Effects of FCS on histamine hyperresponsivity in human umbilical smooth muscle cells. Cells were stimulated with different concentrations of histamine in the absence (open circles) or presence (filled circles) of 5% FCS for 1 hr. The histamine-induced PGE2 production was used as a functional measure to determine the histamine responses in these cells. Results represent the mean and standard error of three independent experiments. Statistically significant differences were calculated using the Mest; **p < 0.01.