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J. Anim. Sci. 2002. 80:2942-2948
© 2002 American Society of Animal Science

Leptin in horses: Tissue localization and relationship between peripheral concentrations of leptin and body condition

P. R. Buff*, A. C. Dodds*, C. D. Morrison*, N. C. Whitley{dagger}, E. L. McFadin*, J. A. Daniel*, J. Djiane{ddagger} and D. H. Keisler1

* Animal Sciences Department, University of Missouri, Columbia 65211; and {dagger} University of Maryland Eastern Shore, Princess Anne; and and {ddagger} Laboratorie de Biologie Cellulaire, Institut National de la Recherche Agronomique, Centre de Recherche de Jouy, Jouy-en-Josas, Cedex, France

1 Correspondence:
160 Animal Science Research Center (phone: 573-882-7267; fax: 573-882-6827; E-mail:
KeislerD{at}missouri.edu).


   Abstract
Top
 Abstract
Introduction
 Materials and Methods
 Results
 Discussion
 Implications
 Literature Cited
 
Obesity has been a major concern in the horse industry for many years, and the recent discovery of leptin and leptin receptors in numerous nonequine species has provided a basis for new approaches to study this problem in equine. The objectives were to: 1) clone a partial sequence of the equine leptin and leptin receptor genes so as to enable the design of primers for RT-PCR determination of leptin and leptin receptor gene presence and distribution in tissues, 2) develop a radioimmunoassay to quantify peripheral concentrations of leptin in equine, 3) determine if peripheral concentrations of leptin correlate with body condition scores in equine, and 4) determine if changing body condition scores would influence peripheral concentrations of leptin in equine. In Experiment 1, equine leptin (GenBank accession number AF179275) and the long-form of the equine leptin receptor (GenBank accession number AF139663) genes were partially sequenced. Equine leptin receptor mRNA was detected in liver, lung, testis, ovary, choroid plexus, hypothalamus, and subcutaneous adipose tissues using RT-PCR. In Experiment 2, 71 horses were categorized by gender, age, and body condition score and blood samples were collected. Sera were assayed for leptin using a heterologous leptin radioimmunoassay developed for equine sera. Serum concentrations of leptin increased in horses with body condition score (1 = thin to 9 = fat; r = 0.64; P = 0.0001). Furthermore, serum concentrations of leptin were greater in geldings and stallions than in mares (P = 0.0002), and tended to increase with age of the animal (P = 0.08). In Experiment 3, blood samples, body weights, and body condition scores were collected every 14 d from 18 pony mares assigned to gain or lose weight over a 14-wk interval based on initial body condition score. Although statistical changes (P = 0.001) in body condition scores were achieved, congruent statistical changes in peripheral concentrations of leptin were not observed, likely due to the small range of change that occurred. Nonetheless, serum concentrations of leptin tended to be greater in fat-restricted mares than in thin-supplemented mares (P = 0.09). We conclude that leptin and leptin receptors are present in equine tissues and that peripheral concentrations of leptin reflect a significant influence of fat mass in equine.

Key Words: Body Condition • Horses • Leptin


   Introduction
Top
 Abstract
 Introduction
Materials and Methods
 Results
 Discussion
 Implications
 Literature Cited
 
The discovery of the obese (ob) gene product leptin and its receptors in mice led to the identification of leptin and its receptors in sheep, cattle, and pigs (Zhang et al., 1994; Tartaglia et al., 1995; Neuenschwander et al., 1996; Pfister-Genskow et al., 1996; Dyer et al., 1997a,b). In addition, work in rodents and selected livestock has provided evidence that leptin is an important endocrine indicator of adipose mass and nutritional status, as well as an important regulator of various aspects of feed intake, growth, metabolism, and reproduction (Barb et al., 1998; Houseknecht et al., 1998; Henry et al., 1999; Harris, 2000; Nagatani et. al., 2000; Schwartz et al. 2000; Woods et al., 2000; Morrison et al., 2002). Obesity is a growing problem within the horse industry. Obese horses have a propensity for developing laminitis and other health abnormalities. To date, leptin has not been characterized nor quantified in horses, yet it serves as a likely candidate to mediate nutritional influences on growth, adiposity, and reproductive performance.

Because leptin may serve as an important endocrine signal of nutritional status and body fat-mass in the horse, our objectives were fourfold. Our first objective was to partially sequence the leptin and leptin-receptor genes in the equine so as to enable the design of primers for RT-PCR determination of leptin and leptin-receptor gene presence and distribution in various equine tissues. Our second objective was to establish an equine leptin radioimmunoassay to quantitate peripheral concentrations of leptin in equine. Our third objective was to quantify serum concentrations of leptin in equine for the purpose of correlating serum concentrations of leptin with estimates of body fat-mass (body condition scores), and to determine if age and gender of horses affect serum concentrations of leptin. Our fourth objective was to determine if changing body condition scores would influence serum concentrations of leptin.


   Materials and Methods
Top
 Abstract
 Introduction
 Materials and Methods
Results
 Discussion
 Implications
 Literature Cited
 
Experiment 1
RNA Collection and Isolation
Liver, lung, testis, ovary, choroid plexus, hypothalamus, and subcutaneous adipose tissues were collected from adult horses immediately following euthanasia. Following collection, tissues were immediately frozen in crushed dry ice and stored at -80°C until RNA isolation was performed. Total tissue RNA (RNA) was then extracted using the Tri-Reagent product and protocol (Molecular Research Co., Cincinnati, OH).

Reverse Transcriptase Polymerase Reaction (RT-PCR).
The Titan One Tube RT-PCR System (Boehringer Mannheim, Indianapolis, IN) was used to produce equine cDNA encoding leptin, leptin receptor-long form, and ß-actin from equine subcutaneous adipose tissue. Oligonucleotide primers for leptin were designed from homologous regions of human and rodent, previously used to sequence the ovine leptin gene (Dyer et al., 1997a). Primers used to partially sequence the long form of the leptin receptor were designed to match homologous regions of the human, rodent, and ovine leptin receptor-long form. Equine ß-actin primers were used to produce a cDNA product (255 bp) that was used as a positive control. The primers used for each PCR reaction were as follows: for equine leptin, GAC ACC AAA ACC CTC ATC forward and GCT AAA ACC TCT GTG GAG TA reverse; for equine leptin receptor-long form, TGC TTT TGA CTC CAG ATC TT forward and CAG GCC TTC TGA GAA TGG AA reverse; and for equine ß-actin, TGC GTG ACA TCA AGG AGA AG forward and ACA GGT CCT TAC GGA TGT CG reverse. Procedures for RT-PCR, cloning, and sequencing have been previously described (Dyer et al., 1997b). The PCR products were ligated into the pGEM-T vector (Promega, Madison, WI) and transformed into competent cells. Positive clones were verified to contain either the 297-bp equine leptin or the 355-bp leptin-receptor sequence via restriction digests and DNA sequencing (University of Missouri-Columbia DNA Core Facility). Sequences for equine leptin and equine leptin receptor-long form were submitted to GenBank (accession numbers AF179275 and AF139663, respectively). Using the equine leptin receptor-long form primers, RT-PCR was conducted on total RNA from liver, lung, testis, ovary, choroid plexus, hypothalamus, and subcutaneous adipose tissues. The PCR products were separated using agarose gel electrophoresis. A negative control reaction lacking reverse transcriptase was performed on identical samples for identification of possible DNA contamination.

Experiment 2
Animals.
Experiment 2 utilized 71 Quarter Horses (42 mares, 14 stallions, and 15 geldings) ranging in age from 8 d to 24 yr from the University of Missouri Equine Teaching and Research Center, University of Missouri Veterinary College, and a private Quarter Horse farm. All procedures with live animals were approved by the University of Missouri Animal Care and Use Committee.

Procedures.
In Experiment 2, single blood samples were collected from each horse in the afternoon following a morning feeding, via jugular venipuncture using Vacutainer (Becton Dickinson, Franklin Lakes, NJ) tubes with no additive. Blood samples were allowed to clot at room temperature for 1 h then stored at 4°C overnight. Samples were then centrifuged at 2,000 x g for 25 min at 4°C and sera stored at -20°C until assayed for leptin. At the time of sampling, animal gender, age, and body condition scores were determined. Body condition scores were determined for each animal using techniques developed by Henneke and coworkers (1983). Two trained technicians assigned a body condition score to every animal, and the averages of the two scores were used for statistical analyses.

Experiment 3
Animals
Experiment 3 utilized 18 pony mares of mixed breeding, ranging in age from 2 to 15 yr. All mares were housed at the University of Missouri-Columbia research farm on cool season pasture for a minimum of 4 wk prior to experimentation. For the duration of the study, all mares were observed to have normal estrous cycles. Nine of the pony mares were acquired by the University of Missouri and had a body condition score <=5, whereas the remaining pony mares were part of the University of Missouri research herd.

Procedures.
In Experiment 3, 18 ponies were categorized into fat (n = 9; body condition score >=6; mean age = 7 ± 1.3 yr) or thin (n = 9; body condition score <=5; mean age = 5.9 ± 1.8 yr) groups. Fat ponies were restricted to a diet of grass hay (fat-restricted) in an effort to decrease animals’ body condition score to a moderate condition. Thin ponies were supplemented with alfalfa hay and a 14% protein ration (thin-supplemented) to increase body condition scores from thin to moderate. Every 14 d for 14 wk blood samples were collected following an overnight fast, ponies were weighed, and body condition scores were assigned.

Leptin Radioimmunoassay.
Serum concentrations of leptin were quantified using the double-antibody leptin radioimmunoassay procedures described by Delavaud and coworkers (2000) with one modification consisting of the substitution of the reported primary antiserum with a different rabbit anti-ovine leptin primary antiserum (number 7105). Briefly, standard concentrations of recombinant ovine leptin (Gertler et al., 1998; 0.1, 0.2, 0.3, 0.5, 0.8, 1.2, 2.0, 3.5, 5.0 and 7.5 ng in 300 µL/tube) and increasing volumes of serum (25, 40, 60, 100, 175, 250, and 300 µL) from a pool of serum collected from a fat mare were added to assay tubes in quadruplicate and the total volume balanced to 300 µL per tube with buffer consisting of 0.1% gelatin, 0.01 M EDTA, 0.9% NaCl, 0.01 M PO4, 0.01% sodium azide, 0.05% Tween-20, pH = 7.1 (PABET). Likewise, 200 µL of the serum samples to be quantified were added to assay tubes in triplicate and the volume balanced to 300 µL per tube with PABET. Immediately thereafter, 100 µL of rabbit anti-ovine leptin primary antiserum (7105; final tube dilution of 1:15,000 in PABET) was added and samples and standards incubated at 4°C for 24 h. After the initial incubation, 100 µL of 125I-ovine leptin (20,000 c.p.m.) were added to each tube and incubation continued for an additional 24 h at 4°C. The antigen-antibody complex was then precipitated following a 15-min 22°C incubation with 100 µL of a preprecipitated sheep-anti-rabbit second antiserum by centrifugation at 2,000 x g for 30 min, and the supernatant removed by aspiration. Assay tubes containing the pellets were counted for 1 min on a LKB1277 gamma counter (LKB Wallac, Turku, Finland).

Statistics
Analysis of variance was performed on the data from Experiment 2 using GLM procedures of SAS V8 (SAS Inst. Inc., Cary, NC) to determine the effects of gender and age on serum concentrations of leptin. Data were sorted according to the following age categories: less than 2 yr (rapid growth; 6 geldings, 12 mares, 5 stallions), 2 to 4 yr (young, slow growth; 3 geldings, 10 mares, 1 stallion), 5 to 12 yr (mature; 3 geldings, 10 mares, 4 stallions), and greater than 12 yr (aged; 3 geldings, 10 mares, 4 stallions). Effects within the model included gender, age, and gender by age as independent variables, with body condition score as a covariate of serum leptin. In addition, a partial correlation analysis was performed on data collected from Experiment 2 to determine the relationship between serum concentrations of leptin and body condition score after adjusting for age and gender effects. Partial correlation coefficients were determined using a multivariate analysis of variance (MANOVA TEST) and a partial option within the PROC GLM of SAS. Data from Experiment 3 were analyzed as a repeated measures design using the mixed model procedures (PROC MIXED) of SAS to determine the effects of treatment (fat-restricted vs thin-supplemented) and sample (time) on serum concentrations of leptin and body condition scores. Model fitting statistics were used to determine the compound symmetry heterogeneous (CSH), autoregressive (AR{1}) and compound symmetry (CS) models as best fitting for analyses of serum concentrations of leptin, body condition scores, and body weight, respectively. The model used to determine effects on serum concentrations of leptin included treatment, sample, and treatment by sample as independent variables, where sample was the repeated measure and animal within treatment was used as the subject. A second mixed model was used to determine if a linear relationship existed between body condition score and serum concentrations of leptin. The model used was the same as previously described with the addition of body condition score as a covariate and the solution option. The statistical model used to determine effects on body condition score included treatment, sample, and treatment by sample as the independent variable and body weight was used as a covariate. A third mixed model was used to determine changes in body weight over time in the fat-restricted and thin-supplemented ponies. This model included the independent variables of treatment, time, and treatment x time, where time was the repeated measure and animal within treatment was used as the subject. The least squares means option and differences option (PDIFF) were used for the treatment x time interaction.


   Results
Top
 Abstract
 Introduction
 Materials and Methods
 Results
Discussion
 Implications
 Literature Cited
 
Experiment 1
A partial (297 bp) cDNA encoding equine leptin was cloned by RT-PCR of RNA isolated from equine subcutaneous adipose tissue. The cDNA derived from equine RNA was highly homologous (see Table 1Go) to previously published leptin sequences generated from ovine (Dyer et al., 1997a), bovine (Pfister-Genskow et al., 1996), and porcine (Neuenschwander et al., 1996). Also a partial (355 bp) cDNA encoding the long form of the leptin receptor was cloned by RT-PCR of RNA isolated from equine subcutaneous adipose tissue. This cDNA was highly homologous to ovine (Dyer et al., 1997b), bovine (Pfister-Genskow et al., 1997), and porcine (GenBank accession no. AF036908) leptin receptor sequences (Table 1Go). Equine leptin receptor mRNA expression was detected via RT-PCR in liver, lung, muscle, testis, ovary, choroid plexus, hypothalamus, and subcutaneous adipose tissues.


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  		Table 1. Nucleotide and amino acid similarities of cloned equine leptin and equine leptin receptor sequences with those of other species (GenBank accession numbers in parentheses)
 
Leptin Radioimmunoassay
Standards and pooled aliquots of serum from a single source of fat-mare serum were linear (log/logit transformation; R2 > 0.95) and parallel over a mass of 0.1 to 7.5 ng/tube and a serum volume of 25 to 300 µL, respectively (Figure 1Go). Total specific binding was 35%, the minimum detectable concentration was 0.1 ng/tube, percentage recovery of mass was >96% across the range of 25 to 300 µL of sample, and the inter- and intraassay coefficients of variations were less than 10%.



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  		Figure 1. Standard curve (left) of recombinant ovine leptin, log-logit representation (0.1, 0.2, 0.3, 0.5, 0.8, 1.2, 2.0, 3.5, 5.0 and 7.5 ng/300 µL/tube) (R2 = 0.97, slope = -2.0). Dilution curve (right) of equine serum, log-logit representation (25 to 300 µL per tube) (R2 = 0.94, slope = -2.2).

 
Experiment 2
A positive correlation between body condition score and serum leptin was detected in horses (r = 0.64; P < 0.0001; Figure 2Go), with serum leptin being greater in horses with better body condition scores. Serum concentrations of leptin were greater in geldings and stallions than in mares: 3.37 ± 0.38, 3.50 ± 0.45, and 1.85 ± 0.21, respectively (P = 0.0002; Figure 3Go). Serum concentrations of leptin tended to increase with age of the horse (P = 0.08), with mean concentrations consisting of 2.38 ± 0.32, 2.64 ± 0.55, 2.93 ± 0.39, and 3.67 ± 0.38 for horses less than 2 yr, 2 to 4 yr, 5 to 12 yr, and greater than 12 yr in age, respectively (Figure 4Go).



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  		Figure 2. Relationship between serum concentrations of leptin (ng/mL) and body condition scores (arbitrary units; 1 = thin and 9 = fat) in all horses sampled. Individual concentrations of leptin plotted against body condition scores, raw data (n = 71; r = 0.64; P < 0.0001).

 


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  		Figure 3. Serum concentrations of leptin (ng/mL) in geldings, mares, and stallions. Concentrations do not differ between geldings vs stallions but do differ between mares vs geldings and mares vs stallions (n = 71; P = 0.0002).

 


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  		Figure 4. Serum concentrations of leptin (ng/mL) by age classification. Concentrations tended to increase as age of the horse increased (n = 71; P = 0.08).

 
Experiment 3
The nine pony mares categorized as fat animals (body condition score >=6) and fed grass hay and the nine pony mares categorized as thin animals (body condition score <=5) and supplemented with alfalfa hay and a 14% protein ration responded to diets with changes in body condition scores (P = 0.001; Figure 5Go). Body weights for the fat-restricted ponies decreased at wk 2 and fluctuated throughout the remainder of the study. Body weights for the thin supplemented ponies were observed to gradually increase with a change at week 8 (P < 0.001, treatment by time; Figure 6Go). Although changes in body condition scores and body weights were achieved, congruent statistical changes in peripheral concentrations of leptin were not observed (Figure 7Go), likely due to the modest physiological changes in body condition scores (no animal changed more than 2 units in body condition score). Nonetheless, serum concentrations of leptin tended to be greater in the fat-restricted animals than in the thin-supplemented animals, 6.99 ± 1.77 and 2.33 ± 1.88, respectively (P = 0.09). There was a linear relationship between body condition score and serum concentration of leptin in all animals, as revealed by covariant analysis, such that leptin increased 1.11 ± 0.57 ng/mL for every increase in body condition score (P = 0.05).



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  		Figure 5. Change over time in body condition scores among fat-restricted and thin-supplemented pony mares. Fat-restricted mares decreased in body condition and thin-supplemented mares increased in body condition (P = 0.001, sample by treatment).

 


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  		Figure 6. Change over time in body weight among fat-restricted and thin-supplemented pony mares. Fat-restricted mares decreased body weight at wk 2 and then fluctuated during the remaining weeks of the study and thin-supplemented mares increased body weight at wk 8 and continued to do so throughout the study (P < 0.001, treatment by time).

 


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  		Figure 7. Concentrations of leptin over time among fat-restricted and thin-supplemented pony mares. No change in concentrations over time were observed with the exception of wk 12 in the thin-supplemented group (P < 0.05).

 

   Discussion
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
Implications
 Literature Cited
 
Partial sequences of the equine leptin and leptin receptor genes were derived from equine adipose tissue, and these sequences exhibited high homology to ovine, bovine, and porcine leptin (Neuenschwander et al., 1996; Pfister-Genskow et al., 1996; Dyer et al., 1997a) and leptin receptor genes (Dyer et al., 1997b; Pfister-Genskow et al., 1997). From a utility perspective, the high level of species homology among leptin may indicate that recombinant leptin derived from sequences within these species may be efficacious for use in future in vitro and/or in vivo equine studies. Indirect support of this argument is the observation that the ovine leptin antiserum worked well in a radioimmunoassay for determining equine leptin. Finally, the current findings of the broad distribution of the leptin receptor message agreed with findings in other species (Cioffi et al., 1996; Lee et al., 1996; Dyer et al., 1997b). Understanding the relationship between body composition and serum concentrations of leptin may offer insight into possible mechanisms of equine obesity, which is a persistent problem in the equine industry. Thus, the development of the equine leptin RIA provides a necessary tool to examine obesity in horses and ponies, and will allow the exploration of influences associated with equine feeding, metabolism, and therapies to manage this problem.

When horses of different gender and age were sampled for serum leptin, a positive correlation between serum leptin and body condition score was observed. Gender-related differences in serum concentrations of leptin were observed, surprisingly with male horses having greater serum concentrations of leptin than female horses; an effect that was independent of differences in body condition scores across the different genders. These observations differ from that observed in humans whereby gender accounted for nearly 60% of the variance of leptin, with women having been observed to have greater peripheral concentrations of leptin than men (Ostlund et al., 1996). Nonetheless, this indicates that leptin may play a species-specific role. Concentrations of leptin were not different between geldings and stallions, which may lend evidence that testosterone (or the absence of testosterone) is not likely involved in regulating peripheral concentrations of leptin in the horse. A tendency for an age-dependent increase of serum leptin was also observed. Young horses are in the growth phase of development and thus lower concentrations of leptin would be indicative of an animal with lower body fat and requiring greater nutritional resources. Mature horses generally have greater body fat mass and only need resources to match their level of activity. The higher concentrations of leptin observed in horses between 5 and 12 yr of age concur with this observation. The greatest concentrations of leptin were observed in horses greater than 12 yr. Such an increase may be due to less active lifestyles of aged horses.

Fat pony mares tended to have greater serum concentrations of leptin than thin pony mares. However, nutritionally restricting or supplementing pony mares caused changes in body condition scores, and yet no change over time in peripheral concentrations of leptin. Because neither group changed more than 2 body condition scores, it is possible that the equine would have to undergo a greater change in body condition score to observe subsequent changes in leptin profiles or more likely, we simply were unable to detect differences that may have existed due in part to the infrequent sampling paradigm. It should be noted that in Experiment 3, a steady-state group of pony mares was not monitored over the sampling period, which makes it difficult to rule out external variables (such as environmental effects), which may have had an effect on the treatments.

In conclusion, we have identified and localized leptin and the leptin receptor–long form in the horse and have validated a radioimmunoassay to detect serum concentrations of leptin in the horse. We have established a relationship between body condition scores and concentrations of leptin and can use this valuable tool to help assess the fatness or thinness of horses.


   Implications
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Implications
Literature Cited
 
The existence of leptin in the equine was demonstrated, and a radioimmunoassay to detect serum concentrations of leptin in the horse was developed. A relationship was established between leptin concentrations and body condition scores, gender, and age in the equine. Many horses and ponies have been diagnosed as "hard keepers" or "easy keepers," but the physiological mechanisms that take place in either condition are poorly understood. Understanding the role of leptin in horses may provide the insight necessary for treating animals afflicted with these chronic conditions.

Received for publication January 29, 2002. Accepted for publication May 9, 2002.


   Literature Cited
Top
 Abstract
 Introduction
 Materials and Methods
 Results
 Discussion
 Implications
 Literature Cited
 


Barb, C. R., X. Yan, M. J. Azain, R. R. Kraeling, G. B. Rampacek, and T. G. Ramsay. 1998. Recombinant porcine leptin reduces feed intake and stimulates growth hormone secretion in swine. Domest. Anim. Endocrinol. 15:77–86.[Medline]

Cioffi, J. A., A. W. Shafer, T. J. Zupancic, J. Smith-Gbur, A. Mikhail, D. Plantika, and H. R. Snodgrass. 1996. Novel B219/OB receptor isoforms: Possible role of leptin in hematopoiesis and reproduction. Nat. Med. 2:585–589.[Medline]

Delavaud, C., F. Bocquier, Y. Chilliard, D. H. Keisler, A. Gertler, and G. Kann. 2000. Plasma leptin determination in ruminants: effect of nutritional status and body fatness on plasma leptin concentration assessed by a specific RIA in sheep. J. Endocrinol. 165:519–526.[Abstract]

Dyer, C. J., J. M. Simmons, R. L. Matteri, and D. H. Keisler. 1997a. cDNA cloning and tissue-specific gene expression of ovine leptin, NPY-Y1 receptor and NPY-Y2 receptor. Domest. Anim. Endocrinol. 14:295–303.[Medline]

Dyer, C. J., J. M. Simmons, R. L. Matteri, and D. H. Keisler. 1997b. Leptin receptor mRNA is expressed in ewe anterior pituitary and adipose tissues and is differentially expressed in hypothalamic regions of well-fed and feed-restricted ewes. Domest. Anim. Endocrinol. 14:119–128.[Medline]

Gertler, A., J. Simmons, and D. H. Keisler. 1998. Large-scale preparation of biologically active recombinant ovine obese protein (leptin). FEBS Letters. 422:137–140.[Medline]

Harris, R. B. S. 2000. Leptin–much more than a satiety signal. Annu. Rev. Nutr. 20:45–75[Medline]

Henneke, D. R., G. D. Potter, J. L. Kreider, and B. F. Yeates. 1983. Relationship between condition score, physical measurements and body fat percentage in mares. Equine Vet. J. 15:371–372.[Medline]

Henry, B. A., J. W. Goding, W. S. Alexander, A. J. Tilbrook, B. J. Canny, F. Dunshea, A. Rao, A. Mansell, and I. J. Clarke. 1999. Central administration of leptin to ovariectomized ewes inhibits food intake without affecting the secretion of hormones from the pituitary gland: evidence for a dissociation of effects on appetite and neuroendocrine function. Endocrinology 140:1175–1182.[Abstract/Free Full Text]

Houseknecht, K. L., C. A. Baile, R. L. Matteri, and M. E. Spurlock. 1998. The biology of leptin: A review. J. Anim. Sci. 76:1405–1420.[Abstract/Free Full Text]

Lee, G., R. Proence, J. M. Montez, K. M. Carroll, J. G. Darvishzadeh, J. I. Lee, and J. M. Friedman. 1996. Abnormal splicing of the leptin receptor in diabetic mice. Nature (Lond.) 379:632–635.[Medline]

Morrison, C. D., J. A. Daniel, B. J. Holmberg, J. Djiane, N. Raver, A. Gertler, and D. H. Keisler. 2002. Central infusion of leptin into well-fed and undernourished ewe lambs: effects on feed intake and serum concentration of growth hormone and luteinizing hormone. J. Endocrinol. 168 (In press)

Nagatani, S., Y. Zeng, D. H. Keisler, and D. L. Foster. 2000. Leptin regulates pulsatile luteinizing hormone and growth hormone secretion in the sheep. Endocrinology 141:3965–3975.[Abstract/Free Full Text]

Neuenschwander, S., G. Rotenberger, E. Meijerink, H. Jorg, and G. Stranzinger. 1996. Partial characterization of porcine obesity gene (OBS) and its localization to chromosome 18 by somatic cell hybrids.Anim. Genet. 27:275–278.[Medline]

Ostlund, R. E., J. W. Yang, S. Klein, and R. Gingerich. 1996. Relation between plasma leptin concentration and body fat, gender, diet, age, and metabolic covariates. J. Clin. Endocrinol. Metab. 81:3909–3913.[Abstract/Free Full Text]

Pfister-Genskow, M. A., H. Hayes, A. Eggen, and M. D. Bishop. 1996. Chromosomal localization of the bovine obese (OB) gene. Mamm. Genome 7:398–399.[Medline]

Pfister-Genskow, M. A., H. Hayes, A. Eggen, and M. D. Bishop. 1997. The leptin receptor (LEPR) gene maps to bovine chromosome 3q33. Mamm. Genome 8:227.[Medline]

Schwartz, M. W., S. C. Woods, D. Porte, R. L. Seeley, and D. G. Baskin. 2000. Central nervous system control of food intake. Nature (Lond.) 400:661–671.

Tartaglia, L. A., M. Dembski, X. Weng, N. Deng, J. Culpepper, R. Deros, G. J. Richards, L. A. Campfield, F. T. Clark, J. Deeds, C. Muir, S. Sanker, A. Moriarty, K. J. Moore, J. S. Smutko, G. G. Mays, E. A. Wolf, C. A. Monroe, and R. I. Tepper. 1995. Identification and expression cloning of a leptin receptor, OB-R. Cell 83:1263–1271.[Medline]

Woods, S. C., M. W. Schwartz, D. G. Baskin, and R. J. Seeley. 2000. Food intake and the regulation of body weight. Annu. Rev. Psychol. 51:255–277.[Medline]

Zhang, Y., R. Proenca, M. Maffei, M. Barone, L. Leopold, and J. M. Friedman. 1994. Positional cloning of the mouse obese gene and its human homologue. Nature (Lond.) 372:425–432.[Medline]


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P. R. Buff, C. D. Morrison, V. K. Ganjam, and D. H. Keisler
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Leptin as a predictor of carcass composition in beef cattle
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Serum concentrations of leptin in six genetic lines of swine and relationship with growth and carcass characteristics
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