Glucose Partition Coefficient and Diffusivity in the Lower Skin Layers

Purpose This work aims to estimate the diffusivity and partitioning of glucose in the dermis and the viable epidermis of human skin. Methods The partition coefficient of glucose between phosphate-buffered saline and dermis, tape-stripped epidermis (TSE), stratum corneum (SC), and split-thickness skin, was measured in vitro using human cadaver skin. Glucose permeability across dermis and tape-stripped split-thickness skin (TSS) was measured using side-by-side diffusion cells. Glucose desorption from TSE and human epidermal membrane (HEM) was measured. All measurements were conducted at 32°C. Results The partition coefficient for glucose [mean ± SD (no. of samples)] was 0.65 ± 0.09 (n = 25) for dermis, 0.81 ± 0.06 (n = 10) for TSE, and 0.53 ± 0.12 (n = 9) for SC. Glucose diffusivity in dermis was calculated to be 2.64 ± 0.42 × 10⁻⁶ cm²/s (n = 14). Glucose diffusivities in the viable epidermis estimated from TSS permeation, TSE desorption, and HEM desorption were 0.075 ± 0.050 × 10⁻⁶ cm²/s (n = 5), 0.037 ± 0.018 × 10⁻⁶ cm²/s (n = 4), and 1.0 ± 0.6 × 10⁻⁶ cm²/s (n = 4), respectively. Conclusion The tissue/buffer partition coefficient of glucose in all skin layers was found to be less than unity, suggestive of excluded volumes in each layer. Glucose diffusivity in human dermis was found to be one third of its value in water, indicative of hindered diffusion related to the structural components of the tissue. A substantially lower value for glucose diffusivity in viable epidermis is suggested.     

Characterization of autonomic receptors in the rat sublingual gland by biochemical and radioligand assays

Summary The autonomic receptors of the rat sublingual gland were characterized by radioligand binding and by specific functional responses involving the release of K⁺ and the generation of cyclic AMP in vitro. Both muscarinic cholinergic and alpha₂-adrenergic receptors were present in moderately high density in the sublingual gland, as judged by the binding of the specific radioligands ³H-QNB and ³H-clonidine (B _max in pmol/g tissue=18.4±2.4 and 9.9±1.3, respectively). By contrast, although alpha₁ and beta-adrenergic receptors were detected, they were not present in large numbers. The B _max (pmol/g tissue) for the binding of ³H-prazosin and ³H-DHA were, respectively, 3.2±0.6 and 3.6±0.4. Stimulation of muscarinic cholinergic receptors with carbamylcholine (2×10^–5 M) caused a net release of K⁺ from sublingual slices incubated in an enriched, oxygenated Krebs Ringer bicarbonate medium of 35±7% after 10 min of incubation. Norepinephrine, phenylephrine, clonidine and isoproterenol did not induced K⁺ release from the slice preparation, but actually reduced the basal or unstimulated release of K⁺. As in the submandibular and parotid glands, the release of K⁺ from sublingual slices had two components, a passive efflux and an active uptake which depended on the activation of an ouabain-sensitive Na⁺, K⁺ ATPase. The release of K⁺ was also dependent on the presence of Ca²⁺ (2.7 mM) in the incubation medium. Stimulation of beta-adrenergic receptors with isoproterenol (10^–5 M) caused a 9-fold increase in the content of glandular cyclic AMP (from 4.0±0.6 to 36.0±2 pmol/mg/10 min). A similar increase was observed with norepinephrine (10^–4 M) in the presence of phentolamine (10^–4 M). Clonidine at concentrations of 10^–5 and 10^–4 M reduced the cyclic AMP content to below basal levels. The rat sublingual gland has functional cholinergic receptors and can release K⁺ in vitro in the presence of cholinergic agents. In contrast to the other major salivary glands, it has a low density of alpha₁-adrenergic receptors and fails to release K⁺ upon stimulation with alpha₁-agonists. The functional significance of a low density of beta-adrenergic receptors is still unclear, although there is a definite glandular cyclic AMP response upon stimulation with isoproterenol. Abundant alpha₂-adrenergic receptors in the sublingual gland are apparently negatively coupled to adenylate cyclase.     

Analysis of the beta 1 and beta 2 adrenoceptor interactions of the partial agonist, clenbuterol (NAB365), in the rat jugular vein and atria

Summary The potent bronchodilator, clenbuterol, was compared to other beta adrenoceptor agonists with regard to affinity and efficacy for interaction with beta₁ and beta₂ adrenoceptors in the rat jugular vein and atria. Clenbuterol was a potent partial beta adrenoceptor agonist in both tissues based on the following observations: 1. Maximal relaxation of the jugular vein and increases in atrial rate to clenbuterol were less than maximal responses to other beta adrenoceptor agonists. 2. Clenbuterol antagonized responses to the stronger agonist, isoproterenol, in both tissues and 3. the equilibrium dissociation constant for clenbuterol approximated the ED₅₀ concentration for vascular relaxation and increase in atrial rate, a characteristic of some, but not all, partial agonists. Relative to other beta adrenoceptor agonists, clenbuterol showed high affinity toward both beta₁ and beta₂ adrenoceptors and selectivity toward beta₂ adrenoceptors. Equilibrium dissociation constants were 38 and 6.3 nM for beta₁ and beta₂ adrenoceptors, respectively. The high affinity of clenbuterol toward beta₁ and beta₂ adrenoceptors was coupled to a low relative efficacy of clenbuterol to activate either beta₁ or beta₂ adrenoceptors. Most beta₂ adrenoceptor agonists such as isoproterenol or salbutamol require approximately 1–3% adrenoceptor occupation for 40–50% relaxation of the jugular vein whereas clenbuterol required approximately 100% adrenoceptor occupation for a similar response. Thus, based on our analysis, the high agonist potency of clenbuterol results primarily from the high affinity toward beta adrenoceptors rather than efficient activation of the adrenoceptor as occurs with isoproterenol or salbutamol.     

Stimulation of parotid cell glucose oxidation: Role of alpha1-adrenergic receptors and calcium mobilization

Epinephrine stimulated glucose oxidation in isolated rat parotid cell aggregates through alpha- and beta-adrenergic mechanisms. The alpha-adrenergic component appeared to be of the alpha₁-receptor subtype as evidenced by inhibition studies with selective antagonists. Calcium mobilization in the presence of the ionophore A23187 was as capable as epinephrine in eliciting this response. Epinephrine stimulation of glucose oxidation was, however, only partially dependent on extracellular calcium. Only the upper 50% of the maximal (10^?5M) epinephrine response required external calcium, since stimulation by 10^?6M epinephrine, which elicits only about 40% of the maximal (10^?5M epinephrine) response, was independent of external calcium. Furthermore, no external calcium dependence was observed for pure alpha- or beta-adrenergic stimulation alone, which comprised about 60 and 40%. respectively, of the maximal epinephrine response. Thus, adrenergic mediated parotid cell glucose oxidation may proceed by different mechanisms depending on the extent and nature of cellular stimulation.     

Endothelial cells contain beta adrenoceptors

Summary The direct identification of beta adrenoceptors in endothelial cell cultures has not been possible until the advent of a new beta-adrenergic radioligand, [¹²⁵I]iodocyanopindolol ([¹²⁵I]ICYP). Using [¹²⁵I]ICYP, we report thes successful identification of a beta adrenoceptor in cultured bovine aortic endothelial cells. At 37°C, specific binding is saturable, stable and reversible. There is a single class of binding sites (21,500±2,900 sites/cell) with an equilibrium dissociation constant (K _d) of 109±26 pM. The rate constant of association, k ₁, is 1.22×10⁹ M^–1 min^–1 and of dissociation, k _–1, is 0.01 min^–1. Binding studies on monolayers of endothelial cells grown in microtiter plates yield similar data (K _d=53±9 pM, B _max=20,000±1,900 sites/cell). Stereoselectivity of binding for the (–)-isomer is demonstrable for both agonists and antagonists. A series of adrenergic agonists competes with [¹²⁵I]ICYP for binding with an order of potency suggesting beta₂ subselectivity; isoproterenol (0.73 M) > epinephrine (15 M) > norepinephrine (71 M). Furthermore, the beta₂ inhibitor butoxamine is more potent than the beta₁ inhibitor practolol (7.7 M vs 22 M respectively). The GTP analogue, Gpp(NH)p, reduces isoproterenol affinity to 1.9 M and increases the Hill coefficient from 0.62–0.90.     

Pharmacological characterization of the alpha adrenoceptors of the dog basilar artery

Summary The effects of alpha adrenoceptor agonists and antagonists on the postsynaptic alpha receptors were examined in the dog basilar, mesenteric and renal arteries and the type of alpha adrenoceptors present was characterized. In the basilar artery, noradrenaline, clonidine and phenylephrine produced almost the same maximal contraction, the pD₂ values being 6.51±0.11, 5.49±0.16 and 5.65±0.13, respectively. Yohimbine (1–3×10^–8 M) inhibited the contractile responses to noradrenaline and clonidine competitively and the response to phenylephrine noncompetitively. Corynanthine (10^–6 M) had no effect on such contractile responses. In the mesenteric and renal arteries, the maximal responses to noradrenaline and phenylephrine were markedly greater than those to clonidine. Yohimbine (10^–7–10^–5 M) and corynanthine (10^–7–10^–5 M) both antagonized noradrenaline competitively in these vessels. In the basilar, mesenteric and renal arteries preloaded with ³H-noradrenaline, ³H-efflux induced by electrical transmural stimulation was attenuated by clonidine (10^–10–10^–7 M), while phenylephrine (10^–10–10^–8 M) was without effect. Yohimbine at considerably lower concentrations than corynanthine increased the ³H-efflux clicited by electrical stimulation. These results indicate that presynaptic and postsynaptic alpha receptors of the dog basilar artery are largely alpha₂ in contrast to those of peripheral arteries.This work was supported by a Grant-in-Aid for Co-operative Research (No. 00437006), by a Grant-in-Aid for Special Project Research (No. 56220016) and by a Grant-in-Aid for Encouragement of Young Scientists (No. 577106, 56770118) from the Ministry of Education, Science and Culture, Japan     

Inhibition of erythrocyte “apoptosis” by catecholamines

Osmotic shock, oxidative stress and Cl⁻ removal activate a non-selective Ca²⁺-permeable cation conductance in human erythrocytes. The entry of Ca²⁺ leads to activation of a scramblase with subsequent exposure of phosphatidylserine at the cell surface. Phosphatidylserine mediates binding to phosphatidylserine receptors on macrophages which engulf and degrade phosphatidylserine exposing cells. Moreover, phosphatidylserine exposure may lead to adherence of erythrocytes to the vascular wall. In the present study, we explored whether activation of the non-selective cation conductance and subsequent phosphatidylserine exposure might be influenced by catecholamines. Phosphatidylserine exposure has been determined by FITC-annexin V binding while cell volume was estimated from forward scatter in FACS analysis. Removal of Cl⁻ enhanced annexin binding and decreased forward scatter, an effect significantly blunted by the β agonist isoproterenol (IC₅₀ approx. 1 μM). Fluo-3 fluorescence measurements revealed an increase of cytosolic Ca²⁺ activity following Cl⁻ removal, an effect again significantly blunted by isoproterenol exposure (10 μM). Whole-cell patch-clamp experiments performed in Cl⁻ free bath solution indeed disclosed a time-dependent inactivation of a non-selective cation conductance following isoproterenol exposure (10 μM). Phenylephrine (IC₅₀<10 μM), dobutamine (IC₅₀ approx. 1 μM) and dopamine (IC₅₀ approx. 3 μM) similarly inhibited the effect of Cl⁻ removal on annexin binding and forward scatter. In conclusion, several catecholamines inhibit the Cl⁻ removal-activated Ca²⁺ entry into erythrocytes, thus preventing increase of cytosolic Ca²⁺ activity, subsequent cell shrinkage and activation of erythrocyte scramblase. The catecholamines thus counteract erythrocyte phosphatidylserine exposure and subsequent clearance of erythrocytes from circulating blood.     

Impairment of endothelium- and nerve-mediated relaxation responses in the cavernosal smooth muscle of experimentally diabetic rabbits: role of weight loss and duration of diabetes

The effects of short- and long-term experimental diabetes on corporal nerve, endothelium and smooth-muscle responses were investigated, and the reasons for possible alterations in corporal smooth muscle responses such as hyperglycaemia, duration of experimental diabetes and/or altered tissue weight were evaluated. Rabbits were injected with alloxan (125 mg/kg) to induce diabetes. Age-matched non-diabetic and diabetic (3 and 9 weeks) and weight-matched non-diabetic groups (9 weeks) were used as control. In all groups, relaxation (carbachol, electrical field stimulation and sodiumnitroprusside) responses were examined. The relaxation responses were expressed as percentage of the precontraction to phenylephrine and as g response/g tissue weight. The effects of elevated glucose were also examined by incubating cavernosal strips in Krebs–Henseleit solution containing 44.4 mM glucose for 6 h. Cavernosal tissues of non-diabetic and 9-week diabetic rabbits were evaluated histologically. Sodiumnitroprusside (10⁻⁷−10⁻⁴ M) responses were similar in all groups. Relaxation responses to electrical field stimulation (10 s train; amplitude 50 V; frequency 0.5–32 Hz; width 0.8 ms) were only attenuated in the 9-week diabetic group compared to the non-diabetic group. Carbachol (10⁻⁸−3×10⁻⁵ M) responses were attenuated in both diabetic groups. When the relaxation responses expressed as g response/g tissue weight were evaluated, results were similar compared to those expressed as percentage of phenylephrine (10⁻⁵ M). Neither carbachol nor electrical field stimulation mediated responses were impaired with glucose incubation. No morphological degenerations were observed in the endothelium. Diabetes may interfere with the synthesis and/or release of nitric oxide from both nerves and endothelium in corpus cavernosum, and alterations in endothelium-derived responses occur earlier than neurological disturbances. The sensitivity of cavernosal smooth muscle to nitric oxide did not alter in diabetes. Attenuation of responses was not due to decreased tissue weight caused by diabetes.     

Studies on the mechanism of methyl-Dopa-induced mydriasis in the cat

Summary alpha-methyl-Dopa (10–100 mg/kg, i.v.) produced a dose-dependent mydriasis in cats anaesthetized with pentobarbital (30 mg/kg, i.p.). The onset was gradual, reaching a maximum plateau in 2–2.5 h. Intracerebroventricular administration of 1 or 3 mg of alpha-methyl Dopa (MD) also produced pupillary dilation with a similar time course. These dosages were without effect when given intravenously. Pretreatment with the alpha ₂-adrenoceptor antagonist, yohimbine (0.5 mg/kg, i.v.), blocked the pupillary response to MD. The alpha ₁-adrenoceptor antagonist, prazosin (1.0 mg/kg, i.p.), was ineffective. Selective enzymatic blockade with 3-hydroxy-benzyl-hydrazine (NSD-1015; 25 mg/kg, i.p.), a Dopa-decarboxylase enzyme inhibitor, as well as with bis (4-methyl-homopiperazinyl-thiocarbonyl) disulfide (FLA-63; 2.5 mg/kg, i.p.), a dopamine-beta-hydroxylase blocker, prevented the mydriatic effect of MD. These results support the hypothesis that MD produces a clonidine-like, CNS mediated mydriasis in the cat, primarily by action of its metabolite alpha-methyl-noradrenaline acting on alpha ₂-adrenoceptors.     

Role of alpha1A adrenoceptor subtype in production of the positive inotropic effect mediated via myocardial alpha,adrenoceptors in the rabbit papillary muscle: influence of selective alpha1A subtype antagonists WB 4101 and 5-methylurapidil

Summary In order to elucidate the contribution of alpha_1A subtype to the positive inotropic effect mediated by myocardial alpha, adrenoceptors, the influence of the alpha_1A selective antagonists WB 4101 and 5-methylurapidil on the alpha,-mediated positive inotropic effect (induced by phenylephrine in the presence of a beta adrenoceptor blocking agent bupranolol) was assessed in the isolated rabbit papillary muscle. WB 4101 (10^–9-10^–7mol/l) shifted the concentration-response curve of the alpha,-mediated positive inotropic effect to the right in parallel, but the slope of Schild plot did not meet the competitive antagonism: WB 4101 shifted the curve by log one unit at 10^–9 mol/1, whereas it did not cause further shift at higher concentrations of 10^–8 and 10^–7 mol/l. WB 4101 did not affect the beta adrenoceptor-mediated positive inotropic effect. 5-Methylurapidil (10^–9 to 10^–7 mol/l) shifted the curve of alpha₁-mediated positive inotropic effect to the right and downwards in a concentration-dependent manner; the slope of Schild plot calculated at the level of 20% of the maximum response to phenylephrine was close to unity. 5-Methylurapidil at 3 × 10^–7 mol/1 abolished the alpha₁-mediated positive inotropic effect. In addition, 5-methylurapidil inhibited the beta adrenoceptor-mediated positive inotropic effect in the same concentration range as it antagonized the alpha₁-mediated positive inotropic effect, indicating that 5-methylurapidil is not selective for myocardial alpha, adrenoceptors. In the membrane fraction derived from the rabbit ventricular muscle, 5-methylurapidil displaced the specific binding of [³H]CGP-12177 with high affinity, whereas WB 4101 did not affect the [³H]CGP-12177 binding in the concentration range that it antagonized the alpha,-mediated positive inotropic effect. The present results indicate that alpha_1A adrenoceptor subtype plays a role in production of the positive inotropic effect mediated by myocardial alpha, adrenoceptors, but the extent is less than that mediated by alpha_1B subtype in the rabbit ventricular myocardium. Send offprint requests to M. Endoh at the above address     

Urotensin II acutely increases myocardial length and distensibility: potential implications for diastolic function and ventricular remodeling

Urotensin II (U-II) is a cyclic peptide that may be involved in cardiovascular dysfunction. In the present study, the acute effects of U-II on diastolic properties of the myocardium were investigated. Increasing concentrations of U-II (10⁻⁸ to 10⁻⁶ M) were added to rabbit papillary muscles in the absence (n = 15) or presence of: (1) damaged endocardial endothelium (EE; n = 9); (2) U-II receptor antagonist, urantide (10⁻⁵ M; n = 7); (3) nitric oxide (NO) synthase inhibitor, N^G-Nitro-l-Arginine (10⁻⁵ M; n = 9); (4) cyclooxygenase inhibitor, indomethacin (10⁻⁵ M; n = 8); (5) NO synthase and cyclooxygenase inhibitors, N^G-Nitro-l-Arginine (10⁻⁵ M) and indomethacin (10⁻⁵ M), respectively, (n = 8); or (6) protein kinase C (PKC) inhibitor, chelerythrine (10⁻⁵ M; n = 9). Passive length–tension relations were constructed before and after a single concentration of U-II (10⁻⁶ M; n = 3). U-II concentration dependently decreased inotropy and increased resting muscle length (RL). At 10⁻⁶ M, active tension decreased 13.8 ± 5.4%, and RL increased to 1.007 ± 0.001 L/L _max. Correcting RL to its initial value resulted in an 18.1 ± 3.0% decrease in resting tension, indicating decreased muscle stiffness, which was also suggested by the down and rightward shift of the passive length–tension relation. This effect remained unaffected by EE damage and PKC inhibition. In contrast, the presence of urantide and NO inhibition abolished the effects of U-II on myocardial stiffness, while cyclooxygenase inhibition significantly attenuated them. U-II decreases myocardial stiffness, an effect that is mediated by the urotensin-II receptor, NO, and prostaglandins. This represents a novel mechanism of acute neurohumoral modulation of diastolic function, suggesting that U-II is an important regulator of cardiac filling. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Presented in part at the American Heart Association Scientific Sessions conference, 2006, in Chicago, Illinois.     

The reduction in alcohol intake in rats by isoproterenol is attenuated by indomethacin but not enalapril: relationship to blood glucose levels

 Many adrenergic agonists including isoproterenol, a β _{1,  2}-adrenergic agonist, reduce alcohol consumption, but the mechanism of this effect is not known. Adrenergic agonists have a variety of effects, among which are their ability to raise both angiotensin (ANG) II activity and plasma glucose levels. Previous research has shown that ANG II and enhanced glucose levels are accompanied by reductions in alcohol intake. Therefore, the following experiments assessed the roles of each of these factors in the suppression of alcohol intake by isoproterenol. Male Wistar rats were trained to drink a quantity of 6% (w/v) alcohol using the limited access procedure, which offers a daily 40-min access to alcohol and water. In experiment 1, isoproterenol or vehicle was administered SC just prior to alcohol availability, and only the group receiving isoproterenol showed a marked reduction in alcohol intake. Following this, the groups were pretreated IP with either vehicle or ascending doses of the prostaglandin synthetase inhibitor, indomethacin (2, 4 mg/kg), followed by either isoproterenol or vehicle. Control groups received either two vehicle injections or vehicle and indomethacin. Indomethacin alone did not affect alcohol intake at any of the doses tested but did dose-dependently attenuate the reduction in alcohol intake produced by isoproterenol. In experiment 2, isoproterenol was administered just prior to alcohol availability and when the suppression of alcohol intake stabilized, ascending doses of the angiotensin converting enzyme inhibitor, enalapril (1, 20, 40 mg/kg), were given IP 1 h prior to the isoproterenol. Enalapril altered water intake but had no effect on the isoproterenol-induced reduction in alcohol intake. These results show that the inhibition of alcohol drinking by isoproterenol varies more closely with altered glucose levels than with increased ANG II synthesis. They also demonstrate that downstream consequences of a drug may play a role in its effect on alcohol intake. Received: 19 June 1997 / Final version: 11 November 1997     

Dose-independent pharmacokinetics of a new peroxisome proliferator-activated receptor-γ agonist,KR-62980, in Sprague-Dawley rats and ICR mice

The pharmacokinetics of a novel peroxisome proliferator-activated receptor-γ agonist, KR-62980, were characterized in vitro with respect to liver metabolic stability, cell permeability, and plasma protein binding and in vivo using Sprague-Dawley rats and ICR mice. The metabolic half-life of 0.1–10 μM KR-62980 was 11.5–15.2 min in rat liver microsomes and 25.8–28.8 min in human liver microsomes. KR-62980 showed high permeability across MDCK cell monolayers, with apparent permeability coefficients of 20.4 × 10⁻⁶ to 30.8 × 10⁻⁶ cm/sec. The plasma protein binding rate of KR-62980 was 89.4%, and most was bound to serum albumin. After intravenous administration of KR-62980 (2 mg/kg), the systemic clearance was 2.50 L/h/kg, and the volume of distribution at steady-state was 9.16 L/kg. The bioavailability after oral administration was approximately 60.9%. The dose-normalized AUC values were 0.50 ± 0.09, 0.41 ± 0.20, and 0.62 ± 0.08 h·μg/mL after oral administration of 2, 5, and 10 mg/kg KR-62980, respectively, showing no dose-dependency. The in vivo pharmacokinetic parameters in ICR mice were also dose independent. These data suggest that KR-62980 is not significantly dose dependent in rats or mice, although it may disappear rapidly from the systemic circulation via metabolism in the liver.     

Fluvastatin reduces endothelin secretion of cultured human umbilical vein endothelial cells

Objective: Fluvastatin is an agent of a new lipid lowering drug class, the 3-hydroxy-3-methylglutaryl-coenzyme A reductase inhibitors, which seems to elicit direct effects on the vasculature. Methods: The effect of fluvastatin on endothelin secretion in endothelial cell cultures from human umbilical veins was investigated. Results: Fluvastatin significantly reduced endothelin secretion by 13% at a concentration of 10⁻⁸ M, by 41% at 10⁻⁷ M and by 62% at 10⁻⁶ M. Conclusion: Since endothelin is a potent vasoconstrictor which may be associated with the aetiology of cardiovascular diseases, the reduction of its synthesis by fluvastatin may contribute to the beneficial effects of this substance on the cardiovascular system. Received: 12 April 1999 / Accepted in revised form: 23 August 1999     

Influence of beta-blockers on melatonin release

Objective: Melatonin is a mediator in the establishment of the circadian rhythm of biological processes. It is produced in the pineal gland mainly during the night by stimulation of adrenergic beta₁- and alpha₁-receptors. Sleep disturbances are common side-effects of beta-blockers. The influence of specific beta-blockade as well as that of combined alpha-and beta-blockade on melatonin production has not been investigated in humans before. Methods: We performed a randomized, double-blind, placebo-controlled, cross-over study in 15 healthy volunteers. Subjects received single oral doses of 40 mg (R)-propranolol, 40 mg (S)-propranolol, 50 mg (R)-atenolol, 50 mg (S)-atenolol, 25 mg (R,S)-carvedilol, 120 mg (R,S)-verapamil or placebo at 1800 hours. Urine was collected between 2200 hours and 0600 hours, and 6-sulfatoxy-melatonin (aMT6s), the main metabolite of melatonin which is almost completely eliminated in urine, was determined by radioimmunoassay (RIA). Results: Mean nocturnal excretion of aMT6s in urine after intake of the drugs was as follows (in μg): placebo 26; (R)-propranolol 24 (−7%, NS); (S)-propranolol 5 (−80%, P < 0.001); (R)-atenolol 27 (+7%, NS); (S)-atenolol 4 (−86%, P < 0.01); (R,S)-carvedilol 23 (−10%, NS); (R,S)-verapamil 29 (+14%, NS). These data show that only the specifically beta-blocking (S)-enantiomers of propranolol and atenolol decrease the nocturnal production of melatonin whereas the non-beta-blocking (R)-enantiomers have no effect. Unexpectedly, (R,S)-carvedilol which inhibits both alpha- and beta-adrenoceptors does not decrease melatonin production. Conclusion: These findings indicate that beta-blockers decrease melatonin release via specific inhibition of adrenergic beta₁-receptors. Since lower nocturnal melatonin levels might be the reason for sleep disturbances, further clinical studies should investigate whether or not oral administration of melatonin might avoid this well-known side-effect of beta-blockers. The reason why (R,S)-carvedilol does not influence melatonin production remains to be determined. Received: 10 August 1998 / Accepted in revised form: 25 November 1998     

Male reproductive toxicity of four bisphenol antioxidants in mice and rats and their estrogenic effect

Male mice and rats were fed a diet containing four bisphenol antioxidants, 2,2′-methylenebis(4-ethyl-6-tert-butylphenol) (ME), 2,2′-methylenebis(4-methyl-6-tert-butylphenol) (MM), 4,4′-butylidenebis(3-methyl-6-tert-butylphenol) (BM), or 4,4′-thiobis(3-methyl-6-tert-butylphenol) (TM) at levels of 0.06–0.25% for 2 months. BM and TM decreased epididymal, seminal vesicular, prostate and preputial weights, and injured seminiferous tubules in mice in a dose-dependent fashion. BM and TM also reduced sex accessory organ weights and sperm production capacity in rats, but MM and ME were more toxic to rats than BM and TM. ME and MM did not bind ER_α up to 10⁻³ M, while BM and TM competitively bound ER_α against β-estradiol (E2). Fifty percent inhibitory concentrations (IC₅₀ s) of BM, TM, and bisphenol A (positive control) against E2-binding were 7.3×10⁻⁶ M, 1.8×10⁻⁵ M, and 1.4×10⁻⁵ M, respectively. When ovariectomized (OVX) mice were sc administered TM at doses of 60 and 300 mg/kg/day for 4 days, or when OVX mice were fed BM in the diet at a level of 0.25% for 2 months, uterine weight was significantly increased. These results suggest that BM and TM are weakly toxic, possibly through an estrogenic mechanism to male reproductive organs in mice as well as rats, while MM and ME may be the direct testicular toxins in rats but not mice. A part of this study was presented at the 74th annual meeting of the Japanese Society for Hygiene held from 24–27 March 2004 in Tokyo, Japan.     

Inhibitory effects of L- and T-type calcium antagonists on contractions of human detrusor muscle

The inhibitory and relaxant effects of the L-type calcium antagonists nifedipine, nimodipine, verapamil and diltiazem, and of the T-type calcium antagonist mibefradil, on contractions of isolated human detrusor muscle were investigated. The tissue was obtained from 10 patients undergoing cystectomy due to bladder cancer. Effects of the calcium antagonists at different concentrations on the concentration-response curves for carbachol were investigated. Furthermore, concentration-relaxation curves were performed using potassium-precontracted muscle strips. All L-type calcium antagonists suppressed the mean concentration-response curve of carbachol significantly at a concentration of 10⁻⁶ M. Mibefradil up to 10⁻⁵ M did not significantly suppress it. Nifedipine significantly reduced the carbachol-induced maximum contraction to 75% and 44%, verapamil to 75% and 67% of the appropriate control value at concentrations of 10⁻⁷ and 10⁻⁶ M, respectively. Diltiazem reduced it insignificantly to 96% and 71% at the above-mentioned concentrations. The concentration-relaxation experiments revealed following pD2-values and maximum relaxations of nifedipine, nimodipine, verapamil and diltiazem, respectively: 6.23, 6.37, 5.66, 5.81 and 85%, 83%, 82%, 90%. Maximum relaxations and pD2-values were not significantly different from each other. The lowest concentration, for which a significant effect compared to control in Student`s t-test was found, amounted to 10⁻¹⁰ M, 10⁻⁹ M, 10⁻⁷ M, 10^−6.5 M and 10⁻⁴ M for nimodipine, nifedipine, diltiazem, verapamil and mibefradil, respectively. L-type calcium antagonists are very potent relaxant agents of the human detrusor muscle in vitro.     

Antiestrogenic effect of paradichlorobenzene in immature mice and rats

A significant increase/decrease in uterine and ovarian weights was occasionally seen in immature mice and rats subcutaneously administered paradichlorobenzene (PDCB) at doses of 22–67 mg/kg/day, but the results were not necessarily reproducible. PDCB at a dose of 800 mg/kg/day always reduced uterine and ovarian weights. Intraperitoneal PDCB at doses more than 400 mg/kg/day significantly inhibited the uterotrophic effect of β-estradiol (E2) in CD-1 (ICR) mice. E2-induced uterotrophy was dose-dependently prevented by 204–400 mg PDCB/kg/day in C57BL/6N (Ah responsive) mice but not DBA/2N (Ah non-responsive) mice. While PDCB did not bind to estrogen receptor (ER_α) up to 10⁻³ M. Hepatic ethoxyresorufin-O-deethylase in adult female C57BL/6N mice was induced by ip administration of PDCB. Induction activity of PDCB may be 10⁵–10⁶ times lower than that of 2,3,7,8-tetrachlorodibenzo-p-dioxin. These results suggest that PDCB is a weak antiestrogenic/antiuterotrophic compound possibly due to ER modulation through arylhydrocarbon receptor. This study presented at the 9th annual meeting of the Japanese Society of Endocrine Disrupters Research held from 11–12 November 2006 in Tokyo, Japan.     

Biological effects of the dihydroorotate dehydrogenase inhibitor polyporic acid, a toxic constituent of the mushroom Hapalopilus rutilans , in rats and humans

Inhibitors of dihydroorotate dehydrogenase (DHO-DH), such as brequinar or leflunomide, have been intensively tested for their antitumour and immunomodulating effects. Polyporic acid (PA) from the mushroom Hapalopilus rutilans (H. r.) also is a DHO-DH inhibitor (50% inhibitory concn., IC₅₀, 10⁻⁴–10⁻³ M). As three people had been poisoned following ingestion of H. r. we wanted to investigate the effects of PA in rats and in cell cultures. Rats given PA via probang (100–800 mg/kg) within 24 h developed strongly reduced locomotor activity, depressed visual placing response and impaired wire manoeuvre. Laboratory investigation of blood revealed hepatorenal failure, metabolic acidosis as well as hypokalaemia and hypocalcaemia. All symptoms closely paralleled the effects seen in the poisoned people. Proliferation of cultured cells (including rat brain neurons and glia, fibroblasts, tumour cells) was depressed at 10⁻⁴–10⁻³ M PA. We conclude that the intoxication of people poisoned with H. r. is due to the high content of the DHO-DH inhibitor PA. Received: 6 July 1998 / Accepted: 7 September 1998     

In vitro immunoregulatory effects of lithium in healthy volunteers

Rationale: There is now some evidence that major depression is associated with activation of the inflammatory response system (IRS). Lithium is effective in the treatment and prophylaxis of major depression and shows significant immunoregulatory functions. Objective: The aims of the present study were to examine the in vitro effects of lithium on the unstimulated and lipolysaccharide (LPS) + phytohemagglutinin (PHA)-induced production of proinflammatory cytokines, such as interleukin-6 (IL-6), IL-8, tumor necrosis factor-α (TNFα) and interferon-γ (IFNγ), and negative immunoregulatory cytokines or proteins, such as IL-10 and the IL-1 receptor antagonist (IL-1RA). Methods: The in vitro effects of lithium carbonate at low (10⁻⁴ M and 10⁻⁵ M) and therapeutic (10⁻³ M) concentrations on the above cytokines and the IL-1RA were examined in nine healthy volunteers on whole blood supernatant cultured for 72 h. Results: Lithium (10⁻³ M) in the presence of LPS+PHA significantly increased the stimulated production of IFNγ, IL-8, TNFα, IL-1RA and IL-10. Lithium (10⁻³ M) significantly increased the unstimulated production of IL-8 and IL-10. Conclusions: The results suggest that lithium has significant immunoregulatory effects by increasing the production of both proinflammatory cytokines (IFNγ, TNFα and IL-8) and negative immunoregulatory cytokines or proteins (IL-10 and the IL-1RA). Received: 26 June 1998/Final version: 30 November 1998