POSTPNEUMONECTOMY LUNG GROWTH FOLLOWING THYROPARATHYROIDECTOMY

Hormonal regulation of compensatory lung growth is not well understood , but it may be similar to that during compensatory growth of other or gans. Liver regeneration is blocked by hypocalcemia in thyroparathyroi dectomized (TPX) animals. Although calcium status is an important regu lator of growth in many biological systems, the effect of TPX on compe nsatory lung growth is unknown. In male Sprague-Dawley rats, TPX lower ed blood ionized calcium by 42% (p < .01) within two days; it remained depressed for at least one additional week. Thyroid-intact and TPX an imals were therefore subjected either to sham thoracotomy or to left p neumonectomy on post-TPX day 2. Growth of the right lung was assessed on day 9 when, in pneumonectomized animals, lung mass had increased 23 % (p < .01). TPX had no effect on right lung mass in sham animals. Sim ilarly, TPX had no effect on the postpneumonectomy increase in right l ung mass, which reached 118% (p < .01) of that in TPX controls. Analys is of right lung DNA, RNA, and protein concentrations on day 9 reveale d that tissue macromolecule content increased postoperatively in both PNX and TPX/PNX rats in proportion to lung growth. These results demon strate that postpneumonectomy compensatory growth of the lung is not b locked in the thyroparathyroprivic hypocalcemic rat.