Receptors for vasoactive intestinal peptide (VIP) on human mononuclear leucocytes are upregulated during prolonged strain and energy deficiency

VIP receptors on blood mononuclear leucocytes and plasma VIP concentrations were studied during a ranger training course lasting for five days with almost continuous physical activity, and energy deficiency. The maximum binding capacity (Bmax) for the high affinity receptor increased (p less than 0.0005) from 0.71 (SEM = 0.11, N = 10) fmol/million cells to a maximum of 7.33 (SEM = 1.0) fmol/million cells on Day 4. There was no significant change in the dissociation constant (Kd) for the high affinity receptor, and no effect on Kd nor Bmax for the low affinity VIP receptor was detected. Plasma VIP concentration increased (p less than 0.0005) from 8.8 pmol/l (SEM = 0.6) to a maximum of 23.4 (SEM = 1.9) on the second day of the course. However, the highest plasma concentrations were about one order of magnitude lower than the dissociation constant (Kd) for the high affinity VIP receptor on the mononuclear leucocytes. These data indicate that heterologous upregulation of the high affinity VIP receptor on mononuclear blood cells takes place during combined strenuous physical exercise, and calorie deficiency.