Systemic application of the transient receptor potential vanilloid-type 4 antagonist GSK2193874 induces tail vasodilation in a mouse model of thermoregulation

Abstract

In humans, skin is a primary thermoregulatory organ, with vasodilation leading to rapid body cooling, whereas in Rodentia the tail performs an analogous function. Many thermodetection mechanisms are likely to be involved including transient receptor potential vanilloid-type 4 (TRPV4), an ion channel with thermosensitive properties. Previous studies have shown that TRPV4 is a vasodilator by local action in blood vessels, so here, we investigated whether constitutive TRPV4 activity affects Mus muscularis tail vascular tone and thermoregulation. We measured tail blood flow by pressure plethysmography in lightly sedated M. muscularis (CD1 strain) at a range of ambient temperatures, with and without intraperitoneal administration of the blood-brain barrier crossing TRPV4 antagonist GSK2193874. We also measured heart rate (HR) and blood pressure. As expected for a thermoregulatory organ, we found that tail blood flow increased with temperature. However, unexpectedly, we found that GSK2193874 increased tail blood flow at all temperatures, and we observed changes in HR variability. Since local TRPV4 activation causes vasodilation that would increase tail blood flow, these data suggest that increases in tail blood flow resulting from the TRPV4 antagonist may arise from a site other than the blood vessels themselves, perhaps in central cardiovascular control centres.

Keywords: 3Rs; TRPV4; ion channels; non-invasive blood pressure; tail blood flow; thermoregulation.

Figure 1.

Effects of pharmacological inhibition of TRPV4 on blood pressure, HR and blood flow. (a) Mean arterial pressure at a range of ambient temperatures in control and GSK2193874, there was a significant association with temperature, but not drug. There was also no significant association between temperature and drug (mixed effects model: see main text for details). (b) Mean HR across a range of ambient temperature in control and GSK2193874, overall there was a significant change of HR with temperature, but no significant difference with drug and no significant association between drug and temperature (mixed effects model: see main text for details). (c) Tail blood flow across a range of ambient temperatures in control and GSK2193874. Overall, there was a statistically significant increase of blood flow with temperature and with GSK2193874 and a significant interaction (mixed effects model: see main text for details). Overall, n = 14 animals or for each temperature; 31°C n = (9,4) 32°C n = (10,4), 33°C n = (11,6), 34°C n = (10,7), 35°C n = (11,7) and 35°C n = (12,5). To investigate specific temperature points that were different to the 31°C value, we treated temperature as a factor and ran the estimated-marginal means method with the R-package Emmeans. This consists of 66 pairwise comparisons and we used Benjamini–Hochberg multiple comparison correction. In control, no individual flow is significantly greater than that at 31°C; however, in GSK2193874, blood flow at both 35°C and 36°C was significantly greater than at 31°C (p < 0.05).

Figure 2.

Short-range HRV analysis. (a) Stacked Lomb periodograms for 3000 simulated ECG inter-beat interval datasets. Y-axis is the duration of the simulated ECG record, x-axis is the frequency component of each Lomb–Scargle. The periodograms have been normalized and scaled therefore the power (colour bar on the right) is in arbitrary units (AU). Below are periodogram surfaces recorded at different temperatures under control (b), or after injection GSK2193874 (c). Power is given in the scale bars. MANOVA (Minitab) analyses show these two distributions are significantly different, Wilks lambda p < 0.05. Overall, n = 14 animals.