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.

Chronic arterial vasodilation, central hemodynamics, and cardiac hypertrophy in spontaneously hypertensive rats

To determine the possible contribution of cardiac volume overload in the failure of arterial vasodilators to induce regression of left ventricular hypertrophy (LVH), we evaluated in spontaneously hypertensive rats (SHRs) the changes in central hemodynamics caused by treatment with hydralazine or minoxidil. Cardiac output measured by the thermodilution technique and filling pressures were measured in conscious, freely moving rats. Increases in cardiac output were observed after 1 day of treatment, and persisted during chronic treatment; ganglionic blockade did not affect this increase. However, the LV end-diastolic pressure and right atrial pressure of SHRs were not increased by hydralazine or minoxidil. Minoxidil increased the LV weight, and decreased the LV wall thickness to LV internal radius ratio, whereas hydralazine did not change these parameters. We conclude that in SHRs changes in filling pressures do not represent the primary stimulus for the persistence or progression of cardiac hypertrophy during chronic arterial vasodilation.

Minoxidil-induced changes in the contraction of collagen lattices by human skin fibroblasts

This investigation has studied the effect of minoxidil on the contraction of hydrated collagen lattices by human dermal fibroblasts. Type I collagen was mixed with a fibroblast suspension and polymerized, and minoxidil 10 to 800 micrograms/ml (0.05 to 4 mM) was added at the time the lattices were released. Minoxidil at concentrations from 100 to 600 micrograms/ml inhibited contraction in a dose-dependent manner, whereas 800 micrograms/ml prevented contraction completely, most cells remaining rounded. Considerable inhibition was already evident within 24 hours. Visualization of living cells with MTT and cell counts showed that inhibition in the first 48 hours was not due to fibroblast death. Exchange of minoxidil to normal medium led to a resumption of contraction and a return to an elongate morphology. Minoxidil at 10 micrograms/ml had no significant effect on lattice contraction, whereas at 100 micrograms/ml it slowed contraction without affecting proliferation or morphology, as observed under the light microscope. The inhibitory effect of minoxidil should be investigated further in relation to the control of contraction of wounds in vivo.

Renal response to atrial natriuretic peptide in nonedematous sodium-retaining dogs

ANP administered to cirrhotic dogs or chronic caval dogs with ascites and urinary sodium retention (USR) usually causes heterogeneity of natriuretic response. To assess whether this same phenomenon would occur in the absence of edema, ANP at 100 ng/kg/min was given to dogs before and after the induction of USR by a variety of techniques. Eight dogs were over-diuresed with furosemide over a 2-day period, and 9 dogs were subjected to subacute hemorrhage over a similar period. These dogs were retested with ANP one day later. All 8 dogs given furosemide showed no response to ANP (delta UNa V = 7.4 +/- 4.8 microEq/min), compared to a normal response prior to the diuretic (delta UNa V = 128 +/- 34 microEq/min). The 9 hemorrhaged dogs also responded normally to ANP prior to this manipulation (delta UNa V = 74 +/- 14 microEq/min), but a blunted response post-hemorrhage (delta UNa V = 35 +/- 13 microEq/min). This profile was made up of 5 dogs who responded to ANP (delta UNaV = 62 microEq/min) and 4 who had no response whatsoever (delta UNa V = 3 microEq/min). When 8 dogs were given USR because of continuous mineralocorticoid administration, none responded, but all had a magnified natriuretic response to ANP during the 'escape' phase. Eight dogs were administered minoxidil (10 mg) by mouth daily to induce USR. All 8 dogs responded to ANP (delta UNa V = 93 +/- 6 microEq/min) which was no different from the pretreatment response (delta UNa V = 65 +/- 3 microEq/min).(ABSTRACT TRUNCATED AT 250 WORDS)

Minoxidil specifically decreases the expression of lysine hydroxylase in cultured human skin fibroblasts

The levels of lysine hydroxylase protein and the levels of the mRNAs for lysine hydroxylase and the alpha- and beta-subunits of proline 4-hydroxylase were measured in cultured human skin fibroblasts treated with 1 mM-minoxidil. The data demonstrate that minoxidil decreases the amount of lysine hydroxylase protein, this being due to a decrease in the level of lysine hydroxylase mRNA. The effect of minoxidil appears to be highly specific, as no changes were observed in the amounts of mRNAs for the alpha- and beta-subunits of proline 4-hydroxylase.

Potassium channel conductance: a mechanism affecting hair growth both in vitro and in vivo

The opening of intracellular potassium channels has been suggested as a mechanism regulating hair growth. Enhancing the flux of potassium ions is a mechanism shared by several structurally diverse antihypertensive agents including minoxidil sulfate (the active metabolite of minoxidil), pinacidil, P-1075 (a potent pinacidil analog), RP-49,356, diazoxide, cromakalim, and nicorandil. Of these drugs, minoxidil, pinacidil, and diazoxide have been reported to elicit hypertrichosis in humans. This potassium channel hypothesis was examined by testing these drugs for effects on hair growth both in vitro and in vivo. For the in vitro studies, mouse vibrissae follicles were cultured for 3 d with drug and the effects on hair growth were measured by metabolic labeling. All drugs, except diazoxide, enhanced cysteine incorporation into the hair shafts of the cultured vibrissae. Diazoxide was poorly soluble and thus was tested only at low doses. Minoxidil, P-1075, cromakalim, and RP-49,356 were also evaluated in vivo by measuring hair growth effects in balding stumptail macaque monkeys. The drugs were administered topically to defined sites on balding scalps once per day for 4-5 months and the amount of hair grown was determined by monthly measurements of shaved hair weight. Three of the drugs produced significant increases in hair weight whereas, the RP-49,356 had no effect. These studies provide correlative evidence that the opening of potassium channels is an important regulatory mechanism for hair growth. This provides the impetus for further studies on this potentially important mechanism affecting hair biology.

Hair growth effects of oral administration of finasteride, a steroid 5 alpha-reductase inhibitor, alone and in combination with topical minoxidil in the balding stumptail macaque

A 5 alpha-reductase inhibitor, finasteride, was administered orally at 0.5 mg/day, alone or in combination with topical 2% minoxidil, for 20 weeks to determine the effects on scalp hair growth in balding adult male stumptail macaque monkeys. A 7-day dose-finding study showed that both 0.5- and 2.0-mg doses of the drug produced a similar diminution in serum dihydrotestosterone (DHT) in male stumptails. Hair growth was evaluated by shaving and weighing scalp hair at baseline and at 4-week intervals during treatment to obtain cumulative delta hair weight (sum of the 4-week changes in hair weight from baseline) for the 20-week study. The activity of the 5 alpha-reductase enzyme was assessed by RIA of serum testosterone (T) and DHT at 4-week intervals. The combination of finasteride and minoxidil generated significant augmentation of hair weight (additive effect) compared to either drug alone. Finasteride increased hair weight in four of five monkeys. When the data of the one nonresponsive monkey were excluded, finasteride elicited a significant elevation in hair weight compared to topical vehicle alone. Minoxidil also evoked a significant increase in hair weight compared to vehicle alone. Serum T was unchanged, whereas serum DHT was significantly depressed in monkeys that received either finasteride or the combination of finasteride and minoxidil. These data suggest that inhibition of the conversion of T to DHT by this 5 alpha-reductase inhibitor reverses the balding process and enhances hair regrowth by topical minoxidil in the male balding stumptail macaque.

Minoxidil overdose with ECG changes: case report and review

A 20-year-old female ingested an unknown quantity of minoxidil tablets as a suicide gesture. She presented to the emergency department about 90 minutes later with tachycardia, diffuse T wave inversion, and S-T segment depression on the ECG, labile hypotension, and a substantially elevated total serum minoxidil concentration of 3140 ng/mL. She responded to supportive therapy with intravenous fluids, and was discharged 32 hours later with stable blood pressure and mild residual tachycardia. The clinical toxicology, treatment, and previous case reports of minoxidil overdose are reviewed.

Interaction of minoxidil with pigment in cells of the hair follicle: an example of binding without apparent biological effects

To identify minoxidil target cells in hair follicles we followed the uptake of radiolabeled drug in mouse vibrissae follicles both in vitro and in vivo. Autoradiography showed that both 3H-minoxidil and 3H-minoxidil sulfate accumulated in the differentiating epithelial matrix cells superior to the dermal papilla, a distribution similar to that of pigment. Minoxidil localized in melanocytes, melanocyte processes, and areas of greater melanin concentrations within the epithelial cells. Although uptake of minoxidil was significantly less in unpigmented follicles, the drug stimulated proliferation and differentiation of both pigmented and unpigmented follicles. Labeled minoxidil bound to Sepia melanin and was displaced with unlabeled minoxidil and other electron donor drugs. This interaction with melanin acts as a targeting mechanism of minoxidil to pigmented hair follicles but has no apparent functional significance in hair growth. This work illustrates how measurement of drugs in hair may be biased by pigmentation.

Structure-activity relationship of minoxidil analogs as inhibitors of lysyl hydroxylase in cultured fibroblasts

The structural features that confer upon minoxidil the ability to suppress lysyl hydroxylase activity in human skin fibroblasts were investigated. Substitution of the amino group in position 2 or 6 of the pyrimidine ring with a methyl group had no significant effect on the inhibitory activity of minoxidil, whereas substitution of both amino groups with methyl groups resulted in a complete loss of inhibitory activity. Together, these observations indicate that only one of the two amino groups ortho to the nitroxide oxygen is essential for the enzyme-suppressing effect of minoxidil. Derivatives of minoxidil formed by hydroxylation at position 3 or 4 of the piperidine ring were as active as the parent compound in suppressing lysyl hydroxylase activity. However, replacement of the piperidinyl group in position 4 of the pyrimidine ring with a pyrrolidinyl, morpholinyl, or N-methylpiperazinyl group resulted in loss of inhibitory activity, demonstrating that the piperidinyl group para to the nitroxide oxygen is essential for the enzyme-suppressing effect of minoxidil. Removing the nitroxide oxygen from position 1 of the pyrimidine ring resulted in a partial loss of the specificity of minoxidil for suppression of lysyl hydroxylase activity. The results indicate that distinct structural elements determine the enzyme-suppressing effect and the antihypertensive effect of minoxidil.

Comparison of the in vitro effects of K+ channel modulators on detrusor and portal vein strips from guinea pigs

The effects of K+ channel openers and blockers on smooth muscles of vascular and nonvascular origin from guinea pigs have been investigated. Cromakalim, pinacidil, nicorandil and minoxidil sulfate all abolished the spontaneous myogenic activity of the guinea pig portal vein and the KCl-evoked activity of detrusor strips with the same rank order of ptoency. Whereas both apamin and charybdotoxin stimulated myogenic activity of the detrusor strips, they produced insignificant effects on spontaneously active portal vein strips and failed to antagonize the mechanoinhibitory effects of cromakalim in the two tissues. Glibenclamide, on the other hand, only stimulated the myogenic activity of portal vein strips but antagonized the mechanoinhibitory effects of cromakalim, pinacidil, nicorandil and minoxidil sulfate in both tissues. Rubidium, at millimolar concentrations, stimulated the myogenic activity, and antagonized the actions of cromakalim in both tissues. The data indicate that there are definite functional dissimilarities as exhibited by the differential response of the two tissues to K+ channel modulators. These findings may be exploited in the design of new drugs with tissue selectivity.

High-sulfur protein gene expression in a transgenic mouse

We analyzed the effect of minoxidil on hair follicles isolated from transgenic mice. These transgenic animals synthesize the reporter enzyme CAT in their hair follicles only during the active phases of hair growth. The recombinant gene used to generate these mice contained the bacterial enzyme CAT under the control of the promoter from the gene of UHS protein. Studies using in situ hybridization showed that UHS proteins are expressed specifically in the matrix cells of the hair follicle during the terminal stages of hair differentiation. Hence the expression of the UHS proteins is a clear sign of active hair growth. With other in situ hybridization studies we demonstrated that CAT mRNA is expressed in differentiating matrix cells of the hair shaft in a location similar to that in which mRNA encodes UHS proteins. Thus we can use the levels of CAT activity as a measure of hair growth. We have confirmed that expression of the transgene is found in hair that is high in anagen and low in catagen follicles. The usefulness of our model was further demonstrated by showing that minoxidil, a drug that stimulates hair growth, increased the expression of CAT in cultured hair follicles. Thus we have demonstrated that expression of this reporter gene is sensitive, hair specific, and also useful for monitoring effects in cultured hair follicles. Hence these transgenic mice provide a model system for studying the biology of hair growth.

[Treatment of androgenic alopecia with topical minoxidil]

Minoxidil, a vasodilator, was first marketed in 1979 as an oral antihypertensive. Since hypertrichosis occurred as an adverse effect in most patients treated, a 2% topical solution was developed for use in men with androgenic alopecia. It was approved by the American Food and Drug Administration and by the Israel Ministry of Health. A follow-up of 30 cases treated with the preparation is presented. Efficacy of treatment was assessed by hair counts in a marked area on the balding scalp, as well as by subjective evaluations of patients and physicians. The treatment was beneficial in 63%: balding was slowed in most, while in a minority hair density actually increased. However, in only 6.6% was dramatic cosmetic improvement achieved.

Role of protein sulfation in vasodilation induced by minoxidil sulfate, a K+ channel opener

Evidence from contractile, radioisotope ion flux and electrophysiological studies suggest that minoxidil sulfate (MNXS) acts as a K+ channel opener in vascular smooth muscle. This study was designed to examine possible biochemical mechanisms by which MNXS exerts such an effect. Experiments performed in the isolated rabbit mesenteric artery (RMA) showed that MNXS, 5 microM, but not the parent compound minoxidil, was a potent vasodilator. Whereas the relaxant effects of an another K+ channel opener vasodilator, BRL-34915 (cromakalim), were removed by washing with physiological saline solution, the effects of MNXS persisted after repeated washout attempts. Furthermore, after an initial exposure of segments of intact RMA to [35S] MNXS, greater than 30% of the radiolabel was retained 2 hr after removal of the drug. In contrast, retention of radiolabel was not detected with either [3H]MNXS (label on the piperidine ring of MNXS) or [3H]minoxidil (each less than 3% after a 2-hr washout). These data suggested that the sulfate moiety from MNXS was closely associated with the vascular tissue. To determine if proteins were the acceptors of sulfate from MNXS, intact RMAs were incubated with [35S]MNXS, and then 35S-labeled proteins were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and analyzed by fluorography. Preferential labeling of a 116 kD protein was detected by 2 and 5 min of treatment. A 43 kD protein (resembling actin) also showed significant labeling. A similar profile of 35S-labeled proteins was observed in [35S] MNXS-treated A7r5 rat aortic smooth muscle cells, suggesting that the majority of proteins labeled by [35S]MNXS in intact RMA were components of smooth muscle cells. (ABSTRACT TRUNCATED AT 250 WORDS)

Minoxidil: inhibition of proliferation of keratinocytes in vitro

Previous studies have suggested that minoxidil stimulates growth of keratinocytes, possibly in a manner similar to the action of epidermal growth factor. Using both a short-term assay, thymidine incorporation, and a longer term assay, cell counting, to assess proliferative growth, we tested the activity of minoxidil in human keratinocyte cultures grown in 0.1 mM Ca(++). Minoxidil failed to stimulate growth in these assays. At concentrations of 5-10 micrograms per ml, minoxidil showed half-maximal inhibition of both EGF- and placental extract-stimulated thymidine incorporation. Minoxidil also inhibited proliferative growth in the presence or absence of placental extract. Direct measurement of the ability of minoxidil to compete for binding to the EGF receptor indicated that minoxidil probably does not bind to the EGF receptor. Minoxidil was not toxic, as keratinocytes continued to survive and grow, although at a slower rate, in the presence of minoxidil.

The metabolism of fibroblasts from normal and fibrotic skin is inhibited by minoxidil in vitro

The effects of minoxidil in vitro were studied using fibroblasts grown from the lesional skin of patients with lichen sclerosus et atrophicus, morphoea and from the skin of normal individuals. The proliferation of all fibroblast lines over 3 days was inhibited in proportion to the concentration of minoxidil, being 20% or less of controls at 1 mM, where cell viability was only marginally reduced (84 +/- 2% vs. 88 +/- 2% (SEM) in controls). At 5 mM there was usually a net loss of cells and only 72% of those remaining were viable. In contrast, minoxidil at 0.1-1 mM stimulated the proliferation of foreskin keratinocytes by up to 130%. Contraction of collagen lattices containing the three types of fibroblasts was inhibited by 22-26% with 1 mM minoxidil after 5 days and by 50-94% with 5 mM. Secretion of glycosaminoglycans by normal fibroblasts showed concentration-dependent reduction, being 25 +/- 6% of that of untreated cultures with 1 mM minoxidil. These findings show that minoxidil has a range of inhibitory effects on both normal and abnormal skin fibroblasts in vitro, which contrast with its stimulation of skin epithelial cells, and support suggestions that it may provide a useful topical treatment for keloids and other fibroses.

Some degree of overlap exists between the K(+)-channels opened by cromakalim and those opened by minoxidil sulphate in rat isolated aorta

The effects of the K+ channel opening drugs minoxidil sulphate and cromakalim, on 42K+ and 86Rb+ efflux and on vasorelaxation in rat isolated aorta, were compared. In rat aortic rings precontracted with noradrenaline (100 nmol/l), minoxidil sulphate and cromakalim concentration-dependently inhibited induced tension by up to 90%, with pD2 values of 7.35 +/- 0.1 and 7.17 +/- 0.1, respectively. Glibenclamide (300 nmol/l), produced 2200- and 19-fold rightward shifts in the concentration-relaxation curves to minoxidil sulphate and cromakalim, respectively, without an effect on the maximum relaxation. Both minoxidil sulphate and cromakalim increased the efflux of 42K+ and 86Rb+ from aorta in a concentration-dependent manner, with midpoints in the mumol/l range; the maximum efflux induced by minoxidil sulphate being approximately one tenth of that induced by cromakalim. The ratio of stimulated 86Rb+/42K+ efflux increased from 0.22 to 0.48 with increasing cromakalim concentrations, but was approximately constant (approximately 0.39) when the minoxidil sulphate concentration was varied. In the presence of minoxidil sulphate, the effects of cromakalim on 42K+ and 86Rb+ efflux were inhibited in a concentration-dependent manner, by up to 60%. In the continuing presence of cromakalim (300 nmol/l), minoxidil sulphate (10 mumol/l)-induced increases in 42K+ and 86Rb+ efflux were inhibited by 45%, whereas conditioning with cromakalim (1 mumol/l) inhibited the 86Rb+ efflux stimulated by additional superfusion of cromakalim (1 mumol/l) by 85%. Glibenclamide inhibited minoxidil sulphate (10 mumol/l)- and cromakalim (1 mumol/l)-induced increases in 42K+ and 86Rb+ efflux in a concentration-dependent manner with IC50 values of approximately 80 nmol/l.(ABSTRACT TRUNCATED AT 250 WORDS)