Putrescine and biopterine test in cell culture. Putrescine was added at 10 μM final concentration in defined media HX25M (HX25M+P) and AR-103 (AR-103+P). Biopterin was added at final concentration of 1 μM in defined medium HX25M with (HX25M+P+B) or without (HX25M+B) putrescine. Epimastigote cells counts were performed every three days, then all cultures were diluted to 1e + 06 cells/ml (start point of cultivation). Values plotted refer to the average of three biological replicates counted every cell passage after three days of culture. Epimastigote cultures were maintained for six passages in HX25M+P defined medium (green line), whereas cells cultivated in AR-103+P defined medium (dashed line), even with putrescine, died after the third passage. Epimastigotes cultivated in HX25M+B medium (red line) died after the third passage. Epimastigotes cultivated in HX25M+P+B medium (black line) showed a significant increase in growth rate compared to HX25M+P medium (P < 0.01) (green line).