Compensatory growth of the lung following partial pneumonectomy.

In a variety of species, partial resection of the lung initiates rapid compensatory growth of the remaining tissue adequate to restore normal total lung mass. Increases in tissue content of protein, RNA, and DNA in proportion to dry lung weight suggest hyperplastic growth of the tissue, rather than cellular hypertrophy. A general acceleration of cell division is supported further by the results of quantitative morphometric studies, which indicate that both cellular and functional characteristics of the peripheral lung, including alveolar and capillary volumes and thickness and surface area of the blood-gas barrier, are maintained when compensatory growth is complete. The rate and nature of the growth response are subject to hormonal modulation, particularly by adrenal steroids and growth hormone. Little is known, however, regarding the specific actions of these agents or of additional factors that may be primary regulators of the initiation and cessation of accelerated compensatory growth. Definition of such regulatory mechanisms is of critical importance in understanding normal growth and development of the lung and the response of the lung to injury, as well as in future efforts to manipulate growth and/or repair of the tissue.