The vasopressin receptor of the blood-brain barrier in the rat hippocampus is linked to calcium signalling

The signal transduction system of the vasopressin receptor in cerebral microvessels is not known but appears not to be adenylate cyclase/cyclic AMP. We determined the effect of arginine vasopressin (AVP) on the intracellular free calcium concentration [Ca 2+] i in endothelial cells of isolated hippocampal microvessels of rats, using the fura-2 fluorescence technique. AVP administration caused a rapid and transient rise of cytosolic free calcium which was absent after extracellular calcium was removed, and could be blocked with the vasopressin V1 receptor antagonist, d(CH 2) 5 Tyr-(Me)AVP. The vasopressin V2 receptor agonist, 1-deamino-8, d-AVP, on the contrary, failed to affect the intracellular free calcium level, and was unable to inhibit the AVP-induced rise of [Ca 2+] i in the preparation. Our results, therefore, demonstrate the presence of a calcium-signalling, i.e. V1 vasopressin receptor at the blood-brain barrier in the hippocampus of the rat.