We have found that activation of human adult T cell leukemia (Jurkat) cells with anti-Fas Ab leads, in a concentration-dependent manner, to an early burst of production of nitric oxide (NO), which inhibits cell respiration. This results in mitochondrial hyperpolarization, dependent on the hydrolysis of glycolytic ATP by the F1Fo-ATPase acting in reverse mode. During this early phase of activation, there is a transient release of superoxide anion. All these processes can be prevented by an inhibitor of NO synthase. Approximately 2 h after stimulation with anti-Fas Ab, a distinct second phase can be detected. This comprises a concentrationdependent collapse in mitochondrial membrane potential, a second wave of free radical production, and activation of caspase-8 leading to apoptosis. This second phase is abolished by an inhibitor of caspase activation. In contrast, inhibition of NO synthesis leads to an enhancement and acceleration of these latter processes, suggesting that the early NO-dependent phase represents a protective mechanism. The significance of the two phases in relation to cell survival and death remains to be studied.

A single intraperitoneal injection of endotoxin (40 microg/kg) significantly delayed gastric emptying of a solid nutrient meal. Blockade of nitric oxide synthase (NOS) with 30 mg/kg ip N(G)-nitro-L-arginine methyl ester or 20 mg/kg ip 7-nitroindazole [neuronal NOS (nNOS) inhibitor] significantly delayed gastric emptying in control animals but failed to modify gastric emptying in endotoxin-treated rats. Administration of 2.5, 5, and 10 mg/kg ip N(6)-iminoethyl-L-lysine [inducible NOS (iNOS) inhibitor] had no effect in either experimental group. Indomethacin (5 mg/kg sc), NS-398 (cyclooxygenase-2 inhibitor; 10 mg/kg ip), and dexamethasone (10 mg/kg sc) but not quinacrine (20 mg/kg ip) significantly prevented delay in gastric emptying induced by endotoxin but failed to modify gastric emptying in vehicle-treated animals. Ca(2+)-dependent NOS activity in the antrum pylorus of the stomach was diminished by endotoxin, whereas Ca(2+)-independent NOS activity was not changed. In addition, decreased nNOS mRNA and protein were observed in the antrum pylorus of endotoxin-treated rats. Our results suggest that downregulation of nNOS in the antrum pylorus of the stomach and synthesis of prostaglandins mediate the delay in gastric emptying of a solid nutrient meal induced by endotoxin.

1 This study analyses the neural pathway involved in the modulation of gastric motor function by stress. 2 Systemic administration of low doses of endotoxin (40 mg kg 71 , i.v.) prevents the increase in gastric tone induced by 2-deoxy-D-glucose (200 mg kg 71 , i.v., 2-DG) in urethane-anaesthetized rats. increased the number of Fos-immunoreactive cells induced by 2-DG, both in the nucleus tractus solitarii (NTS) and in the dorsal motor nucleus (DMN) of the DVC. Pre-treatment with L-NAME prevented the increase in Fos expression induced by endotoxin in both nuclei. 6 Endotoxin (40 mg kg 71 , i.p.) increased Ca 2+ -dependent nitric oxide synthase (cNOS) activity in the brainstem. Addition of 7-nitroindazole (600 mM, 7-NI) to the assay signi®cantly inhibited the increase in cNOS activity caused by endotoxin. No change in NOS activity of any isoform was observed in the stomach of animals treated with endotoxin. 7 The present study suggests that inhibition of gastric motor function by low doses of endotoxin involves activation of capsaicin-sensitive a erent neurones and neuronal NOS in the brainstem.

The effects of endotoxin on gastric emptying of a solid nutrient meal and the neural mechanisms involved in such a response were investigated in conscious rats. The intraperitoneal (i.p.) administration of E. coli endotoxin (40 microg/kg) significantly reduced the 4-h rate of gastric emptying of a standard solid nutrient meal. Ablation of primary afferent neurons by systemic administration of high doses of capsaicin (20+30+50 mg/kg s.c.) to adult rats did not modify the rate of gastric emptying in control animals but prevented the delay in gastric transit induced by endotoxin. Local application of capsaicin to the vagus nerve rather than application of capsaicin to the celiac ganglion significantly repressed endotoxin-induced delay in gastric emptying. Neither treatment modified the rate of gastric emptying in vehicle-treated animals. Blockade of CGRP receptors (CGRP 8-37, 100 microg/kg i.v.) did not alter gastric emptying in control animals but significantly prevented endotoxin-induced inhibition of gastric emptying. In contrast, a tachykinin receptor antagonist ([D-Pro2, D-Trp7.9]-substance P, 2 mg/kg i.p.) significantly reduced the rate of gastric emptying in control animals and did not modify the inhibitory effects of endotoxin. Adrenergic blockade with phentolamine (3 mg/kg i.p.) +/- propranolol (5 mg/kg i.p.) or muscarinic antagonism with atropine (0.1 mg/kg i.p.) failed to reverse the delay in gastric emptying induced by endotoxin. These observations indicate that endotoxin-induced delay in gastric emptying of a solid nutrient meal is mediated by capsaicin-sensitive afferent neurons.