Mitogenic activity of insulin in the culture of a trypanosome: duration and dose response

The effects of insulin on the in vitro growth characteristics of Trypanosoma granulosum were investigated. The insulin growth stimulus had a rapid onset with little or no lag phase but was relatively short lived, growth peaking typically on day 3 or 4 of culture. This contrasted with medium containing 10% foetal calf serum, normally used for in vitro culture of this trypanosome, which after a 3 day lag stimulated sustained log-phase growth. Insulin demonstrated a biphasic dose response with maximum growth typically occurring at 3-10 microg/ml and a much reduced effect at higher concentrations. These findings suggest a possible role for host insulin and/or trypanosomal insulin-like molecules in regulating parasite growth in vivo.