Is a kininogenase necessary for human sweating

Are Thermoregulatory Sweating and Active Vasodilation in Skin Controlled by Separate Nerves During Passive Heat Stress in Persons With Spinal Cord Injury?

Background

Sudomotor responses (SR) and active vasodilation (AVD) are the primary means of heat dissipation during passive heat stress (PHS). It is unknown if they are controlled by a single or separate set of nerves. Older qualitative studies suggest that persons with spinal cord injury (SCI) have discordant areas of sweating and vasodilation.

Objectives

To test the hypothesis that neural control of SR and AVD is through separate nerves by measuring SR and vasodilation in persons with SCI to determine if these areas are concordant or discordant.

Methods

Nine persons with tetraplegia, 13 with paraplegia, and nine able-bodied controls underwent PHS (core temperature rise 1°C) twice. Initially, the starch iodine test measured SR post-PHS in skin surface areas surrounding the level of injury. Subsequently, laser Doppler imagery scans measured vasodilation pre- and post-PHS in areas with and without SR. Percent change in red blood cell (RBC) flux was compared in areas with and without SR.

Results

Persons with tetraplegia were anhidrotic on all areas; however, the same areas demonstrated minimal RBC flux change significantly less than equivalent able-bodied skin surface areas. In persons with paraplegia, areas of intact SR correlated with areas of RBC flux change quantitatively comparable to able-bodied persons. In anhidrotic areas, RBC flux change was significantly less than areas with SR and likely resulted from non-AVD mechanisms.

Conclusion

In persons with SCI under PHS, areas with intact SR and AVD are concordant, suggesting these two aspects of thermoregulation are controlled by a single set of nerves.

Current concepts of active vasodilation in human skin

In humans, an increase in internal core temperature elicits large increases in skin blood flow and sweating. The increase in skin blood flow serves to transfer heat via convection from the body core to the skin surface while sweating results in evaporative cooling of the skin. Cutaneous vasodilation and sudomotor activity are controlled by a sympathetic cholinergic active vasodilator system that is hypothesized to operate through a co-transmission mechanism. To date, mechanisms of cutaneous active vasodilation remain equivocal despite many years of research by several productive laboratory groups. The purpose of this review is to highlight recent advancements in the field of cutaneous active vasodilation framed in the context of some of the historical findings that laid the groundwork for our current understanding of cutaneous active vasodilation.

Cutaneous vasodilator and vasoconstrictor mechanisms in temperature regulation

In this review, we focus on significant developments in our understanding of the mechanisms that control the cutaneous vasculature in humans, with emphasis on the literature of the last half-century. To provide a background for subsequent sections, we review methods of measurement and techniques of importance in elucidating control mechanisms for studying skin blood flow. In addition, the anatomy of the skin relevant to its thermoregulatory function is outlined. The mechanisms by which sympathetic nerves mediate cutaneous active vasodilation during whole body heating and cutaneous vasoconstriction during whole body cooling are reviewed, including discussions of mechanisms involving cotransmission, NO, and other effectors. Current concepts for the mechanisms that effect local cutaneous vascular responses to local skin warming and cooling are examined, including the roles of temperature sensitive afferent neurons as well as NO and other mediators. Factors that can modulate control mechanisms of the cutaneous vasculature, such as gender, aging, and clinical conditions, are discussed, as are nonthermoregulatory reflex modifiers of thermoregulatory cutaneous vascular responses.

Cholinergic mechanisms of cutaneous active vasodilation during heat stress in cystic fibrosis

To test the hypothesis that cutaneous active vasodilation in heat stress is mediated by a redundant cholinergic cotransmitter system, we examined the effects of atropine on skin blood flow (SkBF) increases during heat stress in persons with (CF) and without cystic fibrosis (non-CF). Vasoactive intestinal peptide (VIP) has been implicated as a mediator of cutaneous vasodilation in heat stress. VIP-containing cutaneous neurons are sparse in CF, yet SkBF increases during heat stress are normal. In CF, augmented ACh release or muscarinic receptor sensitivity could compensate for decreased VIP; if so, active vasodilation would be attenuated by atropine in CF relative to non-CF. Atropine was administered into skin by iontophoresis in seven CF and seven matched non-CF subjects. SkBF was monitored by laser-Doppler flowmetry (LDF) at atropine treated and untreated sites. Blood pressure [mean arterial pressure (MAP)] was monitored (Finapres), and cutaneous vascular conductance was calculated (CVC = LDF/MAP). The protocol began with a normothermic period followed by a 3-min cold stress and 30-45 min of heat stress. Finally, LDF sites were warmed to 42 degrees C to effect maximal vasodilation. CVC was normalized to its site-specific maximum. During heat stress, CVC increased in both CF and non-CF (P < 0.01). CVC increases were attenuated by atropine in both groups (P < 0.01); however, the responses did not differ between groups (P = 0.99). We conclude that in CF there is not greater dependence on redundant cholinergic mechanisms for cutaneous active vasodilation than in non-CF.

In vivo mechanisms of cutaneous vasodilation and vasoconstriction in humans during thermoregulatory challenges

This review focuses on the neural and local mechanisms that have been demonstrated to effect cutaneous vasodilation and vasoconstriction in response to heat and cold stress in vivo in humans. First, our present understanding of the mechanisms by which sympathetic cholinergic nerves mediate cutaneous active vasodilation during reflex responses to whole body heating is discussed. These mechanisms include roles for cotransmission as well as nitric oxide (NO). Next, the mechanisms by which sympathetic noradrenergic nerves mediate cutaneous active vasoconstriction during whole body cooling are reviewed, including cotransmission by neuropeptide Y (NPY) acting through NPY Y1 receptors. Subsequently, current concepts for the mechanisms that effect local cutaneous vascular responses to direct skin warming are examined. These mechanisms include the roles of temperature-sensitive afferent neurons as well as NO in causing vasodilation during local heating of skin. This section is followed by a review of the mechanisms that cause local cutaneous vasoconstriction in response to direct cooling of the skin, including the dependence of these responses on intact sensory and sympathetic, noradrenergic innervation as well as roles for nonneural mechanisms. Finally, unresolved issues that warrant further research on mechanisms that control cutaneous vascular responses to heating and cooling are discussed.

Human temperature regulation during cycling with moderate leg ischaemia

The effect of graded ischaemia in the legs on the regulation of body temperature during steady-state exercise was investigated in seven healthy males. It was hypothesised that graded ischaemia in the working muscles increases heat storage within the muscles, which in turn potentiates sweat secretion during exercise. Blood perfusion in the working muscles was reduced by applying a supra-atmospheric pressure (+6.6 kPa) around the legs, which reduced maximal working capacity by 29%. Each subject conducted three separate test trials comprising 30 min of steady-state cycling in a supine position. Exercise with unrestricted blood flow (Control trial) was compared to ischaemic exercise conducted at an identical relative work rate (Relative trial), as well as at an identical absolute work rate (Absolute trial); the latter corresponding to a 20% increase in relative workload. The average (SD) increases in both the rectal and oesophageal temperatures during steady-state cycling was 0.3 (0.2) degrees C and did not significantly differ between the three trials. The increase in muscle temperature was similar in the Control (2.7 (0.3) degrees C) and Absolute (2.4 (0.7) degrees C) trials, but was substantially lower (P < 0.01) in the Relative trial (1.4 (0.8) degrees C). Ischaemia potentiated (P < 0.01) sweating on the forehead in the Absolute trial (24.2 (7.3) g m(-2) min(-1)) compared to the Control trial (13.4 (6.2) g m(-2) min(-1)), concomitant with an attenuated (P < 0.05) vasodilatation in the skin during exercise. It is concluded that graded ischaemia in working muscles potentiates the exercise sweating response and attenuates vasodilatation in the skin initiated by increased core temperature, effects which may be attributed to an augmented muscle metaboreflex.

Bradykinin does not mediate cutaneous active vasodilation during heat stress in humans

To test the hypothesis that bradykinin effects cutaneous active vasodilation during hyperthermia, we examined whether the increase in skin blood flow (SkBF) during heat stress was affected by blockade of bradykinin B(2) receptors with the receptor antagonist HOE-140. Two adjacent sites on the forearm were instrumented with intradermal microdialysis probes for local delivery of drugs in eight healthy subjects. HOE-140 was dissolved in Ringer solution (40 microM) and perfused at one site, whereas the second site was perfused with Ringer alone. SkBF was monitored by laser-Doppler flowmetry (LDF) at both sites. Mean arterial pressure (MAP) was monitored from a finger, and cutaneous vascular conductance (CVC) was calculated (CVC = LDF/MAP). Water-perfused suits were used to control body temperature and evoke hyperthermia. After hyperthermia, both microdialysis sites were perfused with 28 mM nitroprusside to effect maximal vasodilation. During hyperthermia, CVC increased at HOE-140 (69 +/- 2% maximal CVC, P < 0.01) and untreated sites (65 +/- 2% maximal CVC, P < 0.01). These responses did not differ between sites (P > 0.05). Because the bradykinin B(2)-receptor antagonist HOE-140 did not alter SkBF responses to heat stress, we conclude that bradykinin does not mediate cutaneous active vasodilation.

Sympathetic blockade does not enhance tissue warming during isolated heated limb perfusion

Isolated, heated limb perfusion is used for the treatment of locally recurrent melanoma, intransit metastases, and acral lentiginous melanomas. Tissue warming during this procedure requires adequate perfusion within the isolated extremity. At our institution, spinal or epidural anesthesia was used to produce sympathetic blockade and vasodilation for lower extremity procedures. More recently, we began using mild systemic hyperthermia to produce active thermoregulatory vasodilation. In the presence of heat stress, sympathetic blockade may actually decrease skin blood flow because active cutaneous vasodilation, which is associated with sweating, is dependent on intact sympathetic innervation. We therefore investigated whether the continued use of neuraxial blockade was justified. Twenty patients undergoing lower extremity perfusions were alternately assigned to receive either combined general and spinal anesthesia or general anesthesia alone. All were aggressively warmed using forced air and circulating water. There were no significant differences in tissue temperatures (measured at four sites in the isolated limb) between groups at any time before or after the start of perfusion. Similarly, pump flow (715 +/- 211 mL/min versus 965 +/- 514 mL/min) and the time required to achieve an average tissue temperature of 39 degrees C (43 +/- 16 vs 34 +/- 13 min) were not different between groups (spinal versus no spinal). Sweating was observed in all but three patients at esophageal temperatures of 37.9 +/- 0.6 degrees C. We conclude that sympathetic blockade confers no added benefit for tissue warming during isolated limb perfusions in the presence of induced mild systemic hyperthermia.

IMPLICATIONS

Sympathetic blockade prevents adrenergic vasoconstriction, but also inhibits active, neurally mediated cutaneous vasodilation (a normal thermoregulatory response to heat). In slightly hyperthermic patients, we demonstrated that spinal anesthesia does not improve convective tissue warming during isolated, heated limb perfusion. Mild systemic hyperthermia may promote greater vasodilation than sympathetic blockade.

Human eccrine sweat contains tissue kallikrein and kininase II

We attempted to determine the level of sweat kallikrein (kininogenase) and to purify and characterize it using sweat collected over a white petrolatum barrier. Thermally induced eccrine sweat obtained from 24 healthy subjects showed kallikrein activity of 24.4 ng kinins generated/1 mg of sweat protein when heated plasma was used as the substrate and 16.1 ng kinin when purified low molecular weight bovine kininogen was used as the substrate. Sweat was sequentially purified by Sephacryl S-200, diethyaminoethyl Sephacel, and fast flow liquid chromatography Mono Q chromatography. Sweat kallikrein had a M(r) of 40,000 and was inhibited by aprotinin but not by soybean trypsin inhibitor. The peptide generated by sweat kallikrein was identified as lys-bradykinin using reverse phase high-performance liquid chromatography and by its amino acid sequence. Anti-human urinary kallikrein immunoglobulin G neutralized the sweat kallikrein activity completely, indicating that the sweat kallikrein is the glandular type. Purified sweat and salivary kallikrein showed similar M(r) and responses to inhibitors and antibodies. Using immunohistochemistry, kallikrein activity was localized in luminal ductal cells and in the peripheral rim of secretory coil segments, presumably the outer membrane of the myoepithelium. We also observed kininase activity in sweat at M(r) 160,000, which was inhibited by ethylenediamine tetraacetic acid, captopril, and angiotensin converting enzyme inhibitor peptide, indicating that it is kininase II (or angiotensin converting enzyme). Sweat also contains abundant non-kallikrein hydrolases for S-2266 and S-2302. The demonstration of glandular kallikrein, its tissue localization, and the presence of kininase II in sweat provide the basis for future studies on the physiologic role of the kallikrein/kinin system in the eccrine sweat gland.

Tissue kallikrein and kininogen in human sweat glands and psoriatic skin

The cellular localization of immunoreactive tissue kallikrein and kininogen was studied in normal and psoriatic human skin. Immunoreactivity to both enzyme and substrate was observed in secretory granules of the dark cells in the secretory fundus (acinus) of the sweat glands. Double immunostaining revealed a segmental distribution of the two antigens. Each acinar section contained either tissue kallikrein or kininogen. However, there appeared to be a junctional zone in which both were present, but in separate dark cells. Immunoreactivity for both antigens was also observed in close apposition to the luminal microvilli of the duct cells. No specific immunostaining was seen in sebaceous glands, hair follicles, keratinocytes and other cells of the secretory unit such as myoepithelial or clear cells. In psoriatic skin there were in addition many neutrophils immunoreactive for tissue kallikrein in the epidermis and psoriatic scales. Mitogenic action of kinins may account to some extent for the characteristic accelerated turnover of epidermal cells in psoriasis and locally applied kinin antagonists may prove of value in the treatment of this disease.

Partial purification of plasma and tissue kallikreins in psoriatic epidermis

Human psoriatic scale extracts produced kinins from heated plasma (11.3 +/- 5.5 ng kinin/mg protein) and from purified low molecular weight (LMW) bovine kininogen (4.4 +/- 1.7 ng/mg). Sephacryl S-200 gel filtration of the extracts showed three peaks of kininogenase activity with Mr values of 90,000 (K-I), 65,000 (K-II), and 35,000 (K-III). Upon DEAE-Sepharose chromatography of the Sephacryl peaks, K-I activity was found in the nonadsorbed fraction and formed kinins only from heated plasma. Peak K-II activity was resolved into two peaks, K-IIa (in the nonadsorbed fraction), which formed kinins only from heated plasma, and K-IIb (in the adsorbed fraction), which formed kinins from both heated plasma and LMW bovine kininogen. K-III kininogenase activity appeared at the same position as K-IIb and also formed kinins from both substrates. Kininogenases K-I and K-IIa had the same Km value (0.3 mM) with Pro-Phe-Arg-p-nitroanilide(pNA), similar to that found with human plasma kallikrein. The Km value of K-IIb with Val-Leu-Arg-pNA (0.8 mM) was like that found for human salivary kallikrein, whereas K-III had a low affinity for this substrate. Like plasma kallikrein, K-I and K-IIa were inhibited by soybean trypsin inhibitor, but only weakly by aprotinin. In addition the kininogenase activity of both K-I and K-IIa was neutralized by adding antihuman prekallikrein immunoglobulin G (IgG). In contrast, K-IIb and K-III were strongly inhibited by aprotinin but not by soybean trypsin inhibitor, consistent with their being tissue kallikreins. It was confirmed that K-IIb and K-III shares antigenic determinant of urinary kallikrein.

Kinin-forming enzyme in human skin: the purification and characterization of a kinin-forming enzyme

A kinin-forming-enzyme in human skin extract was further purified by successive column chromatography on DEAE-cellulose, Hydroxylapatite-cellulose and Sepharose-4B. By these procedures, 2.7 mg of purified enzyme was obtained from 10 gm of original skin. The purified material was homogeneous as ascertained by cellulose acetate membrane electrophoresis, sodium dodecyl sulfate polyacrylamide gel disc electrophoresis and ultracentrifugation. It had an S20,w value of 4.3 and an apparent molecular weight of 104,000 as measured by gel filtration on Sephadex G-200. The purified enzyme was comparatively heat-stable, but was unstable below pH values of 5 and above pH 9. It possessed arginine or lysine esterolytic activity, but not tyrosine or tryptophane esterolytic activity and denatured proteolytic activity. This enzyme was not affected by metal ion, cystein, glutathion or rho-chloromercuribenzoate, but was strongly inhibited by alpha-N-rho-tosyl-L-lysine chloromethyl ketone or soybean-trypsin inhibitor. It was also inhibited by alpha 1-antitrypsin, but not by alpha 2-macroglobulin. This enzyme was confirmed to be immunologically distinct from human plasma, urinary or pancreas kallikrein.