An oral yohimbine/L-arginine combination (NMI 861) for the treatment of male erectile dysfunction: a pharmacokinetic, pharmacodynamic and interaction study with intravenous nitroglycerine in healthy male subjects

AIMS

Interaction of phosphodiesterase type 5 inhibitors for the treatment of erectile dysfunction with organic nitrates could lead to severe hypotension. NMI 861 is a combination of 7.7 mg yohimbine tartrate and 6 g l-arginine glutamate. A similar oral combination, which contains the same amount of yohimbine and L-arginine, has been shown to improve erectile function in previous studies.

METHODS

In two placebo-controlled, randomized, double-blind, two-way crossover design studies we aimed to assess first the pharmacokinetics and pharmacodynamics of a single oral dose of NMI 861 administered in 16 healthy male subjects, and then the pharmacodynamics of orally administered NMI 861 in combination with intravenous nitroglycerine (GTN) in 12 healthy male subjects. Systolic (SBP) and diastolic (DBP) blood pressures, pulse rate and adverse events were measured in each study.

RESULTS

NMI 861 was well tolerated by all subjects with no significant adverse reactions reported. For L-arginine, mean C(max) +/- SEM (range) was 42 +/- 2.2 (28-63) microg ml(-1) and t(max) (range) was 0.88 (0.50-1.5) h. AUC and t(1/2) were not calculated for L-arginine because of the presence of endogenous concentrations and the contribution from food sources. For yohimbine, mean C(max) was 42 +/- 11 (2.8-128) ng ml(-1); t(max) was 0.57 (0.25-1.0) h; mean AUC(0,8 h) was 65 +/- 24 (5.4-332), ng ml(-1) h and t(1/2) was 1.0 +/- 0.34 (0.40-6.0) h. There was a small but significant difference in the mean change from baseline for SBP from 0 to 6 h after NMI 861 treatment compared with placebo (0.8 +/- 1.4 vs-4.1 +/- 2.1 mmHg, respectively; 95% CI 0.0, 9.8 mmHg (P = 0.047)). There was no significant difference in SBP between treatments for the studied periods 6-12 h and 12-24 h. There was no significant difference in DBP or pulse between NMI 861 and placebo treatments for the three studied time periods. In the study designed to investigate the interaction of organic nitrate with NMI 861, subjects were infused intravenously with increasing doses of GTN (15 min each dose) at 2.5, 5, 10, 20 and 40 microg min(-1) starting 40 min after a single oral dose of either NMI 861 or placebo. There was no significant difference in the hypotensive response induced by GTN between the NMI 861 and placebo treatments. The mean maximum changes from baseline during GTN infusion for subjects administered with either NMI 861 or placebo were a decrease of 16.9 +/- 3.4 vs 13.6 +/- 2.4 mmHg (mean difference between treatments -3.3 mmHg, 95% CI -12.7, 6.0 mmHg (P = 0.460)) for SBP, a decrease of 14.7 +/- 2.0 vs 14.0 +/- 2.0 mmHg for DBP (mean difference -0.7 mmHg, 95% CI -8.2, 6.8 mmHg (P = 0.835)), and an increase of 11.8 +/- 1.9 vs 14.1 +/- 2.4 beats min(-1) for pulse, respectively (mean difference -2.3 beats min(-1), 95% CI -9.3, 4.5 beats min(-1) (P = 0.464)).

CONCLUSIONS

Acute oral administration of NMI 861 was found to be well tolerated and bioavailable in healthy male subjects and no significant hypotensive interaction with intravenous GTN was detected at the doses investigated.

Yohimbine: a clinical review

Although yohimbine (YOH) has been available for the treatment of male erectile dysfunction (ED) for longer than Viagra, there is a perception that little is known about the clinical performance of the drug. This review attempts, by comprehensive analysis of the literature, to cover the clinical, pharmacological, and therapeutic profiles of YOH, relevant to its potential utility in the management of patients with ED. Relatively few well-designed studies have been completed. From these, however, it can be concluded that YOH as monotherapy possesses only modest efficacy in ED patients. In acute and chronic (long-term) studies, YOH has been found to be relatively free of side effects over the dose range predicted to be effective in ED. At much higher doses, the most frequently observed effects, consistent with the primary pharmacological action of the drug, are elevation of blood pressure, a slight anxiogenic action, and increased frequency of urination. These side effects are all easily reversible on termination of YOH therapy. There is increasing evidence that the erectogenic action of YOH can be augmented by concomitant administration of agents that augment the release and/or action of nitric oxide in the corpus cavernosum. YOH has yet to be studied in female sexual dysfunction. Overall, the benefit risk profile of YOH would indicate that it has potential, more probably as part of a combination strategy, e.g., with a drug that enhances the nitric oxide pathway, in the treatment of ED.

Angiotensin-converting enzyme in rat brain and extraneural tissues visualized by quantitative autoradiography using 3H-trandolaprilate

Tritium-labeled trandolaprilate (RU 44403), the active diacid form of the potent and long-acting angiotensin-converting enzyme (ACE) inhibitor trandolapril, has been evaluated as a new autoradiographic marker for the enzyme. The characteristics of 3H-trandolaprilate binding were first determined autoradiographically in tissue sections from rat brain (caudate-putamen) and kidney. 3H-Trandolaprilate binds saturably to these tissues, and with very high affinity (Kd values, 0.36 and 0.13 nM, respectively), and appears to show good selectivity for the enzyme. Due to its high affinity (approximately 100 times that of captopril), the performance of 3H-trandolaprilate as an autoradiographic marker is comparable to that of the recently described 125I-labeled derivative of lisinopril (125I-351A). Saturation and displacement studies in serial sections from a variety of central and peripheral tissues confirmed that the specificity of labeling was similar throughout. The anatomical distribution of ACE visualized with 3H-trandolaprilate in these tissues was close to that described for 3H-captopril and 125I-351A with some minor differences which might arise from difference in the specificity of the ligands.

Comparison of the effects of the ace inhibitors trandolapril and enalapril on phlogogen induced foot pad oedema in the rat

Two angiotensin converting enzyme (ACE) inhibitors, trandolapril and enalapril, were compared for their effects on rat food-pad oedema induced by carrageenin, bradykinin, dextran and platelet activating factor (PAF). Trandolapril (0.03-30.0 mg/kg, per os) potentiated carrageenin-induced oedemas. Enalapril produced the same effect at 3-10 fold higher doses (0.3-30.0 mg/kg per os). Both ACE inhibitors were equiactive in potentiating bradykinin-induced oedema. Neither compound affected dextran-induced oedema. In marked contrast PAF-induced oedema was reduced by both ACE inhibitors, trandolapril being approximately 10 fold more active than enalapril. The observed differences in potency between the two ACE inhibitors corresponded with their previously described actions on inhibition of plasma and tissue ACE and in inducing hypotension. The results suggest a crucial role of kinins in the oedemagenic response to carrageenin. The reason why the ACE inhibitors reduced PAF-induced oedema is not clear, but could involve peripheral vasodilation.

[Ex vivo and in vitro effects of trandolapril on the efflux of 22Na from the caudal artery of the SHR rat. Inhibition of vascular angiotensin II production]

The inhibition of converting enzyme (CE) activity in target tissues other than blood and lung vascular endothelium may be important for the antihypertensive action of CE inhibitors (ICE) (Unger et al 1983). In order to determine if ICE may have an effect on the transmembrane Na movements implicated in the regulation of vascular tone, we have studied the effects of trandolapril and enalapril on 22Na effluxes from the tail artery of 20 weeks old SHR. In vivo, the chronic oral treatment (14 days) with trandolapril (1.3 mg/kg/day) decreased the ouabain-sensitive 22Na efflux (controls: 0.050 +/- 0.004 min-1 (n = 8); trandolapril (1 mg/kg): 0.030 +/- 0.03 min-1 (n = 10) p less than 0.01), and the ouabain-insensitive 22Na efflux (controls: 0.088 +/- 0.0030 min-1; trandolapril (1 mg/kg): 0.080 +/- 0.003 min-1 (n = 10) p less than 0.05). Enalapril had no effect at the dose of 10 mg/kg/day (14 days). In vitro, trandolapril diacid (RU 44403) decreased the ouabain-sensitive 22Na efflux (controls: 0.045 +/- 0.002 min-1 (n = 6); RU 44403 (10(-9) M): 0.031 +/- 0.002 min-1 (n = 6) p less than 0.01), and the ouabain-insensitive efflux (controls: 0.096 +/- 0.004 min-1 (n = 6); RU 44403 (10(-9) M): 0.084 +/- 0.006 min-1 (n = 6) p less than 0.05). The effects were dose-dependent. Enalapril diacid (MK 422) also dose-dependently decreased 22Na effluxes but it was approximately 10 fold less active.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin-converting enzyme inhibition, anti-hypertensive activity and hemodynamic profile of trandolapril (RU 44570)

Trandolapril (RU 44570), a new non-sulfhydryl angiotensin-converting enzyme (ACE) inhibitor chemically related to enalapril, and its diacid (RU 44403), were investigated for their ability to inhibit angiotensin-converting enzyme. Trandolapril attenuated angiotensin I (Ang I)-induced pressor responses following i.v. administration to rats and dogs with ID50 values of 13.1 +/- 1.3 and 21.1 +/- 2.3 micrograms/kg. RU 44403 produced corresponding values of 9.9 +/- 0.7 and 7.2 +/- 2.3 micrograms/kg. Trandolapril (3-300 micrograms/kg) produced a dose-related attenuation of Ang I-induced pressor responses (ID50 30 micrograms/kg) following oral administration to rats. Oral administration of trandolapril (30-1000 micrograms/kg) to dogs inhibited Ang I pressor responses for over 6 h. The depressor action of bradykinin in the rat was potentiated by i.v. trandolapril and RU 44403 with ED50 values of 5.5 +/- 0.8 and 4.9 +/- 0.3 micrograms/kg respectively. Trandolapril was 2.3-10-fold more potent than enalapril in all experiments, depending on species or route of administration. RU 44403 and MK 422 were approximately equipotent, implying that trandolapril was more readily hydrolysed than enalapril. Trandolapril (0.3-30 mg/kg) produced dose-related, long-lasting (greater than 24 h) reductions in blood pressure (BP) in spontaneously hypertensive rats (SHR) following oral administration. The anti-hypertensive effect was potentiated significantly in hydrochlorothiazide-pretreated SHR when the plasma renin activity was increased. Enalapril was 10-fold less potent than trandolapril in reducing BP. The anti-hypertensive action of trandolapril (3 mg/kg) was abolished in SHR that were bilaterally nephrectomized 24 h beforehand, but was maintained in SHR pretreated by indomethacin (5 mg/kg p.o.). Trandolapril (1 mg/kg i.v.) produced a modest and transient reduction in BP in anesthetized dogs. Trandolapril produced dose-related (30-1000 micrograms/kg) reductions in BP, total peripheral resistance and heart work in dogs pretreated with hydrochlorothiazide to increase plasma renin activity.

Differential effects of oral trandolapril and enalapril on rat tissue angiotensin-converting enzyme

Trandolapril (3-100 micrograms/kg) and enalapril (10-300 micrograms/kg) were administered orally to conscious rats. Angiotensin-converting enzyme (CE) activity was inhibited in serum, heart ventricle, renal inner cortex, lung, aorta, adrenal cortex and adrenal medulla, but not in the striatum. Inhibition was maximal at 2 h and with trandolapril was maintained for 24 h. Blood pressure and heart rate were not affected by either compound. Trandolapril was 6-10-fold more potent than enalapril. Differences between trandolapril and enalapril in CE inhibition observed in heart ventricle, adrenal cortex and medulla could be due to the presence of more than one type of CE or CE-like activity.

Structure-activity relationship in PAF-acether. 4. Synthesis and biological activities of carboxylate isosteres

The synthesis and biological characterization of some 3-carboxylate isosteres of PAF-acether structurally modified in positions 1 (ether, carbamate), 2 (acetoyl, ethoxy), and 3 (chain length and polar head group) are reported. All derivatives present antagonist activities against PAF-acether-induced effects in vitro (platelet aggregation) and in vivo (bronchoconstriction and thrombocytopenia in guinea pig and, to a lesser extent, hypotension in rat). The functional modifications presented here do not modify dramatically the potency of antagonist activities, and there is no enantioselectivity. All of the isosteres are specific PAF-acether antagonists, except the 1-carbamoyl analogue, which is also potent against acetylcholine-induced hypotension and bronchoconstriction.

Interaction between aldosterone and vasopressin on vascular smooth muscle permeability to sodium

The s.c. injection of aldosterone (10 micrograms/kg) induces a release of vasopressin. The peak of plasma vasopressin level occurs at the same time as the late in vivo effect of aldosterone on passive 22Na efflux from arterial smooth muscle. These results indicate that vasopressin mediates the delayed in vivo effects of aldosterone on ouabain-insensitive 22Na efflux, since on the other hand, it has been possible to show that the action of the peptide is accelerated by a previous exposure to the mineralocorticoid. Indeed, after a 120-min pretreatment with 10(-8) M aldosterone, vasopressin induces an effect on 22Na efflux in 30 min, as opposed to the 120 min needed in the absence of the steroid.

Prevention by calcitonin of the pathological modifications of the rabbit arterial wall induced by immunization with elastin peptides: effect on vascular smooth muscle permeability to ions

Immunization of rabbits with elastin peptides prepared from purified bovine ligamentum nuchae elastin produces calcified arteriosclerotic lesions and fragmentation of elastic lamellae. Simultaneous administration of porcine calcitonin largely prevents the development of lesions. Experiments were carried out to clarify the mechanisms involved in the development of lesions as well as those involved in the preventive effect of calcitonin. Control experiments were carried out using bovine serum albumin (BSA) as antigen. Circulating antibodies and soluble immune complexes increased steadily in the sera of animals immunized with elastin peptides or BSA. The cellular immune reaction was weak as assessed by [3H]thymidine incorporation into lymphocytes in the presence of antigen or phytohemagglutinin. Arterial lesions appeared only in the animals immunized with elastin peptides, not in those immunized with BSA. Ion flux measurements were also carried out on strips of aorta obtained from immunized and control animals. Immunization with elastin peptides significantly increased the ouabain-insensitive 22Na+ efflux, the 86Rb efflux (indicator of K+ efflux), and the 45Ca2+ influx. Simultaneous calcitonin administration prevented the increase in Ca2+ influx but did enhance passive permeability to Na+ and K+ as well as the sodium pump. When calcitonin was administered without immunization, it decreased arterial smooth muscle permeability to Na+ and K+ and also decreased the basal Ca2+ influx. It is concluded that the pathological modifications of the arterial wall triggered by immunization with elastin peptides is at least partly mediated by the effect of antielastin antibodies and immune complexes on the ion permeability of arterial smooth muscle. Prevention of the increased Ca2+ influx by calcitonin is probably a key effect in the prevention of the development of lesions. The fact that calcitonin alone can modify the ion permeability of arterial smooth muscle suggests that this hormone may play a role in the regulation of vascular homeostasis.

[Involvement of vasopressin in the effects of aldosterone on the arterial wall]

We have previously shown that an humoral factor is involved in the delayed effect of aldosterone on the passive transmembrane movements of Na+ from arterial smooth muscle (Moura and Worcel, 1984). In absence of vasopressin, the effects of aldosterone on the same Na transports suggest that vasopressin may be this humoral factor (Moura, Angeli and Worcel, 1986) (Angeli, Moura and Worcel, 1986). We show here that the s.c. injection of aldosterone (10 micrograms/kg) to adrenalectomized Sprague Dawley rats induces a release of vasopressin. This peptide exerts a direct action on ouabain-sensitive and insensitive components of 22Na efflux from the rat tail artery, and potentiates the late effect of aldosterone on passive Na+ efflux. There is no additive effect of the two hormones on Na+ pump activity. In conclusion vasopressin is the humoral factor involved in the late effect of aldosterone on passive transmembrane movement of Na from vascular smooth muscle.

Arterial effects of aldosterone and antimineralocorticoid compounds mechanism of action

The aim of our work was to study the mechanism of action of aldosterone and antialdosterone compounds on Na+ and K+ fluxes in vascular smooth muscle. In the long term, regulation of salt metabolism depends on aldosterone effects on Na+, K+, H+ and H2O transport by the renal tubules. Furthermore, it has been shown that aldosterone modifies several epithelial transports, inducing a positive sodium balance. The chronic in vivo administration of aldosterone modifies transmembrane ionic fluxes in vascular smooth muscle. Garwitz and Jones suggested that aldosterone may enhance net Na+ transport through the stimulation of the sodium pump. The results obtained in our laboratory indicate that aldosterone has a direct stimulatory action on ouabain-dependent and on ouabain-independent Na efflux. Furthermore, the mineralocorticoid enhances passive K permeability, as well as the Na pump dependent K influx. Both effects are blocked by antimineralocorticoid compounds. Recent experiments have shown that vasopressin potentiates some of the in vivo effects of aldosterone.

Antiarrhythmic and hemodynamic effects of prifuroline

The antiarrhythmic activity of 4-(2-benzofuranyl)-2-(dimethylamino)-1-pyrroline (prifuroline) has been evaluated in rats, guinea-pigs and dogs. Prifuroline dose-dependently antagonizes the arrhythmogenic action of aconitine in rats, when administered either intravenously (5, 10 or 20 mg/kg) or intraduodenally (10, 20 or 50 mg/kg); it exhibits effectiveness by the digestive route at doses only twice as greater as the active i.v. doses: its intravenous anti-aconitine activity is comparable to that of disopyramide, and superior to that of quinidine; lidocaine is inactive in this test. Prifuroline also diminishes ventricular susceptibility to electrical stimulation in open-chest rats; its effect is comparable to that of disopyramide and amiodarone at the same dose levels; quinidine and lidocaine are less effective. Only prifuroline and propranolol were able to antagonize ouabain toxicity in guinea-pigs, quinidine showing only borderline activity, and disopyramide, lidocaine and verapamil being ineffective. In a model of arrhythmias induced by anoxic stress in rats, all the tested compounds were found active, with prifuroline and disopyramide providing complete protection at high dose levels. The arrhythmias induced in dogs by coronary artery ligation were markedly antagonized by prifuroline after doses of 5 and 10 mg/kg i.v. or 30 mg/kg intraduodenally; the duration of its antiarrhythmic activity in this model of arrhythmias in conscious dogs was much longer after intraduodenal than after i.v. administration. Prifuroline was also able to restore sinus rhythm in guinea-pigs after intracardiac conduction blockade with acetylcholine, although being devoid of anticholinergic activity. It also diminishes the maximal frequency of guinea-pig atria electrically stimulated in viro (EC25 = 5 X 10(-6) g/ml).(ABSTRACT TRUNCATED AT 250 WORDS)

[Effects of aldosterone and vasopressin on transmembrane efflux of sodium from the arterial wall]

We have previously shown that, injected s.c. to adrenalectomized Sprague-Dawley rats (SD.ADx), aldosterone has a mineralocorticoid specific effect on transmembrane movements of 22Na from arterial smooth muscle. These effects appear to be partly due to the action of an humoral factor. Indeed, in vitro, the late increase in passive 22Na efflux is not observed (Moura and Worcel, 1984). In rats perfused with a specific antagonists of the pressor effect of vasopressin (Vp), the in vivo administration of aldosterone induced a kinetic action similar to that observed after in vitro exposure to the mineralocorticoid. These results suggested that Vp may be the humoral factor (Moura, Angeli and Worcel, 1985). In adrenalectomized homozygous Brattleboro rats (DI.ADx), aldosterone (10(-8)M) increases ouabain independent 22Na efflux (DI.AX: 0.073 +/- 0.002 min-1(n = 15); DI.ADx + Aldo: 0.096 +/- 0.002 min-1(n = 12)p less than 0.01) and ouabain-dependent 22Na efflux (DI.ADx: 0.031 +/- 0.001 min-1; DI.ADx + Aldo: 0.037 +/- 0.002 min-1 p less than 0.01). Vp also increases ouabain sensitive and insensitive 22Na effluxes and potentiates the effects of aldosterone on passive Na+ transferts (DI.ADx + Aldo + Vp: 0.015 +/- 0.003 min-1 (n = 16) p less than 0.01). In conclusion, these results suggest that Vp may be involved in the effects of aldosterone on 22Na effluxes. Furthermore Vp potentiates the effects of aldosterone on passive 22Na effluxes. But it is not yet possible to ascertain if Vp action is additive or permissive.

The effects of some slow channel blocking drugs on high affinity serotonin uptake by rat brain synaptosomes

The effects of some slow channel blocking drugs were investigated on high affinity serotonin uptake into crude rat brain synaptosomes. Serotonin uptake was sodium-dependent and competitively inhibited by imipramine (IC50 0.6 microM, Ki 0.26 microM). Bepridil, verapamil and diltiazem produced an apparent competitive inhibition of serotonin uptake with respective IC50 of 4.8, 5.2 and 308 microM. Nitrendipine and the sodium channel blocker, lidocaine, were without effect, even at 100 microM. The mechanism of the inhibitory effect is unknown but may involve an allosteric interaction with the sodium-dependent transporter.

Arterial smooth muscle effects of aldosterone and vasopressin: action on ionic fluxes

We have shown previously that aldosterone injected s.c. to adrenalectomized rats has a mineralocorticoid specific action on the transmembrane movements of sodium and potassium from the rat tail artery. These effects appeared to be partly due to an unknown humoral factor. Indeed, the late in vivo effects of aldosterone on 22Na and 86Rb effluxes are suppressed or reduced after in vitro exposure to the hormone. In rats perfused with a specific antagonist of the pressor effect of vasopressin, the in vitro administration of aldosterone induced a kinetic action similar to that observed after in vitro exposure to the mineralocorticoid. Vasopressin exerts a direct action on 22Na and 86Rb effluxes. These effects were correlated in the time with the late in vivo effects of aldosterone. Moreover, vasopressin appears to potentiate the in vitro effects of aldosterone on 22Na and 86Rb effluxes. It is not yet possible to ascertain if this effect is additive or permissive.

Peripheral cardiovascular effects of tabernanthine tartrate in anaesthetized rats

The peripheral cardiovascular effects of tabernanthine tartrate have been studied in anaesthetized rats. Our results confirm that the bradycardic effect of tabernanthine is not inhibited by vagotomy, atropine or propranolol. On the contrary, bivagotomy, atropine treatment, as well as carotid artery occlusion, potentiate the bradycardic effect of tabernanthine. The same is true for its hypotensive action and can be explained by the suppression of a compensatory mechanism involving the central nervous system, the parasympathetic system and/or a baroreflex mechanism. In addition, domperidone and sulpiride, two dopaminolytic drugs, are able to potentiate the decrease in heart rate produced by tabernanthine. In pithed rat, tabernanthine 1 mg/kg, potentiates the increases in systolic blood pressure produced either by norepinephrine or serotonine; conversely the systolic blood pressure responses to angiotensin II are significantly inhibited by tabernanthine 1 mg/kg. Thus, tabernanthine appears to possess a complex cardiovascular mechanism of action, depending probably on a simultaneous stimulation of beta 2-vascular adrenoceptors and alteration of cellular movements of calcium. Part of the direct bradycardic effect, as well as the inhibition of the pressor responses of angiotensin II could be explained by a calcium antagonist action of the alcaloid.

Effects of antiglucocorticoids on glucocorticoid hypertension in the rat

The early phase of hypertension induced in rats by a glucocorticoid agonist RU 26988 was studied. Systolic blood pressure increased by 35 mm Hg. Water and sodium urinary excretion increased transiently, and plasma volume decreased. Total and ouabain-sensitive sodium efflux, as well as rubidium efflux, were enhanced by glucocorticoid administration. Low salt intake did not prevent hypertension. Pretreatment with RU 38486, a steroid with antiglucocorticoid properties, largely prevented the rise in blood pressure (+10 mm Hg) and suppressed transient natriuresis and the decrease in plasma volume. Changes in total and ouabain-sensitive sodium efflux were completely prevented, whereas changes in rubidium efflux were only partly reversed. Similarly, administration of progesterone, a steroid with antiglucocorticoid effects, prevented glucocorticoid hypertension (+11 mm Hg) and vascular ionic changes. In contrast administration of RU 28318, an antimineralocorticoid agent, was without effect on glucocorticoid hypertension (+38 mm Hg). Progesterone or RU 38486 administered after glucocorticoid also decreased blood pressure. Present data indicate that glucocorticoid hypertension may be prevented or reversed in its early phase by steroid drugs with antiglucocorticoid properties. These drugs also appeared to prevent the sodium and rubidium flux abnormalities induced by glucocorticoid. We suggest that activation of the vascular glucocorticoid receptors may be involved in the pathophysiology of glucocorticoid hypertension.

[Effect of an antiglucocorticoid steroid on the arterial hypertension induced by glucocorticoids in the rat]

Hypertension was induced in male rats by administration of a glucocorticoid agonist, RU 26988. Systolic blood pressure (SBP) increased by 35 mmHg. Administration of an antimineralocorticoid derivative, RU 28318, did not modify hypertension. In contrast administration of a steroid derivative with antiglucocorticoid properties, RU 38486, prevented glucocorticoid-induced hypertension in a large part. SBP augmented only by 10 mmHg. The glucocorticoid increased total and active, ouabain-sensitive, 22Na efflux, as measured from caudal arteries, whereas concomitant administration of the antiglucocorticoid derivative prevented these changes. It is suggested that glucocorticoid-induced hypertension may be related to vascular Na pump activation and to the subsequent ionic changes. These changes, as well as hypertension, are antagonized by steroid derivatives with antiglucocorticoid properties.

Experimental brain ischemia: neuron-specific enolase level in cerebrospinal fluid as an index of neuronal damage

Levels of neuron-specific enolase (NSE) were measured in rat CSF following occlusion of the four major arteries to the brain for 10, 20, or 30 min. In the CSF of rats submitted to 30 min of total ischemia, an up to nine-fold increase of NSE level occurred within the first few hours and then slowly diminished. Significant levels were seen for as long as 8 days. Histological observations 3 days after ischemia showed neuronal loss as well as neuronal damage in several forebrain regions such as hippocampus, striatum, and thalamus. Ischemia was followed by transient decreases in exploration behavior and neurological states that were no longer visible 24 h later. After 10 or 20 min ischemia, NSE levels were increased to a lesser degree and fewer damaged neurons were observed. The positive correlation between duration of ischemia and amount of NSE release in CSF indicates that the measurement of NSE in the CSF is a sensitive and reliable index of neuronal lesions.

Direct action of aldosterone on transmembrane 22Na efflux from arterial smooth muscle. Rapid and delayed effects

Acute subcutaneous (s.c.) administration of aldosterone increases ex vivo 22Na efflux from rat tail artery smooth muscle, which appears to be due to a specific action on mineralocorticoid receptors. Indeed, this effect is blocked by the antimineralocorticoid compounds RU 28318 [17 beta-hydroxy-3-oxo,7 alpha-propyl(17 alpha)-pregn 4-ene, 21 potassium carboxylate] and spironolactone. The specific glucocorticoid receptor agonist RU 26988 [11 beta,17 beta-dihydroxy-17-(1-propynyl) androesta-1,4,6 trien-3-one] does not modify 22Na efflux. We show here that aldosterone has, at physiological concentrations, a mineralocorticoid specific stimulating effect on passive and sodium pump dependent transmembrane movements of sodium from the rat tail artery smooth muscle. Aldosterone exerts two types of action on sodium transport: 1) a delayed stimulation of ouabain-dependent 22Na efflux and ouabain-independent 22Na efflux, which are completely blocked by actinomycin D; and 2) a very rapid increase of passive 22Na efflux, which is insensitive to actinomycin D and therefore does not seem to depend on transcription of genomic information.

Effect of hydralazine on tension and membrane potential in the rat caudal artery

To determine whether the vasodilator, hydralazine (HYD), produces hyperpolarization of vascular muscle cells, we measured the effect of HYD on membrane potential and contractile responses to phenylephrine and K+. HYD (1 microM) caused a 4 mV hyperpolarization of phenylephrine-depolarized arteries (compared with controls without HYD), which could possibly account for up to three-fourths of the 39% decrease in tension measured. K+-contracted vessels were also 34% relaxed by 1 microM HYD without an effect on membrane potential. In addition, HYD further relaxed phenylephrine-stimulated vessels previously relaxed by D-600, suggesting that Ca++ channel blockade may not be an important mechanism of vasodilation for HYD. The evidence suggests that a nonmembrane action of HYD on arterial muscle probably multiplies the relaxant effect of membrane potential hyperpolarization. Both mechanisms would attenuate the effects of adrenergic stimulation.

Beta 2-adrenoceptor-induced hypotension in the ganglion-blocked angiotensin II-supported rat

An in vivo method is described to demonstrate vascular beta 2-adrenoceptor agonist and antagonist activity. Agonist activity was shown by the ability of i.v. injected compounds to reduce blood pressure in ganglion-blocked, phenoxybenzamine-treated, angiotensin II-supported rats. Procaterol was employed to assess the relative beta 2 blocking activity of propranolol IPS 339 and atenolol. Arunlakshana and Schild analysis of the data revealed that all these compounds were competitively beta 2 antagonists, their relative potencies being 100 : 80 : 0.56 respectively.

Pre- and postjunctional actions of hydralazine in vascular and nonvascular smooth muscle in vitro

This study investigated the in vitro prejunctional and postjunctional actions of hydralazine in vascular and nonvascular smooth muscle. Low concentrations (micromolar) of hydralazine blocked phenylephrine-induced increases in perfusion pressure in the innervated rat kidney, whereas high concentrations (greater than 10 microM) were required in the perfused, innervated rabbit ear artery. High concentrations of hydralazine were required to block phenylephrine-induced contractions of innervated rat vas deferens and anococcygeus muscle. After in vitro denervation, rabbit ear arteries became sensitive to low concentrations of hydralazine, but this was not observed in the rat vas deferens or anococcygeus muscle. Hydralazine (1-3 microM) was without effect on 3H-release from rat vas deferens, anococcygeus muscle and kidney previously incubated with [3H]norepinephrine. Hydralazine (1 microM) decreased field stimulation-induced 3H-release from [3H]norepinephrine-loaded rabbit ear arteries. The results from the rabbit ear artery confirm that in some vessels the presence of sympathetic nerve terminals can modify the postjunctional actions of low concentrations of hydralazine. However, the other vascular tissue studied (rat renal vascular bed) was sensitive to low concentrations of hydralazine while innervated. In conclusion, the existence of a postjunctional relaxant effect of hydralazine, observed in vitro at concentrations compatible with therapeutic blood levels found in humans, has been confirmed using two different vascular preparations. The relevance of the prejunctional effect of hydralazine remains to be ascertained.

Mode of action of cyclothiazide and triamterene. Ex vivo effect on 22Na and 86Rb efflux from arterial smooth muscle

Acute oral cyclothiazide treatment of conscious rats increased ex vivo 86Rb efflux from tail artery smooth muscle. This effect was blocked by oral triamterene. Identical results were obtained in binephrectomized rats, suggesting that the two drugs had a direct effect on smooth muscle K+ (86Rb) permeability. Decreased ex vivo smooth muscle 22Na efflux induced by oral cyclothiazide and triamterene is probably secondary to their renal actions, since there was no effect in binephrectomized rats.

Effects of angiotensin II on ionic fluxes in rat myometrium

1. The action of angiotensin II (At II) on 24Na, 42K and 36 Cl fluxes was examined using longitudinal strips of rat myometrium as an experimental model. 2. In normally polarized muscles, At II 3.3 x 10(-6)M, a concentration 10 times higher than necessary to produce a maximal contraction of the muscle, increases 42K and 36 Cl efflux rates as well as 42K uptake. The action of At II on 42K and 36Cl effluxes is concentration-dependent. Under the same conditions 24Na efflux is not affected by At II, but a significant increase of 24Na uptake is obtained. In order to know whether the observed effects were membrane potential dependent, we reexamined the action of the peptide in preparations previously depolarized by a 101 mM K+ solution (K+ replacing Na+). In depolarized preparations, At II 3.3 x 10(-6)M still increases 24Na uptake, but the effects previously observed on 42K and 36Cl fluxes in normally polarized preparations are suppressed. It is concluded that At II produces a primary increase in the membrane permeability to Na+ and that the stimulation of 42K and 36Cl fluxes induced by At II in myometrial strips appears to be mainly potential dependent.

Mechanism of action of angiotensin II on excitation-contraction coupling in the rat portal vein

1 The action of angiotensin II (At II) has been studied on the electrical and mechanical activity of the vascular smooth muscle of the rat portal vein.2 At low concentrations (between 5 x 10(-10) and 10(-9) M) At II induces an acceleration of spontaneous action potential (AP) discharge without change in the resting membrane potential. The frequency and size of the associated contractions are simultaneously augmented. Under these conditions the size of the spikes is not affected, thus suggesting that At II triggers the release of Ca(2+) from internal stores.3 The increase in AP discharge rate produced by low concentrations of At II results from an acceleration of the pacemaker potential. Furthermore, in the presence of 10 mM tetraethylammonium (TEA), there is an acceleration of the repolarizing phase of AP.4 Ouabain (10(-3) M) inhibits the increase in rhythmic activity induced by low concentrations of At II (in the presence of 10 mM TEA), thus suggesting that the Na-K pump is directly or indirectly involved in this action of the peptide.5 At higher concentrations, At II produces a concentration-dependent depolarization with an EC(50) of 1.2 x 10(-8) M and a maximum of 10(-7) M. The associated contraction has an EC(50) of 3.3 x 10(-8) M and a maximum of 3 x 10(-7) M.6 Ouabain (3 x 10(-3) M) depolarizes the cell membrane. Under these conditions, At II (10(-7) M) has a slight depolarizing effect, but it still produces a large tonic contraction.7 It is concluded, that At II acts on different steps of excitation-contraction coupling, depending on the concentration. At low levels, the peptide mainly accelerates spike discharge, through a mechanism involving the Na-K pump. At higher concentrations, At II depolarizes the cell membrane. The contraction is then activated by the influx of Ca(2+) due to secondary AP discharge and the release of Ca(2+) from intracellular stores. Pharmacomechanical coupling has an important role in the triggering of contractions both at high and at low concentrations of At II.

Interactions between hydralazine, propildazine and purines on arterial smooth muscle

1 The interaction of hydralazine (Hyd) and propildazine (Pyd) with purine compounds was studied in the isolated tail artery from normotensive Wistar (NW) rats.2 Exogenously added purines inhibit non competitively the antispasmogenic response to Hyd in denervated NW segments. The order of potency is 2-Cl-adenosine > adenosine > adenosine 5'-triphosphate (ATP) > inosine. Pyd action is modified only by the most active purine 2-Cl-adenosine, which displaces the dose-response curves to the right. Hyd and Pyd seem to act on the same site, since their maximal effects are not additive.3 Theophylline (Theo) 50 muM induces the appearance of the antispasmogenic effect of Hyd in the usually poorly responsive innervated proximal NW arterial segments. The potentiating action of Theo is identical to the enhancement of the Hyd response observed after 6-hydroxydopamine denervation. This result suggests that the release of endogenous purines from sympathetic nerves is sufficient to block the smooth muscle responses to Hyd, under our experimental conditions. A similar potentiating effect is obtained with propranolol (5 muM).4 The spontaneous release of (3)H, after loading with [(3)H]-noradrenaline, was considered as an indirect indication of purine leakage from nerve terminals. There is an inverse relationship between the rate of (3)H release, under these conditions, and the magnitude of the relaxant response to Hyd, i.e., (3)H leakage is higher in proximal NW segments.5 The most satisfactory explanation for the interaction of Hyd and Pyd with exogenous purines, and for the modulating actions of sympathetic nerve terminals, is that both antihypertensives act on a common receptor, sensitive to endogenous ATP and adenosine.

Hydralazine: mode of action at the neuroarterial junction

1. Hydralazine relaxes the rat tail artery by a direct action on vascular smooth muscle cells, which appears to be modulated by the action of sympathetic nerve terminals. 2. There is a gradient of response to hydralazine in arteries from normotensive Wistar rats, the proximal segments being poorly responsive. This gradient disappears after denervation with 6-hydroxydopamine in vitro. 3. Exogenously added purines inhibit noncompetitively the vasodilator response to hydralazine in denervated segments from normotensive Wistar rats. Their order of potency is 2-Cl-adenosine > adenosine > ATP > inosine. 4. The effect of hydralazine in innervated, poorly responsive segments is greatly potentiated by theophylline (50 mumol/l) and propranolol (5 mumol/l). These results, together with the effect of denervation, suggest that there are endogenous purines leaking from the nerve terminals under our experimental conditions. 5. Hydralazine produces a marked inhibition of stimulus-induced contraction and 3H release after [3H]noradrenaline loading. The mechanism of this prejunctional action appears to be different from the mechanism of the postjunctional effect.

Hydralazine: effect on the outflow of noradrenaline and mechanical responses evoked by sympathetic nerve stimulation of the rat tail artery

1 The effects of hydralazine on the vasoconstrictor responses to field stimulation of sympathetic nerves were studied in the isolated proximal segments of the rat tail artery. Vasoconstrictor responses to transmural stimulation were depressed by superfusion of hydrazine (0.3, 3 and 30 muM) in a concentration-dependent manner. The inhibition appeared slowly and was not easily reversed by washing. 2 Hydralazine (30 nM, 0.3 and 3 muM) reduced the stimulation-induced overflow of tritium from proximal and distal segments of the tail artery labelled with [3H]-noradrenaline in a concentration-dependent manner. This phenomenon appeared rapidly and was easily reversed by washing. 3 Theophylline (0.5 mM) did not affect the inhibitory effect of hydralazine on the stimulation-induced tritium efflux from the distal segment of the rat tail artery. 4 The present results indicate that hydralazine has, in addition to its action on vascular smooth muscle, a very marked effect on sympathetic nerve terminals. The mechanism of this presynaptic inhibition appears to be different from the postsynaptic effect, in view of the much shorter delay, the shape of the dose-effect curve, and the lack of interaction with theophylline.

Relationship between the (--)-[3H]-dihydroalprenolol binding to beta-adrenoceptors and transmembrane 86Rb efflux of the BC3H1 nonfusing muscle cell line

1 We have studied the binding properties of the beta-adrenoceptor antagonist [3H]-dihydroalprenolol ([3H]-DHA) on a membrane preparation of the non-fusing muscle cells BC3H1. 2 [3H]-DHA appears to bind to two classes of sites. The first site has a high affinity (KD = 0.53 nM) and a low capcity (Bmax = 58 fmol/mg of protein). The second site has a low affinity (KD = 110 nM) and a high capacity (Bmax = 1100 fmol/mg of protein). 3 The pharmacological properties of the high affinity low capacity site correspond to the known properties of the beta 2-adrenoceptors since the agonists inhibit [3H]-DHA binding following the series isoprenaline greater than adrenaline greater than noradrenaline greater than phenylephrine and the antagonists following the series alprenolol congruent to propranolol greater than butoxamine greater than practolol greater than phentolamine. 4 The binding properties of the beta-adrenoceptors were correlated with the effect of beta-adrenoceptor agonists and antagonists on 86Rb efflux rate from BC3H1 Cells. 5 There is very good correlation between the dissociation constants obtained by inhibition of [3H]-DHA binding by the antagonists alprenolol and propranolol, and the inhibition constants calculated from their antagonism of the 86Rb efflux rate stimulation by adrenaline. The ratio of the dissociation constants obtained by inhibition of [3H]-DHA binding by agonists and their EC50, calculated from 86Rb efflux curves, is higher than 1. This high KD/EC50 ratio indicates a high coupling efficiency between receptor occupancy by agonists and the biological effect measured.

Electrophysiological study of the action of angiotensin II on the rat myometrium

Angiotensin II (A II) produces a contraction of visceral and vascular smooth muscles of different species. The accompanying electrophysiological changes were measured on strips of rat myometrium at 35 degrees C using the double sucrose-gap technique. A II at concentrations from 5 x 10(-10) to 10(-6)M produces a depolarization and an increase in membrane conductance. This increase in membrane conductance is not membrane potential dependent since it is observed even when the membrane potential is maintained at the resting level. When all Na + in the test solution is replaced by either Li + or Mg (2+), the depolarizing effect of 10(-6)M A II is either markedly reduced or abolished. Under these conditions, A II produces a small initial hyperpolarization, which is modified by external potassium concentration changes and abolished by tetraethylammonium chloride. When all Cl- is replaced by either NO (-3) or cyclohexanesulfamate, A II (10(-6) M) still produces a 20-m V depolarization. The removal of extracellular Ca (2+) or K+ does not have any effect on the depolarizing action of A II, which also is not changed by 10(-3) M ouabain. In conclusion, A II produces a depolarization of the uterine smooth muscle membrane through an increase in the membrane conductance to Na+. The membrane conductance to potassium is increased simultaneously. The contraction induced by A II shows two components: a phasic component triggered by the Ca (2+) entry associated with spike production and a tonic component due to the release of Ca(2+) from intracellular stores.

Electrophysiological study of the action of neurotensin on the smooth muscle of the guinea-pig taenia coli

The effects of neurotensin on the membrane potential and conductance, and on the tension of the guinea-pig taenia coli were investigated using the sucrose gap method. In preparations spontaneously active at 37 degrees C, neurotensin (0.5--10 nM) increased the frequency of spikes and induced a smooth muscle membrane depolarization which led to a block of spike discharges. These electrical events were accompanied by phasic and tonic contractions of the smooth muscle. At 20 degrees C the guinea-pig taenia coli exhibited little or no spontaneous activity. Neurotensin (50 nM) rapidly depolarized the smooth muscle membrane and increased its conductance. Concentration--response curves of neurotensin-induced depolarization and contraction gave an EC50 of 1.7 nM and 4.5 nM respectively, with a maximally effective concentration of peptide around 50 nM for both effects. Studies in modified or substituted salt solutions indicated that the neurotensin-induced increase in smooth muscle membrane conductance was primarily due to an increase in Na+ and Ca2+ conductances.

Identification of different sodium compartments from smooth muscle cells, fibroblasts and endothelial cells, in arteries and tissue culture

1. The (22)Na efflux curve from the rat tail artery, at 35 degrees C, can be analysed as the sum of three distinct components, from 0 to 90 min of washout. After an initial diffusional component the two late exponential components Be(-kBt) and Ce(-kCt) have the following values: B = 3.03 +/- 0.15 m-mole/kg wet wt. and C = 0.56 +/- 0.04; k(B) = 0.145 +/- 0.005 min(-1) and k(C) = 0.015 +/- 0.007.2. In order to identify the cellular origin of the different compartments we compared the (22)Na efflux curve from the rat tail artery with the curves obtained from whole rabbit aortal strips, rabbit aortal medial or adventitial strips; and primary cultures from rabbit aorta medial smooth muscle cells, cultures of a non-fusing muscle cell line (BC(3)H1), fibroblasts and endothelial cells.3. It is possible to identify under these experimental conditions the cellular compartments from which the different exponential components of the efflux from the whole arteries originate. Fibroblasts and endothelial cultures, as well as adventitial strips exchange (22)Na slowly with exponential constants resembling k(C). Their efflux rate constants are: fibroblast cultures 0.010 +/- 0.002 min(-1), endothelial cells 0.015 +/- 0.003 min(-1) and adventitia 0.019 +/- 0.007 min(-1). Smooth muscle cells are exclusively responsible for the intermediate component Be(-kBt), but they present also a slow component, indistinguishible from the slow exponential component from the other types of cells in the artery. The rate constants for muscle cells are: rabbit aortic media k(B) 0.25 +/- 0.09 min(-1) and k(C) = 0.013 +/- 0.004 min(-1); medial cultures k(B) = 0.202 +/- 0.005 min(-1) and k(C1) = 0.020 +/- 0.003 min(-1); and BC(3)H1 cell culture k(B) = 0.205 +/- 0.083 min(-1) and k(C) = 0.016 +/- 0.003 min(-1).4. The efflux from compartment B of smooth muscle cells is inhibited by ouabain and in the absence of extracellular K(+). The efflux from compartment C is inhibited only by ouabain but not by the suppression of extracellular K(+).5. We propose a distribution of Na(+) in smooth muscle cells in two intracellular compartments: (1) Na(+) freely dissolved in the sarcoplasm, exchanging with the kinetics of compartment B and (2) a second cellular compartment which could be contained in the sarcoplasmic reticulum exchanging with the kinetics of compartment C.6. On the basis of the previous model of Na(+) distribution, considering our values, and without any correction, the estimated sarcoplasmic concentration of Na(+) is 9.6 mM, compatible with the direct measurements obtained in skeletal and heart muscle. The Na(+) concentration in the sarcoplasmic reticulum would be 4-10 times higher than in the cytoplasm. In order to increase the accuracy of our calculations it would be necessary to account for the interdiffusion and back diffusion of Na(+) between compartments. It is not possible to attain this goal at the present time.

Pharmacology of the adrenoceptors and cholinoceptors of the BC3H1 nonfusing muscle cell line

1. We have studied the action of different transmitters on the transmembrane 42K or 86Rb efflux from tissue cultures of the BC3H1 muscle cell line. 2. The effect of catecholamines and carbachol (CCh) on the isotope efflux rate was measured by addition of the drugs at different times during the washout. 3. Noradrenaline (NA), phenylephrine (Phe), isoprenaline (Iso) and CCh increased 42K and 86Rb efflux rate in a dose-dependent manner. 4. The action of NA seems to be due exclusively to the stimulation of alpha-receptors, since its effect was blocked by phentolamine but not by propranolol. The effects of Iso on the 86Rb efflux were inhibited by propranolol. The beta-receptors in the BC3H1 cells seem to be the beta2-type since they are stimulated by Iso and insensitive to NA. 5. The effect of CCh was blocked (+)-tubocurarine but not by atropine. This result confirms the presence of nicotinic receptors in BC3H1 cells.

Evidence for a visceral smooth muscle abnormality in Okamoto spontaneous hypertension

1. In order to discover whether the changes in reactivity are related to the primary cause of hypertension in spontaneously hypertensive rats (SHR) or are just an adaptation induced by the high arterial blood pressure we tested the contractile response of a visceral smooth muscle from such rats. 2. Longitudinal strips of the fundus from 20 week old male and female SHR and Wistar normotensive (NW) rats were used. Dose-response curves to Ba2+ in SHR strips were displaced to the right as compared to NW rats. Maximal responses were identical. Male SHR fundus strips contracted much more with Sr2+ (SHR: 42+/-3% of maximum response to Ba2+, n=10; NW: 19+/-4%, n=10, P less than 0.01) than NW strips. There was no difference in the response to both BaCl2 and SrCl2 between female SHR and NW fundus strips, and MnCl2 and LaCl3 were relaxant in all cases. 3. Dose-response curves to Ca2+ of depolarized SHR and NW fundus strips were obtained and the effect of diazoxide on Ca2+ contractions was observed. The contractile action of Ca2+ in depolarized preparations was enhanced in both male and female SHR strips. The effect of diazoxide was more marked in SHR strips than in NW fundus strips. 4. SHR fundus smooth muscle shows the same modification of reactivity to Ba2+, Sr2+, Ca2+ and diazoxide that was previously described in arterial smooth muscle. This indicates that the cellular modification responsible for the increase of vascular tonus in SHR is not an adaptive reaction to high blood pressure. The differences between female SHR and male SHR responses are not unexpected, considering the natural evolution of hypertension in Okamoto rats which is milder in the female.

Calcium uptake by myometrial membranes: effect of A 23187, a calcium ionophore

A subcellular fraction, relatively enriched with plasma membranes, showed an ATP-dependent Ca2+ uptake. The addition of a Ca2+. Other drugs (angiotensin, prostaglandin F2alpha, 5-hydroxytryptamine and cyclic nucleotides) had negligible effects on Ca2+ transport. The preparation appears to transport Ca2+, although binding is negligible.