insulin and glucose were not significantly different in summer and winter between obese and non-obese subjects. Leptin, total cholesterol and triglyceride concentrations were significantly higher in winter in obese than non-obese men. Results from the POMS questionnaire showed a significant rise in Confusion at lower environmental temperatures (winter) in obese subjects. In this pilot study, increased blood pressure may have been due to increased secretion of noradrenaline in obese men in winter, and the results suggest that blood pressure control in obese men is particularly important in winter.     

Circadian patterns of plasma leptin,insulin and glucose concentration in the toad-headed lizard Phrynocephalus versicolor

To understand the circadian rhythms of the glucose metabolism and related hormones in desert reptiles, we studied the daily changes in plasma leptin, insulin, and glucose in the toad-headed lizard, Phrynocephalus versicolor, in the semi-desert of the Alashan Plateau. Blood samples were obtained from groups of 20 lizards (about equal sex ratio for each group) at 4-h intervals throughout a 24-h period. Leptin, insulin, and glucose levels were determined using ELISA, RIA, and the glucose oxidase method, respectively. Ambient temperature and humidity were also measured when the blood samples were taken. We found that: (1) there was a significant difference in plasma leptin concentrations at different times of day; (2) no significant circadian rhythm could be measured for plasma insulin and glucose; (3) ambient temperature, humidity, and body condition had no significant effect on plasma leptin, insulin, and glucose levels; and (4) there were significant correlations between plasma glucose concentrations and leptin concentrations 8 h later, and between insulin concentrations and leptin concentration 8–12 h later. These results suggested that the secretions of leptin and insulin played an important role in glucose metabolism in reptiles in an arid environment.     

Leptin concentrations in cord blood in normal newborn infants and offspring of diabetic mothers.

Leptin has been implicated in the regulation of body weight and energy balance; Leptin is produced by adipocytes and placental tissue. Chronic fetal hyperinsulinemia and accelerated fetal growth with increased amounts of body fat are frequent findings in the offspring of diabetic mothers. In this study, we examined whether leptin levels in cord blood of infants of type 1 diabetic mothers (n = 29), gestational diabetic mothers (n = 6 and controls (n = 96) correlated with level of maternal glucose control, maternal leptin level at delivery, gender, fetal and placental size, and C-peptide in cord blood at birth. Leptin was significantly elevated in infants of type 1 diabetic (24.7 ng/ml) and gestational diabetic mothers (29.3 ng/ml) as compared to controls (7.9 ng/ml). C-peptide was also significantly higher in infants of type 1 diabetic (0.91 nmol/l) and gestational diabetic mothers (0.99 nmol/l) vs controls (0.34 nmol/l). Infants of type 1 diabetic mothers with a leptin level in cord blood above the upper normal range, i.e. > 30 ng/ml (n = 13), had an average maternal HbA1c level of 5.4% (normal < 5.5%) that was not different from 5.2% in infants with a leptin level < 30 ng/ml (n = 15). In both neonatal groups of diabetic mothers, leptin in cord blood did not correlate with maternal leptin concentrations, placental weight, birthweight, gender and cord blood C-peptide. In controls, leptin in cord blood was higher in girls than in boys (p = 0.044) and correlated significantly with birthweight (p = 0.41, p < 0.001) and cord blood C-peptide (p = 0.44, p < 0.001) but not with maternal leptin level or placental weight. The 3-4 times higher leptin levels in the offspring of diabetic mothers than normal could reflect increased adipose tissue mass and/or increased contribution from other sources such as placental tissue.     

Leptin acts peripherally to limit meal-induced increases in plasma insulin concentrations in mice: a brief communication

Leptin inhibits food intake and lowers plasma insulin concentrations. This study was designed to determine whether leptin acts independent of food-intake regulation to affect meal-induced increases in plasma insulin concentrations. Leptin-deficient, Lep(ob)/Lep(ob) mice were administered 1 microg leptin intracerebroventricularly (ICV) or intraperitoneally. Food intake and plasma insulin concentrations of mice administered leptin ICV before a meal were lower, as expected, than were intakes and plasma insulin concentrations of mice administered vehicle ICV. However when food intake was controlled, meal-induced increases in plasma insulin were unaffected by ICV administration of leptin. Intraperitoneal administration of 1 microg leptin before a meal lowered meal-induced increases in plasma insulin concentrations without influencing the size of the meal. We conclude that plasma leptin concentrations can affect meal-induced insulin secretion independent of the central nervous system actions of leptin associated with food-intake regulation.