Severe acute intoxication with yohimbine: Four simultaneous poisoning cases.

Yohimbine is an indole alkaloid from the leaves and bark of the Pausinystalia johimbe tree that has acquired an enviable reputation in treating erectile dysfunction. This report presents four simultaneous severe poisoning/death cases caused by yohimbine. The test samples comprised the venous blood of four middle-aged men (aged 47-65) who were suspected of poisoning; one of the men died due to ineffective rescue. Ethanol concentration determination and toxicological routine screening were performed using gas chromatography with flame ionization detection (GC-FID) and liquid chromatography-tandem mass spectrometry (LC-MS/MS). A specific LC-MS/MS method was developed to quantify yohimbine, which showed concentrations of 459, 249, and 301ng/mL in three poisoned blood samples and concentrations as high as 5631ng/mL in the deceased. Moreover, the deceased's autopsy ruled out death from trauma and previous illness, and no other common toxic components were detected in his blood. Therefore, yohimbine poisoning appears to be the most likely cause of death. As a type of alkaloid that can be employed in the treatment of clinical diseases and additives for supplements, the danger of yohimbine should be of widespread concern in society.

Quantification of microdosed oral yohimbine and its major metabolite in human plasma in the picogram range.

Aim: Pharmacokinetics after oral microdosing of the anticipated CYP2D6 substrate yohimbine and its metabolite 11-OH-yohimbine is potentially useful for drug-drug interaction trials and profiling of CYP2D6 enzyme activity. Materials & methods: We developed an ultrasensitive ultra performance liquid chromatography coupled to tandem mass spectrometry assay for quantification of yohimbine and its main metabolite 11-OH-yohimbine in plasma with a linear calibration range of 5-2500 pg/ml and validated it according to US FDA's and EMA's guidelines. Sample preparation was performed using fast liquid-liquid extraction. The assay was applied for the determination of concentrations of yohimbine and 11-OH-yohimbine in plasma after oral administration of 50 µg yohimbine to two subjects. Conclusion: Ultrasensitive quantification of yohimbine and its metabolite enables the determination of their concentrations in plasma after microdosing which would be applicable to use in CYP2D6 phenotyping.

PEEK tube-based online solid-phase microextraction-high-performance liquid chromatography for the determination of yohimbine in rat plasma and its application in pharmacokinetics study.

Yohimbine is a novel compound for the treatment of erectile dysfunction derived from natural products, and pharmacokinetic study is important for its further development as a new medicine. In this work, we developed a novel PEEK tube-based solid-phase microextraction (SPME)-HPLC method for analysis of yohimbine in plasma and further for pharmacokinetic study. Poly (AA-EGDMA) was synthesized inside a PEEK tube as the sorbent for microextraction of yohimbine, and parameters that could influence extraction efficiency were systematically investigated. Under optimum conditions, the PEEK tube-based SPME method exhibits excellent enrichment efficiency towards yohimbine. By using berberine as internal standard, an online SPME-HPLC method was developed for analysis of yohimbine in human plasma sample. The method has wide linear range (2-1000 ng/mL) with an R2 of 0.9962; the limit of detection was determined and was as low as 0.1 ng/mL using UV detection. Finally, a pharmacokinetic study of yohimbine was carried out by the online SPME-HPLC method and the results have been compared with those of reported methods.

Effects of three antagonists on selected pharmacodynamic effects of sublingually administered detomidine in the horse.

OBJECTIVE: To describe the effects of alpha2 -adrenergic receptor antagonists on the pharmacodynamics of sublingual (SL) detomidine in the horse. STUDY DESIGN: Randomized crossover design. ANIMALS: Nine healthy adult horses with an average age of 7.6 ± 6.5 years. METHODS: Four treatment groups were studied: 1) 0.04 mg kg(-1) detomidine SL; 2) 0.04 mg kg(-1) detomidine SL followed 1 hour later by 0.075 mg kg(-1) yohimbine intravenously (IV); 3) 0.04 mg kg(-1) detomidine SL followed 1 hour later by 4 mg kg(-1) tolazoline IV; and 4) 0.04 mg kg(-1) detomidine SL followed 1 hour later by 0.12 mg kg(-1) atipamezole IV. Each horse received all treatments with a minimum of 1 week between treatments. Blood samples were obtained and plasma analyzed for yohimbine, atipamezole and tolazoline concentrations by liquid chromatography-mass spectrometry. Behavioral effects, heart rate and rhythm, glucose, packed cell volume (PCV) and plasma proteins were monitored. RESULTS: Chin-to-ground distance increased following administration of the antagonists, however, this effect was transient, with a return to pre-reversal values as early as 1 hour. Detomidine induced bradycardia and increased incidence of atrioventricular blocks were either transiently or incompletely antagonized by all antagonists. PCV and glucose concentrations increased with tolazoline administration, and atipamezole subjectively increased urination frequency but not volume. CONCLUSIONS AND CLINICAL RELEVANCE: At the doses administered in this study, the alpha2 -adrenergic antagonistic effects of tolazoline, yohimbine and atipamezole on cardiac and behavioral effects elicited by SL administration of detomidine are transient and incomplete.

A qualitative/quantitative approach for the detection of 37 tryptamine-derived designer drugs, 5 ß-carbolines, ibogaine, and yohimbine in human urine and plasma using standard urine screening and multi-analyte approaches.

The first synthetic tryptamines have entered the designer drug market in the late 1990s and were distributed as psychedelic recreational drugs. In the meantime, several analogs have been brought onto the market indicating a growing interest in this drug class. So far, only scarce analytical data were available on the detectability of tryptamines in human biosamples. Therefore, the aim of the presented study was the development and full validation of a method for their detection in human urine and plasma and their quantification in human plasma. The liquid chromatography-linear ion trap mass spectrometry method presented covered 37 tryptamines as well as five ß-carbolines, ibogaine, and yohimbine. Compounds were analyzed after protein precipitation of urine or fast liquid-liquid extraction of plasma using an LXQ linear ion trap coupled to an Accela ultra ultra high-performance liquid chromatography system. Data mining was performed via information-dependent acquisition or targeted product ion scan mode with positive electrospray ionization. The assay was selective for all tested substances with limits of detection in urine between 10 and 100 ng/mL and in plasma between 1 and 100 ng/mL. A validated quantification in plasma according to international recommendation could be demonstrated for 33 out of 44 analytes.

Case study: two fatal case reports of acute yohimbine intoxication.

Yohimbine is an alkaloid that has been encountered on the streets as an aphrodisiac, hallucinogen, dietary supplement and erectile dysfunction drug. Yohimbine hydrochloride is an alpha 2-adrenoreceptor antagonist, blocking the pre- and postsynaptic alpha-2 adrenoreceptors and causing an increased release of noradrenaline and dopamine. An average oral dose of 5-15 mg produces a therapeutic whole blood level range of 40-400 ng/mL. Overdoses leading to neurotoxic effects have been seen with blood concentrations up to 5,000 ng/mL. The laboratories from the Maricopa County Medical Examiner and the Los Angeles County Department of Coroner each encountered a case in which yohimbine was identified in whole blood by means of a liquid-liquid basic drug extraction with detection on a GC-MS. Because validated quantitative methods for yohimbine did not exist at either facility, both agencies referred the blood specimens to NMS Labs, Inc. The reference laboratory analyzed the blood specimens with an LC-MS-MS and determined the quantitative values of yohimbine to be 7,400 and 5,400 ng/mL. Given the absence of other significant positive findings and the substantial yohimbine blood concentrations cited, the respective Medical Examiners determined the cause of death to be acute yohimbine intoxication with the mode being an accident. Yohimbine is a rarely encountered drug in medical examiner casework, and interpretation of the results is difficult to assess toward the cause and manner of death without such case studies being described.

The effects of yohimbine on the pharmacokinetic parameters of detomidine in the horse.

OBJECTIVE: To describe the pharmacokinetics of detomidine and yohimbine when administered in combination. STUDY DESIGN: Randomized crossover design. ANIMALS: Nine healthy adult horses aged 9 ± 4 years and weighing of 561 ± 56 kg. METHODS: Three dose regimens were employed in the current study. 1) 0.03 mg kg(-1) detomidine IV (D), 2) 0.2 mg kg(-1) yohimbine IV (Y) and 3) 0.03 mg kg(-1) detomidine IV followed 15 minutes later by 0.2 mg kg(-1) yohimbine IV (DY). Each horse received all three dose regimens with a minimum of 1 week in between subsequent regimens. Blood samples were obtained and plasma analyzed for detomidine and yohimbine concentrations by liquid chromatography-mass spectrometry. Data were analyzed using both non-compartmental and compartmental analysis. RESULTS: The maximum measured detomidine concentrations were 76.0 and 129.9 ng mL(-1) for the D and DY treatments, respectively. Systemic clearance and volume of distribution of detomidine were not significantly different for either treatment. There was a significant increase in the maximum measured yohimbine plasma concentrations from Y (173.9 ng mL(-1)) to DY (289.8 ng mL(-1)). Both the Cl and V(d) for yohimbine were significantly less (6.8 mL minute(-1) kg(-1) (Cl) and 1.7 L kg(-1) (V(d) )) for the DY as compared to the Y treatments (13.9 mL minute(-1) kg(-1) (Cl) and 2.7 L kg(-1) (V(d))). Plasma concentrations were below the limit of quantitation (0.05 and 0.5 ng mL(-1)) by 18 hours for both detomidine and yohimbine. CONCLUSION AND CLINICAL RELEVANCE: The Cl and V(d) of yohimbine were affected by prior administration of detomidine. The elimination half life of yohimbine remained unaffected when administered subsequent to detomidine. However, the increased plasma concentrations in the presence of detomidine has the potential to cause untoward effects and therefore further studies to assess the physiologic effects of this combination of drugs are warranted.

Pharmacokinetics of yohimbine following intravenous administration to horses.

Yohimbine is an alpha 2 adrenergic receptor antagonist used most commonly in veterinary medicine to reverse the effects of the alpha 2 receptor agonists, xylazine and detomidine. Most notably, yohimbine has been shown to counteract the CNS depressant effects of alpha 2 receptor agonists in a number of species. The recent identification of a yohimbine positive urine sample collected from a horse racing in California has led to the investigation of the pharmacokinetics of this compound. Eight healthy adult horses received a single intravenous dose of 0.12 mg/kg yohimbine. Blood samples were collected at time 0 (prior to drug administration) and at various times up to 72 h post drug administration. Plasma samples were analyzed using liquid chromatography-mass spectrometry (LC-MS) and data analyzed using both noncompartmental and compartmental analysis. Peak plasma concentration was 114.5 + 31.8 ng/mL and occurred at 0.09 + 0.03 h. Mean ± SD systemic clearance (Cls) and steady-state volume of distribution (Vdss) were 13.5 + 2.1 mL/min/kg and 3.3 + 1.3 L/kg following noncompartmental analysis. For compartmental analysis, plasma yohimbine vs. time data were best fitted to a two compartment model. Mean ± SD Cls and Vdss of yohimbine were 13.6 ± 2.0 mL/min/kg and 3.2 ± 1.1 L/kg, respectively. Mean ± SD terminal elimination half-life was 4.4 ± 0.9 h following noncompartmental analysis. Immediately following administration, two horses showed signs of sedation, while the other six appeared behaviorally unaffected. Gastrointestinal sounds were moderately increased compared to baseline while fecal consistency appeared normal.

Pharmacokinetics and pharmacodynamics of three intravenous doses of yohimbine in the horse.

Yohimbine is an alpha 2 adrenergic receptor antagonist, which has been shown to counteract the CNS depressant effects of alpha 2 receptor agonists in a number of species. Recently, our laboratory identified yohimbine in the absence of detectable concentrations of an alpha 2 agonist in a regulatory sample collected from a horse racing in California. This coupled with anecdotal reports of CNS stimulation and documented reports of cardiovascular changes when administered in conjunction with an agonist led us to investigate the pharmacokinetics and pharmacodynamics of yohimbine when administered alone. Nine healthy adult horses received a single intravenous dose of 0.1, 0.2, and 0.4 mg/kg yohimbine. Blood samples were collected at time 0 (prior to drug administration) and at various times up to 24 h postdrug administration. Plasma samples were analyzed using liquid chromatography-mass spectrometry (LC-MS), and resulting data analyzed using both noncompartmental and compartmental analysis. Peak plasma concentrations were 106.0 ± 28.9, 156.7 ± 34.3, and 223.0 ± 44.5 ng/mL for doses of 0.1, 0.2, and 0.4 mg/kg, respectively. Immediately following administration, two horses showed signs of sedation, one horse appeared excited, while the other six appeared behaviorally unaffected. Episodes of tachycardia were noted within minutes of administration for all horses at all doses; however, there was no correlation between behavioral responses and episodes of increased heart rate. Sixty-three percent of the horses (8, 6, and 4 of the 9 horses in the 0.1, 0.2, and 0.4 mg/kg dose groups, respectively) exhibited second-degree atrial-ventricular conduction blocks and bradycardia prior to drug administration that transiently improved or disappeared upon administration of yohimbine. Gastrointestinal sounds were transiently increased following all doses.

Acute neurotoxicity after yohimbine ingestion by a body builder.

Yohimbine is an alkaloid obtained from the Corynanthe yohimbe tree and other biological sources. Yohimbine is currently approved in the United States for erectile dysfunction and has undergone resurgence in street use as an aphrodisiac and mild hallucinogen. In recent years yohimbine use has become common in body-building communities for its presumed lipolytic and sympathomimetic effects. We describe a 37-year-old bodybuilder in which severe acute neurotoxic effects occurred in 2 h after yohimbine ingestion. The patient presented with malaise, vomiting, loss of consciousness, and repeated seizures after ingestion of 5 g of yohimbine during a body-building competition in a gymnasium. His Glasgow Coma Score was 3, requiring orotracheal intubation. Two hours after admission, vital signs were blood pressure 259/107 mmHg and heart rate 140 beats/min. Treatment with furosemide, labetalol, clonidine, and urapidil and gastrointestinal decontamination were performed. Twelve hours later the patient was extubated with normal hemodynamic parameters and neurological examination. The yohimbine blood levels at 3, 6, 14, and 22 h after ingestion were 5,240; 2,250; 1,530; and 865 ng/mL, respectively, with a mean half-life of 2 h. Few data are available about yohimbine toxicity and the related blood levels. This is a case of a large ingestion of yohimbine in which severe hemodynamic and neurological manifestations occurred and elevated blood levels of yohimbine were detected.

Human sympathetic activation by alpha2-adrenergic blockade with yohimbine: Bimodal, epistatic influence of cytochrome P450-mediated drug metabolism.

BACKGROUND: alpha2-Adrenergic blockade responses suggest adrenergic dysfunction in hypertension. alpha2-Blockade is also used to treat autonomic dysfunction. However, pharmacokinetic determinants of yohimbine disposition are not understood. METHODS: We evaluated alpha2-blockade with intravenous yohimbine in 172 individuals. Specific cytochrome P450 (CYP) isoform-mediated metabolism was investigated. Results were evaluated by ANOVA and by maximum likelihood analysis for bimodality of response distributions. RESULTS: Yohimbine metabolism to 11-hydroxy-yohimbine displayed greater than 1000-fold variability, with 17 individuals showing no metabolism. Nonmetabolizers differed from others in ethnicity but not in age, sex, body habitus, blood pressure, heart rate, or family history of hypertension. Bimodality of metabolism was suggested by frequency histogram, as well as maximum likelihood and cluster analysis. Among ethnic groups, subjects of European ancestry had the highest frequency of nonmetabolism. In vitro oxidation suggested that the major route of metabolism (lowest Michaelis-Menten constant and greatest intrinsic clearance) was likely via CYP2D6 to 11-hydroxy-yohimbine. In vivo genotypes at both CYP2D6 and CYP3A4 were necessary to predict metabolism (overall F = 3.03, P =.005); an interaction of alleles at these 2 loci (interaction F = 3.05, P =.033) suggested an epistatic effect on drug metabolism in vivo. Nonmetabolizers had greater activation of sympathetic nervous system activity. Yohimbine increased blood pressure, an effect mediated hemodynamically by elevation of cardiac output rather than systemic vascular resistance. Blood pressure and cardiac output responses did not differ by metabolizer group. CONCLUSIONS: We conclude that heterogeneous, bimodally distributed yohimbine metabolism depends on common genetic variation in both CYP2D6 and CYP3A4 and contributes to differences in sympathetic neuronal response to alpha2-blockade. These results have implications for both diagnostic and therapeutic uses of this alpha2-antagonist.

Low baseline and yohimbine-stimulated plasma neuropeptide Y (NPY) levels in combat-related PTSD.

BACKGROUND: Consistent with many studies demonstrating enhanced reactivity of the sympathetic nervous system in posttraumatic stress disorder (PTSD), the administration of yohimbine, a noradrenergic alpha(2)-antagonist, has been shown to increase core symptoms of PTSD and to induce greater increases in plasma 3-methyl-4-hydroxy-phenyl-glycol (MHPG) in subjects with PTSD compared with healthy control subjects. In turn, neuropeptide Y (NPY) has been shown to inhibit the release of norepinephrine from sympathetic noradrenergic neurons. METHODS: In the following study, plasma NPY responses to yohimbine and placebo were measured in a subgroup of 18 subjects with PTSD and 8 healthy control subjects who participated in the previous study of the effect of yohimbine on plasma MHPG. RESULTS: The PTSD subjects had lower baseline plasma NPY and blunted yohimbine-stimulated increases in plasma NPY compared with the healthy control subjects. Within the PTSD group, baseline plasma NPY levels correlated negatively with combat exposure scale scores, baseline PTSD and panic symptoms, and yohimbine-stimulated increases in MHPG and systolic blood pressure. CONCLUSIONS: This study suggests that combat stress-induced decreases in plasma NPY may mediate, in part, the noradrenergic system hyperreactivity observed in combat-related PTSD. The persistence of this decrease in plasma NPY may contribute to symptoms of hyperarousal and the expression of exaggerated alarm reactions, anxiety reactions, or both in combat veterans with PTSD long after war.

Peripheral markers of serotonergic and noradrenergic function in post-pubertal, caucasian males with autistic disorder.

Some studies have suggested that disorders in the peripheral and central metabolism of serotonin (5-HT) and noradrenaline may play a role in the pathophysiology of autistic disorder. This study examines serotonergic and noradrenergic markers in a study group of 13 male, post-pubertal, caucasian autistic patients (age 12-18 y; I.Q. > 55) and 13 matched volunteers. [3H]-paroxetine binding Kd values were significantly higher in patients with autism than in healthy volunteers. Plasma concentrations of tryptophan, the precursor of 5-HT, were significantly lower in autistic patients than in healthy volunteers. There were no significant differences between autistic and normal children in the serum concentrations of 5-HT, or the 24-hr urinary excretion of 5-hydroxy-indoleacetic acid (5-HIAA), adrenaline, noradrenaline, and dopamine. There were no significant differences in [3H]-rauwolscine binding Bmax or Kd values, or in the serum concentrations of tyrosine, the precursor of noradrenaline, between both study groups. There were highly significant positive correlations between age and 24-hr urinary excretion of 5-HIAA and serum tryptophan. The results suggest that: 1) serotonergic disturbances, such as defects in the 5-HT transporter system and lowered plasma tryptophan, may play a role in the pathophysiology of autism; 2) autism is not associated with alterations in the noradrenergic system; and 3) the metabolism of serotonin in humans undergoes significant changes between the ages of 12 and 18 years.

Biopharmaceutics and metabolism of yohimbine in humans.

The biopharmaceutics of yohimbine (YO) and the pharmacokinetics of 10-hydroxy-yohimbine (10-OH-YO) and 11-hydroxy-yohimbine (11-OH-YO) were investigated in healthy subjects following i.v. (5 mg) and oral (8 mg) dosing. One subject was found as a slow hydroxylator of YO. The mean (+/-S.D.) oral absolute bioavailability of YO was 22.3+/-21. 5%. Total plasma clearance (CL) and renal clearance (CL(r)) of YO following i.v. dosing were 0.728+/-0.256 ml/min and 0.001+/-0.002 ml/min, respectively. Based on the steady-state volume of distribution (V(ss)), YO had a relatively low distribution (V(ss) = 32.2+/-12.1 l). The overall renal excretion of YO, 10-OH-YO and 11-OH-YO, expressed as percent of the dose of YO administered, were not different following i.v. and oral dosing, and were around 0.1, 0.2 and 14%, respectively. Following i.v. dosing of YO, the mean apparent terminal half-life of 11-OH-YO (347+/-63 min) was almost four times higher than that of YO (91.0+/-33.6 min) suggesting an elimination rate-limited kinetics for 11-OH-YO.

Patterns of cerebrospinal fluid catechols support increased central noradrenergic responsiveness in aging and Alzheimer's disease.

BACKGROUND: High cerebrospinal fluid (CSF) norepinephrine (NE) concentrations in aging and Alzheimer's disease (AD) could reflect decreased NE clearance from central nervous system (CNS) extracellular fluid or increased release of NE into CNS extracellular fluid. Measuring CSF concentrations of the intraneuronal NE metabolite dihydroxyphenylglycol (DHPG), an estimate of NE clearance, and the NE precursor dihydroxyphenylacetic acid (DOPA), an estimate of NE biosynthesis, can help differentiate these mechanisms. METHODS: NE, DHPG, and DOPA were determined by HPLC in CSF and plasma obtained following yohimbine, clonidine, and placebo. Ten AD, 10 older, and 11 young subjects were studied. RESULTS: CSF DOPA following yohimbine was higher in older and AD than in young subjects. CSF DHPG did not differ among groups. Plasma DOPA following yohimbine was higher in AD than in young subjects. CONCLUSIONS: During alpha-2 adrenoreceptor blockade in both aging and AD, there are increased responses of CNS NE biosynthesis and release with unchanged CNS NE clearance. This pattern is consistent with partial loss of CNS noradrenergic neurons with compensatory activation of remaining CNS noradrenergic neurons. Given the marked loss of locus coeruleus (LC) noradrenergic neurons in AD, achievement of high CSF NE suggests particularly prominent compensatory activation of remaining LC neurons in this disorder.

Serotonergic and noradrenergic markers of post-traumatic stress disorder with and without major depression.

Some studies have suggested that disorders in the peripheral and central metabolism of serotonin (5-HT) and noradrenaline (NE) may play roles in the pathophysiology of post-traumatic stress disorder (PTSD). This study examines (1) the availability of plasma total tryptophan, the precursor of 5-HT, and tyrosine, the precursor of NE; and (2) the platelet 5-HT transporter and alpha 2-adrenoceptor (alpha 2-AR) binding sites in patients with PTSD and healthy volunteers. High-performance liquid chromatography (HPLC) was employed to measure plasma tryptophan and tyrosine as well as amino acids known to compete with the same cerebral transport system; that is, valine, leucine, phenylalanine, and isoleucine. The maximum number of binding sites (Bmax) and their affinity (Kd) for binding to [3H]-paroxetine and [3H]-rauwolscine, a selective alpha 2-AR antagonist, were determined. [3H]-paroxetine and [3H]-rauwolscine binding Kd values were significantly higher in patients with PTSD than in healthy volunteers. [3H]-rauwolscine binding Kd values were significantly higher in patients with PTSD and concurrent major depression (MD) than in PTSD patients without MD and healthy volunteers. Plasma tyrosine concentrations and the ratio of tyrosine/valine + leucine + isoleucine + phenylalanine + tryptophan were significantly higher in PTSD patients with MD than in those without MD and healthy volunteers. The results show that PTSD is accompanied by lower affinity of paroxetine binding sites and that PTSD with concurrent MD is accompanied by lower affinity of alpha 2-ARs and increased plasma tyrosine availability to the brain. The results suggest that (1) serotonergic mechanisms, such as defects in the 5-HT transporter system, may play a role in the pathophysiology of PTSD; and (2) that catecholaminergic mechanisms, such as increased precursor availability and lowered affinity of alpha 2-ARs, may play a role in the pathophysiology of PTSD with concurrent MD.

Study of human serum albumin structure by dynamic light scattering: two types of reactions under different pH and interaction with physiologically active compounds.

The effect of pH and binding of ten physiologically active compounds (isoproterenol, yohimbine, propranolol, clonidine, phenylephrine, carbachol, tripeptide fMLP, diphenhydramine, chlorpromazine and atropine) on the molecular structure of human serum albumin (HSA) has been studied using the dynamic light scattering. It was found that albumin globule has the most compact configuration (Stokes diameter 59-62 A) at physiological pH 7.4. The changes in pH, both increase to 8.0 and decrease to 5.4, result in the growth of globule size to 72-81 A. At acidic shift of pH an additional peak arises in the correlation spectra caused by the light scattering on the structures with the Stokes diameters of 29-37 A. Those conform to the sizes of the albumin subdomains. The indicated peak is not displayed at basic shift of pH. The interaction with propranolol, clonidine, phenylephrine, carbachol and tripeptide fMLP which hinder adenylate cyclase (AdC) and activate Ca-polyphosphoinositide (Ca-PPI) signaling system of a cell initiates structural rearrangements similar to acidic transitions. Isoproterenol, yohimbine diphenhydramine, chlorpromazine and atropine, which activate AdC and hinder Ca-PPI, cause conformational changes of HSA similar to basic transitions.

Plasma MHPG response to yohimbine treatment in women with hypoactive sexual desire.

The use of yohimbine to treat impotence has suggested that decreased male sexual desire may relate to decreased activity of central noradrenergic neurons. Previous trials of yohimbine to treat female sexual problems are not available. Yohimbine is an alpha 2-adrenergic antagonist that stimulates norepinephrine (NE) release. In the present study, plasma concentrations of 3-methoxy-4-hydroxyphenylglycol (MHPG), the major central nervous system metabolite of NE, were measured in 9 women diagnosed with hypoactive sexual desire. Daily logs of mood and sexual activity, and trimonthly MHPG blood drawings, were obtained over an initial baseline menstrual cycle followed by two subsequent treatment cycles (yohimbine or placebo), in randomized order. Blood samples were obtained at 9:00 a.m. during (a) the early follicular phase of each cycle (24 hr after the onset of each cycle), (b) the ovulatory phase (i.e., within 1 day of an oral temperature rise), and (c) the midluteal phase (i.e., 20-25 days into each cycle). Comparisons were made with a group of 7 healthy female controls. Women with hypoactive sexual desire had slightly lower plasma MHPG values than controls at baseline, although there was only a trend toward significance during the early follicular phase (p = .09). Yohimbine (5.4 mg orally, 3 times daily, beginning at menses) caused a sustained rise in plasma MHPG of similar magnitude to that reported in men. However, in terms of improved sexual desire, yohimbine had no obvious therapeutic effect. Thus, plasma MHPG and the alpha 2-adrenergic response to yohimbine appeared within normal ranges in women with hypoactive sexual desire, with no therapeutic response to yohimbine.

Yohimbine elimination in normal volunteers is characterized by both one- and two-compartment behavior.

We sought to determine the safety, pharmacodynamic response, and single- and multiple-dose pharmacokinetic profile of yohimbine hydrochloride. Thirty-two healthy volunteers received 6 days of yohimbine, 5.4 mg 3 times daily (t.i.d.), 10.8 mg t.i.d., 16.2 mg t.i.d., or 21.6 mg twice daily (b.i.d.), with determination of plasma catecholamine levels and mood/anxiety-inventory scores. The pharmacokinetic profile of yohimbine was determined after the first and last dose. Yohimbine exhibited one-compartment elimination in most subjects, with dose-dependent increases in maximal concentration (Cmax) and area under the curve (AUC) but no evidence of drug accumulation. At least two subjects in each cohort exhibited two-compartment elimination of yohimbine, with nonsignificant increases in day 7 AUC, Cmax, and terminal elimination half-life (t1/2beta). Plasma catecholamine levels increased significantly in relation to both average yohimbine AUC and Cmax, but there were no significant effects on heart rate, blood pressure, or anxiety/mood-inventory scores. The single- and multiple-dose pharmacokinetic profile of yohimbine exhibits a substantial degree of interpatient and intrapatient variability, possibly resulting from variability in first-pass and hepatic metabolism. There is a significant correlation between plasma norepinephrine levels and yohimbine AUC or Cmax. Further multiple-dose studies are warranted definitively to address the relation between yohimbine AUC or Cmax and pharmacologic effect.

Cerebrospinal fluid and plasma disposition of yohimbine and 11-hydroxy-yohimbine in young and older healthy subjects, and Alzheimer's disease patients.

OBJECTIVE: The plasma and cerebrospinal fluid (CSF) disposition of yohimbine (YO) and 11-hydroxy-yohimbine (11-OH-YO), after oral administration of a single dose of YO (0.65 mg.kg-1) were studied in young and older healthy subjects and in patients with Alzheimer's disease (AD). RESULTS: Plasma disposition of YO displayed large variability; no significant differences among subject groups were observed. In contrast, 11-OH-YO Cmax and AUC were significantly lower in the older normal subjects than in the young normal or AD subjects. A strong positive correlation between CSF and plasma YO concentrations was observed. A weak positive correlation between CSF and plasma concentrations of 11-OH-YO was also observed. CSF to plasma concentration ratios for yohimbine and 11-OH-YO were low (approximately 2%).