Ionic and secretory response of pancreatic islet cells to minoxidil sulfate

Minoxidil sulfate is an antihypertensive agent belonging to the new class of vasodilators, the "K+ channel openers." The present study was undertaken to characterize the effects of minoxidil sulfate on ionic and secretory events in rat pancreatic islets. The drug unexpectedly provoked a concentration-dependent decrease in 86Rb outflow. This inhibitory effect was reduced in a concentration-dependent manner by glucose and tolbutamide. Minoxidil sulfate did not affect 45Ca outflow from islets perfused in the presence of extracellular Ca++ and absence or presence of glucose. However, in islets exposed to a medium deprived of extracellular Ca++, the drug provoked a rise in 45Ca outflow. Whether in the absence or presence of extracellular Ca++, minoxidil sulfate increased the cytosolic free Ca++ concentration of islet cells. Lastly, minoxidil sulfate increased the release of insulin from glucose-stimulated pancreatic islets. These results suggest that minoxidil sulfate reduces the activity of the ATP-sensitive K+ channels and promotes an intracellular translocation of Ca++. The latter change might account for the effect of the drug on the insulin-releasing process. However, the secretory response to minoxidil sulfate could also be mediated, at least in part, by a modest Ca++ entry.

Ro 42-5892 is a potent orally active renin inhibitor in primates

The goal of the present study was to characterize the new renin inhibitor Ro 42-5892 in vitro and in vivo. In vitro, Ro 42-5892 inhibited purified human renin and human plasma renin specifically with an IC50 of 0.7 nM and 0.8 nM, respectively. In vivo, Ro 42-5892 reduced mean arterial blood pressure in sodium-depleted marmosets and squirrel monkeys with as low a dose as 0.1 mg/kg orally. Higher doses reduced pressure by 30-35 mm Hg in both species. The duration of blood pressure decrease with 3 mg/kg orally was more than 24 hours. Maximal changes of plasma renin activity, immunoreactive angiotensin I, and immunoreactive angiotensin II were observed at 15 minutes. Renin was reduced by 74 +/- 31%, angiotensin I by 85 +/- 14%, angiotensin II by 89 +/- 17%, and immunoreactive active renin was increased by 70 +/- 39%. However, unlike pressure, these maximal effects were only transient with complete recovery of renin at 60 minutes under still reduced levels of angiotensin I (61 +/- 24%) and angiotensin II (71 +/- 38%) and increased concentrations of active renin (86 +/- 30%). The blood pressure lowering was due to specific renin inhibition as exemplified by the influence of the kidney, sodium status, species, or stereoselectivity. Moreover, the reduction of arterial blood pressure was similar to the action of the angiotensin converting enzyme inhibitor cilazapril and was not associated with reflex tachycardia in contrast to the pure vasodilator minoxidil. We conclude that Ro 42-5892 is a potent orally active renin inhibitor acting mainly by inhibition of renin in an extraplasmatic compartment.

Arterial vasodilation and cardiovascular structural changes in normotensive rats

In normotensive rats, the arterial vasodilator minoxidil causes right ventricular hypertrophy (RVH) and eccentric left ventricular hypertrophy (LVH). To assess whether this trophic effect of minoxidil extends to the vasculature and to examine possible mechanisms involved, alterations in cardiac and arterial (superior, large and small mesenteric arteries, carotid and basilar arteries) structure were evaluated in relation to changes in indexes of cardiac volume load and cardiac and arterial sympathetic activity during long-term (35 and 70 days) treatment of normotensive rats with minoxidil alone or in combination with the diuretic hydrochlorothiazide (HCTZ). Minoxidil alone increased LV and RV weights, LV internal diameter, and medial area of the superior mesenteric artery but did not affect any of the other arteries evaluated. When combined with HCTZ, long-term minoxidil caused concentric LVH rather than eccentric LVH and no longer increased the medial area of the superior mesenteric artery. Neither treatment had any persistent effect on blood pressure, heart rate, or plasma catecholamines. However, minoxidil significantly increased cardiac and arterial (superior and large mesenteric artery) norepinephrine turnover rates, cardiac filling pressures, and plasma and blood volumes. When combined with HCTZ, short-term (1 wk) minoxidil still increased cardiac filling pressures. However, intravascular volume expansion during chronic treatment was significantly attenuated. These results suggest that chronic cardiac volume load appears to determine the type of cardiac hypertrophy induced by a nonhemodynamic mechanism (possibly cardiac sympathetic activity) activated by minoxidil. Intravascular volume expansion or increased arterial flow appears to be responsible for medial hypertrophy of the superior mesenteric artery, but absence of a trophic response in other arteries suggests that another, local mechanism contributes.

Quinapril, an angiotensin converting enzyme inhibitor, prevents cardiac hypertrophy during episodic hypertension

Six control dogs, six dogs treated with 1.5 mg/kg b.i.d. quinapril, and six dogs treated with 8 mg/kg q.d. minoxidil underwent 6 hours daily of hindquarter compression for 9 weeks. Minoxidil significantly decreased baseline blood pressure (-17 mm Hg; p less than or equal to 0.01), whereas quinapril decreased baseline blood pressure 11 mm Hg but not significantly (p = 0.15). Hindquarter compression elicited blood pressure increases in all three groups (control +18, quinapril +13, minoxidil +19 mm Hg). After 9 weeks, left ventricular mass in control dogs increased 22% (p less than 0.004); a similar increase was seen in minoxidil-treated dogs (+22%, p less than 0.0001) but not in the quinapril-treated group (+4%, p less than 0.15). The increase in left ventricular mass in control dogs was concentric (increased epicardial volume only), whereas in the minoxidil group, the hypertrophy was eccentric (both epicardial and endocardial volumes increased). The minimal hypertrophy in the quinapril group was concentric (no change in epicardial, but a decrease in endocardial volume). Quinapril had little hypotensive effect, but prevented the development of left ventricular hypertrophy, whereas minoxidil did not prevent hypertrophy in spite of its hypotensive effect. The mechanism of this differential effect of direct vasodilation versus converting enzyme inhibition on left ventricular hypertrophy is not fully elucidated. The results with quinapril suggest that some antihypertensive agents may positively affect left ventricular hypertrophy in spite of the absence of a large effect on baseline blood pressure or on blood pressure reactivity.

Comparison of the effects of the K(+)-channel openers cromakalim and minoxidil sulphate on vascular smooth muscle

1 The actions of the potassium channel openers, cromakalim and minoxidil sulphate, were compared in a range of isolated blood vessel preparations. 2 Cromakalim and minoxidil sulphate inhibited spontaneous mechanical activity of the guinea-pig portal vein and relaxed the noradrenaline precontracted rat aorta with similar potency. In contrast, minoxidil sulphate was less potent than cromakalim in inhibiting spontaneous activity in the rat portal vein and was essentially inactive in the noradrenaline precontracted rat mesenteric artery and rabbit aorta. 3 Minoxidil sulphate did not antagonize the effects of cromakalim in the rabbit aorta indicating it was not acting as a partial 'agonist'. 4 Charybdotoxin, noxiustoxin and rubidium failed to discriminate between cromakalim and minoxidil sulphate indicating that the apparently selective effects of minoxidil sulphate were not mediated by either Ca(2+)-activated potassium channels, delayed rectifiers or rubidium impermeable potassium channels. 5 Glibenclamide antagonized the effects of cromakalim in an apparently competitive manner whereas the effects of minoxidil sulphate were antagonized in a non-competitive manner. The involvement of subtypes of ATP-sensitive potassium channels is discussed.

Superoxide production in the isolated rabbit aorta and the effect of alloxan, indomethacin and nitrovasodilators

The purpose of this investigation was to develop a simple model to assess superoxide production from isolated vessels and to use this model to study the effects of various compounds on superoxide generation. The established method of cytochrome C reduction by superoxide was modified to measure superoxide production in vascular rings from rabbit aortae. The diabetogenic compound alloxan significantly increased superoxide production in a concentration-dependent manner. The nitrovasodilators nitroprusside and minoxidil exhibited contrasting effects. Nitroprusside inhibited alloxan-stimulated production of superoxide, but minoxidil had no effect, suggesting different mechanisms of action for these drugs. The cyclooxygenase inhibitor indomethacin had no effect on the production of superoxide stimulated by alloxan, demonstrating that superoxide production induced by this compound is not affected by mechanisms involving cyclooxygenase. These data demonstrate the use of a simple, rapid and inexpensive method for measuring superoxide produced by intact vessels. This may be useful in testing drugs exhibiting antioxidant and vasoactive properties. Finally, because superoxide is implicated in the destruction of endothelium-derived relaxing factor, and the presence of the vasodilator nitroprusside reduces superoxide production, it is concluded that some nitrovasodilators may have additional vascular effects through the suppression of superoxide formation.

Opposite effects of arterial vasodilators on cardiac vs. arterial hypertrophy and sympathetic activity in spontaneously hypertensive rats

To investigate whether cardiac and arterial structure and sympathetic activity changes in a similar fashion during chronic arterial vasodilation, we evaluated the morphology and sympathetic activity of the mesenteric arterial bed and the left (LV) and right (RV) ventricles of 16-week-old Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHRs) after 35 and 70 days of treatment with the arterial vasodilator minoxidil. The minoxidil-induced antihypertensive response was associated with an increase in ventricular sympathetic activity, potentiation of RV hypertrophy (RVH), and the development of eccentric LV hypertrophy (LVH). In the mesenteric arterial bed, minoxidil decreased the sympathetic activity, increased the lumen of the superior mesenteric artery, and decreased the medial area of the large and small mesenteric arteries. We conclude that the contrasting effects of minoxidil on cardiac vs. arterial structure may--in part--relate to selective effects on regional sympathetic activity.

Contrasting effects of calcium antagonists vs. arterial vasodilators on cardiac anatomy and sympathetic activity in spontaneously hypertensive rats

In spontaneously hypertensive rats (SHRs) we evaluated the effects of 35 and 70 days of treatment with nisoldipine (2 mg/g of food) vs. minoxidil (120 mg/L of drinking water) on cardiac anatomy [i.e., left ventricular (LV) and right ventricular (RV) weights and LV internal diameter and wall thickness] and cardiac sympathetic activity assessed by the norepinephrine turnover rate. The minoxidil-induced antihypertensive response was associated with a marked increase in cardiac sympathetic activity, potentiation of RV hypertrophy (RVH), and the development of eccentric LV hypertrophy (LVH). Nisoldipine decreased both blood pressure (BP) and cardiac sympathetic activity, but caused only small decreases in LV weight and LV wall thickness and no change in RV weight. With regard to minoxidil, the increase in sympathetic activity may contribute to the minoxidil-induced potentiation of cardiac mass. Nisoldipine, despite decreasing BP as well as cardiac sympathetic activity, unexpectedly resulted in only a small decrease in cardiac mass, suggesting that additional mechanisms may play a role in the effects of calcium antagonists on cardiac mass.

A sensitive in vitro functional assay to detect K(+)-channel-dependent vasodilators

This study describes a sensitive in vitro relaxation assay using isolated rabbit mesenteric artery to detect the activity of a vasodilator as a K(+)-channel activator. Thus, comparison of several known K(+)-channel activators was made with other vasodilators known to work via various cellular mechanisms. The vasodilators used were minoxidil sulfate (MNXS; 5 microM), BRL-34915 (cromakalim, 0.1 microM), nicorandil (10 microM), pinacidil (1 microM), diazoxide (100 microM), sodium nitroprusside (10 microM), forskolin (1 microM), D600 (0.5 and 10 microM), hydralazine (10 microM), and viprostal (PGE1 analog, 5 microM). The concentrations chosen were equipotent to produce greater than 80% relaxation of the maximal norepinephrine (NE) (5 microM) contraction. At these concentrations, MNXS, cromakalim, pinacidil, nicorandil, and diazoxide were found to be ineffective in producing relaxation of 80 mM K(+)-contractions. Subsequently, pretreatment of tissues with 20 mM K+ before NE contraction was found to attenuate relaxation significantly by these agents, but had not effect on the relaxations by forskolin or D600. These initial criteria helped to establish cromakalim, pinacidil, nicorandil, and diazoxide as compounds acting similarly to MNXS as K(+)-channel-dependent. In another set of experiments, the effects of tetraethylammonium (TEA) (10 mM), Ba2+ (0.5 mM), and glyburide (1 microM) as K(+)-channel blockers were examined. Again it was found that these blockers had the most inhibitory effect on the class of compounds identified as K(+)-channel activators. Additionally, it was found that these K(+)-channel activators were without any significant effect on the NE-sensitive intracellular Ca2+ release as studied by contraction in a Ca2(+)-free solution. Thus, this series of functional criteria clearly show that the profile of these K(+)-channel activators is distinctly different from the vasodilators working via other mechanisms such as cyclic AMP (cAMP) (forskolin), cyclic GMP (cGMP) (nitroprusside), and Ca2+ antagonists (D600). It is suggested that appropriately defined, systematic functional studies, such as the one described here, can provide a sensitive and reproducible vascular model to discover and delineate the role of pharmacologically relevant mechanisms for vasodilation.

Minoxidil sulfate is the active metabolite that stimulates hair follicles

An important step in understanding minoxidil's mechanism of action on hair follicles was to determine the drug's active form. We used organ-cultured vibrissa follicles to test whether it is minoxidil or its sulfated metabolite, minoxidil sulfate, that stimulates hair growth. Follicles from neonatal mice were cultured with or without drugs and effects were assessed by measuring incorporation of radiolabeled cysteine in hair shafts of the treated follicles. Assays of minoxidil sulfotransferase activity indicated that vibrissae follicles metabolize minoxidil to minoxidil sulfate. Dose-response studies showed that minoxidil sulfate is 14 times more potent than minoxidil in stimulating cysteine incorporation in cultured follicles. Three drugs that block production of intrafollicular minoxidil sulfate were tested for their effects on drug-induced hair growth. Diethylcarbamazine proved to be a noncompetitive inhibitor of sulfotransferase and prevented hair growth stimulation by minoxidil but not by minoxidil sulfate. Inhibiting the formation of intracellular PAPS with chlorate also blocked the action of minoxidil but not of minoxidil sulfate. Acetaminophen, a potent sulfate scavenger blocked cysteine incorporation by minoxidil. It also blocked follicular stimulation by minoxidil sulfate apparently by directly removing the sulfate from the drug. Experiments with U-51,607, a potent minoxidil analog that also forms a sulfated metabolite, showed that its activity was inhibited by both chlorate and diethylcarbamazine. These studies show that sulfation is a critical step for hair-growth effects of minoxidil and that it is the sulfated metabolite that directly affects hair follicles.

The antiinflammatory effects of adenosine receptor agonists on the carrageenan-induced pleural inflammatory response in rats

Adenosine and adenosine receptor agonists have a variety of inhibitory effects on the generation of inflammatory mediators by neutrophils and other cell types. In human neutrophils stimulated with the chemotactic peptide FMLP, adenosine agonists inhibit O2- generation and degranulation. Because these findings suggest that the agonists may have potential as antiinflammatory agents, several compounds were evaluated for effects on the exudative and cellular phases of carrageenan-induced pleural inflammation in rats. All of the agonists tested inhibited both parameters of the inflammatory response. Inhibition appeared to correlate better with binding to the A1 than to the A2 receptor and was reversible by a known adenosine receptor antagonist, 8-phenyltheophylline. In mechanistic studies, R-N-(1-methyl-2-phenylethyl)adenosine, a standard A1 selective agonist, reversed the drop in circulating neutrophil count that occurs after injection of carrageenan. These results suggest that the agonists may prevent cell emigration by inhibiting adhesion to the endothelium or diapedesis. In addition (R)-N-(1-methyl-2-phenylethyl)adenosine had weak inhibitory effects on superoxide production by FMLP-stimulated rat neutrophils. Control studies showed that the effects of the agonists were not the result of agonist-induced hypotension nor corticosterone production by the adrenal glands. These findings indicate that adenosine receptor agonists are effective new pharmacologic tools for the study of inflammatory processes.

[Effect of long-term administration of vasodilators and "antitrophic" agents on the structure and function of the heart in hypertensive rats]

In this study, we determined whether the persistency of cardiac hypertrophy after chronic vasodilation therapy with minoxidil (minox) was associated with functional or metabolic alterations in hypertensive rat hearts before, during and after an ischemic insult. In addition, we investigated the effects of the simultaneous administration of difluoromethylornithine (dfmo), a substance that could block hypertrophy by a direct inhibition of protein synthesis. Four groups of male Wistar rats were prepared: 1) normotensive controls (n = 8), 2) untreated renovascular hypertensive rats (HT, n = 15), 3) hypertensives treated with minox (8 mg/kg, n = 19), 4) hypertensives treated with minox and dfmo (1.7 g/kg, n = 20). After 21 days of treatment, the animals were sacrificed. In a small number of hearts, ornithine decarboxylase (ODC) activity was assayed in order to verify that dfmo, which is a suicide inhibitor of ODC, had effectively interrupted the polyamines pathway. The other hearts were prepared for retrograde perfusion at 35 degrees C and at constant flow (10 ml/min x g). Cardiac function was monitored via the balloon inserted in the left ventricle (LV) and the following protocol was applied: a) baseline period (24 min), b) ischemia (24 min), c) recovery (36 min). Finally, the hearts were weighed and LV wall thickness and inner radius were measured. Blood pressure was maintained near normotension in the two treated groups. Mean systolic pressure (in mmHg) was 145 +/- 4 with minox and 144 +/- 3 with minox + dfmo versus 181 +/- 4 in the HT group (p less than 0.0001).(ABSTRACT TRUNCATED AT 250 WORDS)

The action of diazoxide and minoxidil sulphate on rat blood vessels: a comparison with cromakalim

1. The actions of diazoxide and minoxidil sulphate have been compared with those of cromakalim in rat aorta and portal vein. 2. Diazoxide and minoxidil sulphate hyperpolarized the rat portal vein in a similar manner to cromakalim. 3. Cromakalim, diazoxide and minoxidil sulphate increased 42K and 86Rb efflux from rat portal vein, although minoxidil sulphate had only a small effect on 86Rb efflux. 4. Cromakalim, diazoxide and minoxidil sulphate increased 42K efflux from rat aorta but only cromakalim and diazoxide increased 86Rb efflux from this tissue. 5. Glibenclamide inhibited the relaxant actions of cromakalim, diazoxide and minoxidil sulphate on rat aorta and the increase in 42K efflux produced by these agents in this tissue. 6. Diazoxide relaxed an 80 mM KCl-induced contraction of rat aorta, whilst cromakalim and minoxidil sulphate were without effect. 7. Cromakalim, diazoxide and minoxidil sulphate had no effect on cyclic AMP or cyclic GMP concentrations in rat aorta. 8. It is concluded that diazoxide and minoxidil sulphate like cromakalim exhibit K+ channel opening properties in vascular smooth muscle. Diazoxide exerts an additional inhibitory action not related to the production of cyclic AMP or cyclic GMP. The action of minoxidil sulphate may be primarily located at a K+ channel which is relatively impermeable to 86Rb.

Hydroxylation of collagen by lungs of rats administered bleomycin

Collagen synthesized by tissue minces from lungs of rats administered 1 unit of bleomycin by intratracheal instillation 1 or 2 wk earlier contained relatively more hydroxylysine than did collagen made by lungs from saline-instilled control animals. Most, if not all, of the relative increase in lysine hydroxylation could be localized to the alpha 1 (I) chain of type I collagen. Lung homogenates from bleomycin-treated rats showed increased activity of lysyl hydroxylase (EC 1.14.11.4), the enzyme catalyzing the conversion of collagen-bound lysine to hydroxylysine. Thus, the increased hydroxylation of lysine and of lysine-derived cross-links previously observed in collagen of diseased human lungs and in animal models of lung fibrosis is reflected in an in vitro system.

Role of endogenous ANP on endocrine function investigated with a monoclonal antibody

Substantial volume expansion in conscious rats induces a strong natriuresis, cyclic GMP excretion, increase in cyclic GMP in plasma and kidney tissue, decrease in plasma renin activity and plasma aldosterone concentration. These effects are directly related to an increase in plasma levels of atrial natriuretic peptides. The renal response and the changes in plasma and kidney cyclic GMP, plasma renin activity and aldosterone could be totally blocked by simultaneous administration of monoclonal antibodies directed against ANP. From this study it seems to be clear that the rise in cyclic GMP and the inhibition of the renin-aldosterone system is not a direct effect of volume expansion but is specifically mediated by the released ANP. The great importance of ANP in acute volume expansion made us wonder about the role of ANP in chronic volume expansion and under basal conditions without volume loading. Chronic volume loading was induced pharmacologically by the sodium retaining vasodilatator minoxidil. Under both chronic volume expansion and basal conditions the neutralization of the circulation ANP by antibody administration leads to reduced plasma cyclic GMP levels. No alterations in urinary sodium excretion, plasma renin activity and plasma aldosterone concentration could be observed: In conclusion, the monoclonal antibody directed against ANP is a useful tool for the investigation of the physiological role of endogenous ANP.

The effect of topical minoxidil on hair follicular cycles of rats

To explore an easily accessible and reproducible model for examining the effect of minoxidil on hair growth, we studied the effect of minoxidil on the natural hair cycles of rats from birth to 80 days of age. During the 1st and 2nd postnatal cycles, the hair follicles grew very rapidly and the size of anagen follicles were markedly enlarged. In the 3rd cycle (50 days to approximately 100 days of age), duration of the telogen phase lasted approximately 20 days. Topical minoxidil, 1%, 3%, or 5% solution, applied on the backs of the rats from 23 days (weaning) to 80 days, induced a remarkable shortening of the telogen phase in the 3rd cycle. Although the dose-dependent response was very minimal, rats treated with 3% or 5% minoxidil showed similar effects in the 4th cycle. Minoxidil, however, did not induce prolongation of the anagen phase, but increased the rate of DNA synthesis in the anagen bulb during the 2nd and 3rd cycles. These results suggest that minoxidil specifically stimulates the secondary germ of the telogen follicles, resulting in rapid progression to anagen follicles.

Uridine kinase inhibition is involved in the vasodilator effects of minoxidil in the rat

1. Since minoxidil is a pyrimidine derivative, its actions on vascular smooth muscle may derive from structural relationships to the uridine nucleotides, which have been shown to be vasoconstrictive in the rat. 2. Minoxidil at a low vasodepressor dose of 0.03 mg/kg per min abolished the pressor response to uridine at doses from 2 to 8 mumol/kg per min, but did not reduce the responses to uridine monophosphate or uridine diphosphate in similar pressor doses, suggesting an action on either transport of uridine into cells or on uridine kinase which catalyses phosphorylation of uridine to uridine monophosphate, the mediator of uridine's vascular actions. 3. The active metabolite of minoxidil was found to inhibit rat liver uridine kinase in vivo using an HPLC technique. 4. Plasma uridine concentration was significantly higher in 11 hypertensive patients on minoxidil compared with pretreatment values, suggesting that uridine kinase inhibition is of a degree sufficient to increase the circulating pool of uridine. 5. The data is consistent with uridine kinase inhibition being a mechanism for the vasodilator actions of minoxidil.

Uptake kinetics and the effect of minoxidil on human keratinocyte cultures

The antihypertensive drug minoxidil (Lonolox) is rapidly taken up by human keratinocytes (HaCaT-cells). After 3 h the uptake is half of its maximum. Specific minoxidil receptors could not be found. High minoxidil concentrations (greater than 100 micrograms/ml) inhibited the incorporation of thymidine into DNA (ED50 = 263 micrograms/ml) and the incorporation of amino acids into proteins (ED50 = 251 micrograms/ml). The inhibition was reversible up to a concentration of 400 micrograms/ml. In the presence of 100 micrograms/ml minoxidil, the cell division remained active for a longer period of time and a higher cell density was achieved as opposed to the parallel control group. A prolongation of the proliferative capability of keratinocytes may be partially responsible for the positive effect of minoxidil on hair growth.

Intravascular and interstitial fluid dynamics in rats treated with minoxidil

Edema is a major complication of vasodilatory therapy. However, the pathophysiologic mechanisms leading to the formation of vasodilator-mediated edema are insufficiently understood. The present study therefore examined the effect of the chronic administration of the potent arteriolar vasodilator, minoxidil (Mx), on extracellular fluid dynamics in rats. Extracellular volume (ECV), plasma volume (PV), interstitial fluid volume (IV), arterial pressure (AP), and interstitial fluid pressure (IP) were measured in rats treated for 10 days with Mx (1.5 mg/kg/day) and in control animals. In addition to a decreased AP, Mx-treated animals had diminished water and sodium excretion. ECV, PV, and IV and plasma renin concentration (PRC) were also increased in the Mx-treated rats. IP, which was subatmospheric in control rats (-2.6 +/- 0.04 mm Hg), was near zero in Mx-treated animals (-0.2 +/- 0.02 mm Hg, p less than 0.05). Saline ECV expansion (20 min, Ringer infusion, 3% body weight) or rat albumin injection (300 mg/2 ml) induced similar changes in the volume of the extracellular fluid compartments in both groups. However, changes in IP were blunted in Mx-treated rats. These results, therefore, show that Mx-treated rats have changes in interstitial fluid dynamics prior to any macroscopic evidence of edema accumulation. These alterations in the extracellular compartment dynamics may be a consequence of the sustained arteriolar vasodilation induced by Mx.

Differences in activity of minoxidil and cyclosporin A on hair growth in nude and normal mice. Comparisons of in vivo and in vitro studies

Hair growth effects of minoxidil and cyclosporin A were assessed in a series of experiments using nude mice. Systematic monitoring of coat hair showed that untreated nude mice grow extremely sparse and transient hair in cycles. This monitoring was done by photographing each animal through at least one full growth cycle and rating peak growth on a 1 to 4 scale. Topical administration of minoxidil or minoxidil sulfate did not influence this cyclic hair growth. Orally administered minoxidil also had no effect but oral cyclosporin A increased peak hair growth. None of the treatments altered the length of the hair cycle. Direct drug effects on follicles were tested in vitro using organ cultured vibrissae from both nude and normal mice. Minoxidil stimulated hair growth in follicles from normal but not nude mice. In contrast, cyclosporin A stimulated growth only in vibrissae follicles from nude but not normal animals. These studies show that minoxidil and cyclosporin A influence hair growth differentially. Cyclosporin A directly affects nude hair follicles by apparently compensating for a genetic defect inherent in nude follicles. Minoxidil does not have a similar effect. Apparently, the biochemical pathway activated by minoxidil is not a critical defect of hair growth in nude mice. We conclude that nude mice are not useful for studying minoxidil effects but they may be useful in studying pleiotropic effects of the nude gene on hair growth.

Pharmacologic nephrectomy with chronic angiotensin converting enzyme inhibitor treatment in renovascular hypertension in the rat

Angiotensin converting enzyme (ACE) inhibitor treatment in renovascular hypertension is associated with acute compromise of renal function in patients with bilateral renal artery stenosis or with arterial stenosis to a single functioning kidney. Recent evidence has suggested that renal function is also compromised in the stenosed kidney of patients with unilateral renal artery stenosis. The long-term consequence of this reduction in renal function is not known. We have studied the effect of chronic ACE inhibition with enalapril on renal structure and function in rats with the two-kidney one-clip model of renovascular hypertension. Four weeks after placement of a clip on the left renal artery, hypertensive rats were randomized to treatment with enalapril, minoxidil, or to a no treatment group. Twelve months later split kidney function was determined by chromium 51-labeled ethylenediamine-tetraacetic acid clearance in surviving rats. Clearance of the clipped kidney was 0.0 ml/min (enalapril group), 0.26 +/- 0.23 ml/min (minoxidil group), and 0.74 +/- 0.13 ml/min (untreated group). The clipped kidney from the enalapril treated rats weighed much less than the minoxidil group or the untreated group (0.46 +/- 0.1 gm, 1.2 +/- 0.07 gm, and 1.14 +/- 0.10 gm, respectively). Enalapril treatment was stopped for 2 weeks in five rats. The clipped kidney remained small and nonfunctional. Histologic examination revealed marked interstitial fibrosis and tubular atrophy of the clipped kidneys from the enalapril treated group in contrast to minor changes in the minoxidil treated and untreated groups. After 12 months of treatment, survival in the enalapril group was 84%, 48% in the minoxidil group, and 15% in the untreated group.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of nisoldipine on atrial natriuretic peptides, blood pressure and cardiac hypertrophy in Dahl rats

The role of the calcium antagonist nisoldipine and the arteriolar vasodilator minoxidil on plasma levels of atrial natriuretic peptides (ANP), systolic blood pressure and heart weight was estimated in inbred Dahl salt sensitive (S) rats and inbred Dahl resistant (R) rats in long-term experiments. S rats develop quickly malignant hypertension, cardiac hypertrophy and have increased ANP plasma levels when fed a high salt diet (8% NaCl), while R rats on a high salt stay normotensive. In S rats 5 weeks on a high salt diet, therapeutic treatment with nisoldipine for 5 weeks not only decreased blood pressure but also produced a regression in cardiac hypertrophy and a reduction in elevated ANP plasma levels in comparison to the untreated salt-loaded S controls. Similar results were achieved in a preventive trial. In contrast with nisoldipine, therapeutic treatment with minoxidil in salt-loaded S rats lead to no reduction in cardiac hypertrophy and produced an additional increase in plasma ANP despite a reduction in blood pressure. The increase in plasma ANP level in this model of hypertension and its modulation by antihypertensive treatment with a calcium antagonist or an arteriolar vasodilator show that the changes in ANP plasma levels are probably secondary to hypertensive disease and the associated cardiac volume overload.