Exogenous zinc improves blood fluidity but has no effect on the mechanisms of vascular response to acetylcholine iontophoresis in humans

Recent findings in cellular signaling function of zinc through the mobilization intracellular calcium or by inducing ATP release suggest that extracellular zinc plays an important role in many physiological functions. However, such an extracellular signaling action of zinc for most cells is not known. Therefore, we investigated whether zinc plays any role in endothe-lium-dependent acetylcholine (ACh)-induced vasodilatation in microvascular beds. Transdermal iontophoresis was used to transport ACh through the forearm skin and cutaneous perfusion was measured using a laser Doppler flowmeter (LDF). Experiments were repeated using (1) zinc instead of ACh to test the effect of zinc ions alone and (2) concomitant iontophoresis of ACh and zinc to explore the effect of zinc on ACh-induced vasodilatation. Although zinc augments blood flow, curve-fitting to LDF signals indicate that zinc has no effect on the neural and endothelial component of ACh-induced vasodilatation. Additionally, no effect of Zn²⁺ on blood flow was found during its iontophoresis alone. Therefore, it is suggested from the Fourier analysis of LDF signals that the Zn⁺ might influence blood fluidity by its action on red blood cells deformability/aggregability during a high-blood-flow condition, which might, in turn, decrease blood viscosity and improve blood flow in vivo.     

Iontophoresis of endothelin receptor antagonists in rats and men

Introduction

The treatment of scleroderma-related digital ulcers is challenging. The oral endothelin receptor antagonist (ERA) bosentan has been approved but it may induce liver toxicity. The objective of this study was to test whether ERAs bosentan and sitaxentan could be locally delivered using iontophoresis.

Methods

Cathodal and anodal iontophoresis of bosentan and sitaxentan were performed on anaesthetized rat hindquarters without and during endothelin-1 infusion. Skin blood flow was quantified using laser-Doppler imaging and cutaneous tolerability was assessed. Iontophoresis of sitaxentan (20 min, 20 or 100 µA) was subsequently performed on the forearm skin of healthy men (n = 5).

Results

In rats neither bosentan nor sitaxentan increased skin blood flux compared to NaCl. When simultaneously infusing endothelin-1, cathodal iontophoresis of sitaxentan increased skin blood flux compared to NaCl (AUC_0–20 were 44032.2±12277 and 14957.5±23818.8 %BL.s, respectively; P = 0.01). In humans, sitaxentan did not significantly increase skin blood flux as compared to NaCl. Iontophoresis of ERAs was well tolerated both in animals and humans.

Conclusions

This study shows that cathodal iontophoresis of sitaxentan but not bosentan partially reverses endothelin-induced skin vasoconstriction in rats, suggesting that sitaxentan diffuses into the dermis. However, sitaxentan does not influence basal skin microvascular tone in rats or in humans.     

Impaired microvascular perfusion: a consequence of vascular dysfunction and a potential cause of insulin resistance in muscle

Insulin has an exercise-like action to increase microvascular perfusion of skeletal muscle and thereby enhance delivery of hormone and nutrient to the myocytes. With insulin resistance, insulin's action to increase microvascular perfusion is markedly impaired. This review examines the present status of these observations and techniques available to measure such changes as well as the possible underpinning mechanisms. Low physiological doses of insulin and light exercise have been shown to increase microvascular perfusion without increasing bulk blood flow. In these circumstances, blood flow is proposed to be redirected from the nonnutritive route to the nutritive route with flow becoming dominant in the nonnutritive route when insulin resistance has developed. Increased vasomotion controlled by vascular smooth muscle may be part of the explanation by which insulin mediates an increase in microvascular perfusion, as seen from the effects of insulin on both muscle and skin microvascular blood flow. In addition, vascular dysfunction appears to be an early development in the onset of insulin resistance, with the consequence that impaired glucose delivery, more so than insulin delivery, accounts for the diminished glucose uptake by insulin-resistant muscle. Regular exercise may prevent and ameliorate insulin resistance by increasing "vascular fitness" and thereby recovering insulin-mediated capillary recruitment.     

The effects of diabetes and aminoguanidine treatment on endothelial function in a primate model of type 1 diabetes

Abnormalities of endothelial function have been demonstrated in diabetes and are thought to play a role in the pathogenesis of diabetic complications. The aims of this study were to determine whether aminoguanidine, an inhibitor of glycation, can prevent endothelial and microcirculation abnormalities in a primate model of type 1 diabetes. Male baboons (Papio hamadryas) were assigned to one of the four groups: control, diabetes, control treated with aminoguanidine or diabetes treated with aminoguanidine. Diabetes was induced by streptozocin (60 mg/kg) and treated with once daily injection of insulin. Aminoguanidine was given subcutaneously (10 mg/kg), once a day. Diabetic animals had a mean duration of diabetes of 8.9 +/- 3.4 years and HbA1c of 8.9 +/- 1.1%. Microvascular function was measured by laser Doppler velocimetry, with examination of endothelium-dependent increase in skin blood flow (SkBF) following iontophoresis of acetylcholine (ACh) and endothelium-independent increase in SkBF in response to the nitric oxide (NO) donor sodium nitroprusside (SNP). Multiple regression analysis identified diabetes (P = 0.049) and aminioguanidine treatment (P = 0.026) as significant determinants of ACh response. The diabetic baboons treated with aminoguanidine had less Ach-mediated SkBF response compared with controls (1.39 +/- 0.32 vs. 2.26 +/- 0.61, F = 3.3, P = 0.04), but there was no difference between groups in SkBF response to SNP. We conclude that endothelial dysfunction can be demonstrated in this primate model of type 1 diabetes at a stage when overt diabetic complications are not present. This occurred in the absence of insulin resistance or significant hypercholesterolemia. Administration of aminoguanidine from the onset of diabetes was not able to prevent this abnormality and in fact aggravated the endothelial response. Effects of aminoguanidine on NO synthase may contribute to this phenomenon.     

利用微血管环技术检测肠系膜动脉三级分支张力的方法

目的：以肠系膜动脉三级分支为样本,观察利用微血管技术检测血管张力功能的整个过程,以便研究各种微血管相关疾病中的微血管功能状态。方法：利用DMT张力测定仪和PowerLab数据采集系统检测微血管收缩、舒张功能,将肠系膜三级动脉血管游离,固定,标准化和激活后,通过加入血管收缩药物及舒张药物,完成对微血管张力功能的检测。结果：本文制备的肠系膜动脉三级分支血管环对血管活性药物出现良好的收缩、舒张反应,加入10^-5mol／L的去甲肾上腺素（NE）后收缩张力达19mN,之后依次加入10^-9～10^-5mol／L的乙酰胆碱（ACh）或硝普钠（SNP）,血管张力呈梯度降低,ACh和SNP引起的最大舒张率分别为80％和95％。结论：利用该微血管环技术成功检测出肠系膜动脉三级分支的收缩舒张功能。     

Skin blood flowmotion and microvascular reactivity investigation in hypercholesterolemic patients without clinically manifest arterial diseases

Fourier spectral analysis of forearm skin laser Doppler flowmetry (LDF) signal was performed in fifteen hypercholesterolemic patients (HP), without clinically manifest arterial diseases, and in fifteen age-matched healthy control subjects (CS), in order to investigate skin blood flowmotion (SBF). The LDF frequency intervals studied were: 0.01-1.6 Hz total spectrum, as well as 0.01-0.02 Hz (endothelial), 0.02-0.06 Hz (sympathetic), 0.06-0.2 Hz (myogenic), 0.2-0.6 Hz (respiratory) and 0.6-1.6 Hz (cardiac). Skin microvascular reactivity (MVR) to acetylcholine (ACh) and to sodium nitroprusside (SNP) iontophoresis was also investigated. HP showed a lower post-ACh increase in power spectral density (PSD) of the 0.01-0.02 Hz SBF subinterval compared to CS (1.80+/-1.73 PU(2)/Hz vs 3.59+/-1.78 PU(2)/Hz, respectively; p<0.005), while they did not differ in MVR from CS. In eleven HP the 0.01-0.02 Hz SBF subinterval showed a higher post-ACh PSD increase near to the statistical significance after 10 weeks of rosuvastatin therapy (10 mg/day) compared to pretreatment test (3.04+/-2.95 PU(2)/Hz vs 1.91+/-1.94 PU(2)/Hz; p=0.07). The blunted post-ACh increase in PSD of the 0.01-0.02 Hz SBF subinterval in HP suggests a skin endothelial dysfunction in these patients. This SBF abnormality showed a tendency to improve after rosuvastatin therapy in eleven treated patients.     

Numerical simulation of iontophoresis in the drug delivery system

The architecture and composition of stratum corneum act as barriers and limit the diffusion of most drug molecules and ions. Much effort has been made to overcome this barrier and it can be seen that iontophoresis has shown a good effect. Iontophoresis represents the application of low electrical potential to increase the transport of drugs into and across the skin or tissue. Iontophoresis is a noninvasive drug delivery system, and therefore, it is a useful alternative to drug transportation by injection. In this study, we present a numerical model and effects of electrical potential on the drug diffusion in the buccal tissue and the stratum corneum. The initial numerical results are in good comparison with experimental observation. We demonstrate that the application of an applied voltage can greatly improve the efficacy of localized drug delivery as compared to diffusion alone.     

Cellular mechanisms underlying cutaneous pressure-induced vasodilation: in vivo involvement of potassium channels

In the skin of humans and rodents, local pressure induces localized cutaneous vasodilation, which may be protective against pressure-induced microvascular dysfunction and lesion formation. Once activated by the local pressure application, capsaicin-sensitive nerve fibers release neuropeptides that act on the endothelium to synthesize and release nitric oxide (NO) and prostaglandins, leading to the development of the cutaneous pressure-induced vasodilation (PIV). The present study was undertaken to test in vivo the hypothesis that PIV is mediated or modulated by differential activation of K+ channels in anesthetized rats using pharmacological methods. Local pressure was applied at 11.1 Pa/s. Endothelium-independent and -dependent vasodilation were tested using iontophoretic delivery of sodium nitroprusside (SNP) and acetylcholine (ACh), respectively, and was correlated with PIV response. PIV was reduced after systemic administration of tetraethylammonium (a nonspecific K+ channel blocker), iberiotoxin [a specific large-conductance Ca2+-activated K+ (BKCa) channel blocker], and glibenclamide [a specific ATP-sensitive K+ (KATP) channel blocker], whereas PIV was unchanged by apamin (a specific small-conductance Ca2+-activated K+ channel blocker) and 4-aminopyridine (a specific voltage-sensitive K+ channel blocker). The responses to SNP and ACh were reduced by iberiotoxin but were unchanged by glibenclamide. We conclude that the cellular mechanism of PIV in skin involves BKCa and KATP channels. We suggest that the opening of BKCa and KATP channels contributes to the hyperpolarization of vascular smooth muscle cells to produce PIV development mainly via the NO and prostaglandin pathways, respectively.     

Acetylcholine-induced vasodilation is mediated by nitric oxide and prostaglandins in human skin.

Acetylcholine (ACh) can effect vasodilation by several mechanisms, including activation of endothelial nitric oxide (NO) synthase and prostaglandin (PG) production. In human skin, exogenous ACh increases both skin blood flow (SkBF) and bioavailable NO levels, but the relative increase is much greater in SkBF than NO. This led us to speculate ACh may dilate cutaneous blood vessels through PGs, as well as NO. To test this hypothesis, we performed a study in 11 healthy people. We measured SkBF by laser-Doppler flowmetry (LDF) at four skin sites instrumented for intradermal microdialysis. One site was treated with ketorolac (Keto), a nonselective cyclooxygenase antagonist. A second site was treated with NG-nitro-L-arginine methyl ester (L-NAME) to inhibit NO synthase. A third site was treated with a combination of Keto and L-NAME. The fourth site was an untreated control site. After the three treated sites received the different inhibiting agents, ACh was administered to all four sites by intradermal microdialysis. Finally, sodium nitroprusside (SNP) was administered to all four sites. Mean arterial pressure (MAP) was monitored by Finapres, and cutaneous vascular conductance (CVC) was calculated (CVC = LDF/MAP). For data analysis, CVC values for each site were normalized to their respective maxima as effected by SNP. The results showed that both Keto and L-NAME each attenuated the vasodilation induced by exogenous ACh (ACh control = 79 +/- 4% maximal CVC, Keto = 55 +/- 7% maximal CVC, L-NAME = 46 +/- 6% maximal CVC; P < 0.05, ACh vs. Keto or L-NAME). The combination of the two agents produced an even greater attenuation of ACh-induced vasodilation (31 +/- 5% maximal CVC; P < 0.05 vs. all other sites). We conclude that a portion of the vasodilation effected by exogenous ACh in skin is due to NO; however, a significant portion is also mediated by PGs.     

No alpha-adrenoreceptor-induced C-fiber activation in healthy human skin.

In healthy volunteers, flare responses induced by norepinephrine (NE) iontophoresis have been observed. However, as NE iontophoresis is a combined electrical and chemical stimulus axon, reflexes cannot be directly linked to pharmocological activity of NE. Different concentrations of NE, clonidine (CL), and phenylephrine (PE) (NE: 10(-10)-10(-3) M; CL and PE: 10(-8)-10(-3) M) were applied via intradermal microdialysis fibers into the skin of healthy volunteers. Simultaneously, skin blood flow was visualized by laser-Doppler imaging scans and quantified in a vasoconstriction skin area directly above the membranes to control drug effects and in expected axon reflex vasodilation areas that were 0.75 cm apart. NE, PE, and CL caused dose-dependent vasoconstriction. However, neither in the presumed axon reflex areas (quantitative analysis) nor on laser-Doppler imaging pictures (qualitative analysis) were any vasodilation observed. Even at concentrations causing maximum vasoconstriction (10(-3) M for any drug), no vasodilation was induced. Our results indicate that, in healthy human skin, exogenously supplied alpha-adrenoreceptor agonists alone do not activate nociceptors sufficiently to induce axon reflex flare.     

Reactivity of the aorta and mesenteric resistance arteries from the obese spontaneously hypertensive rat: effects of glitazones

The obese spontaneously hypertensive rat (SHROB) is a model of metabolic syndrome in which, to our knowledge, vascular function has never been studied. The actions of insulin sensitizers (glitazones) on vascular function have not been analyzed either. Our purpose was to characterize microvascular and macrovascular responses of the SHROB and to study the effects of glitazones on these responses. The reactivity of mesenteric resistance arteries (MRAs) and the aorta from SHROBs and control rats to cumulative concentrations of phenylephrine, ACh, and sodium nitroprusside (SNP) was myographically analyzed. Some animals were orally treated with rosiglitazone (3 mg·kg(-1)·day(-1), 3 wk), and myography was performed. Phenylephrine, ACh, and SNP dose-response curves were impaired to different extents in arteries of SHROBs. Incubation with N-nitro-L-arginine methyl ester caused little effects on phenylephrine and ACh curves in MRAs but enhanced phenylephrine contractions and abolished ACh-induced relaxations of aortae. Incubation with indomethacin reduced phenylephrine reactivity and improved ACh-induced relaxations of all vessels studied. NS-398 and tempol increased relaxations to ACh of MRAs. Incubation with pioglitazone or rosiglitazone (both 10(-5) M) or oral treatment with rosiglitazone improved, to different extents, ACh and SNP curves in all vessels. Glitazone incubation diminished aortic ACh sensitivity. The release of thromboxane A(2) and PGI(2) metabolites (thromboxane B(2) and 6-keto-PGF(1α)) was analyzed. ACh increased the MRA release of thromboxane B(2) from SHROBs but not control rats, and the former was prevented by rosiglitazone coincubation. In contrast, in aortae, ACh failed to alter the release of metabolites, and rosiglitazone treatment increased that of 6-keto-PGF(1α). Thus, SHROBs displayed microvascular and macrovascular dysfunction. MRAs, but not aortae, of SHROBs revealed an impaired endothelial nitric oxide pathway, whereas both, but especially MRAs, displayed an impaired cyclooxygenase pathway. Glitazones elicited beneficial effects on macrovascular and, especially, microvascular function of SHROBs.     

Correlated effects of acetylcholine and cyclic guanosine monophosphate on membrane properties of mammalian neocortical neurons

The effects of successive extracellular iontophoresis of acetylcholine (ACh) and atropine, and intracellular hyperpolarizing iontophoresis of cyclic GMP (cGMP) were studied in single neurons of the coronal-pericruciate cortex of awake cats. (a) Fifty-seven percent of the neurons that were tested responded to ACh with an increase in neuronal input resistance (Rm) and 50% responded to ACh with an increase in firing rate; 65% responded to cGMP with an increase in Rm and 60% responded to cGMP with an increase in firing rate. (b) After application of atropine, increases in Rm and firing rate associated with iontophoresis of ACh failed to recur. (c) Persistent increases in Rm following application of ACh accompanied by current-induced neuronal discharge were not diminished by subsequent application of atropine. (d) Atropine did not prevent increases in Rm and firing rate associated with intracellular iontophoresis of cGMP. (e) All cells tested with both ACh and cGMP that were shown initially to respond to extracellular ACh with increases in Rm were later shown to have comparable responses to cGMP.     

Modulation of microvascular function following low-dose exposure to the organophosphorous compound malathion in human skin in vivo.

This study investigates whether malathion, a widely used organophosphate insecticide, has its effects on cutaneous vasculature in healthy human volunteers through its anticholinergic activity or through the modulation of other, noncholinergic pathways. Acute, low-dose exposure to malathion (10 mg/ml for 5 h under occlusive dressing) caused a significant increase in cutaneous blood flux, monitored by using laser-Doppler flowmetry and imaging. It had little effect on tissue levels of ACh, nitric oxide, and histamine assayed in dermal dialysate collected from malathion-exposed and control-treated skin. The duration of the cutaneous vascular response to exogenous ACh (2%) delivered by iontophoresis was significantly enhanced by preexposure to malathion, both <1 h after its removal and 24 h later (P < 0.001). At <1 h, the time to 50% decay of the response was 24 +/- 4 and 50 +/- 8 min in control and malathion-treated skin, respectively. Malathion also enhanced the size and duration of the axon reflex-mediated vasoresponse to ACh. The increase in blood flux to malathion and the endothelium-mediated response to exogenous ACh, both in the presence and absence of malathion, were attenuated by pretreatment of the skin with atropine and local anesthesia (P < 0.01). We conclude that short-term exposure to a single low dose of malathion causes prolonged modulation of the physiological function of the cutaneous vasculature and that this is, in part, through its action on acetylcholinesterase at both neuronal and nonneuronal sites.     

Enhanced endothelium-dependent vasodilatation in human skin vasculature induced by physical conditioning

Functional alterations to the endothelial cells of the vascular system may contribute to the improved circulatory performance induced by physical conditioning. We evaluated microvascular reactivity to iontophoretic application of acetylcholine (ACh) and sodium nitroprusside (SNP) through the skin and blood perfusion measurements in the same area using laser Doppler flowmetry. Whereas ACh acts on smooth muscle cells of the vascular system via the production of vasodilator substances from the endothelium, SNP is an endothelium-independent vasodilator acting on vascular smooth muscle cells directly. The study was performed using two groups of subjects with different levels of aerobic endurance, long distance runners competing at national level (n = 9) and controls (n = 9). The subjects were tested for 40 min on a treadmill before and after an exercise test at 80% of their maximal oxygen uptake. During stimulation by ACh cutaneous perfusion increased to a higher level in the athletes than in the controls (overall P<0.05), whereas an acute period of exercise abolished this difference (overall P>0.6). There was no significant difference between the athletes and the controls with respect to the SNP-induced increase in cutaneous perfusion either before (P>0.9) or after (P>0.9) exercise. The higher cutaneous perfusion responses to stimulation with ACh in the athletes than in the controls may support the hypothesis that regular exercise modifies the responsiveness of the cutaneous endothelium. The difference in ACh-induced perfusion and in unstimulated forearm perfusion between the two groups was present only at rest. This finding indicated that mechanisms were introduced during exercise, which compensated for the lower endothelial sensitivity to stimulation in the controls at rest.     

Delivery of antisense oligonucleotide to the cornea by iontophoresis

We wished to evaluate the potential of iontophoresis to promote the delivery of antisense oligonucleotides (ODN) directed at the vascular endothelial growth factor (VEGF)-R2 receptor (KDR/Flk) to the cornea of the rat eye. Fluorescence (CY5)-labeled ODNs in phosphate-buffered saline (PBS) (20 microM) were locally administered to rat eyes, and their fate within the anterior segment was studied. Thirty-four male, 5-week-old Wistar rats were used for all experiments. The rats were divided in four groups. In group I (12 rats, 12 eyes), the ODNs (20 microM) were delivered by iontophoresis (300 microA for 5 minutes) using a specially designed corneal applicator. In group II (12 rats, 12 eyes), the ODNs (20 microM) were delivered using the same applicator, but no electrical current was applied. In group III (6 rats, 6 eyes), a corneal neovascular reaction was induced prior to the application of ODNs (20 microM), and iontophoresis electrical current was delivered as for group I rats. Group IV (4 rats, 4 eyes) received ODN (60 microM) iontophoresis application (300 microA for 5 minutes) and were used for ODN integrity studies. The animals were killed 5 minutes, 90 minutes, and 24 hours after a single ODN application and studied. Topically applied ODNs using the same iontophoresis applicator but without current do not penetrate the cornea and remain confined to the superficial epithelial layer. ODNs delivered with transcorneoscleral iontophoresis penetrate into all corneal layers and are also detected in the iris. In corneas with neovascularization, ODNs were particularly localized within the vascular endothelial cells of the stroma. ODNs extracted from eye tissues 24 hours after iontophoresis remained unaltered. The iontophoresis current did not cause any detectable ocular damage under these conditions. Iontophoresis promotes the delivery of ODNs to the anterior segment of the eye, including all corneal layers. Iontophoresis of ODNs directed at VEGF-R2 may be used for the design of specific antiangiogenic strategy in diseases of the cornea.     

Transcardiac adiponectin gradient is independently related to endothelial vasomotor function in large and resistance coronary arteries in humans

Adiponectin, an adipocyte-derived protein, has been shown to have vasculoprotective effects. This study examined the possible relationship between coronary vasomotor function and the transcardiac gradient of adiponectin, reflecting adiponectin utilization and/or accumulation in the coronary vascular bed. The epicardial diameter and blood flow response of the left anterior descending coronary artery to intracoronary infusions of ACh was analyzed in 108 consecutive subjects who had a normal coronary angiogram and left ventriculogram. Adiponectin levels were measured by ELISA in plasma obtained from the aortic root (Ao) and the anterior interventricular vein (AIV). Adiponectin levels in the AIV were lower than levels in the Ao. In multivariate linear regression analysis, the transcardiac gradient of adiponectin (Ao - AIV levels) showed a positive correlation with increases in epicardial coronary diameter and coronary blood flow in response to ACh that was independent of traditional coronary risk factors. The transcardiac gradient of adiponectin was not significantly associated with the coronary dilator response to isosorbide dinitrate and the coronary flow response to sodium nitroprusside. In other groups of patients with coronary spastic angina (n = 41) or microvascular angina (n = 32) who had impaired coronary vasomotor responses, there was no significant gradient of adiponectin between the Ao and AIV. The transcardiac gradient of adiponectin may modulate endothelial vasomotor function in large and resistance coronary arteries and may play a role in the pathogenesis of diseases presenting with coronary vasomotor dysfunction.     

Correlated effects of acetylcholine and cyclic guanosine monophosphate on membrane properties of mammalian neocortical neurons.

The effects of successive extracellular iontophoresis of acetylcholine (ACh) and atropine, and intracellular hyperpolarizing iontophoresis of cyclic GMP (cGMP) were studied in single neurons of the coronal-pericruciate cortex of awake cats. (a) Fifty-seven percent of the neurons that were tested responded to ACh with an increase in neuronal input resistance (Rm) and 50% responded to ACh with an increase in firing rate; 65% responded to cGMP with an increase in Rm and 60% responded to cGMP with an increase in firing rate. (b) After application of atropine, increases in Rm and firing rate associated with iontophoresis of ACh failed to recur. (c) Persistent increases in Rm following application of ACh accompanied by current-induced neuronal discharge were not diminished by subsequent application of atropine. (d) Atropine did not prevent increases in Rm and firing rate associated with intracellular iontophoresis of cGMP. (e) All cells tested with both ACh and cGMP that were shown initially to respond to extracellular ACh with increases in Rm were later shown to have comparable responses to cGMP.     

Immersion in CO<Subscript>2</Subscript>-rich water containing NaCl diminishes blood pressure fluctuation in anesthetized rats

Remarkably, bathing in hot springs containing high concentrations of carbon dioxide (CO₂) influences cardiovascular function more than bathing in fresh water. The CO₂-enriched water in hot springs generally contains many salts, whose interactions remain unknown. We separately evaluated the actions of individual factors in CO₂-enriched water and confirmed that CO₂ and NaCl have combined effects on blood pressure fluctuations in anesthetized rats. Animals equipped with sensor probes to monitor body temperature, skin blood flow and arterial blood pressure were immersed in bathwater (35°C) containing CO₂ with NaCl, KCl or sucrose. The effects of these factors on cardiovascular function were evaluated using power-spectral analysis of fluctuations in blood pressure and heart rate. Compared with immersion in tap water, heart rate and skin vascular resistance were reduced during immersion in CO₂-enriched water irrespective of the presence of other components. In terms of the very low frequency range (0.02–0.195 Hz), the power of blood pressure fluctuation during immersion was significantly reduced when the CO₂-enriched water contained more than 1.5% NaCl but was not influenced by other components of similar osmotic pressure and the same specific gravity. The results indicated that the coexistence of CO₂ and sodium ions in bathwater reduce blood pressure fluctuations, and suggested that this combination effect of CO₂ and salt contributes to the sedative effect on human cardiovascular functions while bathing in CO₂-hot springs.     

Enhancement of iontophoretic transport of diphenhydramine hydrochloride thermosensitive gel by optimization of pH, polymer concentration, electrode design, and pulse rate

The purpose of the present study was to explore the passive and electrically assisted transdermal transport of diphenhydramine hydrochloride (DPH) by iontophoresis. For better bioavailability, better patient compliance, and enhanced delivery of DPH, an iontophoretic drug delivery system of a thermosensitive DPH gel was formulated using Lutrol F-127. The study was conducted using silver-silver chloride electrodes across hairless pig skin. The effects of pH, polymer concentration, electrode design, and pulse rate on the DPH permeation were investigated. The relationship between temperature, viscosity, and conductance of DPH was correlated using conductometry. Iontophoretic transport of DPH was found to increase with a decrease in the pH of the medium and an increase in the surface area of the electrode. Viscosity measurements and flux calculations indicated the suitability of the Lutrol gel for transdermal iontophoretic delivery of DPH. Anodal pulsed iontophoresis with disc electrode significantly increased the DPH skin permeation as compared with the passive controls.     

Regulation of ion and water transport across the eel intestine: effects of acetylcholine and serotonin

Summary Both acetylcholine (ACh) and serotonin (5-HT) lowered the serosa-negative transepithelial potential difference (PD) and the short-circuit current (I_sc), accompanied by a decrease in NaCl and water absorption across the eel intestine. These inhibitory effects of ACh and 5-HT were blocked by atropine, a muscarinic receptor antagonist, and ICS-205930, a 5-HT₃ receptor antagonist, respectively. Even after blocking the ACh receptor with atropine, 5-HT inhibited the PD and I_sc, and ACh lowered them after blocking the 5-HT receptor with ICS-205930, indicating that ACh and 5-HT act independently. Similar inhibition in the PD and the I_sc was observed after electrical field stimulation (EFS) which is expected to release endogenous regulators. These effects of EFS were reduced by 70% after simultaneous addition of atropine and ICS-205930. Since atropine and ICS-205930 block ACh and 5-HT receptors, respectively, these results suggest that endogenous ACh and 5-HT are released by EFS.Abbreviations ACh acetylcholine - EFS electrical field stimulation - 5-HT serotonin - I _sc short-circuit current - PD transepithelial potential difference - R _t tissue resistance - TTX tetrodotoxin