Endogenous nitric oxide is implicated in the regulation of lipolysis through antioxidant-related effect.

We studied the influence of nitric oxide (NO) endogenously produced by adipocytes in lipolysis regulation. Diphenyliodonium (DPI), a nitric oxide synthase (NOS) inhibitor, was found to completely suppress NO synthesis in intact adipocytes and was thus used in lipolysis experiments. DPI was found to decrease both basal and dibutyryl cAMP (DBcAMP)-stimulated lipolysis. Inhibition of DBcAMP-stimulated lipolysis by DPI was prevented by S-nitroso-N-acetyl-penicillamine (SNAP), a NO donor. This antilipolytic effect of DPI was also prevented by two antioxidants, ascorbate or diethyldithiocarbamic acid (DDC). Preincubation of isolated adipocytes with DPI (30 min) before exposure to DBcAMP almost completely abolished the stimulated lipolysis. Addition of SNAP or antioxidant during DPI preincubation restored the lipolytic response to DBcAMP, whereas no preventive effects were observed when these compounds were added simultaneously to DBcAMP. Exposure of isolated adipocytes to an extracellular generating system of oxygen species (xanthine/xanthine oxidase) or to H(2)O(2) also resulted in an inhibition of the lipolytic response to DBcAMP. H(2)O(2) or DPI decreased cAMP-dependent protein kinase (PKA) activation. The DPI effect on PKA activity was prevented by SNAP, ascorbate, or DDC. These results provide clear evidence that 1) the DPI antilipolytic effect is related to adipocyte NOS inhibition leading to PKA alterations, and 2) endogenous NO is required for the cAMP lipolytic process through antioxidant-related effect.

Modulation of white adipose tissue lipolysis by nitric oxide.

In isolated adipocytes, the nitrosothiols S-nitroso-N-acetyl-penicillamine (SNAP) and S-nitrosoglutathione stimulate basal lipolysis, whereas the nitric oxide (NO.) donor 1-propamine, 3-(2-hydroxy-2-nitroso-1-propylhydrazine) (PAPA-NONOate) or NO gas have no effect. The increase in basal lipolysis due to nitrosothiols was prevented by dithiothreitol but not by a guanylate cyclase inhibitor. In addition the cyclic GMP-inhibited low Km, cyclic AMP phosphodiesterase activity was inhibited by SNAP suggesting that SNAP acting as NO+ donor increases basal lipolysis through a S-nitrosylation mediated inhibition of phosphodiesterase. Contrasting with these findings, SNAP reduced both isoproterenol-stimulated lipolysis and cyclic AMP production, whereas it failed to modify forskolin-, dibutyryl cyclic AMP-, or isobutylmethylxanthine-stimulated lipolysis, suggesting that SNAP interferes with the beta-adrenergic signal transduction pathway upstream the adenylate cyclase. In contrast with SNAP, PAPA-NONOate or NO gas inhibited stimulated lipolysis whatever the stimulating agents used without altering cyclic AMP production. Moreover PAPA-NONOate slightly reduces (30%) the hormone-sensitive lipase (HSL) activity indicating that stimulated lipolysis inhibition by NO. is linked to both inhibition of the HSL activity and the cyclic AMP-dependent activation of HSL. These data suggest that NO. or related redox species like NO+/NO- are potential regulators of lipolysis through distinct mechanisms.

White adipose tissue nitric oxide synthase: a potential source for NO production.

Nitric oxide synthase (NOS) activity was detected in soluble and membranous fractions of adipose tissue homogenates of control rats. After LPS-treatment, this activity was (i) markedly increased (about 10-fold) in both fractions, (ii) unaltered after dexamethasone pretreatment, (iii) partly calcium-calmodulin sensitive, and (iv) almost entirely accounted by the NOS activity found in isolated adipocytes. In adipose tissue homogenates from control rats, Western blot analysis demonstrated the presence of the endothelial (eNOS) isoform in the membranous fraction of control rats and of the inducible (iNOS) isoform in the soluble and membranous fractions. After LPS treatment, the amount of immunoreactive iNOS protein was dramatically increased, suggesting that adipose tissue is an important site of NO production during the endotoxic shock.

Estrogen binding sites in hamster white adipose tissue: sex- and site-related variations; modulation by testosterone.

Estrogen binding sites (ER) were studied, using 17 beta-[3H]estradiol as the ligand, in epididymal or parametrial and subcutaneous adipose tissues of male and female hamsters. Compared with other mammalian fat deposits, intact male and female hamsters possess abundant estrogen binding sites with moderate affinity for estradiol and which occur as a single class of receptor in males but as two populations in females. The levels of estrogen receptors depend on both sex and tissue localization. In males, receptor densities are higher in both localizations when compared to those of females and ER are more abundant in superficial adipose deposits than in the deep fat tissue. In females, there are two estrogen binding populations; the one with the highest affinity is similar to the classical estrogen receptor and both populations are more abundant in deep fat than in subcutaneous deposits, in contrast to male hamsters. These characteristics depend on androgen status: in male adipose tissues, testosterone (TP) up-regulates the ER levels. Conversely, in female fat deposits, TP down-regulates the highest affinity estrogen receptors and the lowest affinity population disappears. Binding affinities are never affected by testosterone. These results suggest that, in hamster adipose tissue, estrogen receptors exhibit site- and sex-related differences, as previously described for androgen receptors. Furthermore, estrogen receptor expression is modulated by the androgen status, depending on gender, which could be related to some physiological situations observed in the hamster.

Androgen receptors in cultured rat adipose precursor cells during proliferation and differentiation: regional specificities and regulation by testosterone.

Different studies suggest that sex hormones affect adipose tissue metabolism and deposition. To investigate the possibility that androgens may play a role in adipose tissue development, we have studied androgen receptors (AR) in rat adipose precursor cells from two different anatomical fat deposits, one deep intraabdominal (epididymal) and one subcutaneous (inguinal) during the proliferation and differentiation processes. AR were quantified by [(3)H]R1881 specific binding in whole cells and the nuclear fraction and were localized by immunocytofluorimetry in both the cytosol and the nucleus. During the proliferative phase, total AR level decreased from D3 to D6. At confluence (D5), AR were higher in epididymal (64±4 fmol/mg protein) than in subcutaneous (33±3 fmoles/mg proteins) preadipocytes and were up-regulated by testosterone but not by 5α-dihydrotestosterone or by 17ß-estradiol. At differentiation (D10-11), nuclear AR decreased by 50% in both precursor fat cell populations when compared to the confluent state (D5) and AR were no more up-regulated but rather down-regulated by testosterone. Because AR are present in preadipocytes and are differently regulated by testosterone depending on the stage of proliferation and differentiation, this study suggests that testosterone may play a role in the control of the adipogenic process.

Ethanol alters the adenosine receptor-Ni-mediated adenylate cyclase inhibitory response in rat brain cortex in vitro.

It has been suggested that ethanol stimulates adenylate cyclase in vitro through an increased function of Ns, the activatory component of adenylate cyclase. Because of the interaction of Ns with Ni, the adenylate cyclase inhibitory component, we have studied the effect of ethanol (0.05-0.2 M) on Ni-mediated adenylate cyclase inhibition caused by the adenosine analog N6-phenylisopropyladenosine (N6-PIA) in brain cortical membranes. Ethanol did not alter N6-PIA binding to the adenosine Ri-receptors, stimulated slightly basal adenylate cyclase activity but abolished adenylate cyclase inhibition due to N6-PIA, suggesting an effect of ethanol on the inhibitory coupling pathway. This was further supported by loss of the adenylate cyclase inhibitory response to GTP (greater than 10(-5) M). It thus seems that, besides its effect on the Ns system, ethanol may also impair Ni-mediated adenylate cyclase responses in rat cerebral cortex.