Growth of immature lung transplanted into an adult recipient

Syngeneic (Lewis-to-Lewis) and allogeneic (Brown Norway-to-Lewis) unilateral left lung transplants were performed between immature rats aged 6 wk (donors) and adult animals aged 4 mo (recipients). Transplanted animals were killed either 2 wk or 6 mo after operation. Right and left lungs were analyzed separately by quantitative light microscopic techniques, and findings were compared with control animals matched for age and strain. The immature transplanted left lung continued to grow to achieve its predicted adult number of alveoli. Six months after transplantation the alveoli and airways were larger than controls in allogeneic animals (P < 0.001) but were of normal size in syngeneic animals. After both syngeneic and allogeneic transplantation the recipient contralateral mature native right lung showed an increase in volume after 6 mo (P < 0.001), abnormal in a mature lung, due to an increase in size (P < 0.01 in allogeneic, P < 0.05 in syngeneic) and alveolar number (P < 0.02 in both). This study indicates that in rats, transplanted immature lungs can fulfill their growth potential even when transplanted into mature recipients.

Dysanaptic lung growth: an experimental and allometric approach

The postnatal development of the mammalian lung, which at birth has only a fraction of the adult number of alveoli, would suggest a mismatch (dysanapsis) of the changes in airway size and lung size with growth. This may have implications on the efficiency of breathing because for any given lung size the dimensions of the airways are the determinant of the amount of dead space (VD) ventilation and of airflow resistance. A comparison of the allometric functions of tracheal dimensions previously published suggests that the tracheal volume, taken as representative of VD, is smaller in newborns than in adults. This difference becomes more apparent when examined per unit of functional residual capacity (VD/FRC). The relatively smaller tracheal volume is the result of both a shorter and narrower trachea in the newborn. This latter difference implies a slightly but significantly higher resistance of the lower airways, as also demonstrated by experimental measurements of peak expiratory flows at a constant driving pressure in rats of different ages. Because the slightly higher resistance of the lower airways is probably compensated by the smaller resistance of the upper airways (J. Appl. Physiol.: Respirat. Environ. Exercise Physiol. 51: 641–645, 1981), it would seem that the structure of the newborn mammalian lung favors the alveolar ventilatory function without a substantial increase of the energetic losses.

The Post-Larval Stage of Arenicola marina

By “post-larval stage” I wish to indicate that stage in the developmental history of Arenicola at which the full adult number of somites has appeared, and the body is already distinguishable into (a) an anterior chætigerous region, and (b) a posterior achætous region or tail, but in which the gills are not yet completely formed or have not yet even made their appearance.