ATP-sensitive potassium channels mediate the effects of a peripheral injection of glucose on memory storage in an inhibitory avoidance task

A peripheral injection of glucose has been found to improve memory in rats, but the underlying mechanisms are unknown. One possible mechanism by which peripheral glucose might act on memory storage is by regulating ATP-sensitive potassium (K-ATP) channels. The present study investigated the effects of K-ATP channel modulators (minoxidil, a K-ATP channel opener and glibenclamide, a K-ATP channel closer) on memory enhancement induced by peripheral injection of glucose in an inhibitory avoidance task. Rats were trained in a one trial inhibitory avoidance task (50 Hz, 1 mA, 3 s footshock), and minoxidil (12.5,25 or 50 mg/kg) or glibenclamide (2.5,5,10 or 20 mg/kg) was injected interaperitoneally (I.P) 30 min before training. Immediately after training the rats were injected with glucose (100 mg/kg, I.P). Retention was tested 2 days later. The results indicate that systemic post-training injection of glucose improved memory storage and this effect was attenuated and enhanced by pretreatment of minoxidil and glibenclamide, respectively. The drug minoxidil or glibenclamide alone did not significantly affect memory storage. This shows that K-ATP channels mediate the memory improving effects of systemic glucose.

Effects of hypotension and fluid depletion on central angiotensin-induced thirst and salt appetite

We examined the effects of hypotension and fluid depletion on water and sodium ingestion in rats in response to intracerebroventricular infusions of ANG II. Hypotension was produced by intravenous infusion of the vasodilator drug minoxidil (25 microg x kg(-1) x min(-1)) concurrently with the angiotensin-converting enzyme inhibitor captopril (0.33 mg/min) to prevent endogenous ANG II formation. Hypotension increased water intake in response to intracerebroventricular ANG II (30 ng/h) but not intake of 0.3 M NaCl solution and caused significant urinary retention of water and sodium. Acute fluid depletion was produced by subcutaneous injections of furosemide (10 mg/kg body wt) either alone or with captopril (100 mg/kg body wt sc) before intracerebroventricular ANG II (15 or 30 ng/h) administration. Fluid depletion increased water intake in response to the highest dose of intracerebroventricular ANG II but did not affect saline intake. In the presence of captopril, fluid depletion increased intakes of both water and saline in response to both doses of intracerebroventricular ANG II. Because captopril administration causes hypotension in fluid-depleted animals, the results of the two experiments suggest that hypotension in fluid-replete animals preferentially increases water intake in response to intracerebroventricular ANG II and in fluid-depleted animals increases both salt and water intake in response to intracerebroventricular ANG II.

Effect of minoxidil on rabbit lens epithelial cell behavior in vitro and in situ

BACKGROUND

Lens epithelial cell (LEC) proliferation and the associated production of extracellular matrix (ECM) are responsible for capsular opacification after cataract-IOL surgery. Minoxidil is an inhibitor of lysyl hydroxylase, an enzyme involved in procollagen hydroxylation. To evaluate the potential efficacy of minoxidil in inhibiting postoperative capsular opacification, we examined the effects of minoxidil on LEC behavior in cell and organ cultures.

METHODS

We examined minoxidil effects on collagen production, migration and proliferation of cultured rabbit LECs as well as its ultrastructural effects, and also its effects on the cell population in organ-cultured capsular bag.

RESULTS

No cytotoxicity was identified by MTT assay at the concentrations up to 3.0 mM of minoxidil, whereas it decreased the collagen production in LECs. Minoxidil also inhibited migration and proliferation of cells. Ultrastructural observation revealed the presence of dilated endoplasmic reticulum in LECs treated with minoxidil, indicating the accumulation of protein, probably underhydroxylated collagen precursors. The capsules cultured with minoxidil appeared less opaque than control specimens. On histological examination the numbers of cells on equatorial capsules were found to be significantly lower in minoxidil culture than in control culture. No lens cells were detected on the central posterior capsule of minoxidil culture, whereas they were seen in control.

CONCLUSION

Minoxidil inhibited LEC migration and proliferation in vitro, as well as collagen secretion. Collagen secretion may be essential for LEC migration and proliferation. Minoxidil also attenuated repopulation of LECs on the inner surface of organ-cultured capsules. Minoxidil may be a potential inhibitor of postoperative capsular opacification.

Topical application of cyclosporin A induces rapid-remodeling of damaged anagen hair follicles produced in cyclophosphamide administered mice

Adult C3H mice which had either anagen IV or anagen VI hair follicles were given the anti-tumor drug cyclophosphamide, and cyclosporin A or minoxidil were topically applied to the mice daily from the 4th day after cyclophosphamide administration. In the mice that had anagen IV-hair follicles, 0.5% cyclosporin A induced very thick and long hairs after 21 days of cyclophosphamide administration, while vehicle and 1% minoxidil induced sparsely visible, short hairs. In the mice which received cyclosporin A, the injured hair follicles seemed to remodel themselves into intact anagen hair follicles and restart the production of hairs, instead of shifting to telogen. In the mice that had anagen VI-hair follicles at the time of cyclophosphamide administration, complete alopecia occurred within the first 7 days in all groups. After 14 days of cyclophosphamide administration, hair regrowth was observed in both the 0.5% cyclosporin A-group and the 1% minoxidil- group with the predominant effect over the vehicle. This study shows that anagen hair follicles respond to cyclophosphamide in different ways depending on their stages (IV and VI), and that the damaged anagen IV hair follicles have the potential of remodeling themselves, which is promoted by topical cyclosporin A administration.

Effect of ATP sensitive potassium channel modifiers on antinociceptive effect of metoclopramide

Metoclopramide, a prokinetic drug, has been documented to produce antinociceptive response in animal models through opioid pathways. Morphine has been shown to act through ATP sensitive potassium channels (KATP) to produce antinociceptive response. However, such a possibility has not been examined for metoclopramide. The present study investigated this using pharmacological tools. Acetic acid induced abdominal constriction assay procedure was utilized to assess antinociception. The results confirmed that metoclopramide has antinociceptive response. Glibenclamide, a KATP channel blocker, pretreatment antagonized this response. Where as, in minoxidil pretreated animals, metoclopramide elicited an enhanced antinociceptive response. Glibenclamide and minoxidil, which are known KATP channel blocker and opener respectively, interfered with metoclopramide antinociception. These finding are suggestive of a role for KATP channels in metoclopramide antinociception in mice.

Treatments for androgenetic alopecia and alopecia areata: current options and future prospects

Androgenetic alopecia and alopecia areata are common disorders of the hair follicle which may heavily influence self esteem and self image. Androgenetic alopecia is caused by the heightened sensitivity of scalp follicles to dihydro- testosterone whereas alopecia areata is induced by an autoimmune reaction. Current drug treatment approaches include the use of regrowth stimulators such as topical minoxidil and oral finasteride for androgenetic alopecia, as well as topical minoxidil, dithranol (anthralin), corticosteroids, contact sensitisers, and psoralen plus ultraviolet A irradiation (PUVA) therapy for alopecia areata. Combination regimens are also proposed. However, extreme cases of either type of alopecia do not generally respond well to these existing treatments. For this reason, new therapeutic strategies are directed towards both improving the targeting of existing agents, as well as the development of novel hypertrichotic modalities.

The role of minoxidil on endogenous opioid peptides in the spinal cord: a putative co-agonist relationship between K-ATP openers and opioids

ATP-gated K(+) channel openers produce antinociception that is attenuated by opioid receptor antagonists, indicating K-ATP openers produce antinociception, in part, via the release of endogenous opioid peptides. Utilizing the spinal perfusion method, male Sprague-Dawley rats were administered minoxidil intrathecally (i.t.) at doses ranging from 12.5 to 200 microg/rat for 3 min, tested for antinociception using the tail-flick test, and perfused with artificial cerebrospinal fluid (aCSF) to collect endogenous opioid peptides. Endogenous opioid peptide levels were measured by radioimmunoassay. Naltrindole, a delta-opioid receptor antagonist, at 4 mg/kg, subcutaneously (s.c.), blocked minoxidil-induced antinociception. beta-Funaltrexamine, a mu-opioid receptor antagonist, at 100 microg/rat, partially blocked minoxidil, whereas the kappa-opioid receptor antagonist nor-binaltorphimine, at a dose of 100 microg/rat, did not attenuate minoxidil. Although antagonists of the mu- and delta-opioid receptor attenuated minoxidil-induced antinociception, there was no increase in beta-endorphin, an endogenous ligand with affinity for both micro- and delta-opioid receptors or [Leu(5)]enkephalin, an endogenous ligand with affinity for delta-opioid receptors.

KF19418, a new compound for hair growth promotion in vitro and in vivo mouse models

KF19418, a newly synthesized compound, stimulated proliferation of cultured hair bulb cells from new born mice in concentration-dependent manner in the range under 10 microM. In the culture system of whole skin pieces from 4-week-old mice which we earlier established, KF19418 promoted hair follicle elongation as in the case of minoxidil. After topical application for 2 weeks of KF19418 or minoxidil to dorsal skin of hair-clipped mouse alopecia model, KF19418 at 1% suspension accelerated hair regrowth at a rate comparable to 1% minoxidil solution. Thus, it was shown that KF19418 directly stimulated hair follicle in vitro and had hair growth promoting activities in vivo.

Reduction of potassium currents and phosphatidylinositol 3-kinase-dependent AKT phosphorylation by tumor necrosis factor-(alpha) rescues axotomized retinal ganglion cells from retrograde cell death in vivo

Tumor-necrosis-factor-alpha (TNF-alpha) prevented secondary death of retinal ganglion cells (RGCs) after axotomy of the optic nerve in vivo. This RGC rescue was confirmed in vitro in a mixed retinal culture model. In accordance with our previous findings, TNF-alpha decreased outward potassium currents in RGCs. Antagonism of the TNF-alpha-induced decrease in outward potassium currents with the potassium channel opener minoxidilsulfate (as verified by electrophysiology) abolished neuroprotection. Western blot analysis revealed an upregulation of phospho-Akt as a consequence of TNF-alpha-induced potassium current reduction. Inhibition of the phosphatidylinositol 3-kinase-Akt pathway with wortmannin decreased TNF-alpha-promoted RGC survival. These data point to a functionally relevant cytokine-dependent neuroprotective signaling cascade in adult CNS neurons.

An abnormal Ca(2+) response in mutant sarcomere protein-mediated familial hypertrophic cardiomyopathy

Dominant-negative sarcomere protein gene mutations cause familial hypertrophic cardiomyopathy (FHC), a disease characterized by left-ventricular hypertrophy, angina, and dyspnea that can result in sudden death. We report here that a murine model of FHC bearing a cardiac myosin heavy-chain gene missense mutation (alphaMHC(403/+)), when treated with calcineurin inhibitors or a K(+)-channel agonist, developed accentuated hypertrophy, worsened histopathology, and was at risk for early death. Despite distinct pharmacologic targets, each agent augmented diastolic Ca(2+) concentrations in wild-type cardiac myocytes; alphaMHC(403/+) myocytes failed to respond. Pretreatment with a Ca(2+)-channel antagonist abrogated diastolic Ca(2+) changes in wild-type myocytes and prevented the exaggerated hypertrophic response of treated alphaMHC(403/+) mice. We conclude that FHC-causing sarcomere protein gene mutations cause abnormal Ca(2+) responses that initiate a hypertrophic response. These data define an important Ca(2+)-dependent step in the pathway by which mutant sarcomere proteins trigger myocyte growth and remodel the heart, provide definitive evidence that environment influences progression of FHC, and suggest a rational therapeutic approach to this prevalent human disease.

New windows on the mechanism of action of K(ATP) channel openers

K(ATP) channel openers are a diverse group of drugs with a wide range of potential therapeutic uses. Their molecular targets, the K(ATP) channels, exhibit tissue-specific responses because they possess different types of regulatory sulfonylurea receptor subunits. It is well recognized that complex interactions occur between K(ATP) channel openers and nucleotides, but the cloning of the K(ATP) channel has introduced a new dimension to the study of these events and has furthered our understanding of the molecular basis of the action of K(ATP) channel openers.

The effect of minoxidil on keratocyte proliferation in cell culture

PURPOSE

To determine if minoxidil inhibits keratocyte proliferation in a nontoxic manner.

METHODS

Rabbit keratocytes were cultured in Eagle's minimum essential medium supplemented with fetal bovine serum. Minoxidil varying in concentration from 10(0) to 10(3) micrograms/ml was added to the culture medium and incubated for 7 days. The cultures were inspected for morphologic appearance and the cell number was determined at 1, 3 and 7 days after the addition of minoxidil. After 7 days of incubation, minoxidil was withdrawn from the cell culture medium and the cells were examined 3 and 7 days thereafter. In addition, a nonradioactive cytotoxic assay was performed to determine if toxicity is associated with the presence of minoxidil.

RESULTS

Minoxidil inhibited keratocyte proliferation in a dose-dependent fashion. 29% of control growth was achieved when keratocytes were cultured for 7 days in 10(3) micrograms/ml, whereas 82% control growth was achieved when keratocytes were cultured in 10(2) micrograms/ml of minoxidil. Intermediate concentrations between 10(2) and 10(3) micrograms/ml produced a linear decline in cell counts in a dose-dependent fashion. The concentration of minoxidil required for 50% control growth at 7 days extrapolated from the dose-response curve was 600 micrograms/ml. Upon withdrawal of minoxidil, cell counts returned to baseline for concentrations of 10(2) micrograms/ml or less. Phase contrast microscopy revealed that the presence of minoxidil was associated with intercellular separation, enlargement of cell bodies and elongated processes. After the withdrawal of minoxidil, the cells in all media reassumed the morphological features of normal keratocytes which included a regular fusiform shape and extensive intercellular contact. The nonradioactive cytotoxic assay revealed the lack of cytotoxicity at all concentrations of minoxidil based on a lack of lactate dehydrogenase release.

CONCLUSIONS

Minoxidil inhibits keratocyte proliferation by a nontoxic mechanism. It might be particularly useful for modulating corneal wound healing following excimer laser photorefractive keratectomy.

KATP channels regulate mitogenically induced proliferation in primary rat hepatocytes and human liver cell lines. Implications for liver growth control and potential therapeutic targeting

To determine whether K(ATP) channels control liver growth, we used primary rat hepatocytes and several human cancer cell lines for assays. K(ATP) channel openers (minoxidil, cromakalim, and pinacidil) increased cellular DNA synthesis, whereas K(ATP) channel blockers (quinidine and glibenclamide) attenuated DNA synthesis. The channel inhibitor glibenclamide decreased the clonogenicity of HepG2 cells without inducing cytotoxicity or apoptosis. To demonstrate the specificity of drugs for K(+) channels, whole-cell patch-clamp recordings were made. Hepatocytes revealed K(+) currents with K(ATP) channel properties. These K(+) currents were augmented by minoxidil and pinacidil and attenuated by glibenclamide as well as tetraethylammonium, in agreement with established responses of K(ATP) channels. Reverse transcription of total cellular RNA followed by polymerase chain reaction showed expression of K(ATP) channel-specific subunits in rat hepatocytes and human liver cell lines. Calcium fluxes were unperturbed in glibenclamide-treated HepG2 cells and primary rat hepatocytes following induction with ATP and hepatocyte growth factor, respectively, suggesting that the effect of K(ATP) channel activity upon hepatocyte proliferation was not simply due to indirect modulation of intracellular calcium. The regulation of mitogen-related hepatocyte proliferation by K(ATP) channels advances our insights into liver growth control. The findings have implications in mechanisms concerning liver development, regeneration, and oncogenesis.

Minoxidil inhibits proliferation and migration of cultured vascular smooth muscle cells and neointimal formation after balloon catheter injury

The goal of the study was to investigate the in vitro and in vivo inhibition of minoxidil on smooth muscle cell (SMC) proliferation and migration as well as neointimal formation. The in vitro effect of minoxidil was investigated by Boyden chamber assay and cell-cycle analysis. To evaluate the in vivo effect, we treated the animals with minoxidil in their drinking water before and after balloon catheter injury to carotid artery. Results showed that minoxidil inhibited SMC migration across type I collagen membrane in a dose-related manner (13.5% by 0.01 mg/ml; p < 0.05; 16.8% by 0.05 mg/ml: p < 0.01; 40.4% by 0.25 mg/ml; p < 0.001; and 65.8% by 1.25 mg/ml; p < 0.001). Minoxidil (0.8 mg/ml) increased the number of SMCs in G1 phase (p < 0.05) and decreased the number of SMCs in S phase (p < 0.001). In vivo minoxidil treatment reduced neointimal mass by 31.7% (120 mg/L) and 42.3% (200 mg/L), respectively. Data demonstrate that minoxidil inhibits vascular SMC proliferation and migration both in vitro and in vivo, and therefore may be useful to inhibit SMC hyperplasia that occurs in restenosis and other vascular diseases.

Short treatments of normotensive and hypertensive rats by angiotensin II and nitric oxide inhibitor induce an increase of noradrenaline sensitivity in isolated vena portae preparations

The aim of the study was to examine the influence of a short-term treatment of conscious Wistar Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP) by angiotensin II (ANG II) and by ANG II in combination with either l -NAME, HOE 140 or minoxidil on the mean arterial blood pressure (MABP) and the noradrenaline sensitivity in isolated portal vein preparations. MABP was significantly increased by ANG II treatment and ANG II plus l -NAME. However, it was slightly affected by ANG II in association with HOE 140, and significantly lowered by ANG II plus minoxidil. In control animals noradrenaline increased the frequency and the tone of contractile force. While ANG II enhanced the contractile response to noradrenaline, neither in combination with l -NAME, HOE 140 nor minoxidil prevented such an increase in the response to noradrenaline. In the presence of ergotamine, the contractile response to noradrenaline was completely blocked not only in control animals, but also in animals treated with ANG II alone or in combination with minoxidil. However, ergotamine (3 microm) failed to block completely the contractile response to noradrenaline in vessels from animals treated by ANG II in combination with l -NAME or HOE 140. These data suggest that ANG II causes an increase of noradrenaline sensitivity in the isolated portal vein of rat. l -NAME and HOE 140 unmask a contractile response to noradrenaline in the presence of ergotamine which seems to be mediated not only by alpha-adrenoceptors, but may be compensated by an endothelial relaxation.

Induction of rat hepatic aryl sulfotransferase (SULT1A1) gene expression by triamcinolone acetonide: impact on minoxidil-mediated hypotension

The hypotensive agent minoxidil (6-imino-1, 2-dihydro-1-hydroxy-2-imino-4-piperidinopyrimidine) depends upon aryl sulfotransferase (SULT1)-catalyzed sulfation for its bioactivation. Previous reports suggest that glucocorticoids induce class-specific SULT1 and isoform-specific SULT1A1 gene expression in rat liver. In the present study, rats were treated with the glucocorticoid triamcinolone acetonide (TA, 5 mg/kg/day i.p. x 3 days) or its vehicle, 2% Tween-20, prior to minoxidil, and subsequent effects on mean arterial pressure (MAP), heart rate (HR), and hepatic SULT1 gene expression were characterized. Minoxidil treatment (1.5 mg/kg) resulted in a steady decline in MAP values of 16.3 to 18.6% relative to basal control levels at 35 to 60 min following minoxidil injection. Pentachlorophenol (PCP, 40 micromol/kg i.p.), an inhibitor of SULT1 enzyme activity, effectively ablated the hypotensive effects of minoxidil. By contrast, pretreatment with TA significantly enhanced minoxidil-induced hypotension. Relative to vehicle-treated controls, TA-treated rats displayed a steeper rate of decline in MAP and more profound levels of hypotension with decreases in MAP following minoxidil administration of 27.8%. TA also produced significant increases in hepatic SULT1 mRNA expression (of 271%) and SULT1A1 immunoreactive protein levels (of 273%), relative to vehicle-treated controls. These results provide physiological evidence to support the biological relevance of SULT1A1 induction by glucocorticoids. The data indicate that steroid treatment induces SULT1A1 gene expression and, as a consequence, accentuates the hypotensive effects of minoxidil.

Inhibitory mechanism of pinacidil on catecholamine secretion from the rat perfused adrenal gland evoked by cholinergic stimulation and membrane depolarization

1. The present study attempted to investigate the effect of potassium channel openers on secretion of catecholamines (CA) evoked by cholinergic stimulation and membrane depolarization from rat isolated perfused adrenal gland. 2. The perfusion of pinacidil (30-300 microM) into an adrenal vein for 20 min produced dose-dependent inhibition of CA secretion evoked by acetylcholine (ACh; 5.32 mM), high K+ (56 mM), 1,1-dimethyl-4-phenylpiperazinium iodide (DMPP; 100 microM for 2 min), 3-(m-chloro-phenyl-carbamoyl-oxy)-2-butynyl trimethyl ammonium chloride (McN-A-343; 100 microM for 2 min), cyclopiazonic acid (CPA; 10 microM for 4 min) and methyl-1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethylphenyl)-pyri dine-5-carboxylate (Bay-K-8644; 10 microM for 4 min). 3. In the presence of minoxidil (100 microM), which is also known to be a potassium channel activator, CA secretory responses evoked by ACh, high potassium, DMPP, McN-A-343, Bay-K-8644 and CPA were also significantly depressed. 4. In adrenal glands preloaded with pinacidil (100 microM) in the presence of glibenclamide (GB; 1 microM), a specific blocker of ATP-regulated potassium channels, CA secretory responses evoked by ACh, high potassium, DMPP, McN-A-343, Bay-K-8644 and CPA were restored to a considerable extent of the control release as compared with that of pinacidil only. 5. These results suggest that pinacidil causes marked inhibition of CA secretion evoked by stimulation of cholinergic (both nicotinic and muscarinic) receptors, as well as by membrane depolarization, indicating that this effect may be mediated by inhibiting influx of extracellular calcium and release of intracellular calcium in the rat adrenomedullary chromaffin cells. Furthermore, these findings suggest that these potassium channel opener-sensitive membrane potassium channels also play a modulatory role in regulating CA secretion.

Atypical effect of minoxidil sulphate on guinea pig airways

The effects of minoxidil sulphate, an "atypical" K(ATP) channel opener, and bimakalim, a benzopyran-type classical K(ATP) channel opener, on guinea pig airways in vitro and in vivo and on isolated portal veins from rats and guinea pigs were compared. Minoxidil sulphate inhibited the spontaneous activity of isolated guinea pig and rat portal vein preparations with pD2 values of 7.83+/-0.08 and 7.14+/-0.03, respectively (Emax=100% in both preparations). Bimakalim caused a more potent inhibition with pD2 values of 8.80+/-0.05 and 8.20+/-0.04, respectively (Emax=100% in both preparations). Minoxidil sulphate reduced the spontaneous tone of isolated guinea pig tracheal rings with a pIC50 value of 3.92+/-0.02 and the same efficacy as isoprenaline. Bimakalim was more potent (pIC50=7.25+/-0.02) but less efficacious (Emax=75% of the Emax of isoprenaline). The airway relaxant effect of bimakalim, but not minoxidil sulphate, was antagonised by glibenclamide (pA2=7.50) at concentrations above 0.1 microM. Bombesin-induced bronchoconstriction in anaesthetised, ventilated, normoreactive guinea pigs (measured as increase in total lung resistance) was dose-dependently reversed by intratracheally (i.t.) administered bimakalim (ED50=4 microg/kg; Emax=92% of maximally possible inhibition), but not by minoxidil sulphate, at doses up to 1 mg/kg i.t. In the same animals, following i.t. administration of higher doses, both minoxidil sulphate and bimakalim reduced blood pressure. Airways hyperreactivity to histamine induced by acute treatment of guinea pigs with immune complex was dose-dependently reversed by bimakalim (ED50=0.5 microg/kg i.t., Emax=100%). This effect was antagonised by glibenclamide (30 mg/kg i.v.). Minoxidil sulphate had a biphasic effect on airways hyperreactivity: at 1 microg/kg i.t., airways hyperreactivity was augmented, whereas at doses above 3.2 microg/kg i.t. it caused reversal of airways hyperreactivity. Both of the effects of minoxidil sulphate were insensitive to glibenclamide (30 mg/kg i.v.). It is concluded that the pharmacological profile of minoxidil sulphate in guinea pig airways is completely different from that of classical K(ATP) channel openers such as bimakalim. Minoxidil sulphate is either only weakly active or even inactive at K(ATP) channels in guinea pig airways or interacts with these channels in a different manner. The current results are consistent with there being differences between the K(ATP) channels in airways and blood vessels.

Comparison of skin permeability of drugs in mice and human cadaver skin

In vitro percutaneous absorption of four antihypertensive drugs were carried out across the mice and human cavader skin in order to compare their skin permeability. An interesting trend was noticed in these experiments. Poorly water soluble drug prazosin hydrochloride showed 13 times enhanced flux in the mice skin whereas the steady-state flux of the water soluble drug propranolol hydrochloride was almost same in both human cadaver and mice skin. The permeation rate of prazosin hydrochloride and propranolol hydrochloride through the human cadaver skin fluctuated widely over time, but in mice skin, distinct trends were noticed. The study indicates that the overall permeation rate in mice skin is higher than that in the cadaver skin and the meeting of the target-flux in mice skin does not guarantee its good permeability in human skin.

Minoxidil and male-pattern alopecia: a potential role for a local regulator of sebum secretion with vasoconstrictive effects?

Regulation of the hair cycle takes place at the pilo-sebaceous unit with the sebaceous gland as a sex hormone-dependent part. Although minoxidil stimulates proliferation of follicular cells and activation of prostaglandin endoperoxide synthase-1, it was suggested that other mechanisms, such as an increase in the local blood flow, might mediate the drug effect on hair growth. If that is the case, it is possible that minoxidil counteracts some vasoconstrictive mediator of male-pattern alopecia. This hypothetical vasoconstrictive mediator X would have to meet some criteria: (I) vasoconstriction both in the general circulation and in the hair-growing skin; (II) local vasoconstrictive activity in the hair growing skin should be related to the circulating testosterone level; (III) only an increase in the local mediator X activity causes male-pattern alopecia, since hypertensive patients are not balder than expected. The sebaceous gland is a possible place of the mediator X secretion since it is a sex-hormone-dependent part of the pilo-sebaceous unit. ET-1 might be a suitable candidate for the mediator X, since male hormones raise ET-1 plasma levels and female hormones lower them. The speculation presented here is that ET-1, beside vasoconstriction in the general circulation, might also regulate the sebum secretion, by triggering contractions of the myoepithelial cells. This hypothetical mechanism would normally remain confined to the sebaceous gland. During puberty, sex hormones stimulate growth of sebaceous glands in both sexes. In women hypertrophied sebaceous glands under estrogen control would not increase its ET-1 content, while in men, testosterone would increase ET-1 secretion that might affect the neighboring arterioles. Induced vasoconstriction might reduce the hair growth and promote hair loss. If ET-1 plays the described role, then an ET-1 antagonist, i.e. bosentane, should also have some hair-growing properties.

Effects of vasoactive topical agents on the survival of dorsal skin flaps in rats

OBJECTIVE

To evaluate 3 vasoactive topical agents regarding their ability to improve the survival of random skin flaps in rats.

METHOD

Thirty-five adult Sprague-Dawley rats had a single 9 x 2 cm random skin flap raised with topical application of a white petroleum ointment (control group), prostaglandin E2, minoxidil, or nitroglycerin to the flap. The effect of the agents on the viability of the flaps was evaluated.

RESULTS

The control group had an average survival area of 60.8% +/- 7.9%. The nitroglycerin and minoxidil groups were not significantly different, with an average area of survival of 60.1% +/- 8.1% and 63.3% +/- 4.7%, respectively. The prostaglandin E2 group had average area of survival of 74.2% +/- 10.5% (P = 0.002).

CONCLUSION

Prostaglandin E2 demonstrated a significant increase in flap survival. Nitroglycerin ointment and minoxidil had no beneficial effects when compared with control.

Minoxidil increases 17 beta-hydroxysteroid dehydrogenase and 5 alpha-reductase activity of cultured human dermal papilla cells from balding scalp

Minoxidil is known to induce hair growth in male pattern baldness, for which development androgen plays a central role. We studied the effect of minoxidil on testosterone metabolism by cultured dermal papilla cells from balding or nonbalding scalp and dermal fibroblasts. In all three groups, 17beta-hydroxysteroid dehydrogenase activity was much higher than 5alpha-reductase activity. Minoxidil increased 17beta-hydroxysteroid dehydrogenase activity by nearly 40% (P < 0.001) in dermal papilla cells of balding scalp, whereas the effect was less marked in dermal papilla cells from nonbalding scalp and dermal fibroblasts. 5alpha-Reductase activity was also slightly increased by minoxidil in dermal papilla cells from balding scalp. Again, the effect on 5alpha-reductase activity was insignificant in the other two groups of cells. Whether such modification of testosterone metabolism in dermal papilla cells of balding scalp by minoxidil is related to its therapeutic effect remains unknown.

The induction by topical minoxidil of increased fenestration in the perifollicular capillary wall

We report the induction by topical minoxidil of increased fenestration in the perifollicular capillary wall. Male 30-day-old Wistar rats were divided into two groups, i.e. an experimental group which received 4% minoxidil solution topically on the dorsal skin, and a control group which received only vehicle solution topically. Using transmission electron microscopy, follicular and subepidermal capillaries and dermal fibres were compared between both groups. There were no obvious differences in subepidermal capillaries or dermal fibres between the two groups. However, topically applied minoxidil increased fenestration in follicular capillary walls around anagen hair bulbs.

Quinine-induced inhibition of gastrointestinal transit in mice: possible involvement of endogenous opioids

The effect of quinine, a cinchona alkaloid, was studied on gastrointestinal transit in mice. Intraperitoneal (i.p.) administration of quinine inhibited the intestinal propulsion of a charcoal suspension at a dose of 100 mg/kg, comparing favorably with 5 mg/kg morphine. In an attempt to probe into the mechanism underlying this inhibition, a possible modulation by minoxidil (1 mg/kg, p.o.) and glibenclamide (1 mg/kg, p.o.), the drugs that, respectively, open and close ATP-sensitive K+ channels was tested on gastrointestinal transit in animals treated or not with quinine or morphine. While minoxidil produced no significant change of normal transit, glibenclamide significantly increased it. However, both drugs blocked the quinine-induced reduction in gastrointestinal transit. In contrast, the inhibitory effect of morphine on gastrointestinal transit was not modified by either drug. The effects of quinine as well as of morphine on gastrointestinal transit were significantly antagonized by naloxone (2 mg/kg, s.c.), a mu-opioid receptor antagonist but not by yohimbine (1 mg/kg, i.p.), an alpha2-adrenoceptor antagonist. Furthermore, quinine at a lower dose (25 mg/kg) that showed no per se effect on gastrointestinal transit, significantly potentiated the response to 2.5 mg/kg morphine. Although the role of ATP-sensitive K+ channels in the action of quinine and morphine was not clarified by the present results, a possible involvement of endogenous opioid(s) in the quinine-induced inhibition of gastrointestinal transit can be suggested.