Circadian rhythm of the Bmax of [3H]-imipramine binding in rabbit platelets.

[3H]-imipramine binding was measured in rabbit blood platelet membranes on a 24 h cycle. Animals were kept on a 14 h light (L) 10 h dark (D) schedule, and blood samples were collected at L + 2, L + 8, D + 2, D + 8 and L + 2 h on a following cycle. Significant differences were found for Bmax values of [3H]-imipramine binding, with highest values during the dark phase and lowest during the light phase. No significant differences were found in Kd values. These results suggest the existence of a circadian rhythm for the Bmax of [3H]-imipramine binding in blood platelets.