Abstract
Incubation of L-929 and L-2071 fibroblasts with prostaglandin E1 (PGE1) caused a rapid increase in the cyclic AMP content of these cells. A maximal effect was produced with 0.2 μg PGE1 per ml. At a concentration of 4 μg/ml, PGE2 was almost equally effective, but PGF2α and PGA2 were much less so. 2.6 μM epinephrine, 0.4 mM serotonin, and 0.2% ethanol were without effect. In L-929 cells, cyclic AMP concentrations remained elevated for 2-5 hr, and then declined, although even after a 24-hr incubation the medium contained PGE1 in a concentration sufficient to increase maximally the cyclic AMP content of cells not previously exposed to this compound. A second addition of PGE1 after 5 or 24 hr did not produce another increase in the concentration of cyclic AMP. After incubation with PGE1 for 24 hr, cyclic AMP phosphodiesterase activity, assayed with 0.56 μM substrate, was increased 30-100%; the activity rose further between 24 and 48 hr. It is suggested that the increase in phosphodiesterase activity that appears to be a consequence of prolonged elevation of cyclic AMP concentration may account at least in part for the apparent “refractoriness” to PGE1 that develops after incubation for several hours with this compound.
Keywords: mouse L cells, tissue culture, enzyme kinetics, prostaglandin homologues
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