Abstract
Summary
Guanyl cyclase, adenyl cyclase, cyclic 3′,5,′-adenosine monophosphate phosphodiesterase (cAMP PDE), and cyclic 3′,5′-guanosine monophosphate phosphodiesterase (cGMP PDE) activities in heart, lung, liver, and skeletal muscle of rats 26, 45, 70, and 300 days of age were measured. Decreases in each of these enzyme activities, except for that of cAMP PDE in lung, occurred with aging. 3 The most rapid declines in activity occurred within 70 days. The activities of the cyclases decreased more rapidly than those of the phosphodiesterases. Therefore, in our experiments, the rates of synthesis of the cyclic nucleotides declined faster than the rates of degradation with aging. Guanyl cyclase activity had greater decreases in lung homogenate than in other tissues, and adenyl cyclase activity decreased much faster in heart and lung than in liver and skeletal muscle. cGMP PDE and cAMP PDE activities were much greater in lung than in other tissues at all ages. It is not known how or to what extent cyclic nucleotide metabolism might contribute to aging, or by what mechanisms alterations in the metabolism of such compounds are produced with, or by, aging. However, numerous changes in metabolic and endocrine activities are known to occur at different intervals of the lifespan, especially during gestation, maturation, and senescence, and may be related to the decline in activity of these cyclic nucleotide synthetic and degradative enzymes.
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