Reverse pinocytosis induced in cerebral endothelial cells by injection of histamine into the cerebral ventricle.

Histamine dihydrochloride (10 micrograms of 500 micrograms/ml) was infused during 1 min into the lateral cerebral ventricle of rats, which resulted in a significant stimulation of pinocytosis in the endothelial cells. Systemic injections of mepyramine or metiamide could not prevent this activation. In contrast, ranitidine, injected with histamine was able to inhibit the stimulation of pinocytosis. Albumin exudation from the blood was not found. There was also no change in water and electrolyte contents of the brain tissue. The results suggest that histamine reaching the abluminal membrane can activate the pinocytosis in the cerebral endothelial cells in the reverse direction, i.e., from brain to blood, without opening the blood-brain barrier.