Stimulation of Cl conductance by minoxidil sulfate and K conductance by minoxidil in eccrine clear cells

Minoxidil sulfate (MXS), an antihypertensive agent and hair growth promoter, has been reported to stimulate K channels in vascular smooth muscle cells. We now report that MXS stimulates whole cell Cl currents, whereas minoxidil (MX) stimulates K currents in dissociated eccrine clear cells. Using whole cell clamp techniques we observed that: 1) 1 mM MXS stimulated sweat secretion in vitro; 2) MXS depolarized the membrane potential by as much as 40 mV; 3) MXS stimulated membrane conductance, increased inward current and shifted the reversal potential to the right when physiological electrolyte solutions were used; 4) in symmetrical Cl (Cl/Cl) solutions without permeable cations, MXS induced outwardly rectifying current-voltage (I-V) relationships; 5) in the Cl/Cl solutions, the MXS-induced current responses to imposed voltage pulses showed time-dependent activation, especially at the depolarizing potentials; 6) the reversal potential of the MXS-stimulated I-V curves in the Cl/Cl solutions shifted to the right by 55 mV when [Cl] in the bath was decreased from 157 to 7 mM; 7) MXS did not elevate cytosolic Ca or cAMP, although prolonged exposure to a Ca-free solution abolished the effect of MXS and 8) MXS-stimulated conductance was partially inhibited by diphenylamine-2-carboxylic acid, a blocker of Cl channels. The data suggest that MXS stimulates Cl channels, most likely depolarization-activated, outwardly rectifying channels. In contrast, the parent compound MX hyperpolarized the membrane potential and stimulated outward current without elevating cytosolic Ca and was independent of extracellular Ca, suggesting that MX stimulates Ca-insensitive K currents.

Possible presence of the ATP-sensitive K+ channel in isolated spinal dorsal horn neurons of the rat

The ATP-sensitive K+ channel (KATP channel) is a K+ channel inhibited by cytoplasmic ATP. It was originally found in cardiac cells and recently in neuronal cells. Here, we present evidence indicating that the KATP channel also exists in spinal dorsal horn neurons: membrane currents were recorded by whole-cell voltage-clamp in spinal dorsal horn neurons isolated from young rats. The outward current was augmented by KATP channel activators nicorandil and minoxidil and reduced by the blocker glibenclamide. This glibenclamide-induced change in the current was augmented when the intracellular ATP was lowered and the reversal potential was shifted according to the external K+ concentration.

Effect of minoxidil on the mobility and differentiation of cultivated human keratinocytes

The mode of topical action of minoxidil (U-10,858, CAS 38304-91-5) ist not entirely clear. The influence of minoxidil on the ultimate differentiation of keratinocytes was investigated. Human keratinocytes (HaCaT-cells) were incubated with minoxidil containing culture medium (10-250 micrograms/ml). Minoxidil inhibited in a concentration dependent manner cell mobility whereas the adhesion area and the cell circumference were increased. The minoxidil treated cultures had a higher desmosome density compared to parallel control cultures and they expressed the suprabasal keratins 1 and 10 (indicating progress in differentiation) earlier and to a larger extent than the controls. Keratins were revealed immunohistochemically and by two-dimensional polyacrylamide gel electrophoresis. The results suggest that minoxidil supports the differentiation of human keratinocytes.

Inhibition of cultured human RPE cell proliferation and lysyl hydroxylase activity by hydroxy derivatives of minoxidil

PURPOSE

To examine the antiproliferative and lysyl hydroxylase suppressing effects of 3'-hydroxyminoxidil and 4'-hydroxyminoxidil, derivatives of minoxidil devoid of the antihypertensive effect, on human retinal pigment epithelial (RPE) cells in culture.

METHODS

Subconfluent and confluent cultures of RPE cells, exposed to 0.01 to 5 mM 3' or 4'-hydroxyminoxidil for 15 minutes to 7 days, were examined for proliferation, viability, and morphologic changes. Lysyl hydroxylase activity in confluent cultures exposed to 1 mM 3'- or 4'-hydroxyminoxidil was determined by measuring the amount of 3H2O released from L-(4,5-3H)lysine-labeled unhydroxylated procollagen substrate after vacuum distillation.

RESULTS

Both compounds inhibited the proliferation of subconfluent cultures of RPE cells in a dose-dependent fashion. The 50% effect occurred at 0.25 mM for 3'-hydroxyminoxidil and 0.5 mM for 4'-hydroxyminoxidil. The antiproliferative effect was detectable within 24 hours, required a minimum 1-hour exposure, and persisted even after the drug was removed from the culture medium. Cell viability experiments provided no evidence for toxicity. In contrast, the number of cells at confluent density was not affected. Both 3'-hydroxyminoxidil and 4'-hydroxyminoxidil suppressed lysyl hydroxylase activity by 72%.

CONCLUSIONS

The structure of minoxidil can be altered to reduce the antihypertensive activity while preserving the antiproliferative and lysyl hydroxylase suppressing effects. The hydroxy derivatives of minoxidil may be useful in the treatment of proliferative vitreoretinopathy, a disease with unwanted proliferation of RPE cells.

Minimum structural requirements for minoxidil inhibition of lysyl hydroxylase in cultured fibroblasts

The structural features of minoxidil contributing to its inhibitory effect on lysyl hydroxylase in cultured fibroblasts were investigated. Minoxidil analogs in which the pyrimidine ring (two nitrogens) was replaced with a pyridine ring (one nitrogen) or a sym-triazine ring (three nitrogens) suppressed lysyl hydroxylase activity without affecting prolyl hydroxylase activity, as did an analog in which the piperidine ring was replaced with an N,N-diethyl group. By contrast, minoxidil analogs bearing an N-monoalkyl (ethyl or butyl) group in place of the piperidine substituent failed to suppress lysyl hydroxylase activity. The results indicate that nitroxides of pyridine and triazine, in addition to pyrimidine, having an ortho amino group can act as specific inhibitors of lysyl hydroxylase in the cell. The minimum structural requirement for inhibitory activity appears to be an organic moiety containing a tertiary nitrogen para to the nitroxide oxygen, a condition that is best fulfilled by the piperidine ring in minoxidil. Hydroxylation of minoxidil at the 3 or 4 position of the piperidine ring had no impact on its ability to inhibit the post-translational hydroxylation of lysine during collagen biosynthesis. Fibroblasts treated with minoxidil, 3'-hydroxyminoxidil, or 4'-hydroxyminoxidil synthesized a collagen specifically deficient in hydroxylysine by approximately 70%, which completely accounted for the diminished lysyl hydroxylase activity. The percentage of total proteins synthesized as collagen was reduced minimally by minoxidil but not by 3'- or 4'-hydroxyminoxidil. The studies offer a potential means for therapeutic intervention of excessive collagen deposition during fibrosis, using minoxidil or preferably its hydroxy derivatives to limit the supply of hydroxylysine for collagen crosslink formation.

Regulation of lysyl oxidase mRNA in dermal fibroblasts from normal donors and patients with inherited connective tissue disorders

Lysyl oxidase (LO) is an extracellular copper-dependent enzyme that catalyzes the initial reaction in the formation of lysine or hydroxylysine-derived crosslinks during collagen biosynthesis. We have isolated a cDNA for human LO from skin fibroblast poly(A+)RNA by PCR using primers based on the recently published sequence of human LO. This cDNA probe detects a major mRNA of 4.2 kb on Northern blots of RNA from normal fibroblasts. The level of LO mRNA was not significantly affected by cell density or by ascorbate treatment. Treatment of skin fibroblasts with hydralazine (50 microM), which increases the mRNAs for both the alpha and the beta subunits of prolyl hydroxylase (PH) and the mRNAs for lysyl hydroxylase, also increased LO mRNA by fourfold over a 72-h time course. In contrast, hydralazine dramatically decreased the mRNAs for alpha 1(I) collagen. Administration of minoxidil (500 microM), which specifically decreases LH activity without affecting PH activity or collagen biosynthesis in skin fibroblasts, stimulated the level of LO mRNA. Neither the administration of penicillamine (100 microM), which interferes with collagen cross-linking, nor the administration of beta-aminopropionitrile, which is a strong irreversible inhibitor of LO, to fibroblasts significantly changed the levels of LO mRNA over a 72-h time course. However, bleomycin (0.6 microgram/ml) significantly decreased the 4.2-kb LO mRNA in contrast to the levels of the alpha 1(I) collagen mRNAs, which were unchanged. No significant change was observed in the steady-state levels of LO mRNAs in fibroblasts isolated from patients with certain connective tissue disorders, including Marfan syndrome, Menkes disease, cutis laxa, and pseudoxanthoma elasticum.

Renin-angiotensin system and minoxidil-induced cardiac hypertrophy in rats

Besides cardiac volume overload, cardiac sympathetic activity and the renin-angiotensin system (RAS) are activated by arterial vasodilators such as minoxidil. To evaluate the possible involvement of the RAS in the development of minoxidil-induced cardiac hypertrophy, we assessed in normotensive rats minoxidil-induced changes in cardiac and plasma renin activity (PRA) and the potential of chronic treatment with the angiotensin-converting enzyme (ACE) inhibitor enalapril and the nonpeptide angiotensin II receptor blocker losartan to prevent minoxidil-induced cardiac hypertrophy. PRA increased in parallel with the increase in cardiac filling pressures and development of cardiac hypertrophy, whereas the increase in cardiac renin activity was delayed as compared with these changes. Losartan did not decrease left ventricular end-diastolic pressure (LVEDP) but prevented the remodeling of the heart by minoxidil. In contrast, enalapril nearly normalized LVEDP but did not affect the hypertrophic response of the heart. The losartan data indicate that the RAS is involved in the minoxidil-induced cardiac hypertrophy either directly (e.g., by mediating the hypertrophic response of the heart to cardiac volume overload) or indirectly (e.g., by potentiating cardiac sympathetic activity). The ineffectiveness of enalapril has no obvious explanation but may possibly indicate ineffective blockade of angiotensin II formation in the heart in this model.

Synergistic effects of glyburide and U-37883A, two structurally different vascular ATP-sensitive potassium channel antagonists

Glyburide, a sulfonylurea, and U-37883A, a guanidine (4-Morpholinecarboximidine-N-1-Adamantyl-N' cyclohexylhydrochloride), have been previously characterized as antagonists of the vascular ATP-sensitive K+ channels (KATP). In this report, the in vitro interaction between these two chemically distinct KATP antagonists was investigated using isolated rabbit mesenteric artery. The KATP antagonism was functionally studied as the inhibition of vasodilation produced by various KATP openers as follows: pinacidil (1 microM), minoxidil sulfate (5 microM), cromakalim (0.5 microM) and RP-49356 (1 microM). Glyburide alone produced inhibition in the concentration range of 50 to 500 nM with the glyburide IC50 ranging from 72 to 148 nM. U-37883A alone produced inhibition in the concentration range of 0.5 to 5 microM, with the U-37883A IC50 ranging from 0.78 to 1.4 microM. In the presence of a threshold U-37883A concentration of 0.5 microM, the glyburide inhibition dose-response curve against pinacidil was significantly shifted to the left and the glyburide IC50 was lowered from 72 to 3.9 nM, representing an 18-fold decrease. Similarly, in the presence of a threshold glyburide concentration of 50 nM, the U-37883A inhibition dose-response curve against pinacidil was significantly shifted to the left and the U-37883A IC50 was lowered from 780 to 96 nM, representing an eightfold decrease. Thus, glyburide and U-37883A potentiated each other's effects as KATP blockers. This synergistic interaction between glyburide and U-37883A was observed independently of the pinacidil, cromakalim or minoxidil sulfate used to produce vasodilation.(ABSTRACT TRUNCATED AT 250 WORDS)

4-morpholinecarboximidine-N-1-adamantyl-N'-cyclohexylhydrochloride (U-37883A): pharmacological characterization of a novel antagonist of vascular ATP-sensitive K+ channel openers

This study describes the in vitro and in vivo characteristics of a guanidine 4-morpholinecarboximidine-N-1-adamantyl-N'-cyclohexyl-hydroc hloride (U-37883A), as an antagonist of vascular ATP-sensitive K+ channels (KATP). In isolated rabbit mesenteric artery, the antagonistic effects of U-37883A (0.5-5 microM) were studied against vasorelaxation produced by cromakalim (0.5 microM), minoxidil sulfate (5 microM), pinacidil (1 microM) and RP-49356 (1 microM). The dose-response curves for U-37883A against all four potassium channel openers were similar with U-37883A, IC50S ranging from 0.78 to 1.4 microM, suggesting that U-37883A is producing inhibition by acting at a step that is common to all four potassium channel openers during their activation of the vascular KATP. In contrast, U-37883A at 10 microM did not inhibit relaxation dose-response curves by nitroglycerine, forskolin or D600. U-37883A (1 or 10 microM) effectively inhibited as well as reversed 42K efflux-stimulated by cromakalim (1 microM) or minoxidil sulfate (5 microM). Finally, U-37883A (3 mg/kg i.v.) was found to inhibit significantly as well as reverse hypotension produced by minoxidil (1 mg/kg i.v. or 3 mg/kg p.o.), cromakalim (0.5 mg/kg p.o.) and pinacidil (0.3 mg/kg i.v.) in rats, cats and dogs. In contrast, the in vivo responses to phenylephrine, nitroglycerine, sodium nitroprusside or isoproterenol were not altered. U-37883A thus appears to be the first nonsulfonylurea shown to block consistently and selectively the in vitro as well as the in vivo pharmacological responses to various potassium channel openers. This structurally novel KATP antagonist therefore would be useful for further characterizing the mechanisms of pharmacological modulation of the KATP in a variety of cell systems.

Enhanced in vitro hair growth at the air-liquid interface: minoxidil preserves the root sheath in cultured whisker follicles

Inasmuch as hair follicles are difficult to maintain in culture, the study of hair biology using cultured hair follicles has met with only limited success. In our attempts to solve the problem of follicle degeneration, we cultured follicles at the air-surface interface on a modified collagen matrix (Gelfoam). In follicles cultured at the air-surface or submerged, we examined follicular morphology, hair shaft growth, sulfotransferase levels, cysteine incorporation, an expression of a tissue inhibitor of metalloproteinase (TIMP), and ultra-high sulfur keratin (UHSK). Follicles cultured at the air-liquid interface produced a 2.7-fold increase in hair growth and maintained an anagen-like morphology. Substrates such as nylon mesh seeded with fibroblasts, Full Thickness Skin, or 5-microns polycarbonate filter also supported hair growth, whereas Gelfilm, GF-A glass filter, filter paper, or 1-micron polycarbonate filter did not. The UHSK expression was significantly higher in the air-liquid interface cultures compared to the submerged culture. Several potassium channel openers, including minoxidil, a minoxidil analog, and the pinacidil analog (P-1075), all stimulated significant cysteine incorporation in follicles. Minoxidil and its analog specifically preserved the follicular root sheath, in contrast to P-1075 which did not, indicating a difference in the two drug types. The preservation of the root sheath was measured by increased TIMP expression and sulfotransferase activity and indicates that the root sheath is a target tissue for minoxidil. Our results show that follicles cultured at the air-liquid interface maintain a better morphology and produced greater hair growth than follicles cultured on tissue culture plastic.

In vitro inhibition of collagen formation by 2,4-pyridine dicarboxylate and minoxidil in rabbit corneal fibroblasts

Two anti-fibrotic agents were evaluated in vitro for potential application in trabeculectomy. The rate of collagen formation by cultured rabbit corneal fibroblasts was determined by [3H]proline uptake and hydroxylation assay. Incubation of fibroblasts, for 96 hours, with 16 mM 2,4-pyridine dicarboxylic acid (2,4-PDCA), a competitive inhibitor of prolyl 4-hydroxylase, decreased [3H]OH-proline formation from control by 28.2 +/- 3.9%; (average +/- S.E.M), whereas 10 mM minoxidil, an antihypertensive pyrimidine oxide and a lysyl hydroxylase inhibitor, induced a decrease of 17.3 +/- 4.5%. Incubating fibroblasts with a mixture of the two inhibitors, 16 mM 2,4-PDCA and 10 mM minoxidil, resulted in a further decrease in [3H]proline incorporation of 40.7 +/- 5.1%. After 96 hours of incubation with the inhibitors, rabbit corneal fibroblast growth was decreased from control by 17.2 +/- 4.2% and 10.5 +/- 4.5% for 16 mM 2,4-PDCA and 10 mM minoxidil, respectively. These effects were dose dependent. The results suggest that both 2,4-PDCA and minoxidil have an inhibitory effect on collagen formation and may be useful in delaying surgical wound healing.

Ionic mechanism of minoxidil sulfate-induced shortening of action potential durations in guinea pig ventricular myocytes

Patch-clamp techniques were used to study pharmacological effects of minoxidil sulfate (MNXS) on the membrane currents of enzymatically isolated guinea pig ventricular myocytes. In the whole-cell current-clamp mode, MNXS (100 microM) shortened the action potential duration without affecting the resting membrane potential. This action was antagonized in part by 1 microM glibenclamide, a specific blocker of ATP-sensitive K+ channel. Under the whole-cell voltage-clamp condition, MNXS increased the time-independent outward current, in a dose-dependent manner, at voltages more positive to -73.5 mV. This MNXS-induced outward current was inhibited completely by 1 microM glibenclamide. In inside-out patch membranes, MNXS (100 microM) applied to the cytosolic side produced a reversible activation of ATP-sensitive K+ channels. This MNXS-dependent increase in the single-channel activity was abolished by increasing the ATP concentration to 3 mM or by adding 1 microM glibenclamide. Even after complete rundown of the channel activity in inside-out patches, MNXS could reactivate in part the channel in 22 of 35 patches. In addition, MNXS was found to suppress whole-cell L-type Ca++ channel currents in a dose-dependent manner. This MNXS effect on Ca++ currents was not antagonized by 1-3 microM glibenclamide. We conclude that MNXS shortens the cardiac action potential duration by both increasing ATP-sensitive K+ channel currents and decreasing L-type Ca++ channel currents.

Minoxidil inhibits ocular cell proliferation and lysyl hydroxylase activity

PURPOSE

To examine the antiproliferative and lysyl hydroxylase-suppressing effects of minoxidil on cultured proliferating and density-arrested human retinal pigment epithelial cells (hRPE) and Tenon's capsule fibroblasts (hTCF).

METHODS

Proliferating and density-arrested hRPE and hTCF, exposed to minoxidil (0.1-5 mM) for 15 min to 7 days, were examined by proliferation assays, [3H]thymidine incorporation, trypan-blue exclusion, and phase-contrast microscopy. The lysyl hydroxylase-suppressing effects were examined in confluent hRPE exposed to minoxidil (0.01-1 mM) using L-[4,5-3H]-lysine-labeled procollagen substrate and measuring the amount of tritium released as 3H2O after vacuum distillation.

RESULTS

Minoxidil (0.1-5 mM) inhibited the proliferation of subconfluent cultures of hRPE and hTCF in a dose-dependent manner with a half-maximal effect at 1.5 and 2.5 mM, respectively. The antiproliferative effect, detectable within 24 hr, occurred with a limited exposure period and persisted even after removal of minoxidil from the culture medium. In contrast, 1-5 mM minoxidil had minimal effect on density-arrested hRPE and hTCF. However, at doses above 3 mM, although minoxidil had no effect on the number of density-arrested hRPE, morphologic and viability experiments indicated signs of cytotoxicity. Minoxidil (0.1-1 mM) caused a maximum of 71% reduction in the activity of lysyl hydroxylase, an enzyme needed for stable cross-links in collagen.

CONCLUSIONS

Minoxidil may be a useful drug for the treatment of conditions such as proliferative vitreoretinopathy and bleb scarring after trabeculectomy, disorders with unwanted cell proliferation and collagen production.

Mechanism of activation of K+ channels by minoxidil-sulfate in Madin-Darby canine kidney cells

We studied the mechanism of K+ channel activation by minoxidil-sulfate (MxSO4) in fused Madin-Darby canine kidney (MDCK) cells. Patch-clamp techniques were used to assess single channel activity, and fluorescent dye techniques to monitor cell calcium. A Ca(2+)-dependent inward-rectifying K+ channel with slope conductances of 53 +/- 3 (negative potential range) and 20 +/- 3 pS (positive potential range) was identified. Channel activity is minimal in cell-attached patches. MxSO4 initiated both transient channel activation and an increase of intracellular Ca2+ (from 94.2 +/- 9.1 to 475 +/- 12.6 nmol/liter). The observation that K+ channel activity of excised inside-out patches was detected only at Ca2+ concentrations in excess of 10 mumol/liter suggests the involvement of additional mechanisms during channel activation by MxSO4. Transient K+ channel activity was also induced in cell-attached patches by 10 mumol/liter of the protein kinase C activator 1-oleoyl-2-acetyl-glycerol (OAG). OAG (10 mumol/liter in the presence of 1.6 mmol/liter ATP) increased the Ca2+ sensitivity of the K+ channel in inside-out patches significantly by lowering the Km for Ca2+ from 100 mumol/liter to 100 nmol/liter. The channel activation by OAG was reversed by the protein kinase inhibitor H8. Staurosporine, a PKC inhibitor, blocked the effect of MxSO4 on K+ channel activation. We conclude that MxSO4-induced K+ channel activity is mediated by the synergistic effects of an increase in intracellular Ca2+ and a PKC-mediated enhancement of the K+ channel's sensitivity to Ca2+.

Minoxidil. Update on its clinical role

The study and common use of minoxidil have legitimized research in common baldness. Prior to this time, with rare exception, the field was dominated by charlatans and "snake oil merchants." Minoxidil has opened the door to scientific inquiry and allowed support of serious laboratory investigation. Minoxidil is the first "generation" of hair-growing agents. We hope that succeeding generations will fulfill our wildest tonsorial dreams.

Potassium channel openers stimulate DNA synthesis in mouse epidermal keratinocyte and whole hair follicle cultures

We have conducted studies using primary mouse epidermal keratinocyte and whole hair follicle cultures to investigate the mechanism of the hypertrichotic activity of potassium channel openers. In a time course study, the extent of stimulation of epidermal keratinocyte DNA synthesis by minoxidil increased as the rate of DNA synthesis in control cultures declined. Minoxidil stimulation of DNA synthesis in 7-day cultures required prolonged (> 1 day) exposure to the agent. Pinacidil and diazoxide also stimulated DNA synthesis in mouse epidermal keratinocyte cultures. In addition, minoxidil, pinacidil, diazoxide, and cromakalim stimulated DNA synthesis in whole-organ cultures of mouse hair follicles. These results suggest that potassium channel openers retard the loss of proliferative activity of differentiating keratinocytes and support the hypothesis that these agents stimulate hair growth through a direct effect on hair follicles.

Vascular pharmacology of ATP-sensitive K+ channels: interactions between glyburide and K+ channel openers

This study in isolated rabbit superior artery (RMA) investigated the interactions between glyburide, a known blocker of vascular ATP-sensitive K+ channels (KATP), and several chemically diverse potassium channel openers (PCOs): minoxidil sulfate (MNXS; 5 microM), pinacidil (1 microM), cromakalim (0.5 microM) and RP-49356 (1 microM; a PCO from Rhône Poulenc). Relaxation time courses for these PCOs were obtained in norepinephrine (NE; 5 microM)-precontracted RMA, and the concentrations of PCOs found to be equipotent to each other in terms of the degree of maximum relaxation (about 80%) and the time course of relaxation (within 15 min) were chosen for further study. This was taken as a functional indicator of a similar degree as well as similar kinetics of K+ channel opening by these PCOs. Pretreatment with glyburide (10-500 nM) produced a dose-dependent inhibition of the PCO relaxation time course. The glyburide IC50s against pinacidil, MNXS and RP-49356 were statistically similar and ranged from 72-79 nM. The glyburide IC50 against cromakalim was a modest 2-fold higher, at 148 nM. In contrast, pretreatment with charybdotoxin (200 nM) produced no significant inhibition of the maximum relaxation produced by these PCOs. Furthermore, glipizide, a sulfonylurea that is 10- to 25-fold less potent than glyburide for insulin secretion, was found to be 20- to 30-fold less potent than glyburide as a vascular KATP antagonist. These data suggest a mechanistic model in which these structurally diverse PCOs share a common critical step in the sequence of events leading to the KATP opening, and that glyburide interferes with this common critical step to produce a similar type of blockade against all four PCOs. Interaction studies with glyburide and pinacidil demonstrated 15 min to be the optimal pretreatment time for glyburide to produce maximal inhibition. Glyburide also reversed existing pinacidil relaxation regardless of the degree of pre-existing relaxation. These data suggest that glyburide is able to produce its blockade regardless of the state of K+ channel activation. Studies on the effect of pH (6.4 vs. 7.3) showed that at acidic pH, pinacidil became less effective and the effectiveness of glyburide was significantly enhanced, whereas the actions of D600 remained unchanged. These data suggest the effects of both openers and blockers of the KATP are strongly pH dependent.

Transcutaneous minoxidil in the treatment of erectile dysfunctions in spinal cord injured men

We have tested the erectile effect of a topical applied drug (Minoxidil) in 15 spinal cord injured men. Minoxidil exerts a direct relaxant effect on arterial smooth muscles. This topical vasodilatory agent (1 ml of a 2% solution) was applied on the skin of the penile shaft. Increases in diameter and rigidity were measured with the RigiScan device (Dacomed Minneapolis, Minnesota). A total of 4 paraplegic men with a complete dorsal level lesion reported a positive erectile response. 3 of these 4 patients preferred to continue with this noninvasive treatment compared to prostaglandin E1 intracavernous injections. In our study no side effects were emerged and minoxidil proved to be well tolerated at the cutaneous level of the penis. Our results indicate that this treatment should be tested in spinal cord injured men before a invasive therapy is initiated.

Organ culture of human hair follicles in serum-free medium

Human hair follicles were cultured in serum-free media at 31 degrees C in an atmosphere containing 95% O2 and 5% CO2. Results showed that the length of the cultured hair increased time dependently for 96 h. Histological findings revealed that the hair germinative cells maintained their normal morphology throughout the 96 h culture period. DNA synthesis in the hair bulb also increased time dependently for 96 h. Autoradiographs of 3H-thymidine-labelled follicles indicated that they were localized in the germinative cells below Auber's critical line. The effects of minoxidil sulphate on DNA synthesis in this culture system were concentration dependent. Minoxidil sulphate at concentrations of 10(-10), 10(-9) and 10(-8) M significantly increased DNA synthesis compared with DNA synthesis in the control medium. Autoradiographs of the follicles cultured in 10(-10) M minoxidil sulphate showed that 3H-thymidine localized primarily in the germinative cells below Auber's critical line. These results suggest that this organ culture system may be useful for studying DNA synthesis by hair germinative cells in serum-free media.

Characterization of a partial cDNA for lysyl hydroxylase from human skin fibroblasts; lysyl hydroxylase mRNAs are regulated differently by minoxidil derivatives and hydralazine

Lysyl hydroxylase (LH) is an essential enzyme in collagen biosynthesis that catalyzes the formation of hydroxylysine required for intermolecular crosslinking of collagen. We have isolated a partial (2.2-kb) cDNA for LH from human skin fibroblasts using PCR. DNA sequencing revealed 72% homology of the human coding sequence with the chick LH sequence at the nucleotide level and 76% homology predicted at the amino acid level. The LH cDNA hybridized strongly with two mRNA species of 2.4 and 3.4 kb on Northern blots of normal fibroblast RNA. Administration of minoxidil decreased both mRNA species without affecting levels of the mRNAs for the beta subunit of prolyl 4-hydroxylase (PH) or alpha 1(I) collagen. Two derivatives of minoxidil (3' hydroxyminoxidil and 4' hydroxyminoxidil) produced similar decreases in LH mRNAs. In contrast hydralazine increased the mRNAs for LH in parallel with its previously reported effect on the mRNA for the beta subunit of PH. This effect is accompanied by virtual elimination of the alpha 1(I) collagen mRNAs. These results on the action of minoxidil and hydralazine at the pretranslational level correlate well with their previously reported effect on enzyme activity and collagen biosynthesis and indicate that changes in steady-state mRNA levels can account directly for changes at the protein level. Moreover, the unique action of minoxidil in specifically decreasing LH mRNAs contrasts with the less specific stimulatory effects of hydralazine and suggests that these pharmaceuticals are regulating expression of LH at a pretranslational level by different mechanisms.

Development of hypertension in animals with reduced total peripheral resistance

The object of the present study was to determine whether deoxycorticosterone acetate (DOCA)-salt hypertension can be produced in rats in the presence of low total peripheral resistance (TPR) induced by long-term administration of minoxidil, a vasodilator. The rats were divided into four groups: sham-control, DOCA-salt, minoxidil, and DOCA-salt with minoxidil. The rats in both DOCA groups had DOCA pellets implanted subcutaneously and were given saline to drink. The rats in both minoxidil groups were given minoxidil (3 mg/day) in the drinking water throughout the experiment. Final measurements, including mean arterial blood pressure, cardiac index, and renal blood flow were made after 4-6 weeks. Flow measurements were made using radioactive microspheres. Cardiac index (ml.min-1.100 g-1) in sham-control rats averaged 18 +/- 2 and was higher in the other groups: 23 +/- 4 (DOCA-salt), 25 +/- 2 (minoxidil), and 30 +/- 2 (DOCA-salt plus minoxidil). Mean arterial pressure (mm Hg) was increased in both DOCA-salt rats (160 +/- 8) and DOCA-salt plus minoxidil rats (153 +/- 5) as compared with sham-control (116 +/- 2) and minoxidil (113 +/- 3) rats. There was no significant difference in TPR between the sham-control and DOCA-salt rats, but TPR in minoxidil and DOCA-salt plus minoxidil rats was 30% and 28% lower than that in untreated sham-control and DOCA-salt hypertensive rats, respectively. In contrast, renal vascular resistance was significantly increased in both DOCA-salt groups as compared with non-DOCA-salt groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Characteristics of the contractile response of rabbit aorta produced by cromakalim in calcium-free solution

1 The effect of potassium channel opening compounds has been investigated in the smooth muscle of rabbit aorta under Ca-free conditions. Examination of the characteristics of the response has been performed using cromakalim as the prototype compound. 2 In order of potency, Ro 31-6930, cromakalim, minoxidil sulphate and pinacidil each produced a contraction in rabbit aortic strips bathed in Ca-free MOPS-buffered physiological salt solution (PSS). In contrast, forskolin, glyceryl trinitrate and nifedipine each failed to increase tension under identical conditions. Cromakalim also evoked contraction of bovine trachealis muscle bathed in Ca-free PSS. 3. The contractile response to cromakalim in rabbit aortic strips was of delayed onset (15-20 min) and reached a plateau after approximately 120 min (1.8 g maximum with 1 microM cromakalim). No cromakalim-induced tension changes were observed in either 1 mM or 2.5 mM Ca-containing PSS. 4. Raising the [KCl] of the Ca-free PSS to 65.9 mM fully inhibited the cromakalim-induced contraction in rabbit aortic strips. In addition, pretreatment of aortic strips with the sulphonylurea glibenclamide antagonized the subsequent mechanical response to cromakalim. 5. In Ca-free PSS, cromakalim (1 microM) stimulated 42K-efflux with a time-course corresponding to the contractile event. Glibenclamide (1 microM) inhibited this cromakalim-induced 42K-efflux. 6. In sharp microelectrode studies in bovine trachealis, cromakalim (10 microM) produced a sustained membrane hyperpolarization in normal PSS. In contrast, the cromakalim-induced hyperpolarization in Ca-free PSS was not sustained. The fading of the hyperpolarization was temporally correlated with the increase in tension under these experimental conditions. 7. It is concluded that the K-channel opener-induced smooth muscle contractile response revealed in Ca-free PSS is the consequence of K-channel opening. The nature of the detailed mechanism which underlies this contractile phenomenon remains to be determined.

Lack of effect of potassium channel openers on ATP-modulated potassium channels recorded from rat ventromedial hypothalamic neurones

1. Single neuronal cells were freshly isolated from the ventromedial hypothalamic nuclei (VMHN) of the rat brain. Currents through ATP-modulated and large conductance (160 and 250 pS) calcium-activated potassium channels were recorded by the cell-attached and excised inside-out patch techniques. 2. BRL38227 (lemakalim; 30-90 microM) applied to the superfusing medium produced no change in firing rate of isolated glucose-receptive VMHN neurones in cell-attached recordings. 3. BRL38227, at concentrations of between 30-100 microM applied to the intracellular (cytoplasmic) aspect of inside-out patches, had no effect on the activity of ATP-sensitive K+ channels in the absence of ATP or in the presence of a sub-maximal inhibitory concentration (3 mM) of ATP. Cromakalim, pinacidil, minoxidil sulphate and diazoxide also produced no effect under these conditions. 4. The potassium channel openers (KCO's) were tested on ATP-activated potassium channels recorded from a further subpopulation of VMHN neurones. Application of BRL38227 (up to and including 100 microM) to this channel in inside-out patches either in the absence of ATP or when activated by 5 mM ATP had no effect on channel activity. Identical results were obtained with cromakalim and pinacidil. 5. BRL38227 had no effect on either of the large conductance (250 pS and 160 pS) calcium-activated potassium channels in VMHN neurones. 6. Intracellular recordings were made from glucose-receptive VMHN neurones in rat brain slices. Cromakalim (50 microM) or diazoxide (60 microM) did not alter the firing rate or passive membrane properties of these neurones demonstrated to be sensitive to tolbutamide (0.1 mM). 7. These results show that the KCO's tested in this study have no effect either on VMHN neurones contained in brain slices or on the activity of any of the ATP-modulated potassium channels under isolated patch conditions associated with these neurones.

Effects of cepharanthine and minoxidil on proliferation, differentiation and keratinization of cultured cells from the murine hair apparatus

The effects of cepharanthine and minoxidil on proliferation, differentiation and keratinization of cultured cells from the murine hair apparatus were examined electron microscopically. Both cepharanthine and minoxidil stimulated cell proliferation and delayed initiation of differentiation and keratinization of the cultured cells. On day 6, most control cells (87%) cultured in a 0.03 mM calcium medium without cepharanthine and minoxidil were differentiated into several subpopulations corresponding to those of in vivo cell layers of the hair apparatus, while most of the cells cultured with cepharanthine (71%) or minoxidil (70%) were still immature. On day 13, the number of degenerated cells increased (63%) in the control culture, whereas in the culture treated with cepharanthine or minoxidil, cell degeneration scarcely occurred (5% and 8%, respectively). Differentiated cells having tonofilaments were often observed in the cepharanthine- and minoxidil-treated cultures (76% and 72%, respectively). Elevation of extracellular calcium up to 1.0 mM induced keratinization (34%) in the control culture on day 6, while no keratinized cells were observed in the cepharanthine- or minoxidil-treated culture. On day 13 keratinization similarly occurred in the cultures with cepharanthine (30%) or minoxidil (48%). These results show that both cepharanthine and minoxidil may directly influence proliferation, differentiation and keratinization of cultured cells from the hair apparatus.