Leptin, a 167 amino-acid product of the ob or LEP gene, was first reported in 1994 after a 40-year search that began following the emergence of a mutant strain of mice with hyperphagia, early on-set obesity, and delayed sexual maturation. Since then, leptin deficiency has also been reported in the rat, and more recently in humans. It is secreted constitutively primarily by the white adipose tissue, and in smaller quantities by a number of non-adipose tissues. It acts by binding to specific membrane bound leptin receptors, belonging to the class 1 cytokine receptor family, and activating the JAK-STAT system. Leptin regulates appetite and body weight mainly through its actions on the hypothalamus involving the NPYmelanocortin pathway, and, to a lesser extent, through increased energy expenditure by way of sympathoactivation and increased substrate cycling. Its effects on reproduction, puberty in particular, are mediated through actions on the hypothalamic-pituitary-gonadal axis and on the gonads. Leptin also appears to have permissive roles in CNS development during the neonatal period, bone growth and development, and in haemopoietic and immune functions. Although it was its deficiency state that first led to its discovery, it now appears that the clinical significance of leptin lies not only in the consequences of its deficiency but also when it is in excess as occurs in obesity. Emerging evidence is implicating leptin as a link between obesity associated cardiovascular disease risks and infertility. Besides this, leptin is also being implicated as a growth factor in cancer. The story that started with a search for a body weight regulating factor is now unfolding into one that is revealing roles for leptin that stretch beyond the regulation of appetite and body weight.
Hypertensive disorders of pregnancy complicate almost 7 - 10 % of all pregnancies. The dyad of hypertension and proteinuria after 20 weeks of gestation is referred to as pre-eclampsia. It is a major cause of maternal morbidity and mortality and is also associated with increased perinatal problems. Despite intensive research over the years the exact cause of pre-eclampsia remains unknown. Nevertheless, information gleaned from published studies point to the placenta as the probable pathogenetic focus of pre-eclampsia, as the disease usually resolves within 24 - 48 hours after delivery of the placenta. Although the precise involvement of the placenta in pre-eclampsia remains unclear there are indications that the trophoblastic invasion of the uterine spiral arteries is abnormal in women who develop pre-eclampsia. This impaired invasion leads to decreased placental perfusion and ultimately to placental hypoxia. The distressed or ischaemic placenta then secretes a factor(s) into the maternal circulation, which cause/s widespread endothelial cell dysfunction characterized by vasospasm, activation of coagulation system and organ ischaemia. The cause of the defective cytotrophoblastic invasion of the spiral arteries and the link between placental ischaemia and generalized maternal endothelial dysfunction remain unknown. Although the placenta appears to have a major role in the pathogenesis of pre-eclampsia, evidence also suggests that factors like maternal genetic predisposition, dietary, environmental and behaviour, which surface during the stress of pregnancy might also be involved in the development of pre-eclampsia. It is known that not all women with poor cytotrophoblast invasion develop pre-eclampsia and not all women with preeclampsia show poor cytotrophoblast invasion. Over the years, a number of potential risk factors associated with the development of pre-eclampsia are being recognized and it might be appropriate now to develop some preventative strategies based upon the available information.
Despite its important role in numerous physiological functions, including regulation of appetite and body weight, immune function and normal sexual maturation, raised leptin levels could result in significant damaging effects on sperm. The adverse effects of leptin on the male reproductive system result from its direct actions on the reproductive organs and cells instead of the hypothalamus-pituitary-gonadal axis. Binding of leptin to the receptors in the seminiferous tubular cells of the testes increases free radical production and decreases the gene expression and activity of endogenous enzymatic antioxidants. These effects are mediated via the PI3K pathway. The resultant oxidative stress causes significant damage to the seminiferous tubular cells, germ cells and sperm DNA leading to apoptosis, increased sperm DNA fragmentation, decreased sperm count, increased fraction of sperm with abnormal morphology, and decreased seminiferous tubular height and diameter. This review summarises the evidence in the literature on the adverse effects of leptin on sperm, which could underlie the often-reported sperm abnormalities in obese hyperleptinaemic infertile males. Although leptin is necessary for normal reproductive function, its raised levels could be pathologic. There is, therefore, a need to identify the cut-off level in the serum and seminal fluid above which leptin becomes pathological for better management of leptin associated adverse effects on male reproductive function.
This study investigates the effects of tocotrienol-rich palm vitamin E supplementation on exercise-induced lipid peroxidation and endurance performance in the heat. In a double blind, cross-over study, eighteen healthy, male recreational athletes completed two endurance running trials, until exhaustion, on a motorized treadmill at 70% VO2max on two separate occasions following a 6-week supplementation regimen of either tocotrienol-rich palm vitamin E (E) or placebo (P). Both trials were conducted in the heat (31°C, 70% relative humidity). During the trials, rectal temperature (Trec), ratings of perceived exertion (RPE) and oxygen uptake (VO2) were recorded. Blood samples were collected for the determination of plasma volume changes (PVC), malondialdehyde (MDA), creatine kinase (CK), total antioxidant status (TAS) and vitamin E. After the supplementation regimen, serum alpha-tocopherol increased ~33% but serum concentrations of tocotrienols were negligible. No significant differences were evident in mean Trec, RPE, VO2 or in the time to exhaustion between the E-supplemented and the placebo- supplemented groups. Similarly, mean PVC, CK and TAS were also not different between the two groups. Resting plasma mean MDA concentration in the E-supplemented group was significantly lower than that in the placebo-supplemented group. At exhaustion, plasma mean MDA was higher than the resting values in both groups. Although tocotrienol-rich palm vitamin E supplementation decreased lipid peroxidation at rest and, to some extent, during exercise in the heat, as evident from the lower MDA levels, it however did not enhance endurance running performance or prevent exercise-induced muscle damage or influenced body core temperature or plasma volume changes during exercise in the heat. Key Pointsreduced lipid peroxidation at rest.did not enhance endurance running performance in the heat.did not prevent exercise-induced muscle damage as indicated by CK activity.
To date, little is known about the effects of a reduced level of jumping exercise regimens on bone turnover markers and mass. This study investigates the effects of different jumping exercise regimens with varying exercise loads on serum bone turnover markers and bone mass in female rats.
The effects of indomethacin and nabumetone on urine and electrolyte excretion in conscious rats were examined. Male Sprague-Dawley rats were housed individually for a five-week duration, consisting of acclimatization, control, experimental, and recovery phases. During the experimental phase, rats were given either indomethacin (1.5 mg . kg(-1) body weight . day(-1) in 0.5 ml saline, n = 10), nabumetone (15 mg . kg(-1) body weight . day(-1) 0.5 ml saline, n = 10), or 0.5 ml saline alone (n = 10) for a period of two weeks. Water and food intake, body weight, urine output, and electrolyte excretions were estimated. Data were analyzed using two-way ANOVA. Urine output in the indomethacin- and nabumetone-treated groups was not different from the controls, but was significantly different between the drug-treated groups (P<0.01). Sodium, potassium, calcium, and magnesium excretions were not different between nabumetone-treated and control rats. However, sodium and potassium excretion was significantly lower in rats receiving indomethacin when compared to the control rats. Calcium and magnesium outputs, although did not differ from the controls, nevertheless decreased significantly with indomethacin (P<0.01). It appears that indomethacin and nabumetone when given at maximum human therapeutic doses may affect urine and electrolyte output in conscious rats.
Leptin, an adipocyte-derived hormone, serves numerous physiological functions in the body, particularly during puberty and reproduction. The exact mechanism by which leptin activates the gonadotropin-releasing hormone (GnRH) neurons to trigger puberty and reproduction remains unclear. Given the widespread distribution of leptin receptors in the body, both central and peripheral mechanisms involving the hypothalamic-pituitary-gonadal axis have been hypothesized. Leptin is necessary for normal reproductive function, but when present in excess, it can have detrimental effects on the male reproductive system. Human and animal studies point to leptin as a link between infertility and obesity, a suggestion that is corroborated by findings of low sperm count, increased sperm abnormalities, oxidative stress, and increased leptin levels in obese men. In addition, daily leptin administration to normal-weight rats has been shown to result in similar abnormalities in sperm parameters. The major pathways causing these abnormalities remain unidentified; however, these adverse effects have been attributed to leptin-induced increased oxidative stress because they are prevented by concurrently administering melatonin. Studies on leptin and its impact on sperm function are highly relevant in understanding and managing male infertility, particularly in overweight and obese men.
Raised leptin levels have been reported in the placentae and serum of women with elevated blood pressure and proteinuria during pregnancy. The role of leptin in this however remains unknown. This study investigates the effect of leptin administration on systolic blood pressure (SBP) and proteinuria and serum markers of endothelial activation during pregnancy in Sprague Dawley rats. From day 1 of pregnancy, 24 rats were randomised into those given either saline (group 1) or leptin at 60 or 120 μ g/kg/body weight/day (groups 2 and 3 resp.). SBP was measured every 5 days and 24-h urinary protein was measured at days 0 and 20 of pregnancy. Animals were euthanised on day 20 of pregnancy, and serum was collected for estimation of E-selectin and ICAM-1. Compared to group 1, SBP during the latter part of the pregnancy was significantly higher in the leptin-treated group (P < 0.01). Urinary protein excretion, serum E-selectin, and ICAM-1 were significantly higher in leptin-treated rats (P < 0.05). It seems that leptin administration to normotensive Sprague Dawley rats during pregnancy significantly increases SBP, urinary protein excretion, and markers of endothelial activation. However, further studies are required to examine the underlying mechanism responsible for this and its relevance to preeclampsia in humans.
Although melatonin supplementation is known to influence numerous physiological functions, little is however known of its effects on pregnancy outcome. This study investigated the effects of melatonin supplementation on pregnancy outcome in Wistar-Kyoto (WKY) and Sprague-Dawley (SD) rats aged 12-13 weeks. Upon confirmation of proestrus, each female rat was housed overnight with a male of the same strain. On the next morning, following confirmation of mating (vaginal smear), WKY female rats were isolated into individual metabolic cages and given 0, 25, 50 or 100 mg/kg per day of melatonin in drinking water from day 1 of pregnancy to day 21 postpartum. SD females were given 0 or 100 mg/kg per day of melatonin. Maternal weight, duration of pregnancy, litter size, birth weight and body weight of pups up to day 42, and pup mortality were recorded. Data were analyzed using ANOVA for repeated measures. Compared to controls, maternal weight gain during pregnancy was significantly lower in melatonin-supplemented dams (P < 0.01). Litter size was significantly smaller in melatonin-supplemented dams (P < 0.01). Mean birth weight of pups was significantly lower only in pups of dams given 100 mg/kg per day of melatonin (P < 0.001). Mean body weight of pups of dams given melatonin was significantly lower than controls (P < 0.01). Pup mortalities were 9.5% and 21.6% in WKY dams given 25 and 100 mg/kg per day of melatonin respectively, and all pup deaths occurred after day 21 of weaning. The results suggest that melatonin supplementation during antenatal and postpartum period appears to adversely affect litter size, pup growth and mortality in WKY and SD rats. The precise mechanism causing the death is not clear.
The effects of deconditioning on exercise-induced bone gains in rats were investigated in 12-week-old female WKY rats performing a standard jumping exercise regimen for either 8, 12 or 24 weeks, followed by sedentary periods of either 24, 12 or 0 weeks, respectively. Age-matched controls received no exercise over the same period. At the end of the training/sedentary period, the tibiae were harvested for analyses of bone parameters. Gains in tibial fat-free dry weight decayed within 12 weeks of deconditioning, but gains in tibial ultimate bending force (strength), maximum diameter and cortical area were still present at 12 weeks of deconditioning. With the exception of cortical area, all other exercise-induced bone gains decayed by the 24th week of deconditioning. It appears that the decay in exercise-induced bone gains in strength, physical and morphological properties is not uniform, and that gains in fat-free dry weight seem to decay earlier.
This report documents an incidental finding during a study investigating the effects of melatonin supplementation on the development of blood pressure in SHR. Administration of 10 mg/kg/day of melatonin in drinking water during pregnancy to Wistar-Kyoto (WKY) dams caused a loss of more than 50% of the pups by the age of three weeks and 95% by the age of 6 weeks. There was no maternal morbidity or mortality in the two strains or death of any of the SHR pups. No obvious physical defects were present but mean body weight was lower in the surviving WKY rats when compared to that of melatonin supplemented SHR or non-supplemented WKY pups. The reason for the high mortality in WKY pups is uncertain and appears to be strain if not batch specific. There is a need for caution in its use, particularly during pregnancy, and clearly necessitates more detailed studies.
Individuals who are obese are at a greater risk of developing gastric cancer. They are however also hyperleptinaemic. Chronic leptin treatment has been shown to upregulate numerous cancer-causing genes in the stomach of male Sprague-Dawley rats. It is however unclear if leptin enhances the effect of gastric carcinogens in vivo. This study was therefore done to investigate the effect of leptin on gastric carcinogenesis in rats treated with N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). Twenty-four, 6-week old male Sprague-Dawley rats were divided equally into three groups: G1 served as age-matched controls; G2 was treated with MNNG in drinking water ad libitum (200 mg L-1); G3 was given leptin and MNNG. Rats were euthanized after 40 weeks of treatment and their stomachs were removed for histopathology, microarray, and RT-qPCR analysis. Fisher's exact test and one-way ANOVA were used to analyse the data. Fifty percent of the MNNG-treated rats developed gastric hyperplasia (p
This study investigates the effect of ACE2 activation on leptin-induced changes in systolic blood pressure (SBP), proteinuria, endothelial activation and ACE2 expression during pregnancy in Sprague-Dawley rats. Pregnant rats were given subcutaneous injection of either saline, or leptin, or leptin plus xanthenone (ACE2 activator), or xanthenone (XTN) alone. SBP, serum ACE, ACE2, endothelin-1, E-selectin and ICAM-1 levels were estimated; also their gene expressions were determined in the kidney and aorta respectively. Compared to control, SBP was higher in the leptin-only treated group (P<0.001) and lower in rats treated with xanthenone alone (P<0.01). Proteinuria, markers of endothelial activation were significantly higher than controls in leptin-only treated rats (P<0.05). ACE2 activity and expression were lower in leptin-only treated rats when compared to controls (P<0.05). It seems, leptin administration during pregnancy significantly increases SBP, proteinuria, endothelial activation, but decreases ACE2 level and expression. These effects are prevented by concurrent administration of xanthenone.
Although oxidative stress has been implicated in the pathogenesis of hypertension in spontaneously hypertensive rats (SHRs), there is little information on the levels of primary antioxidant enzymes status (AOEs) in pre-hypertensive SHR. This study therefore determined the activities of primary AOEs and their mRNA levels, levels of hydrogen peroxide (H2O2), malondialdehyde (MDA) and total antioxidant status (TAS) in whole kidneys of SHR and age-matched Wistar-Kyoto (WKY) rats aged between 2 and 16 weeks. Compared with age-matched WKY rats, catalase (CAT) activity was significantly higher from the age of 2 weeks (P<0.001) and glutathione peroxide (GPx) activity was lower from the age of 3 weeks (P<0.001) in SHR. CAT mRNA levels were significantly higher in SHR aged 2, 4, 6 and 12 weeks. GPx mRNA levels were significantly lower in SHR at 8 and 12 weeks. Superoxide dismutase activity or its mRNA levels were not different between the two strains. H2O2 levels were significantly lower in SHR from the age of 8 weeks (P<0.01). TAS was significantly higher in SHR from the age of 3 weeks (P<0.05). MDA levels were only significantly higher at 16 weeks of age in the SHR (P<0.05). The data suggest that altered renal CAT and GPx mRNA expression and activity precede the development of hypertension in SHR. The raised CAT activity perhaps contributes to the higher TAS and lower H2O2 levels in SHR. In view of these findings, the precise role of oxidative stress in the pathogenesis of hypertension in SHR needs to be investigated further.
Low sperm concentration, increased fraction of morphologically abnormal sperm, and raised levels of markers of oxidative stress are often reported in the seminal plasma of infertile obese males. The precise reason for changes remains unknown. This short review summarises evidence from human and animal studies linking leptin to the reproductive dysfunction reported in obese males and presents a possible mechanism for this based on the available data in the literature. Serum leptin concentrations correlate positively with body fat mass but its precise link to semen abnormalities reported in obese males has yet to be conclusively established. Decreased sperm concentration, increased fraction of morphologically abnormal sperm and increased markers of oxidative stress have been reported following six weeks of daily leptin treatment to normal weight rats. In addition, decreased expression of endogenous antioxidant enzymes and increased expression of respiratory chain enzymes noted in the testes of leptin treated rats increases the propensity to oxidative stress. Besides that, leptin's interference with histone to protamine transition in the DNA of sperm increases the susceptibility of sperm to free radical attack and may explain the often reported higher DNA fragmentation index in sperm of obese males. Concurrent supplementation of melatonin, a natural anti-oxidant, to these rats prevents the effects of leptin. The role of leptin in obesity-related reproductive dysfunction has to be considered seriously and these effects of leptin might involve increased oxidative stress.
To ascertain the embryotoxicity of peritoneal fluid from infertile women with endometriosis (PF-E), on mouse embryos in culture and to examine the effect of pyruvate in the culture medium on PF-E induced embryotoxicity.
Levels of leptin and marinobufagenin (MBG), a cardiotonic steroid, are elevated in the serum of women with pre-eclampsia. Besides this, leptin administration to pregnant rats increases systolic blood pressure (SBP), urinary protein excretion and serum markers of endothelial activation. The link between leptin and MBG is unknown and it is also unclear if leptin-induced increases in blood pressure and proteinuria in the pregnant rat could be prevented by an MBG antagonist. To ascertain this link, this study investigated the effect of resibufogenin (RBG), a marinobufagenin antagonist, on leptin-induced increases in blood pressure and proteinuria during pregnancy in rats. Four groups of Sprague-Dawley rats, aged 12 weeks, were given either normal saline (CONTROL) or 120 μg/kg/day of leptin (LEP), or 120 μg/kg/day of leptin+30 μg/kg/day of resibufogenin (L + RBG) or 30 μg/kg/day of resibufogenin (RBG) from Day 1-20 of pregnancy. Systolic blood pressure and urinary protein excretion (UPE) were measured during the study period. Animals were euthanized on day 21 of pregnancy and vascular cell adhesion molecule 1, (VCAM-1), soluble intracellular cell adhesion molecule 1 (sICAM-1), E-selectin and endothelin-1 (ET-1) were estimated in the serum. SBP, UPE, VCAM-1, sICAM-1 and ET-1 were significantly higher only in the LEP group when compared with those in CONT and in L + RBG and RBG groups. The prevention by RBG of leptin-induced increases in SBP, proteinuria, and endothelial activation during pregnancy seem to suggest a potential role for MBG in leptin-induced adverse effects on blood pressure, urinary protein excretion and endothelial activity during pregnancy in the rat.
This study investigated the effects of a standardised ethanol and water extract of Ficus deltoidea var. Kunstleri (FDK) on blood pressure, renin-angiotensin-aldosterone system (RAAS), endothelial function and antioxidant system in spontaneously hypertensive rats (SHR). Seven groups of male SHR were administered orally in volumes of 0.5 mL of either FDK at doses of 500, 800, 1000 and 1300 mg kg- 1, or captopril at 50 mg kg- 1 or losartan at 10 mg kg- 1 body weight once daily for 4 weeks or 0.5 mL distilled water. Body weight, systolic blood pressures (SBP) and heart rate (HR) were measured every week. 24-hour urine samples were collected at weeks 0 and 4 for electrolyte analysis. At week 4, sera from rats in the control and 1000 mg kg- 1 of FDK treated groups were analyzed for electrolytes and components of RAAS, endothelial function and anti-oxidant capacity. SBP at week 4 was significantly lower in all treatment groups, including captopril and losartan, when compared to that of the controls. Compared to the controls, ACE activity and concentrations of angiotensin I, angiotensin II and aldosterone were lower whereas concentrations of angiotensinogen and angiotensin converting enzyme 2 were higher in FDK treated rats. Concentration of eNOS and total anti-oxidant capacity were higher in FDK treated rats. Urine calcium excretion was higher in FDK treated rats. In conclusion, it appears that ethanol and water extract of FDK decreases blood pressure in SHR, which might involve mechanisms that include RAAS, anti-oxidant and endothelial system.