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The experiments reported here illustrate a few of the factors apart from genes which can influence hormone-responsive generation of cyclic adenosine 3':5'-monophosphate in human fibroblasts. For both normal and cystic fibrosis fibroblasts, the isoproterenol stimulation ratio was maximal 2 to 3 days after subculture and declined thereafter; prostaglandin E1 stimulation ratio was maximal 7 to 10 days after subculture. Cells dislodged from the plate by either scraping or typsinization had reduced isoproterenol or prostaglandin E1 stimulation ratios compared to cells studied in situ. Fibroblasts from healthy controls and cystic fibrosis patients plated simultaneously and grown in three different culture conditions responded similarly to the change in growth conditions. Addition to the incubation medium of polyamines, calcium, magnesium, or guanosine triphosphate did not alter the stimulation ratios for isoproterenol or prostglandin E1. Repeated measures analysis indicates that cellular content of cyclic adenosine 3':5'-monophosphate is not a reliable measure for comparing cell lines; isoproterenol stimulation ratio is a reliable measure, but there is large variation from cell line to cell line. Isoproterenol stimulation ratio was the same for normal and cystic fibrosis fibroblasts in each of the three culture conditions tested at both three and ten days after subculture.

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