Functional Calcitonin Gene-Related Peptide Type 1 And Adrenomedullin Receptors In Human Trigeminal Ganglia, Brain Vessels, And Cerebromicrovascular Or Astroglial Cells In Culture
Calcitonin gene-related peptide (CGRP) and adrenomedullin (ADM) are potent dilators of human brain arteries, and they have been implicated in the neurogenic inflammation underlying migraine headache and in the evolution of stroke, respectively. However, little is known about the presynaptic and postsynaptic distribution of their respective receptors in the human cerebrovascular bed and trigeminovascular system. In the current study, the expression of mRNA for ADM and the two cloned human CGRP1 receptors (identified here as A-CGRP1 receptors [ Aiyar et al., 1996 ] and K-CGRP1 receptors) [ Kapas and Clark, 1995 ] were evaluated in human brain vessels and trigeminal ganglia. Further, the ability of CGRP and ADM to activate adenylate cyclase in cerebromicrovascular and astroglial cell cultures was determined, and the receptors involved were characterized pharmacologically. Isolated human pial vessels, intracortical microvessels, and capillaries, as well as cultures of brain endothelial (EC), smooth muscle (SMC), and astroglial (AST) cells, all expressed mRNA for the two cloned CGRP1 receptors; however, message for the K-CGRP1 receptor was barely detectable in microvascular tissues and cells. In contrast, only isolated capillaries and cultured AST exhibited message for the ADM receptor. In human trigeminal ganglia, mRNA for ADM and the two CGRP1 receptors was systematically present The CGRP dose-dependently increased (up to 50-fold) cAMP formation in cell cultures, an effect significantly blocked by 0.1 to 10 μmol/L of the CGRP1 receptor antagonist CGRP8–37. The ADM receptor agonist, ADM13–52 (1 μmol/L), similarly increased cAMP production in all cell types, and this response was virtually abolished by 1 μmol/L CGRP8–37. Low concentrations (1 to 10 μmol/L) of the ADM receptor antagonist ADM22–52 blocked the ADM13–52-induced cAMP formation in AST (26% at 10 μmol/L, P < 0.05), whereas they potentiated this response in brain EC and SMC (40% and 100%, P < 0.001, respectively). Even at a higher dose (50 μmol/L), ADM22–52 inhibited the ADM13–52 effect in vascular cells (45%) much less effectively than in AST (95%). These results indicate that both CGRP and ADM can affect human brain vessels through a CGRP1 receptor, and they further suggest the presence of functional ADM receptors in human astroglial cells.