ABSTRACTare collectins, members of the C-type lectin family (4). The collectins are composed of four domains: a short aminoterminal region with interchain disulfide bonds, a long collagen-like domain, a coiled-coil neck region and a calciumdependent carbohydrate recognition domain. The basic structural unit of each collectin is a trimer based on the collagenlike triple helix, but the arrangement of multiple trimers into higher order oligomers varies (4). The close linkage of the mouse collectin genes on chromosome 14 suggests the collectins arose by ancestral gene duplication (5).It is not known whether the genetic and structural relationships among the collectins lead to related functions. There are variable degrees of evidence for each of the collectins having a role in innate immunity (for review, see ref. 6). Humans with low levels of MBP secondary to gene mutations are predisposed to infections (7,8), and mice deficient in SP-A secondary to gene targeting have delayed clearing of certain intratracheal bacterial challenges (9). Consistent with a possible role in innate immunity, SP-D binds to both microbes and phagocytic cells in vitro (6, 10), yet there is no direct evidence that SP-D has a role in host defense in vivo.Although SP-D was initially called a SP because it was expressed in the alveolar type II cell and had striking biochemical similarities to SP-A (1), a role for SP-D in surfactant homeostasis has not been established. Some surfactant phospholipid is associated with SP-D purified from alveolar lavage (11), and SP-D will interact with surfactant phospholipids in vitro under certain circumstances (12-14). SP-D also binds to both type II cell apical membranes and alveolar macrophages (6), cells that participate in alveolar surfactant metabolism (15). To develop a model to test the role of SP-D, we have produced mice lacking in SP-D secondary to the disruption of the single copy mouse SP-D gene by homologous recombination. Initial characterization of the phenotype demonstrates a progressive alveolar surfactant accumulation and a striking increase in foamy alveolar macrophages and alteration in type II cell morphology. These findings differ markedly from the results of SP-A gene targeting (16,17) and show that deletion of SP-D alters surfactant homeostasis. MATERIALS AND METHODS Generation of SP-D-Deficient Mice.A murine 129 strain genomic library (Stratagene) was screened by using a 1.2-kb full-length SP-D cDNA to obtain a 15-kb genomic fragment containing all but the extreme 3Ј end of the structural gene. A replacement-type targeting vector containing 1.2-kb and 4.3-kb homology regions was constructed by standard methods (Fig. 1a). Pgk-neo (1.8 kb) for positive selection replaced all of exon 2, including the translation start site for murine SP-D, and short segments of flanking intronic sequence (2.8 kb). Pgk-tk was inserted 5Ј to the regions of homology for negative selection. The targeting vector was linearized by using a unique NotI site and electroporated into CB1-4 embryonic stem cells as des...

In therapeutic doses paracetamol is a safe analgesic, but in overdosage it can cause severe hepatic necrosis. Following oral administration it is rapidly absorbed from the gastrointestinal tract, its systemic bioavailability being dose-dependent and ranging from 70 to 90%. Its rate of oral absorption is predominantly dependent on the rate of gastric emptying, being delayed by food, propantheline, pethidine and diamorphine and enhanced by metoclopramide. Paracetamol is also well absorbed from the rectum. It distributes rapidly and evenly throughout most tissues and fluids and has a volume of distribution of approximately 0.9L/kg. 10 to 20% of the drug is bound to red blood cells. Paracetamol is extensively metabolised (predominantly in the liver), the major metabolites being the sulphate and glucuronide conjugates. A minor fraction of drug is converted to a highly reactive alkylating metabolite which is inactivated with reduced glutathione and excreted in the urine as cysteine and mercapturic acid conjugates. Large doses of paracetamol (overdoses) cause acute hepatic necrosis as a result of depletion of glutathione and of binding of the excess reactive metabolite to vital cell constituents. This damage can be prevented by the early administration of sulfhydryl compounds such as methionine and N-acetylcysteine. In healthy subjects 85 to 95% of a therapeutic dose is excreted in the urine within 24 hours with about 4, 55, 30, 4 and 4% appearing as unchanged paracetamol and its glucuronide, sulphate, mercapturic acid and cysteine conjugates, respectively. The plasma half-life in such subjects ranges from 1.9 to 2.5 hours and the total body clearance from 4.5 to 5.5 ml/kg/min. Age has little effect on the plasma half-life, which is shortened in patients taking anticonvulsants. The plasma half-life is usually normal in patients with mild chronic liver disease, but its prolonged in those with decompensated liver disease.

Pulmonary surfactant is a lipid-rich material that promotes alveolar stability by lowering the surface tension at the air-fluid interface in the peripheral air spaces. The turnover of surfactant phospholipids in the alveolar space is fast, and several lines of evidence suggest there is rapid formation and replenishment of the phospholipid surface film during normal respiration. Specific proteins may regulate these dynamic surface properties. The predominant surfactant protein is a well-characterized, lipid-associated glycoprotein, SP [28][29][30][31][32][33][34][35][36] Pulmonary surfactant is a lipid-rich material secreted as tightly packed lamellae into the extracellular alveolar fluid layer (1). Within the alveolar space, surfactant lipids are found in a number of different structural forms, including lamellar bodies, tubular myelin, and various vesicular structures (2). Although the lipid compositions of the surfactant structures are similar, the physical properties, particularly the ability ofthe lipoprotein complexes to form a surface film, are quite different (3). Specific proteins appear to influence the structure and surface activity of surfactant-lipid complexes (4-10).The predominant surfactant-associated protein is the glycoprotein SP 28-36 (28-36 kDa) characterized by a collagenlike NH2-terminal domain and variable N-linked glycosylation of the COOH-terminal region (11-13). SP 28-36 is water soluble but readily associates with phospholipids (PLs) (14). In the presence of calcium, SP 28-36 causes PL aggregation and increases the rate of adsorption of surfactant lipids to an air-fluid interface (6,8,14). A second group of very hydrophobic proteins has been identified in lamellar bodies isolated from lung homogenate and in surfactant isolated from the bronchoalveolar wash (4, 9, 10, 15-17). Very little is known about the homogeneity, structure, or function ofthis group of hydrophobic proteins, but it has been reported that at least one of these proteins enhances PL surface film formation (9,10,18 (20). The surfactant in water (-16 mg of PL per ml, 2 mg of protein per ml) was extracted in 1-butanol (1:50, vol/vol) at room temperature (21). The surfactant/butanol mixture was spun twice at 10,000 X gav for 20 min to sediment the butanolinsoluble protein (94% of the total). The butanol supernatant was dried by rotary evaporation and the residue was resuspended in chloroform/methanol/0.1 M HCl, 1:1:0.5, vol/vol). A small amount of insoluble material was removed by centrifugation and the supernatant, containing 30 mg ofPL in 1 ml, was applied to a 1 cm x 45 cm column of Sephadex and eluted at 4 ml/hr with the same solvent at 40C. The eluted fractions, 0.5 ml, were assayed for protein (22) in the presence of 1% NaDodSO4, phosphorus (23) for the calculation of the PL content, and cholesterol (24). An aliquot of each fraction containing protein was analyzed by NaDodSO4/PAGE (25) and silver staining (26). 66The publication costs of this article were defrayed in part by page charge payment. This article...

Eight healthy male volunteers ingested an aqueous solution containing acetaminophen (20 mg/kg) and a nonabsorbable isotopic marker. The concentrations of unconjugated acetaminophen in samples of blood plasma taken at frequent intervals were measured by gas-liquid chromatography. The data points followed a smooth curve in most cases and were fitted to the classical two-compartment pharmacokinetic model to obtain KA, the apparent first-order rate constant for absorption from the gastrointestinal tract. Gastric emptying was measured simultaneously from serial scintiscans of the subject's abdomen. The subjects were also studied after intramuscular injection of meperidine (150 mg) and pentazocine (60 mg) with and without naloxone (1.2 mg). The acetaminophen absorption curves and gastric emptying patterns were consistent with negligible absorption from the stomach. A new model is proposed in which the conventional single compartment used to represent the gastrointestinal tract is replaced by two compartments: one represents the stomach and the other the small intestine, from which absorption occurs rapidly. Pharmacokinetic analysis using this model showed good agreement in all cases, and provided an estimate of KA, the first-order rate constant for drug transfer from the intestinal lumen into the systemic circulation. The mean half-time for transfer was 6.8 +/- 0.9 min. As expected, KA was greater than KG (the first-order rate constant for gastric emptying), showing that gastric emptying was rate-limiting in the absorption of acetaminophen. The value of KA was greater than KA and the two were not related. The value of KA was not equal to KG in most studies because gastric emptying was not a single exponential process.