Calcitonin gene-related peptide increases blood flow and potentiates plasma protein extravasation in the rat knee joint.

1. The effects of calcitonin gene-related peptide (CGRP) and other vasoactive mediators of inflammation on blood flow in the synovial vessels and plasma protein extravasation into the knee (femoro-tibial) joint of the pentobarbitone-anaesthetized rat were measured. 2. Changes in synovial blood flow were estimated by 133xenon clearance from the synovial cavity. CGRP (0.1 pmol and 10 pmol) and prostaglandin E1 (PGE1; 3 pmol and 300 pmol) significantly increased clearance from the knee joint measured 5 min after intra-articular injection. Substance P (10 pmol) had no effect on synovial blood flow. 3. Intra-articular perfusion of the rat knee with CGRP at concentrations up to 0.1 mM, or PGE1 at concentrations up to 10 microM, did not increase plasma extravasation into the synovial cavity measured by accumulation of intravenously injected 125I-albumin in the perfusate. 4. Plasma extravasation into the knee was significantly increased by infusion of bradykinin (0.1 microM), 5-hydroxytryptamine (1 microM) and histamine (0.1 mM), compared with the contralateral joints in the same animals which were perfused with Tyrode solution. 5. Perfusion of the knee joint with substance P did not specifically induce 125I-labelled albumin accumulation in the synovial cavity even at doses that had systemic effects as observed by marked plasma extravasation into other tissues. 6. The increase in plasma extravasation induced by histamine (0.1 mM) was potentiated by co-infusion with CGRP (0.1 microM) and PGE1 (3 microM). However the response to a submaximal dose (0.1 microM) of bradykinin, which induced similar plasma extravasation to histamine (0.1 mM), was not increased by co-infusion with CGRP or PGE1.7. These results show that CGRP is a potent vasodilator in the rat knee. CGRP released from sensory nerves may act synergistically with mediators of increased vascular permeability to modify the inflammatory response in this site.