Human lymphatic vessel contractile activity is inhibited in vitro but not in vivo by the calcium channel blocker nifedipine

Calcium channel blockers (CCB) are widely-prescribed anti-hypertensive agents. The commonest side-effect, peripheral oedema, is attributed to a larger arterial than venous dilation causing increased fluid filtration. Whether CCB treatment is detrimental to human lymphatic vessel function and thereby exacerbates oedema formation is unknown. We observed spontaneous lymphatic contractions in isolated human vessels (thoracic duct and mesenteric lymphatics) maintained under isometric conditions to be inhibited by therapeutic concentrations (nanomolar) of the CCB nifedipine while higher than therapeutic concentrations of verapamil (micromolar) were necessary to inhibit activity. Nifedipine also inhibited spontaneous action potentials measured by sharp microelectrodes. Furthermore, noradrenaline could not elicit normal increases in lymphatic vessel tone with maximal constriction reduced to 29.4 ± 4.9% of control in the presence of 20 nmol/l nifedipine. Transcripts for the L-type calcium channel gene CACNA1C were consistently detected from human thoracic duct samples examined and the CaV1.2 protein was localized by immunoreactivity to lymphatic smooth muscle cells. While human lymphatics ex vivo were highly sensitive to nifedipine this was not apparent in vivo when nifedipine was compared to placebo in a randomized, double-blinded clinical trial: conversely, lymphatic vessel contraction frequency was increased and refill time was faster despite all subjects achieving target nifedipine plasma concentrations. We conclude that human lymphatic vessels are highly sensitive to nifedipine in vitro but that care must be taken when extrapolating in vitro observations of lymphatic vessel function to the clinical situation as similar changes in lymphatic function were not evident in our clinical trial comparing nifedipine treatment to placebo. This article is protected by copyright. All rights reserved.