Regional variation in nitric oxide-dependent cutaneous vasodilatation during local heating in young adults

Skeletal Muscle, Skin, and Bone as Three Major Nitrate Reservoirs in Mammals: Chemiluminescence and 15N-Tracer Studies in Yorkshire Pigs

In mammals, nitric oxide (NO) is generated either by the nitric oxide synthase (NOS) enzymes from arginine or by the reduction of nitrate to nitrite by tissue xanthine oxidoreductase (XOR) and the microbiome and further reducing nitrite to NO by XOR or several heme proteins. Previously, we reported that skeletal muscle acts as a large nitrate reservoir in mammals, and this nitrate reservoir is systemically, as well as locally, used to generate nitrite and NO. Here, we report identifying two additional nitrate storage organs-bone and skin. We used bolus of ingested 15N-labeled nitrate to trace its short-term fluxes and distribution among organs. At baseline conditions, the nitrate concentration in femur bone samples was 96 ± 63 nmol/g, scalp skin 56 ± 22 nmol/g, with gluteus muscle at 57 ± 39 nmol/g. In comparison, plasma and liver contained 34 ± 19 nmol/g and 15 ± 5 nmol/g of nitrate, respectively. Three hours after 15N-nitrate ingestion, its concentration significantly increased in all organs, exceeding the baseline levels in plasma, skin, bone, skeletal muscle, and in liver 5-, 2.4-, 2.4-, 2.1-, and 2-fold, respectively. As expected, nitrate reduction into nitrite was highest in liver but also substantial in skin and skeletal muscle, followed by the distribution of 15N-labeled nitrite. We believe that these results underline the major roles played by skeletal muscle, skin, and bone, the three largest organs in mammals, in maintaining NO homeostasis, especially via the nitrate-nitrite-NO pathway.

Local heating-induced cutaneous vasodilation in reinnervated and noninnervated deep inferior epigastric perforator flaps

INTRODUCTION

Cutaneous vascular reactivity to local heating in free flaps has not been characterized. We aimed to assess local heating-induced cutaneous vasodilation in reinnervated and noninnervated deep inferior epigastric perforator (DIEP) flaps.

METHODS

We conducted a cross-sectional study of 21 female patients with an uncomplicated unilateral delayed DIEP breast reconstruction at least 2 years after surgery. DIEP flaps and contralateral breasts were subjected to direct local heating, and skin blood flow was assessed using laser-Doppler flowmetry. To evaluate sensory-nerve-fiber function, touch perception thresholds were assessed using a 20-piece Touch-test™ Sensory Evaluator, and cutaneous warm detection and heat pain thresholds were measured using a TSA-II device.

RESULTS

Of the participants, 10 had a reinnervated DIEP flap with a single coapted nerve (mean flap weight, 610 ± 296 g) and 11 had a noninnervated DIEP flap (mean flap weight, 613 ± 169 g). Mean age was 58 ± 11 years, mean follow-up time was 5 ± 1 years, and mean BMI was 24 ± 3 kg/m2 . DIEP flaps exhibited significantly weaker cutaneous vasodilation in response to local heating than contralateral breasts (median peak skin blood flow, 59 [25th-75th percentile, 36-71] a.u. for DIEP flaps versus 94 [74-141] a.u. for contralateral breasts; p < .001). The magnitude of the response was similar between reinnervated and noninnervated flaps (median peak skin blood flow, 55 [25th-75th percentile, 39-68] a.u. for reinnervated DIEP flaps versus 66 [36-77] a.u. for noninnervated DIEP flaps; p = .75). Of participants with reinnervated DIEP flaps, 90% perceived heat pain below the 50°C safety threshold, as compared to 36% of participants with noninnervated DIEP flaps (two-tailed p = .02).

CONCLUSION

Our results suggest that free flap transfer causes longstanding impairment, yet not complete abolition, of both the sensory nerve-mediated and nitric oxide-dependent local heating-induced cutaneous vasodilatory systems. We found no statistical evidence that flap reinnervation improves the ability to raise skin blood flow in response to local heating.

Reliability of laser-Doppler flowmetry derived measurements of forearm and calf cutaneous vasodilation during gradual local heating in young adults

OBJECTIVES

Evaluate reliability of laser-Doppler flowmetry derived cutaneous vasodilation on the upper and lower limbs during gradual local heating.

METHODS

In twenty-eight young adults (21 (SD 3) years, 14 females), absolute cutaneous vascular conductance (CVC_abs) and CVC normalized to maximum vasodilation at 44 °C (%CVC_max) were assessed at two adjacent sites on each of the forearm and calf during gradual local skin heating (33-42 °C at 1 °C·5 min^-1) for two identical trials (∼1 week apart). Responses were assessed for baseline, the steady-state heating plateau at 42 °C and the span (i.e. plateau-baseline).

RESULTS

Between-day reliability was characterized as measurement consistency across trials. Within-day reliability was characterized as within-limb measurement consistency across adjacent skin sites. Between- and within-day absolute reliability (coefficient of variation) generally improved with heating, from poor (>25 %) at baseline to good (<10 %) for %CVC_max and moderate (10-25 %) for CVC_abs for plateau and span. However, relative reliability (intraclass correlation coefficient) was generally not acceptable (<0.70) for any condition. Responses were generally consistent for females and males and there were no major forearm and calf differences.

CONCLUSIONS

Consistency of CVC estimates improved during gradual local heating with negligible limb and sex differences, which are important considerations for experimental design and interpretation.

Influence of uncomplicated, controlled hypertension on local heat-induced vasodilation in non-glabrous skin across the body

OBJECTIVE

1) Examine pooled effects of hypertension on nitric oxide (NO)-dependent vasodilation during local heating across multiple non-glabrous skin regions, and 2) explore regional differences.

METHODS

Responses were compared between fourteen participants with uncomplicated hypertension controlled with medication (7 females, 61±6 years) and fourteen age-matched non-hypertensive controls (6 females; 60±5 years). Cutaneous vascular conductance, normalized to maximum vasodilation (%CVC_max) was assessed at the upper chest, abdomen, dorsal forearm, thigh, and lateral calf during local heating. Across all regions, local skin temperatures were simultaneously increased from 33-42°C (1°C·10·s^-1), and held until a stable heating plateau was achieved (~40 min), followed by continuous infusion of 20 mM of N(G)-Nitro-L-arginine methyl ester (L-NAME; ~40min) at all sites until a stable L-NAME plateau was achieved. The difference between heating and L-NAME plateaus was defined as the NO-contribution. Statistical equivalence for each heating phase was determined based on equivalence bounds of ±10%CVC_max for between-group differences.

RESULTS

Pooled (all-regions) %CVC_max responses were equivalent for baseline (two one-sided t-test; p<0.001), heating plateau (p=0.002), L-NAME plateau (p=0.028), and NO-contribution (p=0.003). For individual regions, responses were equivalent at baseline for the abdomen, thigh, and calf, the heating plateau for the thigh, and the L-NAME plateau for the calf (all p<0.05). Conversely, the calf heating plateau was lower in the hypertension group (t-test; p<0.05).

CONCLUSION

Local heat-induced cutaneous vasodilation was statistically equivalent between individuals with uncomplicated, controlled hypertension and non-hypertensive age-matched adults when pooled across multiple skin sites. Conversely, individual between-region comparisons were generally too variable to permit definitive conclusions.