Adenosine 3′:5′-cyclic monophosphate in young and senescent human fibroblasts during growth and stationary phase in vitro. Effects of prostaglandin E1 and of adrenaline

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Abstract
Cyclic AMP levels per mg of cell protein were higher in late-passage (senescent) fibroblasts than in early-passage (young) fibroblasts both during growth and stationary phase, but, because the protein concentration per unit volume in senescent cells was lower than in young cells, the molar concentrations of intracellular cyclic AMP were very similar in the two cell types. In both young and senescent fibroblasts cyclic AMP levels declined during growth and no increase in intracellular cyclic AMP occurred in association with density-dependent inhibition of growth. These results indicate that changes in cyclic AMP concentration do not play a role in controlling the growth or in the senescent decline of human fibroblasts. Prostaglandin E1 (1μm) caused maximal increases in fibroblast cyclic AMP concentration of 60–500-fold after 10–30min, and adrenaline (epinephrine) (10μm) caused maximum increases of 5–25-fold after 2–10min, depending on both the number of passages and the period after subculture. The cyclic AMP level in confluent young cells increased more with prostaglandin E1 and far less with adrenaline than the cyclic AMP level in confluent senescent cells. During growth to confluence the cyclic AMP response to adrenaline declined in young cells and increased in senescent cells. As these responses to prostaglandin E1 and to adrenaline changed independently of each other and of the basal cyclic AMP concentration, it is suggested that the expression of hormone receptors is altered both during growth to confluence and during senescence of human fibroblasts.

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