The intrarenal site of calcitonin gene-related peptide degradation in the isolated perfused rat kidney

Mechanisms mediating the enhanced gene transcription of P2X3 receptor by calcitonin gene-related peptide in trigeminal sensory neurons

The molecular mechanisms underlying migraine pain remain unclear and probably require sustained facilitation in pain-sensing P2X(3) receptors gated by extracellular ATP in nociceptive sensory neurons. The major migraine mediator calcitonin gene-related peptide (CGRP) is known to sensitize P2X(3) receptors to increase impulse flow to brainstem trigeminal nuclei. This process is mediated via changes in the expression and function of P2X(3) receptors initially through enhanced trafficking and, later, perhaps through augmented synthesis of P2X(3) receptors. To clarify the mechanisms responsible for CGRP-evoked long lasting alterations in P2X(3) receptors, we used as a model mouse trigeminal ganglion neurons in culture. CGRP activated Ca(2+)-calmodulin-dependent kinase II, which became localized to the perimembrane region and neuronal processes, a phenomenon already apparent after 30 min and accompanied by a parallel increase in cAMP-response element-binding protein (CREB) phosphorylation and nuclear translocation. These effects triggered increased P2X(3) receptor transcription and were prevented by expressing a dominant negative form of CREB. Increased P2X(3) receptor synthesis was partly mediated by endogenous brain-derived neurotrophic factor (BDNF) because of its block by anti-BDNF antibodies and mimicry by exogenous BDNF. Immunocytochemistry experiments indicated distinct subpopulations of BDNF- or CGRP-sensitive trigeminal neurons with only partial overlap. The present data indicate a novel mechanism for enhancing P2X(3) receptor expression and function in trigeminal sensory neurons by CGRP via CREB phosphorylation. BDNF was an intermediate to extend the sensitizing effect of CGRP also to CGRP-insensitive neurons. This combinatorial action could serve as a powerful process to amplify and prolong pain mediated by P2X(3) receptors.

The role of the kidney in the clearance of calcitonin gene related peptide (CGRP)

Calcitonin gene-related peptide (CGRP) is a 37 amino-acid peptide, undetectable in the plasma in health but elevated in certain disease states such as medullary thyroid cancer, and potentially causes symptoms. The kidney is a major site of and influence on the clearance of exogenously infused CGRP. As CGRP might cause symptoms in renal dysfunction, this study was performed to determine the clearance of CGRP in humans and animals with altered renal function. In chronic renal failure patients, CGRP was not detected in plasma either before or after haemodialysis. In sheep, before and after bilateral nephrectomy, there was an approximate halving of plasma clearance and doubling of the circulating half-life of infused CGRP. This reduction in clearance was greater than that which could be accounted for by the reduction in degradation by renal substance alone. This renal influence on extra-renal CGRP metabolism was not due to the renal production of a circulating peptidase as evidenced by the absence of such peptidase in the plasma of normal and anephric sheep. Further, severity of uraemia had no influence on the extra-renal metabolism. The mechanism by which the kidney influences the extra-renal metabolism of CGRP remains obscure.