Abstract
During the first 2 weeks of postnatal life in the rat, the activities of phosphodiesterase and guanylate cyclase in the lung were found to undergo significant age-related changes. Low constant levels of these enzyme activities during the first 4 postnatal days were followed by a substantial increase to peak levels which plateaued between days 11 and 21 of age, and these changes coincided with the pattern of developmental changes in circulating thyroid hormone levels. When pups were rendered hypothyroid by combined pre- and postnatal treatment with propylthiouracil, the ontogenetic pattern of lung phosphodiesterase was abolished, as were those of serum thyroid hormones; however, that of lung guanylate cyclase was still evident, although slightly depressed. In contrast, treatment of euthyroid pups from the first day of life with daily injections of 1 μg T3 resulted in an advancement of lung phosphodiesterase ontogenesis, whereas that of guanylate cyclase was unaffected. A comparison between euthyroid and hy...
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