Following the discovery of leptin in 1994, the scientific and clinical communities have held great hope that manipulation of the leptin axis may lead to the successful treatment of obesity. This hope is not yet dashed; however the role of the leptin axis is now being shown to be ever more complex than was first envisaged. It is now well established that leptin interacts with pathways in the central nervous system and through direct peripheral mechanisms. In this review, we consider the tissues in which leptin is synthesized and the mechanisms which mediate leptin synthesis, the structure of leptin and the knowledge gained from cloning leptin genes in aiding our understanding of the role of leptin in the periphery. The discoveries of expression of leptin receptor isotypes in a wide range of tissues in the body have encouraged investigation of leptin interactions in the periphery. Many of these interactions appear to be direct, however many are also centrally mediated. Discovery of the relative importance of the centrally mediated and peripheral interactions of leptin under different physiological states and the variations between species is beginning to show the complexity of the leptin axis. Leptin appears to have a range of roles as a growth factor in a range of cell types: as be a mediator of energy expenditure; as a permissive factor for puberty; as a signal of metabolic status and modulation between the foetus and the maternal metabolism; and perhaps importantly in all of these interactions, to also interact with other hormonal mediators and regulators of energy status and metabolism such as insulin, glucagon, the insulin-like growth factors, growth hormone and glucocorticoids. Surely, more interactions are yet to be discovered. Leptin appears to act as an endocrine and a paracrine factor and perhaps also as an autocrine factor. Although the complexity of the leptin axis indicates that it is unlikely that effective treatments for obesity will be simply derived, our improving knowledge and understanding of these complex interactions may point the way to the underlying physiology which predisposes some individuals to apparently unregulated weight gain.

SUMMARY: Planktonic larvae were captured above a shallow coral reef study site on the Great Barrier Reef (GBR) around spring-summer new moon periods (October-February) using light trap or net capture devices. Larvae were identified to the genus or species level by comparison with a phylogenetic tree of tropical marine fish species using mtDNA HVR1 sequence data. Further analysis showed that within-species HVR1 sequence variation was typically 1-3%, whereas between-species variation for the same genus ranged up to 50%, supporting the suitability of HVR1 for species identification. Given the current worldwide interest in DNA barcoding and species identification using an alternative mtDNA gene marker (cox1), we also explored the efficacy of different primer sets for amplification of cox1 in reef fish, and its suitability for species identification. Of those tested, the Fish-F1 and -R1 primer set recently reported by Ward et al. (2005) -Las larvas estudiadas fueron capturadas en el plancton de una zona coralina somera en la Gran Barrera de Coral en períodos de luna-nueva de la estación primavera-verano (octubre-febrero). Su captura se realizó mediante trampas de luz o redes de plancton. Las larvas fueron identificadas a nivel de género o especie por la comparación de un árbol filogenético de especies de peces tropicales marinas usando datos de la secuencia HVR1 del DNA mitocondrial. El análisis adicional demostró que, para una misma especie, la variación de la secuencia HVR1 era típicamente 1-3%, mientras que entre especies del mismo género la variación fue de hasta 50%, apoyando la conveniencia del uso del HVR1 para la identificación a nivel específico. Dado el interés mundial actual en el "código de barras genético" y en la identificación de especies usando otro marcador genético de DNA mitochondrial, el cox1, se exploró también la eficacia de diversos "primers" para la amplificación del cox1 en peces de los arrecifes, y su conveniencia para la identificación específica. De los "primers" probados, el Fish-F1 y el -R1 set recientemente reportado por Ward et al. (2005) dieron los mejores resultados.Palabras clave: peces de coral, mtDNA, HVR1, cox1, DNA identificación específica por código de barras genético.

OBJECTIVE: The pharmacokinetics and tissue distribution of leptin in rats was investigated. DESIGN: A catheter was inserted in the right jugular vein of rats on the day prior to experiment. The next day, blood was sampled and then a tracer dose of radioiodinated hormone was administered via the catheter. Thereafter, small (200 m ml) samples of blood were taken at regular intervals. Two experiments were conducted over different sampling times. TCA precipitated radioactivity was counted in samples of plasma and tissues. Pharmacokinetic parameters were calculated after ®tting a bi-exponential equation describing a two-pool model of plasma leptin distribution. Selected time-point plasma samples were fractioned using size exclusion chromatography and the leptin distribution determined. RESULTS: The two pool model described the pharmacokinetics of leptin in two forms: an initial fast decaying pool (t 3.4 min) and a slower decaying pool (t1a 2 71 min) with an overall clearance rate of 6.16 mlaminakg. Size exclusion chromatography showed a persistent peak (all time-points tested) of 125 I-leptin corresponding to the plasma albumin peak. The size of the free 125 I-leptin peak became diminished or absent in later time-point plasma samples. Tissue distribution of leptin at 60 min and 180 min time-points showed that the small intestine contained the highest concentration of leptin, almost four times the level found in kidneys, liver, stomach and lungs. 125 I-leptin was least abundant in skin, muscle, heart, caecum and brain. CONCLUSION: The pharmacokinetics of leptin are affected by three important factors: 1) its ability to bind to a plasma carrier molecule which increases its half-life; 2) its association with abundant peripheral tissue binding sites which creates an additional pool of leptin and 3) the rate of synthesis of leptin which may be less important than originally believed as the prolonged half-life and the additional pool of tissue binding sites are important factors in determining its plasma concentration.

1 The P-adrenoceptor population was characterized in membrane preparations from rat brown adipose tissue (BAT) and from soleus muscle by use of the radioligand ['25I]-iodocyanopindolol (['251I]-ICYP). In addition, atypical binding sites for [12511-ICYP found in both tissues were examined, and the relationship between these sites and the putative rat P3-adrenoceptor is discussed.2 It was established that BAT membranes host a mixed population of l-and P2-adrenoceptors. Of these two sites, 55% showed a high affinity for the P,-selective ligand CGP 20712A (pK 8.5), and 45% showed a high affinity for the p2-selective antagonist ICI 118551 (pK 8.6). Soleus muscle membranes were found to host a population of P2-adrenoceptors, characterized by a high affinity for ICI 118551 (pK 9.1), but ,I-adrenoceptors could not be detected in this preparation. 5-Hydroxytryptamine receptors were not detected in either preparation.3 In addition to Pl-and P2-adrenoceptors, atypical binding sites were identified in both tissues using high concentrations of radioligand (0.5-0.6 nM) and in the presence of 1 tM (-)-propranolol. The atypical sites were abundant, representing 80 and 81% of the total ['25I]-ICYP binding sites in BAT and soleus muscle respectively. When the pK values for 11 ligands were compared, the correlation coefficient for atypical sites in BAT and soleus muscle was 0.94. 4 The atypical binding sites showed a moderate affinity for (±)-cyanopindolol (pK 7.3-7.7), poor stereoselectivity for the (+)-and (-)-enantiomers of alprenolol (<10 fold), and a low affinity for B-adrenoceptor antagonists and partial agonists in the order: (±)-cyanopindolol>(-)-alprenolol> (-)-propranolol=(±)-ICI 118551>>(±)-CGP20712A. The affinity of these ligands for the atypical sites reflects their behaviour in functional studies of putative P3-adrenoceptors in rat BAT, white adipose tissue, intestine and colon.5 The atypical sites labelled by [1251]-ICYP were resistant to agonist binding, and while the order of affinity of the agonists BRL 37344> isoprenaline> noradrenaline matches their order of potency at putative P3-adrenoceptors, none of these compounds caused displacement of the radioligand at concentrations below 10 DIM. 6 It is concluded that the atypical binding sites for ['251]-ICYP found in rat BAT and soleus muscle membranes are the same, and that these sites show some relationship to the putative rat P3-adrenoceptor identified in functional studies using antagonists. However, under the conditions used in the present study, pK values obtained for 33-agonist binding are not useful.