Sequence of a full-length cDNA for rat lung beta-galactoside-binding protein: primary and secondary structure of the lectin

A full-length cDNA for rat lung beta-galactoside lectin (subunit Mr approximately 14,000, lectin 14K) was cloned and the nucleotide sequence determined. The deduced amino acid sequence agrees with the amino acid composition and direct amino acid sequence analysis of purified rat lung lectin peptides. We found that the amino-terminal alanine is blocked with an acetyl group. Comparison of the amino acid sequence with other proteins shows a high degree of homology only with other vertebrate lectin sequences, supporting the suggestion that these lectins may constitute a unique class of vertebrate proteins. The amino acid composition and sequence of lectin peptides, the sequence of lectin cDNA, and isoelectric focusing of purified lectin indicate that rat lung lectin 14K is composed predominantly of a single protein. In addition, rat uterus lectin 14K was found to be the same protein as that present in lung. We characterized the secondary and tertiary structure of rat lung lectin 14K by circular dichroism, by analytical ultracentrifugation, and by computer analysis of its primary structure. Results of these experiments suggest that lectin 14K is primarily a hydrophilic protein with an asymmetric, elongated structure consisting of approximately equal amounts of alpha helix, beta sheet, beta turn, and random coil. We found that Cys-2 and Cys-130 react most rapidly with iodoacetamide; one or both of these residues may be primarily responsible for the thiol requirement of lectin activity.     

Adrenalectomy and surfactant in adult rats

We examined the effect of adrenalectomy (ADX) on aspects of the surfactant system of adult rats. Five days after bilateral ADX, ADX rats had about 20% less disaturated phosphatidylcholine (DSPC) in lung lavage returns (airway DSPC) than sham-operated rats, but the amount of tissue DSPC was not different between the groups; airway DSPC formed 12.8 +/- 0.5% of total DSPC (airway + tissue) in ADX and 15.9 +/- 0.7% in sham-ADX rats. An ultrastructural morphometric analysis of alveolar type 2 cells did not reveal an effect of ADX on lamellar body volume density or surface-to-volume ratio. ADX rats had heavier lungs (not as a result of edema) than sham-ADX rats. Treatment of ADX rats with hydrocortisone returned the amount of DSPC toward normal and eliminated the increase of lung weight. ADX did not alter the recoil of saline-filled lungs but did slightly increase the recoil of air-filled lungs. We conclude that corticosteroid hormones influence the in vivo functioning of the surfactant system of adult rats, but this effect seems to be slight.     

Surfactant aggregation in rat lungs: influence of temperature and ventilation

We examined the effect of the ventilatory rate and the temperature of excised lungs and of increased body temperature of anesthetized spontaneously breathing rats on the centrifugal sedimentation of disaturated phosphatidylcholine (DSPC) present in lung lavage returns. More DSPC sedimented from lungs ventilated at low than at high rates, and sedimentation of DSPC and lung volume loss were temperature dependent, 41 greater than 37 greater than 4 degrees C. Most of the noncellular sedimented material was tubular and common myelin; these had diminished ability to lower surface tension rapidly compared with less-aggregated surfactant. More aggregated DSPC accumulated and lung volume decreased more in spontaneously breathing rats anesthetized for 30 min than in rats killed immediately after being anesthetized; these changes were greater after 30 min of anesthesia in hyperthermic rats (40.4 +/- 0.3 degrees C) than in normothermic rats (37.4 +/- 0.1 degrees C). These studies have shown a correlation between the increased accumulation of surfactant as large aggregates and the loss of alveolar stability; however, a cause and effect between these events has not yet been shown.     

Effect of neurotensin on pancreatic function in man

The effect of neurotensin on submaximally-stimulated hepatobiliary and pancreatic secretion was studied in 6 healthy subjects. An intravenous infusion of neurotensin 1.4 ± 0.3 pmol/kg/min, designed to reproduce plasma neurotensin immunoreactivity levels within the physiological range, produced a significant increase in pancreatic bicarbonate output. Plasma concentrations of pancreatic polypeptide rose by 83 ± 16 pmol/l and were associated with a small reduction in trypsin, but no significant change in bilirubin outputs.