Protein Deficiency: Effects on Lung Mechanics and the Accumulation of Collagen and Elastin in Rat Lung

Abstract

Groups of weanling (approximately 50 g) or young adult (approximately 300 g) rats were fed ad libitum casein-based diets varying in protein content from 4 to 16%. A group was also fed the 16% protein diet in an amount on a daily basis restricted to that consumed by the protein-deficient group (4% protein). The rats were fed the diets for either 4 weeks (weanling) or 6 weeks (adults). Protein-deficient or "food-restricted" rats (whether weanling or adults) were smaller and had smaller lungs than rats fed ad libitum the diets containing 16% protein. The lung elastin content was more resistant to dietary manipulation than was the lung collagen content. Lung collagen was significantly decreased in both weanling and adult rats fed the 4% protein diet. In weanling rats, pressure-volume relationships derived from saline-filled lungs (analyzed by exponential curve-fitting methods) suggested that lungs from food-restricted rats may be less compliant than lungs from rats fed the control diet ad libitum. When expressed in absolute terms, lungs from protein-deficient rats also appeared to be less compliant than normal rats; however, on a relative basis (percentage of volume at a given recoil pressure or the expression of volume on a weight basis) differences in compliance were less apparent. It is proposed that in weanling rats the differences in lung composition and compliance are the result of retarded lung growth and perhaps development.

Effects of Protein Deprivation from the Neonatal Period on Lung Collagen and Elastin in the Rat

“…The hydroxyproline content of elastin is not so well documented and could be more variable, but the observed amino acid composition of lung elastin of protein-deprived rats did not differ from that of the controls (data not shown). In addition, the elastin content of the control lungs was similar to those reported by Myers et al (8) and by Sahebjami and MacGee (15). Moreover, the elastin contents of the rat lungs were too low to be quantitated by gravimetric techniques.…”

“…Lungs of rats fed on a diet restricted in protein from the neonatal period had decreased recoil pressure (6), whereas protein restriction from d 28 resulted in a moderately increased recoil pressure (7). Inasmuch as we know from the observations of Myers et al (8) rats produces an increase in lung elastin concentration, our second experiment could lend support to their conclusions. We had also observed an increase in the pressure at which the lung of protein-deficient rats ruptured.…”

“…However, lung collagen, whose change is linear and directly related to lung size, should not be affected in the same way. The influence of the time at which protein deficiency is started with regard to the period of elastin accumulation in the growing rat is supported by the rise of elastin concentration in the lung when protein deficiency is started after d 21 (8). We consider from these different findings that in our study the decrease in collagen and in elastin were due to reduced biosynthesis rather than to increased breakdown.…”

“…The present observations suggest that loss of lung elasticity is due to the decrease in elastin concentration. Lung tissue elasticity is well-correlated with elastin concentration in the growing rat (5) and elastin degradation by intratracheal or intraperitoneal administration of elastase results in a loss of lung elastic recoil (1 [8][9][10][11][12][13][14][15][16][17][18][19][20]. In our experiments, the fall in lung elastic recoil does not equal the loss in lung elastin concentration (21 and 34% of control values for recoil pressure and elastin concentration, respectively).…”

Growth, Elastin Concentration, and Collagen Concentration of Perinatal Rat Lung: Effects of Dexamethasone

“…The distinctive time course of collagen and elastin accumulation and the different responses of desmosine and hydroxyproline accumulation to dexamethasone exposure offer further evidence of independence of collagen and elastin metabolism (30). The existence of two or more populations of fibroblasts in the neonatal rat lung, at least one of which produces elastin and another, the lipid-filled interstitial cell, which appears not to be involved in protein synthesis to any great extent, is now well established (3 1).…”