Variations in endothelial function and arterial compliance during the menstrual cycle.

Female sex hormones have been implicated in the cardioprotection of premenopausal women. However, the cardiovascular actions of these hormones and the effects of their natural fluctuations during the menstrual cycle are not fully understood. We studied changes in vascular function during the menstrual cycle in 15 healthy premenopausal women. Four noninvasive procedures were performed during the early follicular (EF), late follicular (LF), early luteal (EL), and late luteal (LL) phases: flow-mediated dilatation (FMD) of the brachial artery during reactive hyperemia, laser Doppler velocimetry (LDV) with direct current iontophoresis of acetylcholine (ACh) and nitroprusside, whole body arterial compliance (WBAC), and pulse wave velocity. Hormone levels were consistent with predicted cycle phase and showed that all subjects ovulated during the cycle studied. FMD, LDV with ACh, and WBAC varied cyclically, with significant increases from the F to LF phase, sharp falls in the EL phase, and significant recoveries in the LL phase. These changes were most marked for FMD [EF, 8.8 +/- 0.6% (mean +/- SEM); LF, 10.0 +/- 0.7; EL, 4.2 +/- 0.6; LL, 8.6 +/- 0.9] and the LDV response to ACh (EF, 2.7 +/- 0.2 V/min; LF, 3.3 +/- 0.4; EL, 1.8 +/- 0.3; LL, 2.7 +/- 0.4). WBAC changed similarly (EF, 0.58 +/- 0.08 arbitrary units; LF, 0.84 +/- 0.06; EL, 0.65 +/- 0.05; LL, 0.68 +/- 0.06). Sodium nitroprusside-induced vasodilatation decreased significantly from EF to EL, with no other significant difference, and pulse wave velocity did not vary significantly over the four time points. Conductance and resistance artery endothelial reactivity and smooth muscle sensitivity to nitric oxide and arterial compliance are modulated significantly in response to the changing hormonal patterns of the menstrual cycle. These findings emphasize the importance of menstrual phase in the interpretation of data on endothelial function and may provide insights into the mechanisms underlying sex differences in cardiovascular risk and other disease processes in premenopausal women.

Rapid actions of insulin on sensory nerve function.

The acute action of insulin on neurogenic flare was investigated using iontophoresis. Twenty-five patients with insulin-dependent diabetes mellitus (IDDM) and 25 age- and gender-matched controls were studied. Axon reflex vasodilatation was evoked by transdermal iontophoresis of acetylcholine (ACh) before and after skin treatment by the iontophoresis of insulin and measured using laser Doppler velocimetry. Axon reflex responses were reduced in IDDM patients compared with controls (p< 0.001) but were restored after the iontophoresis of insulin. Insulin iontophoresis had no effect on the size of the axon reflex response in control subjects (p > 0.05). This study confirms the reduction of the ACh-induced flare in human patients with IDDM and has demonstrated relatively rapid effects of insulin on this cutaneous neurogenic response.

A novel, nongenomic action of estrogen on the cardiovascular system.

To examine the time course and mechanisms of action of single doses of estrogen on the skin microvasculature, two double-blind placebo-controlled cross-over studies were conducted in healthy young men using the noninvasive technique of laser Doppler velocimetry with iontophoretic application of vasodilator substances. Estradiol (2 mg sublingually) produced a significant increase in the response to the endothelial vasodilator acetylcholine (ACh) after 15 min, but not after 20 or 30 min. The mean plasma estradiol concentration increased from 89.4 +/- 9 pmol/L at baseline to 486.6 +/- 218 pmol/L at 15 min. An i.v. bolus of 25 mg conjugated equine estrogens produced significant increases in the responses to ACh at 15 and 20 min but not at 30 min. There was no change in responses to the nonendothelial vasodilators sodium nitroprusside or nicotine, and administration of placebo produced no change in ACh responses at any time point. These experiments show that, at plasma estradiol concentrations within the physiological range for premenopausal women, estrogens act directly on the cutaneous microvasculature through a rapid onset, rapid offset, nongenomic mechanism that is specific to the endothelium; in addition, it supports the view that estrogens can act on the male cardiovascular system in a manner that is potentially clinically beneficial.

Is leptin sensitivity the link between smoking cessation and weight gain?

The known association between smoking cessation and weight gain, and the suggested role of leptin in the control of body weight, led to the present study which examined the association between smoking and serum leptin concentrations. Mean serum leptin levels, independent of body mass index (BMI), were calculated in male smokers and non-smokers from Nauru, Western Samoa and Mauritius. Smokers were generally leaner than non-smokers, and of similar ages. Levels of physical activity and glucose tolerance status were similar for smokers and non-smokers in Nauru and Western Samoa, while in Mauritius smokers were more active and less likely to be diabetic. Leptin concentrations in smokers were significantly lower than in non-smokers, even after adjusting for BMI, waist/hip ratio (WHR) or waist girth (P < or = 0.04). This association was independent of diabetes status. Smoking, via nicotinic mechanisms, may modify the sensitivity of hypothalamic leptin receptors and consequently modulate leptin synthesis and reduce body weight.

Factors associated with impaired vibration perception in Mauritians with normal and abnormal glucose tolerance. Mauritius NCD Study Group.

Vibration perception threshold (VPT) was measured in 1185 Indian, Creole, and Chinese men and women in Mauritius, where the current prevalence of diabetes mellitus in adults aged 25-74 years is estimated to be 13%. Vibration perception threshold was measured using a biothesiometer, at seven sites in the hand, wrist, foot, and ankle, during a population survey in 76% of 574 known diabetic patients (KDM), 79% of 525 newly diagnosed diabetic patients (NDM), 18% of 1121 subjects with impaired glucose tolerance (IGT), and in 127 normal subjects. The association of VPT with glucose tolerance and other risk factors was assessed in order to identify individuals most at risk of foot ulceration and to determine whether risk factors and normal levels for VPT in these ethnic groups were consistent with those reported for Caucasians. After adjusting for age and height, geometric mean VPT at six of seven sites increased significantly with worsening glucose tolerance and increasing duration of diabetes in both men and women, VPT also increased significantly with level of fasting plasma glucose in men, but not women. Smoking and alcohol consumption had no effect on VPT, and body-mass index (BMI) was positively associated only at some sites. Chinese subjects had lower VPTs than Indians or Creoles. In multiple linear regression models, age, male gender, duration of diabetes, ethnic group, and height (lower extremity sites) were significantly associated with VPT among diabetic subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Nicotinic acetylcholine receptors on capsaicin-sensitive nerves.

To study the density of nicotinic acetylcholine receptors on primary afferents and central nociceptive pathways, [3H](-)-nicotine binding was conducted in the cerebral cortex and spinal cord including dorsal roots and ganglia (DRG), of control rats and rats desensitized by neonatal capsaicin treatment. [3H](-)-nicotine binding in capsaicin-treated rats was reduced in cerebral cortex by 35% and spinal cord+DRG by 46% (p < 0.05). Functionally, both iontophoretically applied acetylcholine- and capsaicin-evoked flares (measured by laser Doppler flowmetry) were reduced in capsaicin-treated animals (p < 0.05); similarly, electrical stimulation-evoked flares were significantly lower in the same group, compared with controls (p < 0.05). These data provide direct evidence that many neuronal nicotinic acetylcholine receptors are associated with capsaicin-sensitive peptidergic neurones, including primary afferents, DRG and central nociceptive pathways.

Insulin sensitivity and sensory nerve function in non-diabetic human subjects.

The direct effect of reduced insulin sensitivity (measured by insulin tolerance test and fasting plasma insulin) on sensory nerve function was examined in non-diabetic human subjects. Thermal sensation (measured by warm and cold perception thresholds) deteriorated with fasting hyperinsulinaemia in the presence of normoglycaemia and normal glucose tolerance. The results suggest a possible role for insulin in sensory nerve function, also that deficits in insulin action per se may adversely affect the function of small sensory nerves independent of glycaemic levels, and may thus be implicated in the aetiology of diabetic neuropathy.

Forehead and forearm skin blood flows in newborn infants measured by laser Doppler flowmetry: short-term variability and relationship to sleep states.

Laser doppler flowmeters were used to measure blood flow in the skin of the forehead and volar surface of the forearm of infants at 2-9 days of age, and at 8-12 weeks of age. At both ages mean skin blood flow was higher during active sleep compared to quiet sleep. In infants up to 9 days of age, mean skin blood flow was higher in forehead skin compared to forearm skin. Skin blood flow was highly variable at both recording sites, and was significantly higher and more variable during active compared to quiet sleep in the forehead, but not in the forearm. The results indicate that recordings of skin blood flow over at least two cycles of active and quiet sleep are needed to describe the normal variation with sleep state. The factors which regulate forehead and forearm skin blood flows may differ in importance between the two sites, perhaps reflecting the different thermoregulatory importance of cutaneous blood flow in the forehead and forearm.

Insulin sensitivity and sensory nerve function.

The central and peripheral nervous systems do not require insulin for glucose uptake. However, insulin receptors have been detected in these regions. The aim of this study was to examine peripheral sensory nerve function and its dependence on insulin using healthy non-diabetic control subjects, obese individuals, and diabetic (insulin dependent and non-insulin dependent diabetes mellitus) subjects. The results revealed that the warm and cold perception thresholds, reflecting the functional states of unmyelinated C-fibres and A-delta fibres respectively, increased with reduced insulin sensitivity and with increased fasting insulin concentrations. From such data in non-diabetic subjects with measured insulin sensitivity, it appeared that sensory nerve function was disturbed in normoglycemic but insulin resistant states, suggesting that insulin has an action on nervous tissue in addition to its effects on glucose metabolism. The mechanisms of this action remain to be elucidated.

Maternal nicotine exposure enhances cutaneous axon reflexes in the neonatal rat.

Chronic nicotine exposure enhances axon reflexes in adult rats. Since smoking mothers expose their infants to nicotine, this study investigated whether late gestational and or lactational maternal nicotine exposure affects neonatal axon reflexes. Osmotic pumps, implanted subcutaneously in adult female rats, delivered either nicotine (5 mg kg-1 day-1) or saline. Axon reflex responses of infant progeny, evoked by iontophoresis of 2 mC acetylcholine, were measured by laser Doppler flowmetry. Nicotine-exposed infants showed significantly enhanced axon reflexes during both gestational and lactational nicotine exposure, which recovered after exposure ceased. Controls did not exhibit these changes. Maternal nicotine exposure reversibly sensitized nicotinic cholinoceptors on infant cutaneous sensory nerves, but not muscarinic cholinoceptors on vascular endothelium. This may result from upregulation of cutaneous nicotinic cholinoceptors.

Denervation impairs cutaneous microvascular function and blister healing in the rat hindlimb.

Skin sensory nerve nocifensor functions were investigated non-invasively in rats by measuring neurogenic inflammation and blister healing-rate after unilateral hindlimb denervation. Axon reflexes were evoked by transdermal iontophoresis of acetylcholine (ACh) or noxious electrical stimulation (TNS). Sodium nitroprusside (SNP) evoked direct dilator responses. Resultant changes in skin microvascular blood flux were measured by laser Doppler flowmetry. Compared with their sham-operated control limbs, denervation reduced inflammatory responses (ACh or TNS) by more than 85% and SNP responses by 28% (p < 0.05). Healing of dry-ice blisters raised on the hindpaw 14d post-denervation was significantly slower to complete healing (42d) than controls (26d) and initial inflammation was attenuated, confirming that innervation is important for inflammation and blister-healing.

Evidence for skin microvascular compartmentalization by laser-Doppler and photoplethysmographic techniques.

Indices of perfusion were obtained using commercial laser-Doppler instruments with differing wavelengths on metatarsal skin of sheep (which is abundant with AVAs) and compared with quantitative measurements of AVA and capillary blood flow using microspheres; an infra-red photoplethysmograph was also compared. The data provide physiological evidence that laser-Doppler instruments of longer wavelength sense to a greater depth, and our photoplethysmograph behaves similarly to a "near-infra-red" laser. Thus, we suggest that near-infra-red light, either laser-Doppler or photoplethysmograph, should be used to measure a parameter most representative of total local blood flow, and light of a very much shorter wavelength, probably green light, would allow more confidence in estimates of true capillary perfusion. Because the commonly used visible red light can, but does not necessarily detect deep AVA perfusion, the influence depending upon the magnitude of the AVA perfusion, measurements by an instrument based on such red light is difficult to define.

The role of skin nociceptive afferent nerves in blister healing.

Because sensory neuropeptides improve survival of critical skin and muscle flaps in rats, skin nociceptive sensory nerve function in blister healing was examined. Sensory nerve ablation by unilateral hindlimb denervation or cutaneous axon reflex enhancement by 14 days systemic nicotine treatment (5 mg kg-1 day-1) decreased and increased, respectively, peripheral motor functions of nociceptive (peptidergic) skin nerves. Effects on nociception were measured by a radiant heat tail-flick test. Axon reflex flares were evoked by transdermal iontophoresis of acetylcholine or noxious electrical stimulation under pentobarbitone 40 mg kg-1 anaesthesia. Resultant changes in cutaneous microvascular blood flux were measured non-invasively by laser Doppler flowmetry. In nicotine-treated rats compared with placebo-treated controls, acetylcholine-evoked axon reflex flare was enhanced by 240% (p < 0.01) without enhancement of electrically evoked flare. Thus, nicotine-sensitized nociceptors show stimulus specificity in their enhancement of neurogenic flare responses. No significant changes were seen in other endothelial-dependent or smooth muscle-dependent microvascular dilator responses. Nicotine-treated rats had prolonged tail-flick withdrawal latencies to noxious radiant heat stimuli compared with placebo-treated controls (p < 0.05), suggesting an antinociceptive or analgesic effect of nicotine-treatment. Neurogenic effects on wound healing rate were assessed by measuring the dimensions of standardized blisters twice daily. The blisters were raised on hindpaw glabrous skin using a constant weight and diameter of compressed dry ice pellet applied for 30 secs at constant force. Dry-ice blisters raised on the hindpaw 14 days post-denervation were significantly slower to heal completely (42 days) than controls (30 days: P < 0.05) and the surrounding inflammation was reduced. By contrast, nicotine-treated rats showed more rapid blister healing (25 days) than controls (30 days), seen only in the later phase after day 15. Finally, resting substance P release from blisters, after direct cutaneous nerve stimulation, appears to be enhanced in nicotine-treated rats. Thus nociceptive innervation appears critical for inflammation and rapid healing of blisters in rat skin. The data signal a possible important role for neuropeptides in these processes and question the function of nicotinic receptors on sensory nerves.

Effects of capsaicin on cutaneous vasodilator responses in humans.

The neurovascular responses to noxious electrically evoked axon reflex (EAR) stimulation and iontophoretic application of endothelium-dependent [acetylcholine (ACh)] and independent [sodium nitrite (NaNO2)] vasodilator substances were examined in human forearm skin using laser Doppler flowmetry, before and after repeated topical applications of the neurotoxin capsaicin (chronic capsaicin pre-treatment). Following 3 or 4 days of capsaicin pre-treatment the normal vasodilator response to acute application of capsaicin was significantly reduced as was the EAR response. There were, however, no significant changes in the vasodilator responses to either ACh or NaNO2, suggesting that the neurogenic axon reflex is in series with the endothelial and microvascular smooth muscle mechanisms of vasodilatation. Recovery of normal EAR occurred within 2-4 weeks of cessation of capsaicin pre-treatment.

Confounding factors in non-invasive tests of neurovascular function in diabetes mellitus.

Disturbances of neurovascular function in the extremities may occur in patients with diabetes mellitus, exposure to toxic substances and chronic exposure to vibrating hand tools, as well as in Raynaud's phenomena. In these conditions symptoms of paraesthesia, finger numbness and blanching occur, so nerve conduction studies, vibration and temperature threshold measurements and neurovascular function tests are used for objective assessment of neurological dysfunction. The aim of the present study was to examine some factors which may confound quantitative neuro-vascular function measurements if used to assess neuropathy in diabetics. All subjects were consenting volunteers without exposure to known neurotoxic chemicals. The 5 groups were (a) healthy non-diabetic subjects not exposed to vibration (n = 10, mean age 52.3 yrs) (b) 2 insulin dependent and 8 non-insulin dependent diabetic subjects with a mean of 6 years treatment (n = 10, mean age 55.7 yrs) (c) maintenance employees exposed to high frequency pneumatic hand tools (n = 10, mean age 52.2 yrs) (d) subjects who were not diabetic or exposed to vibrating tools, but were being treated with the ACE-inhibitor enalapril 20 mg daily for hypertension (n = 5, mean age 54 yrs) (e) subjects who had smoked more than 10 cigarettes daily for at least 15 yrs (n = 10, mean age 51 yrs). Neurovascular tests included axon reflex responses measured by laser Doppler velocimeter evoked on the dorsum of the finger by iontophoresis of acetylcholine 16 mC in a circumferential chamber: cutaneous microvascular dilator responses to endothelial stimulation by iontophoretic application of the muscarinic agonist pilocarpine 16 mC and to direct nitrodilator sodium nitroprusside 16 mC. The skin temperature of the digits was held between 33 degrees and 34 degrees C during testing and dilator responses were measured as flux change by on-line computer analysis using 'Perisoft'. There was a significant reduction (P < 0.05) in the neurovascular responses of both diabetics and vibration--exposed subjects to acetylcholine and, in the case of vibration-exposed subjects, to pilocarpine, but nitroprusside responses were not significantly different. Our findings of reductions in neurovascular responses in diabetics and in subjects exposed to higher frequency vibration is consistent with recent epidemiological findings. Furthermore, subjects treated with an ACE-inhibitor (enalapril) showed significant reduction in acetylcholine-evoked axon reflex responses, while the test group of smokers showed a significant reduction in their dilator response to pilocarpine.(ABSTRACT TRUNCATED AT 400 WORDS)

Hereditary sensory radicular neuropathy: defective neurogenic inflammation.

Hereditary sensory radicular neuropathy exhibits autosomal dominant inheritance with complete penetrance in males and incomplete penetrance in females. Newer tests of small sensory nerve function were used in screening 8 family members aged between 14 and 66 years. All exhibited some frequent features of the disorder with an onset in the 2nd or 3rd decade, foot ulceration, foot callus, loss of pin prick, thermal and light touch sensation, and some reduction in vibration acuity and proprioception in the lower limbs. The hands were involved in 3 of 8, muscle involvement was present in 5 of 8, but deafness was not detected by audiometry. Nerve conduction velocity, sensory action potentials, latency and amplitude, thermal acuity, vibration acuity and axon reflex flares were measured in all patients. One sural nerve biopsy confirmed the presence of peripheral fibre loss in this predominantly sensory neuropathy. Chemically evoked axon reflex tests were used to evaluate the extent of primary sensory nerve fibre involvement. All patients were tested using a Moor MBF 3-D dual channel laser Doppler velocimeter. Acetylcholine or phenylephrine iontophoretically applied as 16 mC doses evoked absent or tiny axon reflexes in areas of impaired pin prick sensation. By contrast, direct microvascular dilator responses to nitroprusside (smooth muscle dependent) and acetylcholine (endothelium-dependent) were present but somewhat reduced in areas with defective neurogenic inflammation. These results differ significantly from the responses obtained in age-matched healthy controls (P < 0.05). Foot pressure analysis was performed for orthoses in 2 affected members with foot ulceration using the Musgrave Footprint system.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic nicotine exposure enhances cutaneous axon reflexes in the rat.

The effect of chronic nicotine exposure on the cutaneous neurogenic flare response was investigated non-invasively in rats. Axon reflexes were evoked by transdermal iontophoresis of acetylcholine, and resultant changes in skin microvascular blood flux were measured by laser Doppler flowmetry. Rats given five injections of nicotinesulphate (1 mg kg-1 i.p.) daily for 14 days were compared to saline-injected littermates. Axon reflexes were enhanced by 143% after 7 days exposure to nicotine, and by 336% after 14 days exposure. Controls did not display these increases. Axon reflexes measured 7 days after nicotine cessation were similar to pre-nicotine levels. These results may suggest that nicotinic cholinoceptors on skin nociceptors and primary afferents upregulate in response to chronic nicotine exposure, and return to normal following nicotine cessation.

Palmar cold threshold test and median nerve electrophysiology in carpal tunnel compression neuropathy.

The diagnosis of median nerve compression neuropathy at the carpal tunnel is usually confirmed by clinical electrophysiology. The classical findings of a significantly slowed median nerve conduction velocity for both sensory and motor fibres, with a prolonged distal motor latency and a reduced amplitude compared to age-related norms are unambiguous, but these criteria are often present only in part. In such cases another quantitative indicator of compression neuropathy would be extremely helpful. The present study aimed to test whether measurement of warm and cold sensory acuity in cases of putative median nerve carpal tunnel compression would aid diagnostic certainty. Warm sensation is mediated by unmyelinated C-afferents, while cold sensation is conveyed by thinly myelinated A delta afferents. Because compression usually blocks larger diameter fibres first, cold perception on the skin of the palm distal to the compression should be more impaired than is warm perception. Standard electrophysiological measurements (median and ulnar motor and sensory nerve conduction velocities) were made, then perceptual thresholds for both warm and cold stimuli were measured on the skin of the wrist above the carpal tunnel and on the palm of the affected hand in 59 subjects. There was a significantly reduced median motor nerve conduction velocity and prolonged distal motor latency compared to normals. Further, although both thermal thresholds at the wrist were normal, those on the palm were elevated, cold being significantly raised (P less than 0.02) compared both to warm and to age-matched controls. Correlation of the nerve conduction velocity findings and thermal sensory acuity did not yield significant covariance of the positive and negative findings. Overall the results suggest that detection of preferentially elevated cold perceptual threshold (ie reduced cold sensory acuity) on the skin of the palm may aid in the diagnosis of putative carpal tunnel compression in patients with minimal or ambiguous electrophysiological data and provide a functional index of recovery after decompression.

Noxious heat hyperalgesia test instrument.

A simple feedback thermode has been developed to quantify cutaneous hyperalgesia to noxious heat. A noxious temperature set between 42 degrees C and 60 degrees C is applied to a test site by the subject. A resettable impedance timing circuit measures the contact duration to +/- 0.01s. Despite site-to-site, inter- and intra-subject variability, the test sensitivity is enhanced by comparing affected and corresponding normal skin in the same subject. This test strategy was used in 55 subjects in whom topical 0.025 to 0.05% capsaicin application provoked hyperalgesia on the forearm and foot. Capsaicin-treated sites showed a significant reduction of 52 degrees C withdrawal latency (0.51-0.77 x normal mean; P less than 0.05). The device has been tested clinically in patients with diabetic neuropathy who had hypersensitivity to pinprick on one foot. A significant 42% difference was found between corresponding contralateral sites (P less than 0.05). These data suggest that even mild hyperalgesia is detectable using this instrument. It provides an objective measure of hyperalgesia which can be used to assess changes in nociceptive acuity.