Antagonism of soluble guanylyl cyclase attenuates cutaneous vasodilation during whole body heat stress and local warming in humans

Abstract

We hypothesized that nitric oxide activation of soluble guanylyl cyclase (sGC) participates in cutaneous vasodilation during whole body heat stress and local skin warming. We examined the effects of the sGC inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), on reflex skin blood flow responses to whole body heat stress and on nonreflex responses to increased local skin temperature. Blood flow was monitored by laser-Doppler flowmetry, and blood pressure by Finapres to calculate cutaneous vascular conductance (CVC). Intradermal microdialysis was used to treat one site with 1 mM ODQ in 2% DMSO and Ringer, a second site with 2% DMSO in Ringer, and a third site received Ringer. In protocol 1, after a period of normothermia, whole body heat stress was induced. In protocol 2, local heating units warmed local skin temperature from 34 to 41°C to cause local vasodilation. In protocol 1, in normothermia, CVC did not differ among sites [ODQ, 15 ± 3% maximum CVC (CVC(max)); DMSO, 14 ± 3% CVC(max); Ringer, 17 ± 6% CVC(max); P > 0.05]. During heat stress, ODQ attenuated CVC increases (ODQ, 54 ± 4% CVC(max); DMSO, 64 ± 4% CVC(max); Ringer, 63 ± 4% CVC(max); P < 0.05, ODQ vs. DMSO or Ringer). In protocol 2, at 34°C local temperature, CVC did not differ among sites (ODQ, 17 ± 2% CVC(max); DMSO, 18 ± 4% CVC(max); Ringer, 18 ± 3% CVC(max); P > 0.05). ODQ attenuated CVC increases at 41°C local temperature (ODQ, 54 ± 5% CVC(max); DMSO, 86 ± 4% CVC(max); Ringer, 90 ± 2% CVC(max); P < 0.05 ODQ vs. DMSO or Ringer). sGC participates in neurogenic active vasodilation during heat stress and in the local response to direct skin warming.

Fig. 1.

Attenuation of sodium nitroprusside (SNP) induced vasodilation by 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). SNP (50 μM) increased cutaneous vascular conductance (CVC) to 53 ± 5% maximum CVC at microdialysis sites perfused with Ringer solution and to 56 ± 5% maximum CVC at sites perfused with 2% DMSO (P < 0.01 vs. baseline sites). The addition of 1 mM ODQ dissolved in 2% DMSO solution attenuated this vasodilation to 22 ± 5% maximum CVC. Values are means ± SE. P < 0.01, ODQ vs. Ringer or 2% DMSO with SNP. P > 0.05 vs. Ringer or 2% DMSO baseline sites.

Fig. 2.

Whole body heat stress protocol. This protocol was designed to examine the effects of antagonism of soluble guanylyl cyclase by ODQ on the reflex vasodilation induced by whole body heat stress. Three intradermal microdialysis sites were perfused with either 1 mM ODQ in 2% DMSO, 2% DMSO, or Ringer solution alone. Maximal cutaneous vasodilation was achieved at all sites at the end of the study by perfusion with 58 mM SNP. The perfusion rate at all microdialysis sites was 2 μl/min. AVD, active vasodilator.

Fig. 3.

Local skin warming protocol. This protocol was designed to examine the effects of antagonism of soluble guanylyl cyclase by ODQ on the vasodilation induced by local warming of the skin. Three intradermal microdialysis sites were perfused with 1 mM ODQ in 2% DMSO, 2% DMSO, or Ringer solution. Maximal cutaneous vasodilation was achieved at all sites at the end of the study by perfusion with 58 mM SNP. The perfusion rate at all microdialysis sites was 2 μl/min. T_loc, local skin temperature.

Fig. 4.

CVC responses to the whole body heating protocol in one subject. Perfusion with 1 mM ODQ and 2% DMSO began 8 min into the study. Periods of whole body cooling [cold stress (CS)] and whole body heating are indicated. Perfusion with 58 mM SNP began at 108 min.

Fig. 5.

Summary of CVC responses to whole body heat stress. Values are means ± SE. Under normothermic conditions during perfusion of all sites with Ringer solution, CVC values, normalized to their respective maxima, did not differ significantly among sites (P > 0.05). Also during normothermia, perfusion of one site with 2% DMSO and another with 1 mM ODQ did not produce any significant differences among sites (P > 0.05). In response to CS, CVC fell at all sites compared with normothermia (*P < 0.05), but responses did not differ among sites (P > 0.05). During heat stress, CVC increased at all sites compared with normothermia (P < 0.05). In heat stress, CVC increased to similar levels at sites that received Ringer only and 2% DMSO (P > 0.05), but was significantly attenuated at sites that received 1 mM ODQ (**P < 0.05, ODQ vs. Ringer or 2% DMSO). NS, nonsignificant.

Fig. 6.

CVC responses to the local skin warming protocol in one subject. In the first part of the protocol, T_loc was controlled at 34°C. Perfusion with 1 mM ODQ and 2% DMSO began 9 min into the study. At 66 min into the study, T_loc was increased to 41.5°C. Perfusion with 58 mM SNP began at 111 min.

Fig. 7.

Summary of CVC responses to local skin warming. Values are means ± SE. At T_loc = 34°C during perfusion with Ringer, 2% DMSO, and 1 mM ODQ, there were no statistical differences among sites (P > 0.05). Increasing T_loc from 34 to 41°C increased CVC significantly at all sites (P < 0.05, 34 vs. 41°C). CVC values were significantly less at sites treated with 1 mM ODQ (54 ± 5% maximum) than at either Ringer (90 ± 2% maximum) or 2% DMSO (86 ± 4% maximum) sites when T_loc = 41°C (P < 0.05, ODQ vs. Ringer or DMSO).