Aims/hypothesisWe have previously demonstrated the therapeutic usefulness of leptin in lipoatrophic diabetes and insulin-deficient diabetes in mouse models and could also demonstrate its dramatic effects on lipoatrophic diabetes in humans. The aim of the present study was to explore the therapeutic usefulness of leptin in a mouse model of type 2 diabetes with increased adiposity. Methods To generate a mouse model mimicking human type 2 diabetes with increased adiposity, we used a combination of low-dose streptozotocin (STZ, 120 μg/g body weight) and high-fat diet (HFD, 45% of energy as fat). Recombinant mouse leptin was infused chronically (20 ng [g body weight] −1 h −1 ) for 14 days using a mini-osmotic pump. The effects of leptin on food intake, body weight, metabolic variables, tissue triacylglycerol content and AMP-activated protein kinase (AMPK) activity were examined. Results Low-dose STZ injection led to a substantial reduction of plasma insulin levels and hyperglycaemia. Subsequent HFD feeding increased adiposity and induced insulin resistance and further augmentation of hyperglycaemia. In this model mouse mimicking human type 2 diabetes (STZ/HFD), continuous leptin infusion reduced food intake and body weight and improved glucose and lipid metabolism with enhancement of insulin sensitivity. Leptin also decreased liver and skeletal muscle triacylglycerol content accompanied by an increase of α2 AMPK activity in skeletal muscle. Pairfeeding experiments demonstrated that leptin improved glucose and lipid metabolism independently of the food intake reduction. Conclusions/interpretation This study demonstrates the beneficial effects of leptin on glycaemic and lipid control in a mouse model of type 2 diabetes with increased adiposity, indicating the possible clinical usefulness of leptin as a new glucose-lowering drug in humans.

1Leptin augments glucose and lipid metabolism independent of its effect on satiety. Administration of leptin in rodents increases skeletal muscle ␤-oxidation by activating AMP-activated protein kinase (AMPK). We previously reported that, as hyperleptinemic as obese human subjects, transgenic skinny mice overexpressing leptin in liver (

1 We examined eects of g-aminobutyric acid (GABA) on vasoconstriction and noradrenaline (NA) release induced by electrical renal nerve stimulation (RNS) in the isolated pump-perfused rat kidney. 2 RNS (1 and 2 Hz for 2.5 min each, 0.5-ms duration, supramaximal voltage) increased renal perfusion pressure (PP) and renal NA eux. GABA (3, 10 and 100 mM) attenuated the RNSinduced increases in PP by 10 ± 40% (P50.01) and NA eux by 10 ± 30% (P50.01). GABA did not aect exogenous NA (40 and 60 nM)-induced increases in PP. 3 The selective GABA B agonist baclofen (3, 10 and 100 mM) also attenuated the RNS-induced increases in PP and NA eux, whereas the RNS-induced responses were relatively resistant to the selective GABA A agonist muscimol (3, 10 and 100 mM). 4 The selective GABA B antagonist 2-hydroxysaclofen (50 mM), but not the selective GABA A antagonist bicuculline (50 mM), abolished the inhibitory eects of GABA (10 mM) on the RNSinduced responses. 5 The selective a 2 -adrenoceptor antagonist rauwolscine (10 nM) enhanced the RNS-induced responses. GABA (3, 10 and 100 mM) potently attenuated the RNS-induced increases in PP by 40 ± 60% (P50.01) and NA eux by 20 ± 50% (P50.01) in the presence of rauwolscine. 6 Prazosin (10 and 30 nM) suppressed the RNS-induced increases in PP by about 70 ± 80%. Neither rauwolscine (10 nM) nor GABA (10 mM) suppressed the residual prazosin-resistant PP response. 7 These results suggest that GABA suppresses sympathetic neurotransmitter release via presynaptic GABA B receptors, and thereby attenuates adrenergically induced vasoconstriction in the rat kidney.

In order to define the major sites of persistence of human herpesvirus 6 (HHV-6) and HHV-7, PCR with DNAs from more than 100 specimens of 3 different salivary glands was performed. HHV-6 DNA was detected in 52 (88.1%) of 59 submandibular gland, 17 (63.0%) of 27 parotid gland, and 9 (52.9%) of 17 lip salivary gland specimens. On the other hand, HHV-7 DNA was detected in 59 (100%) of 59 submandibular gland, 23 (85.2%) of 27 parotid gland, and 10 (58.8%) of 17 lip salivary gland specimens. These findings demonstrate that salivary glands are a site of persistent infection of both HHV-6 and HHV-7 and that among the three types of salivary gland examined, the submandibular gland is the primary one in which these herpesviruses, especially HHV-7, persist.

We examined modulation by nitric oxide (NO) of sympathetic neurotransmitter release and vasoconstriction in the isolated pump-perfused rat kidney. Electrical renal nerve stimulation (RNS; 1 and 2 Hz) increased renal perfusion pressure and renal norepinephrine (NE) efflux. Nonselective NO synthase (NOS) inhibitors [N(omega)-nitro-L-arginine methyl ester (L-NAME) or N(omega)-nitro-L-arginine], but not a selective neuronal NO synthase inhibitor (7-nitroindazole sodium salt), suppressed the NE efflux response and enhanced the perfusion pressure response. Pretreatment with L-arginine prevented the effects of L-NAME on the RNS-induced responses. 2-(4-Carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO), which eliminates NO by oxidizing it to NO(2), suppressed the NE efflux response, whereas the perfusion pressure response was less susceptible to carboxy-PTIO. 8-Bromoguanosine cGMP suppressed and a guanylate cyclase inhibitor [4H-8-bromo-1,2,4-oxadiazolo(3,4-d)benz(b)(1,4)oxazin-1-one] enhanced the RNS-induced perfusion pressure response, but neither of these drugs affected the NE efflux response. These results suggest that endogenous NO facilitates the NE release through cGMP-independent mechanisms, NO metabolites formed after NO(2) rather than NO itself counteract the vasoconstriction, and neuronal NOS does not contribute to these modulatory mechanisms in the sympathetic nervous system of the rat kidney.