RDC8 has been recently cloned and characterized as an adenosine A2 receptor. This receptor is expressed exclusively by medium-sized neurons of the striatum as demonstrated by in situ hybridization. We have now studied the relationship of this receptor with three major components of the rat caudate-putamen: enkephalin, substance P, and choline acetyltransferase. Our results demonstrate that the adenosine A2 receptor is expressed exclusively by the enkephalinergic striatal subpopulation but not by the substance P-containing or cholinergic neurons.

Current recommendations for mechanical ventilation in the acute respiratory distress syndrome (ARDS) include the use of small tidal volumes (VT), even at the cost of respiratory acidosis. We evaluated the effects of this permissive hypercapnia on pulmonary gas exchange with the multiple inert gas elimination technique (MIGET) in eight patients with ARDS. After making baseline measurements, we induced permissive hypercapnia by reducing VT from 10 +/- 2 ml/kg to 6 +/- 1 ml/kg (mean +/- SEM) at constant positive end-expiratory pressure. After restoration of initial VT, we infused dobutamine to increase cardiac output (Q) by the same amount as with hypercapnia. Permissive hypercapnia increased Q by an average of 1.4 L. min(-)(1). m(2), decreased arterial oxygen tension from 109 +/- 10 mm Hg to 92 +/- 11 mm Hg (p < 0.05), markedly increased true shunt (Q S/Q T), from 32 +/- 6% to 48 +/- 5% (p < 0.0001), and had no effect on the dispersion of VA/Q.VA/Q. On reinstatement of baseline V T with maintenance of a high Q, Q S/Q T remained increased, to 38 +/- 6% (p < 0.05), and Pa(O(2 ))remained decreased, to 93 +/- 4 mm Hg (p < 0. 05). These results agreed with effects of changes in VT and Q predicted by the mathematical lung model of the MIGET. We conclude that permissive hypercapnia increases pulmonary shunt, and that deterioration in gas exchange is explained by the combined effects of increased Q and decreased alveolar ventilation.

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Sir: Legionella pneumophila remains an important cause of community-acquired pneumonias, with an incidence from 2 to 15 %, that require hospitalization [1]. The highest mortality (80 %) is found among immunosuppressed patients [2] but is much lower in healthy patients (20 %). In pneumonias complicated by the acute respiratory distress syndrome (ARDS), mortality is over 80 % among untreated patients and 50±60 % in treated patients [2]. We describe herein a case of severe Legionella pneumonia successfully treated with imipenem as empirical antibiotic treatment choice.A 55-year-old man was admitted with a 2-day history of fever (40 C), cough and dyspnea. He had adult-onset diabetes mellitus and no smoking habit. On arrival, positive physical findings included subfever (37.6 C) and inspiratory crackles in the base of the right lung on pulmonary auscultation. Blood analysis was characteristic only for renal failure (blood urea nitrogen BUN 46 mg/dl, creatinine 2.5 mg/dl) and inflammatory syndrome (WBC) 14 900/ mm 3 , C-reactive protein 20 mg/dl). Roentgenographic studies revealed pneumonia restricted to the right lower lobe. Sputum showed neutrophils in large numbers but cultures remained negative. He was treated with intravenous amoxicillin-clavulanate (2 g three times daily with diagnosis of community-acquired pneumonia. On day 2, he developed tachycardia, mild hypotension and respiratory distress which required mechanical ventilation. Radiograph of the chest revealed new bilateral infiltrates, right-sided cardiac catheterization and a PaO 2 /FIO 2 ratio < 200, which were compatible with a diagnosis of ARDS.Between days 2 and 5, the patient's clinical course worsened with alteration of the PaO 2 /FIO 2 ratio, increase in WBC and renal failure with oliguria requiring hemodialysis. On day 5, antibiotic treatment was substituted for imipenem (1 g twice daily) and amikacin (250 mg/day) with doses in relation with renal failure.