Figure 2

Platelet levels as a function of α and γ. Platelet 5-HT levels, ser(α, γ), plotted as a function of α (the factor regulating 5-HT release from EC cells) and γ (the rate of 5-HT clearance by the liver, lungs, and other organs). This relationship is described by equation (3), where K is a constant. Note that if α is normal (high), platelet 5-HT levels stay low with any γ, but if α is autistic (low), individuals with a low γ become hyperserotonemic. The black circles mark the points whose coordinates are independent of α and are γ* = R _C /(R _C + F _C ) and ser(α, γ*) = KF _C . Note in equations (1) and (2) that R = R _C if and only if γ = γ*, so the distribution of γ is likely to contain γ*. This guarantees that the distributions of the 5-HT levels in normal autistic groups will always overlap, as observed in clinical studies. For illustrative purposes, the normal and autistic values of α were arbitrarily set at 0.20 and 0.02, respectively. These are realistic values, as follows in the text. The other parameter values were taken from published studies [48, 53, 70] and were F _C = 210 ng/min and R _C = 3000 ng/min.