Plasma leptin concentration in adult cattle: effects of breed,adiposity, feeding level,and meal intake

An ovine-specific RIA, shown to be reliable for bovine leptin determination, was used to study the effects of breed, body fatness, feeding level, and meal intake on plasma leptin level in adult cattle. Eighteen fat Charolais, fat Holstein, and lean Holstein adult cows were either well-fed (130% of maintenance energy requirements [MER]) or underfed (60% of MER) for 3 wk. The breed tended to have a small effect on plasma leptin level, which was decreased by 70% (P < 0.05) in lean compared to fat Holstein cows. A strong curvilinear relationship was found between mean adipocyte volume and plasma leptin concentrations in well-fed (r = +0.95) and underfed (r = +0.91) cows. Underfeeding caused a significant decrease in plasma leptin levels from 8.0+/-3.1 to 6.1+/-2.3 ng/mL (P < 0.01). Nine adult Holstein cows initially fed at 130% of MER (control) were underfed to 21% of MER for 7 d, and five of them were refed to 237% of MER for 21 d. Plasma leptin measured 1 h before meal distribution was decreased from 5.9+/-0.4 to 3.8+/-0.2 ng/mL (P < 0.01) by underfeeding and increased to reach 8.8+/-1.0 ng/mL (P < 0.01) after refeeding. It was positively related to plasma glucose (r = +0.52, P < 0.01) and negatively related to plasma NEFA (r = -0.67, P < 0.001). Plasma leptin measured 4 h after meal distribution was positively related to feeding level and to plasma 3-OH-butyrate (r = +0.61, P < 0.005) and negatively related to plasma NEFA (r = -0.56, P < 0.01). Differences between pre- and postprandial leptin concentrations showed a decrease after meal intake in control and well-fed cows (-7 and -19%, P < 0.01, respectively) and an increase in underfed cows (+12%, P < 0.01). Leptin response to meal intake was positively related to glucose response (r = +0.66, P < 0.001) and negatively related to 3-OH-butyrate response (r = -0.78, P < 0.001). By using the "multispecies" commercial RIA, leptin concentrations were lower and we observed similar physiological responses, although less related to other hormones or metabolites. These data provide evidence, first, that a specific RIA for ruminant leptin determination is necessary to better understand leptin regulation, and second, that plasma leptin is strongly related to adipose cell size and positively related to feeding level in adult cattle, and that an effect of meal intake could be mediated by glucose and(or) ketone bodies.     

Exogenous leptin advances puberty in domestic hen

The present study was undertaken to examine the effect of recombinant chicken leptin administered to fed ad libitum and feed-restricted immature chickens of a layer strain on ovarian development and the timing of sexual maturity. In the first experiment 11-week-old pullets (77 days of age) fed ad libitum were injected daily with leptin at four dose levels (4, 16, 64 and 256 microg/kg body weight) until sexual maturity (lay of the first egg). Leptin treatment at the highest dose significantly (P<0.05) advanced the onset of puberty (day 116.3+/-1.0) in comparison to controls (day 121.3+/-1.2). The rises of luteinizing hormone, estradiol and progesterone in blood plasma were also advanced by leptin treatment. In the second experiment, both full-fed and feed-restricted pullets (79 days of age) were injected daily with leptin (256 microg/kg body weight). In birds fed ad libitum, exogenous leptin again significantly (P<0.05) advanced first ovipostion (day 118.4+/-1.4 versus day 124.4+/-1.7), while abolishing the significant (P<0.05) delay caused by feed restriction (day 131.5+/-1.6) and restoring the normal onset of sexual maturity (day 125.7+/-1.6). Analysis of the ovaries in 106-day-old pullets revealed that leptin injections advanced follicular development, particularly in birds fed ad libitum, and significantly (P<0.01) reduced follicular apoptosis both in full-fed and feed-restricted birds. In conclusion, we have shown that in female chickens exogenous leptin advances the onset of puberty by attenuation of ovarian apoptosis and enhancement of folliculogenesis.     

Plasma leptin concentrations in cats: reference range, effect of weight gain and relationship with adiposity as measured by dual energy X-ray absorptiometry

The aims of our study were to determine a reference range for plasma leptin in healthy, normal-weight cats and to measure the effect of weight gain on plasma leptin levels. To increase our understanding of the association between leptin and feline obesity, we investigated the relationship between plasma leptin and measures of adiposity in cats. Twenty-six normal-weight cats were used to determine the reference range for feline leptin using a multispecies radioimmunoassay. In the second part of the study, plasma leptin concentrations were determined in 16 cats before and after approximately 10 months of spontaneous weight gain. Dual energy X-ray absorptiometry scans (DEXA) were performed after weight gain. The tolerance interval for plasma leptin concentrations was 0.92-11.9 ng/ml Human Equivalent (HE) with a mean concentration of 6.41+/-2.19 ng/ml HE. In part two of the study, 16 cats gained on average 44.2% bodyweight over 10 months. The percentage of body fat in obese cats ranged from 34.2 to 48.7%. Mean plasma leptin concentrations increased from 7.88+/-4.02 ng/ml HE before weight gain to 24.5+/-12.1 ng/ml HE after weight gain, (P<0.001). Total body fat and body fat per cent were the strongest predictors of plasma leptin in obese cats (r=0.8 and r=0.78, P<0.001, respectively). In conclusion, plasma leptin concentrations increased three-fold in cats as a result of weight gain and were strongly correlated with the amount of adipose tissue present. Despite elevated leptin levels, cats continued to eat and gain weight, suggesting decreased sensitivity to leptin. This investigation into the biology of leptin in cats may aid the overall understanding of the role of leptin and the development of future treatments to help prevent and manage feline obesity.     

Sandwich enzyme-linked immunosorbent assay of canine leptin

Leptin is the ob gene product secreted from adipocytes in mammals, and thereby its plasma level reflects body fat content. To establish an assay method for leptin in the dog, rabbit anti-canine leptin antibody was obtained using canine recombinant leptin as an antigen. This antibody reacted to canine leptin much stronger than mouse, rat and human leptins. Sandwich enzyme-linked immunosorbent assay (ELISA) using this antibody was developed. The serum leptin levels of 13 healthy dogs were in a range from 1.4 to 5.6 ng/ml with the mean +/- SEM of 3.0 +/- 0.3 ng/ml.     

Experimental and clinical studies on plasma leptin in obese dogs

Leptin is a protein synthesized and secreted primarily by adipocytes, and the circulating leptin concentration is elevated in obese humans and rodents. Recently, we have established a sandwich enzyme-linked immunosorbent assay for canine leptin. In the present study, plasma leptin concentrations were measured in experimentally developed obese beagles and in clinically obese dogs. When 5 male beagles were given a high-energy diet for 3 months, all of them became obese and the plasma leptin concentration significantly increased from 2.4+/-1.2 to 4.9+/-0.9 ng/ml, positively correlating with body fat content estimated by the deuterium oxide dilution method (r=0.87). The leptin concentrations of plasma samples collected from 59 dogs in veterinary practices were compared with their body condition scores (BCS). The plasma leptin concentrations of obese dogs were 9.7+/-0.7 and 12.3+/-1.5 ng/ml at BCS=4 and BCS=5, respectively, which were significantly higher than those of optimal (BCS=3) dogs (2.7+/-0.3 ng/ml). There was no significant effect of sex and breed. A weak positive correlation (r=0.37) was found between the plasma leptin concentration and age, probably due to the lesser content of visceral fat in puppies younger than 1 year old. These results indicate that plasma leptin is a good index of adiposity in dogs regardless of breed, age and sex, and may be useful for quantitative assessment of obesity in small animal practice.     

Relationship between serum leptin immunoreactivity and body fat mass as estimated by use of a novel gas-phase Fourier transform infrared spectroscopy deuterium dilution method in cats

OBJECTIVE: To validate a recently developed commercially available leptin radioimmunoassay (RIA) for use with feline serum and evaluate the relationship between serum leptin concentrations and body fat mass in domestic cats. ANIMALS: 19 sexually intact male specific-pathogen-free domestic cats that weighed 3.8 to 7.1 kg and were 1.1 to 3.5 years old. PROCEDURE: Specificity for feline leptin was evaluated by use of gel filtration chromatography and reverse-phase high-performance liquid chromatography fractionation of serum. Body fat mass was determined by use of the deuterium oxide (D2O) dilution method. Serum water D2O enrichment was measured by use of gas-phase Fourier transform infrared spectroscopy. RESULTS: Body fat mass and percentage body fat ranged from 0.3 to 2.3 kg and 7.5 to 34.9%, respectively. Serum leptin concentrations were lower in the unfed versus the fed state and ranged between 1.6 and 4.9 ng/ml human equivalent (HE); mean +/- SD value was 2.9 +/- 0.2 ng/ml HE. Leptin concentrations increased with increasing body fat mass and percentage of body fat. CONCLUSIONS: Leptin is in the serum of domestic cats in free (> 78%) and apparently bound forms. The relationship between body fat and serum leptin concentration was similar to that observed in humans and rodents and indicative of a lipostatic role for leptin in cats. Cats that have an overabundance of body fat appear to be less sensitive to the weight-normalizing action of leptin than cats of ideal body condition.     

Variations of plasma leptin in show horses during a work season

Leptin is an adipocytokine mainly expressed by adipose tissue. Secretion of leptin in healthy animals is closely related to fat mass and metabolic activity. The aim of this study was to investigate plasma leptin variations, in relation to nutritional and exercise parameters in adult show horses during a work season. EDTA-blood samples were taken at rest from 37 Iberian horses. Body weight, body condition score and fat percentage determined by ultrasonic measurement of rump fat thickness were measured. Plasma leptin was determined with a multi-species RIA kit. Linear mixed effects model was used to assess relationship between plasma leptin and other biological parameters. Plasma leptin concentration was <12.6 ng/ml (mean = 2.8 ± 1.6 ng/ml) and was significantly higher during training periods (p < 0.0001) (4.5 ± 1.7 ng/ml) than in show periods (2.0 ± 1.1 ng/ml), despite a significant increase (p < 0.0001) in energy intake. The body weight remained almost constant. The plasma leptin concentrations were significantly affected by exercise (p < 0.0001), body weight (p = 0.04) and BCS (p < 0.0001), but were not affected by percentage of fat. In conclusion, the marked decrease in leptin values observed during a period of intense (i.e. excessive) exercise could result from an adaptation to cumulative alterations in energy balance, to exercise per se or to a combination of both.     

Changes in the level of endogenous leptin, FSH, 17beta-oestradiol and metabolites during lupin-induced increase in ovulation rate in ewes

The aim of the study was to determine the changes in the plasma concentration of leptin during lupin feeding-induced increase in the ovulation rate (OR) in ewes. Additionally, alterations in the plasma level of glycogenic amino acids and glucose (as the factors influencing leptin secretion) and the levels of follicle-stimulating hormone (FSH) and 17beta-oestradiol (E-2) (as the hormones regulated by leptin and engaged in recruitment, selection and development of ovulatory follicles) were analysed. Ninety-six female Polish Lowland Sheep were used. All ewes were cyclic and synchronized with PGF2alpha. The ewes were divided into two groups: control (n = 48), fed only with hay, and experimental (n = 48), received additionally lupin (Lupinus angustifolius) grain as a high-protein and a high-energy supplement. They were given lupin from the second to 13th day of the oestrous cycle at increasing doses (150-750 g/day per ewe). On the 11th day of cycle blood samples for analysis of hormones, amino acids and total glucose concentration, were collected from the jugular vein. OR was determined by laparoscopy of ovaries on the sixth day of the following oestrous cycle. Mean OR of ewes supplemented with lupin grain (1.687 +/- 0.463) was 30.67% higher than that of control (1.291 +/- 0.454). In spite of the unchanged body mass, a significant increase (P < or = 0.05) in mean concentration of plasma leptin in the experimental ewes [2.17 +/- 0.15 ng/ml human equivalent (HE)] was found in comparison with control (1.42 +/- 0.12 ng/ml HE). A significantly (P < or = 0.05) higher plasma FSH level in the ewes fed lupin (105.21 +/- 5.87 ng/ml) compared with those fed hay (67.88 +/- 6.03 ng/ml) was also found. However, plasma level of E-2 decreased after lupin feeding. Moreover, in the ewes fed lupin the plasma concentrations of glucose and nine glycogenic amino acids (Gly, Ala, Val, Met, Leu, Ile, Tyr, Phe and Arg) were increased. It can be concluded that lupin feeding exerts the stimulatory effect on the OR in Polish Lowland Sheep. The increase in OR is connected with significantly higher plasma leptin level and coincident with rise in FSH, glycogenic amino acids and glucose concentration. In contrast, the level of plasma E-2 was significantly decreased in lupin-fed ewes.     

Chicken leptin: properties and actions

Chicken leptin cDNA shows a high homology to mammalian homologous, with an expression localized in the liver and adipose tissue. It is noteworthy, that the hepatic expression is most likely associated with the primary role that this organ plays in lipogenic activity in avian species. As in mammals, chicken leptin expression is regulated by hormonal and nutritional status. This regulation is tissue-specific and with a high sensitivity in the liver compared to adipose tissue. The blood leptin levels are regulated by the nutritional state with high levels in the fed state compared to the fasted state. The recombinant chicken leptin markedly inhibits food intake as reported in mammals, suggesting the presence of an hypothalamic leptin receptor. The chicken leptin receptor has been identified and all functional motifs are highly conserved compared to mammalian homologous. Chicken leptin receptor is expressed in the hypothalamus but also in other tissues such as pancreas, where leptin inhibits insulin secretion and thus may have a key role in regulating nutrient utilization in this species.     

Fasting-induced changes in ovulation rate, plasma leptin, gonadotropins, GH, IGF-I and insulin concentrations during oestrus in ewes

The aim of this experiment was to study the changes in the hormonal status and ovulation rate (OR) evoked by starvation during the follicular phase of the oestrous cycle in ewes. To achieve this goal, 12 female crossbreed sheep were synchronized and then half of them were fasted from the 12th to the 16th day of the oestrous cycle. On the 16th day, analysis of hormones and insulin-like growth factor-I (IGF-I) were performed in 10-min intervals. Then, on the 6th day of the following oestrous cycle, the OR in all ewes was determined by laparoscopy. Fasting reduced significantly (P < 0.05) the OR in ewes (1.25 +/- 0.50) in comparison with control (1.75 +/- 0.50). The drop in the OR was coincident with a significant (P < 0.001) decrease in the plasma concentration and pulse amplitude of leptin (0.29 +/- 0.08 ng/ml versus control 0.53 +/- 0.14 ng/ml), the plasma level of luteinizing hormone (LH) (0.19 +/- 0.06 IU/l versus 0.25 +/- 0.09 IU/l in control; P < 0.05) and the mean frequency of LH pulses (2.0/h versus 2.5/h in control). Fasting resulted also in a significant (P < 0.05) decrease in the plasma concentration and pulse amplitude of follicle stimulating hormone (FSH) in comparison with the control. Simultaneously, a significant (P < 0.001) drop in the IGF-I concentration in the fasted ewes (4.78 +/- 0.91 ng/ml) was found in comparison with control (7.63 +/- 1.85 ng/ml). Also the level of insulin were significantly (P < 0.001) lower in the fasted (178.99 +/- 39.08 pM/l respectively) than in the control sheep (302.66 +/- 49.01 pM/l respectively). Meanwhile, a double increase in the growth hormone (GH) pulses frequency and an augmentation in its plasma concentrations as a result of starvation was found. The obtained results shows that the acute fasting exerts an inhibitory effect on the ovulation rate in ewes coincident with suppression in leptin, FSH and LH secretion and changes in signalization mediated by GH.     

Serum leptin concentrations, luteinizing hormone and growth hormone secretion during feed and metabolic fuel restriction in the prepuberal gilt

Two experiments were conducted to determine 1) the effect of acute feed deprivation on leptin secretion and 2) if the effect of metabolic fuel restriction on LH and GH secretion is associated with changes in serum leptin concentrations. Experiment (EXP) I, seven crossbred prepuberal gilts, 66 +/- 1 kg body weight (BW) and 130 d of age were used. All pigs were fed ad libitum. On the day of the EXP, feed was removed from four of the pigs at 0800 (time = 0) and pigs remained without feed for 28 hr. Blood samples were collected every 10 min from zero to 4 hr = Period (P) 1, 12 to 16 hr = P 2, and 24 to 28 hr = P 3 after feed removal. At hr 28 fasted animals were presented with feed and blood samples collected for an additional 2 hr = P 4. EXP II, gilts, averaging 140 d of age (n = 15) and which had been ovariectomized, were individually penned in an environmentally controlled building and exposed to a constant ambient temperature of 22 C and 12:12 hr light: dark photoperiod. Pigs were fed daily at 0700 hr. Gilts were randomly assigned to the following treatments: saline (S, n = 7), 100 (n = 4), or 300 (n = 4) mg/kg BW of 2-deoxy-D-glucose (2DG), a competitive inhibitor of glycolysis, in saline iv. Blood samples were collected every 15 min for 2 hr before and 5 hr after treatment. Blood samples from EXP I and II were assayed for LH, GH and leptin by RIA. Selected samples were quantified for glucose, insulin and free fatty acids (FFA). In EXP I, fasting reduced (P < 0.04) leptin pulse frequency by P 3. Plasma glucose concentrations were reduced (P < 0.02) throughout the fast compared to fed animals, where as serum insulin concentrations did not decrease (P < 0.02) until P 3. Serum FFA concentrations increased (P < 0.02) by P 2 and remained elevated. Subcutaneous back fat thickness was similar among pigs. Serum IGF-I concentration decreased (P < 0.01) by P 2 in fasted animals compared to fed animals and remained lower through periods 3 and 4. Serum LH and GH concentrations were not effected by fast. Realimentation resulted in a marked increase in serum glucose (P < 0.02), insulin (P < 0.02), serum GH (P < 0.01) concentrations and leptin pulse frequency (P < 0.01). EXP II treatment did not alter serum insulin levels but increased (P < 0.01) plasma glucose concentrations in the 300 mg 2DG group. Serum leptin concentrations were 4.0 +/- 0.1, 2.8 +/- 0.2, and 4.9 +/- 0.2 ng/ml for S, 100 and 300 mg 2DG pigs respectively, prior to treatment and remained unchanged following treatment. Serum IGF-I concentrations were not effected by treatment. The 300 mg dose of 2DG increased (P < 0.0001) mean GH concentrations (2.0 +/- 0.2 ng/ml) compared to S (0.8 +/- 0.2 ng/ml) and 100 mg 2DG (0.7 +/- 0.2 ng/ml). Frequency and amplitude of GH pulses were unaffected. However, number of LH pulses/5 hr were decreased (P < 0.01) by the 300 mg dose of 2DG (1.8 +/- 0.5) compared to S (4.0 +/- 0.4) and the 100 mg dose of 2DG (4.5 +/- 0.5). Mean serum LH concentrations and amplitude of LH pulses were unaffected. These results suggest that acute effects of energy deprivation on LH and GH secretion are independent of changes in serum leptin concentrations.     

Effects of immunisation against leptin on feed intake, weight gain, fat deposition and laying performance in chickens

1. Three experiments were conducted to study the effects of leptin on weight gain and body composition in laying hens. 2. The effects of immunisation against chicken leptin on feed intake (FI), fat deposition and laying rate were observed in laying Guangdong yellow-feathered hens. Ten hens were inoculated with leptin immunogen on d 3, 31, 63 and 84, together with 10 control hens immunised with bovine serum albumin (BSA). In the 100-d experiment, immunisation against leptin increased blood anti-leptin antibody titres, slightly reduced plasma T3 concentrations, slightly decreased FI and increased live weight; however, laying rate was significantly depressed and abdominal fat mass was increased by the end of the 100-d experiment. 3. Passive immunisation of 50-d-old pullets with yolk extract containing anti-leptin antibody IgY significantly increased FI within 6 h of treatment compared with physiological saline treated controls. 4. In growing 70-d-old pullets, inoculation with 0.5 (group 1) or 1 (group 2) ml leptin immunogen on d 1 and 28 of the experiment slightly increased FI and significantly increased daily gain compared with BSA-immunised control pullets. Abdominal fat mass on d 49 increased from 48+/-4.5 g in controls to 66+/-3.5 and 80+/-3.1 g in groups 1 and 2, respectively. 5. It was suggested that immunisation against leptin mimicked loss of leptin bioactivity and might become a novel technique to stimulate fat growth in certain types of animal production.     

Evaluation of adrenal function in psittacine birds, using the ACTH stimulation test

The effect of ACTH (16 units) on plasma cortisol and corticosterone concentrations in healthy psittacine birds was evaluated. Plasma corticosterone significantly increased (P less than 0.01) from a mean (+/- SD) basal concentration of 3.25 +/ 3.6 ng/ml to 26.47 +/- 9.25 (one hour after ACTH administration) and 25.69 +/- 13.23 ng/ml (2 hours after ACTH administration). For maximal increase in plasma corticosterone as measured by radioimmunoassay (RIA), heat denaturation was necessary to release corticosteroids from steroid-binding proteins. As measured by RIA, plasma cortisol concentrations did not increase, whether or not the heat denaturation step was included. Addition of cortisol to avian plasma did not prevent accurate quantification of cortisol as measured by RIA. Plasma corticosterone concentrations in cockatoos, macaws, Amazon parrots, conures, and lorikeets before and after ACTH administration indicated that the ACTH stimulation test could be used to evaluate adrenal secretory capacity in psittacine birds.     

Campylobacter jejuni infection in broiler chickens

Day-old, straight-run broiler chickens were procured from a hatchery located in the Pacific Northwest. The chickens were subdivided individually into nine groups of 20 chickens. The chickens were tagged, housed in isolation chambers on wire, fed commercial broiler feed, and given water ad libitum. Three isolates of Campylobacter jejuni of poultry origin and one of human origin were tested in this study. Various C. jejuni cultures were inoculated into 9-day-old chickens by crop gavage. Four groups of 20 chickens were inoculated at a dose level of 0.5 ml of 1 x 10(2) colony-forming units (CFU)/ml. The other four groups were inoculated with 0.5 ml of 1 X 10(4) CFU/ml. One group of 20 chickens was kept as an uninoculated control group. Four randomly selected chickens from each of the inoculated and uninoculated groups were necropsied at 5, 12, and 19 days postinoculation (DPI). The C. jejuni was cultured and enumerated from a composite of the upper and midintestine and the cecum. Body weights of all chicken groups at 7 days of age and at 5, 12, and 19 DPI were measured and statistically analyzed. No significant differences were present in the mean body weights (MBWs) of 7-day-old, 5 DPI, and 12 DPI male and female broiler chickens inoculated with C. jejuni at both dose levels compared with uninoculated controls. Differences in MBWs of the male and female broilers at 19 DPI were observed in some of the groups. Results of the C. jejuni culture enumeration mean (CEM) of composite intestine samples at 5 DPI from all inoculated chicken groups, irrespective of the dose level, ranged from (2.5 +/- 5.0) x 10(2) to (2.8 +/- 4.8) x 10(5) CFU/g (mean +/- SD). Results of cecum C. jejuni CEM at 5 DPI inoculated at both dose levels ranged from (2.5 +/- 5.0) x 10(6) to (1 +/- 0.0) x 10(7) CFU/g in all treatment groups irrespective of the dose level. CEM results from the composite intestine samples at 12 and 19 DPI increased by 1 log unit, or sometimes more. Results of cecum C. jejuni CEM at 5 DPI inoculated at both dose levels ranged from (2.5 +/- 5.0) x 10(6) to (1 +/- 0.0) x 10(7) CFU/g in all treatment groups irrespective of the dose level. Increases of 2-5 log units in C. jejuni CEM was present in chicken groups inoculated with 1 X 10(2) CFU of C. jejuni, and a 2- to 3-log increase was present in groups inoculated with a higher dose level of C. jejuni at 12 DPI. The results of C. jejuni CEM from cecal samples at 19 DPI were similar to chicken groups at 12 DPI. Campylobacterjejuni was not isolated from the uninoculated control chickens at 5, 12, and 19 DPI. Clinical signs of illness or gross pathologic lesions were not present in any of the chicken groups during this study. No lesions were present on histopathologic evaluations in C. jejuni-inoculated chickens or uninoculated control chickens.     

Comparative plasma dispositions of ivermectin and doramectin following subcutaneous and oral administration in dogs

This study evaluates the comparative plasma dispositions of ivermectin (IVM) and doramectin (DRM) following oral and subcutaneous administration (200 microg/kg) over a 40-day period in dogs. Twenty bitches were allocated by weight in to four groups (Groups I-IV) of five animals each. Animals in the first two groups (Groups I and II) received orally the injectable solutions of IVM and DRM, respectively, at the dose of 200 microg/kg bodyweight. The other two groups (Groups III and IV) received subcutaneously injectable solutions at the same dose rate. Blood samples were collected between 1h and 40 days after treatment and the plasma samples were analysed by high performance liquid chromatography (HPLC) using fluorescence detection. The results indicated that IVM produced a significantly higher maximum plasma concentration (C(max): 116.80+/-10.79 ng/ml) with slower absorption (t(max): 0.23+/-0.09 day) and larger area under the concentration versus time curve (AUC: 236.79+/-41.45 ng day/ml) as compared with DRM (C(max): 86.47+/-19.80 ng/ml, t(max): 0.12+/-0.05 day, AUC: 183.48+/-13.17 ng day/ml) following oral administration of both drugs; whereas no significant differences were observed on the pharmacokinetic parameters between IVM and DRM after subcutaneous administrations. In addition, subcutaneously given IVM and DRM presented a significantly lower maximum plasma concentration (C(max): 66.80+/-9.67 ng/ml and 54.78+/-11.99 ng/ml, respectively) with slower absorption (t(max): 1.40+/-1.00 day and 1.70+/-0.76 day, respectively) and larger area under the concentration versus time curve (AUC: 349.18+/-47.79 ng day/ml and 292.10+/-78.76 ng day/ml, respectively) as compared with the oral administration of IVM and DRM, respectively. No difference was observed for the terminal half-lives ((t(1/2lambda(z)) and mean residence times (MRT) of both molecules. Considering the pharmacokinetic parameters, IVM and DRM could be used by the oral or subcutaneous route for the control of parasitic infection in dogs.     

Effects of short-term feed deprivation and melatonin implants on circadian patterns of leptin in the horse

Leptin is a protein hormone produced by adipose tissue that influences hypothalamic mechanisms regulating appetite and energy balance. In species tested thus far, including horses, concentrations of leptin increase as animal fat mass increases. The variables and mechanisms that influence the secretion of leptin are not well known, nor is it known in equine species how the secretion of leptin is influenced by acute alterations in energy balance, circadian patterns, and/or reproductive competence. Our objectives were to determine in horses: 1) whether plasma concentrations of leptin are secreted in a circadian and/or a pulsatile pattern; 2) whether a 48-h period of feed restriction would alter plasma concentrations of leptin, growth hormone, or insulin; and 3) whether ovariectomy and/or a melatonin implant would affect leptin. In Exp. 1, mares exposed to ambient photoperiod of visible light (11 h, 33 min to 11 h, 38 min), received treatments consisting of a 48-h feed restriction (RES) or 48 h of alfalfa hay fed ad libitum (FED). Mares were maintained in a dry lot before sampling and were tethered to a rail during sampling. Analyses revealed that leptin was not secreted in a pulsatile manner, and that mean leptin concentrations were greater (P < 0.001) in FED vs. RES mares (17.20 +/- 0.41 vs. 7.29 +/- 0.41 ng/mL). Plasma growth hormone was pulsatile, and mean concentrations were greater in RES than FED mares (2.15 +/- 0.31 vs. 1.08 +/- 0.31 ng/mL; P = 0.05). Circadian patterns of leptin secretion were observed, but only in FED mares (15.39 +/- 0.58 ng/mL for morning vs. 19.00 +/- 0.58 ng/mL for evening; P < 0.001). In Exp. 2, mares that were ovariectomized or intact received either a s.c. melatonin implant or a sham implant. Thereafter, blood was sampled at weekly intervals at 1000 and 1700. Concentrations of leptin in samples collected at 1700 were greater (P < 0.001) than in those collected at 1000 (28.24 +/- 1.7 vs. 22.07 +/- 1.7 ng/mL). Neither ovariectomy nor chronic treatment with melatonin affected plasma concentrations of leptin or the circadian pattern of secretion. These data provide evidence that plasma leptin concentrations in the equine are sensitive to acute changes in nutritional status and vary in a circadian pattern that is sensitive to fasting but not to melatonin treatment or ovariectomy.     

The effect of interval versus continuous exercise on plasma leptin and ghrelin concentration in young trotters

The effect of interval vs. continuous exercise on plasma leptin and ghrelin concentration in young Standardbred horses was studied. The experiment was conducted on 27 trotters, in the age between 2 and 3 years. They were divided into two groups according to the type of exercise. Blood samples were collected through jugular venipuncture in the following experimental conditions: at rest, immediately after exercise and 30 minutes after the end of the effort. Plasma leptin and ghrelin concentrations were determined using RIA tests. The continuous exercise induced an increase in plasma leptin concentration whereas the interval type of exercise did not influence the level of this hormone (3.47 +/- 0.78 vs. 4.07 +/- 0.94 and 2.31 +/- 0.15 vs. 2.36 +/- 0.21 ng/mL, respectively). The plasma ghrelin concentration measured after the continuous exercise, significantly increased (720 +/- 27.4 vs. 814 +/- 13.8; p < or = 0.05) whereas concentration of this hormone assessed after the interval exercise, significantly dropped (982 +/- 56.5 vs. 842 +/- 35.6 pg/mL; p < or = 0.05). The changes in plasma ghrelin concentration measured after the end of the effort correlated inversely with blood lactic acid concentration. In conclusion, the obtained results showed that medium-intensive type of exercise, such as trot, interval or continuous, slightly affected plasma leptin level but significantly affected plasma ghrelin concentration in young Standardbred trotters.     

Serum leptin levels during the periparturient period in cows

Serum leptin concentrations were measured in antenatal and postnatal cows housed at two different locations. The mean serum leptin concentration was 9.2 +/- 0.6 ng/m l (n=22) in one group, and was slightly lower in the other (7.4 +/- 0.4 ng/ml, n=54), probably because of the different nutritional conditions between the two groups. There was no consistent variation in relation to the menstrual cycle and the periparturient period in both groups. Moreover, serum leptin concentrations during the periparturient period were independent of the number of delivery and the incidence of mastitis and milk fever. These results are quite different from those in rodents and human, suggesting the different regulatory mechanism of circulating leptin concentration in cows.