Alpha 2-antagonist compounds and lipid mobilization: evidence for a lipid mobilizing effect of oral yohimbine in healthy male volunteers

Performance, blood profile and gut morphometry of broiler chickens fed diets supplemented with Yohimbe (Pausynistalia yohimbe) and Larvacide

The need for making livestock products free from antibiotics residue and other synthetic chemicals has resulted to the use of herbal products in livestock production. A 42-day study was conducted to compare the influence of Yohimbe (Pausynistalia yohimbe) and Larvacide on the growth performance, blood profile and gut morphometry of broiler chickens. Two hundred and twenty five 14-day old broiler chickens were randomly allotted into five treatment groups comprising of forty five chicks each. The groups were triplicates of fifteen birds. The five treatment groups consist of Basal (control), Larvacide (5 mg/Kg), three levels of Yohimbe supplementation (60 mg, 120 mg, and 180 mg/Kg) diets. Each supplement was supplied with the specified diets for the two phases of feeding [starter diet (3-4weeks) and the finisher diet (5-8weeks)]. Data collected were subjected to One-way analysis of variance. Results show insignificant effect (p>0.05) on the growth performance parameters at the starter phase. However, at the finisher phase, supplementation of Yohimbe resulted to a progressive reduction in the feed intake (p<0.05) without consequential reduction in the body weights. The chickens fed Basal diet+180 mg Yohimbe had the best Feed Conversion Ratio (FCR). Furthermore, chickens fed basal starter diet+180 mg Yohimbe had the highest (p<0.05) total protein, globulin, Red Blood Cell (RBC), White Blood Cell (WBC), and Eosinophil counts while it had the least (p<0.05) Alanine Transaminase (ALT), uric acid and creatinine. Also, chickens fed basal starter diet + 60 mg Yohimbe had the highest (p<0.05) Mean Corpuscular Volume (MCV) and Mean Corpuscular Haemoglobin (MCH) while chickens fed basal starter diet+120 mg Yohimbe had highest (p<0.05) High Density Lipoprotein (HDL), but lower Very Low Density Lipoprotein (VLDL) and triglyceride. At the finisher phase, chickens fed basal diet+180 mg Yohimbe had the highest (p<0.05) Pack Cell Volume (PCV), haemoglobin and basophils while chickens fed basal diet+60 mg Yohimbe had the highest WBC. Chickens fed basal diet+120 mg Yohimbe had the least ALT and uric acid. Triglyceride, and cholesterol, HDL and VLDL, were lowered (p<0.05) in chickens fed basal diet+Larcacide. Also, chickens fed basal diet+180 mg Yohimbe had the highest (p<0.05) villi height. The study concluded that feeding broiler chickens basal diet+180 mg Yohimbe improved optimum growth performance, blood profile and gut morphology.

Genotype-based treatment of type 2 diabetes with an α2A-adrenergic receptor antagonist

The feasibility of exploiting genomic information for individualized treatment of polygenic diseases remains uncertain. A genetic variant in ADRA2A, which encodes the α(2A)-adrenergic receptor (α(2A)AR), was recently associated with type 2 diabetes. This variant causes receptor overexpression and impaired insulin secretion; thus, we hypothesized that blocking α(2A)AR pharmacologically could improve insulin secretion in patients with the risk genotype. A total of 50 type 2 diabetes patients were recruited on the basis of ADRA2A genotype for a randomized placebo-controlled intervention study with the α(2A)AR antagonist yohimbine. The patients received 0, 10, or 20 mg of yohimbine at three separate visits. The primary endpoint was insulin secretion at 30 min (Ins30) during an oral glucose tolerance test (OGTT). Patients with the risk variant had 25% lower Ins30 than those without risk genotype. After administration of 20 mg of yohimbine, Ins30 was enhanced by 29% in the risk group, making secretion similar to patients carrying the low-risk allele. The corrected insulin response and disposition index in individuals with the high-risk (but not low-risk) allele were improved by 59 ± 18% and 43 ± 14%, respectively. The beneficial effect of yohimbine was not a consequence of improved insulin sensitivity. In summary, the data show that the insulin secretion defect in patients carrying the ADRA2A risk genotype can be corrected by α(2A)AR antagonism. The findings show that knowledge of genetic risk variants can be used to guide therapeutic interventions that directly target the underlying pathophysiology and demonstrate the potential of individualized genotype-specific treatment of type 2 diabetes.

Clinical safety assessment of oral higenamine supplementation in healthy, young men

OBJECTIVE

Higenamine, an herbal agent also known as norcoclaurine, is thought to stimulate β-androgenic receptors and possess lipolytic activity. It is currently making its way into the dietary supplement market. To our knowledge, no studies have been conducted to determine the safety profile of oral higenamine when used alone and in conjunction with other commonly used lipolytic agents.

METHODS

Forty-eight men were assigned to ingest either a placebo, higenamine, caffeine, or higenamine + caffeine + yohimbe bark extract daily for a period of 8 weeks. Before and after 4 and 8 weeks of supplementation, the following variables were measured: resting respiratory rate, heart rate, blood pressure, urinalysis, complete blood count, metabolic panel, liver enzyme activity, and lipid panel.

RESULTS

No interaction effects were noted for any variable (p > 0.05), with no changes of statistical significance occurring across time for any of the four conditions (p > 0.05).

CONCLUSION

This is the first study to determine the safety profile of oral higenamine intake in human subjects. Our data indicate that 8 weeks of daily higenamine supplementation, either alone or in conjunction with caffeine and yohimbe bark extract, does not result in a statistically significant change in any of the measured outcome variables. Additional studies, inclusive of a larger sample size, are needed to extend these initial findings.

Acute oral intake of a higenamine-based dietary supplement increases circulating free fatty acids and energy expenditure in human subjects

Background

Higenamine, also known as norcoclaurine, is an herbal constituent thought to act as a beta-2 adrenergic receptor agonist—possibly stimulating lipolysis. It was the purpose of this study to determine the impact of a higenamine-based dietary supplement on plasma free fatty acids and energy expenditure following acute oral ingestion.

Methods

Sixteen healthy subjects (8 men; 26.1 ± 2.5 yrs; 8 women 22.4 ± 3.1 yrs) ingested a dietary supplement containing a combination of higenamine, caffeine (270 mg), and yohimbe bark extract or a placebo, on two separate occasions in a double-blind, randomized, cross-over design, separated by 6–8 days. Blood samples were collected immediately before ingestion, and at 30, 60, 120, and 180 minutes post ingestion, and analyzed for plasma free fatty acids (FFA) and glycerol. Breath samples were collected at the same times for a measure of kilocalorie expenditure and respiratory exchange ratio (RER) using indirect calorimetry. Heart rate and blood pressure were recorded at all times. Data collection occurred in the morning following a 10 hour overnight fast.

Results

A condition effect was noted for both FFA (p < 0.0001) and kilocalorie expenditure (p = 0.001), with values higher for supplement compared to placebo at 60, 120, and 180 minutes post ingestion. No statistically significant effects were noted for glycerol or RER (p > 0.05). A condition effect was noted for heart rate (p = 0.03) and systolic blood pressure (p < 0.0001), with values higher for supplement compared to placebo.

Conclusion

Ingestion of a higenamine-based dietary supplement stimulates lipolysis and energy expenditure, as evidenced by a significant increase in circulating FFA and kilocalorie expenditure. The same supplement results in a moderate increase in heart rate (~3 bpm) and systolic blood pressure (~12 mmHg), which is consistent with previous studies evaluating moderate doses of caffeine and yohimbine, suggesting that higenamine contributes little to the increase in these hemodynamic variables. These findings are in reference to young, healthy and active men and women.

Thermogenic effect of meltdown RTD energy drink in young healthy women: a double blind, cross-over design study

Background

The purpose of this study was to examine the acute metabolic effects of a high-energy drink in healthy, physically-active women.

Methods

Ten women (20.4 ± 0.70 y; 166.9 ± 7.2 cm; 67.0 ± 7.0 kg; 29.6 ± 6.5% body fat) underwent two testing sessions administered in a randomized and double-blind fashion. Subjects reported to the laboratory in a 3-hr post-absorptive state and were provided either 140 ml of the high-energy drink (SUP; commercially marketed as Meltdown RTD™) or placebo (P). Subjects consumed two 70 ml doses of SUP or P, separated by 30 min and rested in a semi-recumbent position for 3 hours. Resting oxygen consumption (VO₂) and heart rate (HR) were determined every 5 min during the first 30 min and every 10 min during the next 150 min. Blood pressure (BP) was determined every 15 min during the first 30 min and every 30 min thereafter. Area under the curve (AUC) analysis was computed for VO₂, whereas a 3-hour average and hourly averages were calculated for respiratory quotient (RQ), total kcal, HR, BP, and profile of mood states (POMS).

Results

AUC analysis revealed a 10.8% difference (p = 0.03) in VO₂ between SUP and P. No difference in VO₂ was seen between the groups in the first hour, but VO₂ in SUP was significantly greater than P in the second (13.9%, p = 0.01) and third hours (11.9%, p = 0.03). A difference (p = 0.03) in energy expenditure was seen between SUP (1.09 ± 0.10 kcal·min^-1) and P (0.99 ± 0.09 kcal·min^-1) for the 3-hour period. Although no difference in energy expenditure was seen in the first hour, significant differences between SUP and P were observed in the second (1.10 ± 0.11 kcal·min^-1 and 0.99 ± 0.09 kcal·min^-1, respectively; p = 0.02) and third hour (1.08 ± 0.11 kcal·min^-1 and 0.99 ± 0.09 kcal·min^-1, respectively; p = 0.05). Average systolic BP was significantly higher (p = 0.007) for SUP (110.0 ± 3.9 mmHg) compared to P (107.3 ± 4.4 mmHg). No differences were seen in HR, diastolic BP, or POMS at any time point.

Conclusions

Results showed a significant increase in energy expenditure in young, healthy women following an acute ingestion of a high-energy drink.

Effect of the dietary supplement Meltdown on catecholamine secretion, markers of lipolysis, and metabolic rate in men and women: a randomized, placebo controlled, cross-over study

BACKGROUND

We have recently reported that the dietary supplement Meltdown increases plasma norepinephrine (NE), epinephrine (EPI), glycerol, free fatty acids (FFA), and metabolic rate in men. However, in that investigation measurements ceased at 90 minutes post ingestion, with values for blood borne variables peaking at this time. It was the purpose of the present investigation to extend the time course of measurement to 6 hours, and to include women within the design to determine if sex differences to treatment exist.

METHODS

Ten men (24 +/- 4 yrs) and 10 women (22 +/- 2 yrs) ingested Meltdown or a placebo, using a randomized, cross-over design with one week separating conditions. Blood samples were collected immediately before supplementation and at one hour intervals through 6 hours post ingestion. A standard meal was provided after the hour 3 collection. Samples were assayed for EPI, NE, glycerol, and FFA. Five minute breath samples were collected at each time for measurement of metabolic rate and substrate utilization. Area under the curve (AUC) was calculated. Heart rate and blood pressure were recorded at all times. Data were also analyzed using a 2 (sex) x 2 (condition) x 7 (time) repeated measures analysis of variance, with Tukey post hoc testing.

RESULTS

No sex x condition interactions were noted for AUC for any variable (p > 0.05). Hence, AUC data are collapsed across men and women. AUC was greater for Meltdown compared to placebo for EPI (367 +/- 58 pg x mL(-1) x 6 hr(-1) vs. 183 +/- 27 pg x mL(-1) x 6 hr(-1); p = 0.01), NE (2345 +/- 205 pg x mL(-1) x 6 hr(-1) vs. 1659 +/- 184 pg x mL(-1) x 6 hr(-1); p = 0.02), glycerol (79 +/- 8 microg x mL)-1) x 6 hr(-1) vs. 59 +/- 6 microg x mL(-1) x 6 hr(-1); p = 0.03), FFA (2.46 +/- 0.64 mmol x L(-1) x 6 hr(-1) vs. 1.57 +/- 0.42 mmol x L(-1) x 6 hr(-1); p = 0.05), and kilocalorie expenditure (439 +/- 26 kcal x 6 hrs(-1) vs. 380 +/- 14 kcal x 6 hrs(-1); p = 0.02). No effect was noted for substrate utilization (p = 0.39). Both systolic and diastolic blood pressure (p < 0.0001; 1-16 mmHg), as well as heart rate (p = 0.01; 1-9 bpm) were higher for Meltdown. No sex x condition x time interactions were noted for any variable (p > 0.05).

CONCLUSION

Ingestion of Meltdown results in an increase in catecholamine secretion, lipolysis, and metabolic rate in young men and women, with a similar response for both sexes. Meltdown may prove to be an effective intervention strategy for fat loss, assuming individuals are normotensive and their treatment is monitored by a qualified health care professional.

Dietary supplement increases plasma norepinephrine, lipolysis, and metabolic rate in resistance trained men

BACKGROUND

Dietary supplements targeting fat loss and increased thermogenesis are prevalent within the sport nutrition/weight loss market. While some isolated ingredients have been reported to be efficacious when used at high dosages, in particular in animal models and/or via intravenous delivery, little objective evidence is available pertaining to the efficacy of a finished product taken by human subjects in oral form. Moreover, many ingredients function as stimulants, leading to increased hemodynamic responses. The purpose of this investigation was to determine the effects of a finished dietary supplement on plasma catecholamine concentration, markers of lipolysis, metabolic rate, and hemodynamics.

METHODS

Ten resistance trained men (age = 27 +/- 4 yrs; BMI = 25 +/- 3 kg. m-2; body fat = 9 +/- 3%; mean +/- SD) ingested a dietary supplement (Meltdown(R), Vital Pharmaceuticals) or a placebo, in a random order, double blind cross-over design, with one week separating conditions. Fasting blood samples were collected before, and at 30, 60, and 90 minutes post ingestion and were assayed for epinephrine (EPI), norepinephrine (NE), glycerol, and free fatty acids (FFA). Area under the curve (AUC) was calculated for all variables. Gas samples were collected from 30-60 minutes post ingestion for measurement of metabolic rate. Heart rate and blood pressure were recorded at all blood collection times.

RESULTS

AUC was greater for the dietary supplement compared to the placebo for NE (1332 +/- 128 pg.mL-1.90 min-1 vs. 1003 +/- 133 pg.mL-1.90 min-1; p = 0.03), glycerol (44 +/- 3 mug.mL-1.90 min-1 vs. 26 +/- 2 mug.mL-1.90 min-1; p < 0.0001), and FFA (1.24 +/- 0.17 mmol.L-1.90 min-1 vs. 0.88 +/- 0.12 mmol.L-1.90 min-1; p = 0.0003). No difference between conditions was noted for EPI AUC (p > 0.05). For all variables, values were highest at 90 minutes post ingestion. Total kilocalorie expenditure during the 30 minute collection period was 29.6% greater (p = 0.02) for the dietary supplement (35 +/- 3 kcal) compared to placebo (27 +/- 2 kcal). A condition main effect was noted for systolic blood pressure (p = 0.04), with values increasing from 117 +/- 2 mmHg to 123 +/- 2 mmHg with the dietary supplement, while remaining unchanged for placebo. No other hemodynamic changes were noted (p > 0.05).

CONCLUSION

The dietary supplement results in an acute increase in plasma NE and markers of lipolysis, as well as metabolic rate. This occurs without altering hemodynamic variables in a clinically significant manner. Intervention studies to determine the impact of this dietary supplement on weight/fat loss are warranted.

Examination of a pre-exercise, high energy supplement on exercise performance

BACKGROUND

The purpose of this study was to examine the effect of a pre-exercise high energy drink on reaction time and anaerobic power in competitive strength/power athletes. In addition, the effect of the pre-exercise drink on subjective feelings of energy, fatigue, alertness and focus was also explored.

METHODS

Twelve male strength/power athletes (21.1 +/- 1.3 y; 179.8 +/- 7.1 cm; 88.6 +/- 12.1 kg; 17.6 +/- 3.3% body fat) underwent two testing sessions administered in a randomized and double-blind fashion. During each session, subjects reported to the Human Performance Laboratory and were provided with either 120 ml of a high energy drink (SUP), commercially marketed as Redline Extreme(R) or 120 ml of a placebo (PL) that was similar in taste and appearance but contained no active ingredients. Following consumption of the supplement or placebo subjects rested quietly for 10-minutes prior to completing a survey and commencing exercise. The survey consisted of 4 questions asking each subject to describe their feelings of energy, fatigue, alertness and focus for that moment. Following the completion of the questionnaire subjects performed a 2-minute quickness and reaction test on the Makoto testing device (Makoto USA, Centennial CO) and a 20-second Wingate Anaerobic Power test. Following a 10-minute rest subjects repeated the testing sequence and after a similar rest period a third and final testing sequence was performed. The Makoto testing device consisted of subjects reacting to both a visual and auditory stimulus and striking one out of 30 potential targets on three towers.

RESULTS

Significant difference in reaction performance was seen between SUP and PL in both average number of targets struck (55.8 +/- 7.4 versus 51.9 +/- 7.4, respectively) and percent of targets struck (71.9 +/- 10.5% versus 66.8 +/- 10.9%, respectively). No significant differences between trials were seen in any anaerobic power measure. Subjective feelings of energy (3.5 +/- 0.5 versus 3.1 +/- 0.5) and focus (3.8 +/- 0.5 versus 3.3 +/- 0.7) were significantly higher during SUP compared to PL, respectively. In addition, a trend towards an increase in average alertness (p = 0.06) was seen in SUP compared to P.

CONCLUSION

Results indicate a significant increase in reaction performance, with no effect on anaerobic power performance. In addition, ingestion of this supplement significantly improves subjective feelings of focus and energy in male strength/power athletes.

Thermogenic effect of an acute ingestion of a weight loss supplement

Background

The purpose of this study was to examine the acute effects of a weight loss supplement on resting oxygen uptake (VO₂), respiratory quotient (RQ), caloric expenditure (kcal), heart rate (HR), and blood pressure (BP) in healthy and physically active individuals.

Methods

Ten subjects (5 male, 5 female; 20.2 ± 1.2 y; 172.2 ± 8.9 cm; 71.5 ± 17.2 kg; 17.3 ± 2.6% body fat) underwent two testing sessions administered in a randomized and double-blind fashion. During each session, subjects reported to the Human Performance Laboratory after at least 3-h post-absorptive state and were provided either 3 capsules of the weight loss supplement (SUP), commercially marketed as Meltdown^® or 3 capsules of a placebo (P). Subjects then rested in a semi-recumbent position for three hours. VO₂ and HR were determined every 5 min during the first 30 min and every 10 min during the next 150 min. BP was determined every 15 min during the first 30 min and every 30 min thereafter. The profile of mood states was assessed every 30 min.

Results

Area under the curve analysis revealed a significant 28.9% difference in VO₂ between SUP and P for the three hour study period. In addition, a significant difference in energy expenditure was also seen between SUP (1.28 ± 0.33 kcal·min^-1) and P (1.00 ± 0.32 kcal·min^-1). A trend (p = 0.06) towards a greater utilization of stored fat as an energy source was also demonstrated (0.78 ± 0.23 kcal·min^-1 and 0.50 ± 0.38 kcal·min^-1 in P and SUP, respectively). Significant elevations in HR were seen during hours two and three of the study, and significantly higher average systolic BP was observed between SUP (118.0 ± 7.3 mmHg) and P (111.4 ± 8.2 mmHg). No significant differences were seen in diastolic blood pressure at any time point. Significant increases in tension and confusion were seen in SUP.

Conclusion

Results indicate a significant increase in energy expenditure in young, healthy individuals following an acute ingestion of a weight loss supplement. In addition, ingestion of this supplement appears modify mood and elevate HR and systolic BP following ingestion.

Yohimbine: The Effects on Body Composition and Exercise Performance in Soccer Players

The main aim of this study was to determine the effects of yohimbine supplementation on body composition and exercise performance in professional soccer players. The athletes (20 top-level male soccer players) were allocated to two randomly assigned trials. Subjects in the yohimbine group orally ingested tablets that contains yohimbine at a dose of 20 milligrams per day in two equal doses for 21 days. Subjects in the placebo group ingested an equal number of identical-looking pills that contained cellulose. There were no statistically significant changes in body mass and muscle mass within or between trials (p > 0.05) after the supplementation protocol. Percentage of body fat significantly decreased in the yohimbine group after the supplementation protocol (9.3 +/- 1.1 vs. 7.1 +/- 2.2%; p < 0.05). Furthermore, fat mass was significantly lower in the yohimbine versus placebo trial at postsupplementation assessment (7.1 +/- 2.2 vs. 9.2 +/- 1.9%; p < 0.05). There were no changes in exercise performance indicators (bench and leg press, vertical jump, dribble and power test results, shuttle run) within or between. trials (p > 0.05). No subject reported any side effects from yohimbine. The results of the current study indicate that supplementation with yohimbine combined with resistance training does not significantly alter the body mass, muscle mass, or performance indicators in professional soccer players. Nonetheless, yohimbine supplementation appears to be suitable as a fat loss strategy in elite athletes.

Pre-exercise administration of yohimbine may enhance the efficacy of exercise training as a fat loss strategy by boosting lipolysis

The natural alpha-2 antagonist yohimbine promotes sympathetic activity by central as well as peripheral mechanisms, and yet in moderate doses dose not usually raise heart rate, increase blood pressure, or induce anxiety (in contrast to sympathomimetic drugs such as ephedrine). Administered prior to exercise, it boosts lipolysis and serum FFA levels both during and following exercise; blockade of adipocyte alpha-2 adrenoreceptors makes at least a modest contribution to this pro-lipolytic activity. These considerations suggest that pre-exercise administration of yohimbine will lower the respiratory quotient during and following exercise, thus promoting fat loss. Since yohimbine can potentiate postprandial insulin secretion, its bariatric benefits should be greatest if administered on a schedule that minimizes postprandial yohimbine activity. A possible synergism of yohimbine and caffeine should be explored. Pre-exercise yohimbine administration has the potential to down-regulate the lipoprotein lipase activity of visceral adipocytes, increase lipolysis in refractory gynoid fat depots, and improve the impaired lipolytic response to exercise in the elderly.

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.

Modulation of adipocyte lipoprotein lipase expression as a strategy for preventing or treating visceral obesity

As compared to subcutaneous adipocytes, visceral adipocytes have high basal lipolysis, are highly sensitive to catecholamines, and are poorly sensitive to insulin; these traits are amplified when visceral adipocytes hypertrophy. As a result, enlarged visceral fat stores tend to flood the portal circulation with free fatty acids at metabolically inappropriate times when fatty acids are unlikely to be oxidized, thus exposing tissues to excessive free fatty acid levels and giving rise to the insulin resistance syndrome. A logical approach to preventing or correcting visceral obesity is to down-regulate the lipoprotein lipase (LPL) activity of visceral adipocytes relative to that expressed in subcutaneous adipocytes and skeletal muscle. IGF-I activity appears to be a primary determinant of visceral LPL activity in humans; systemic IGF-I activity is decreased when diurnal insulin secretion is low, when hepatocytes detect a relative paucity of certain essential amino acids, and when estrogens are administered orally. The ability of alpha-glucosidase inhibitor therapy to selectively reduce visceral adiposity suggests that down-regulation of diurnal insulin secretion and/or IGF-I activity may indeed have a greater impact on LPL activity in visceral fat than in subcutaneous fat. Thus, low-glycemic-index, vegan, high-protein, or hypocaloric diets can be expected to decrease visceral LPL activity, as can postmenopausal estrogen therapy. Furthermore, estrogen enhances the LPL activity of non-pathogenic gluteofemoral fat cells, whereas testosterone decreases visceral LPL activity in men; this may explain why sex hormone replacement in middle-aged people of both sexes has a favorable impact on visceral fat and insulin sensitivity. Beta-adrenergic activity suppresses transcription of LPL in adipocytes; this phenomenon may contribute to the favorable impact of exercise training on visceral obesity; conceivably, preadministration of safe drugs that boost catecholamine activity (caffeine, yohimbine) could potentiate this beneficial effect of exercise. Glucocorticoids selectively increase the LPL activity of visceral adipocytes; while there is currently no convincing evidence that psychological stress is a major determinant of visceral adiposity, or that stress management techniques can help to correct visceral obesity, reports that anxiolytic therapy can improve glycemic control in type 2 diabetes should encourage further research along these lines.

Insulin secretion and glucose kinetics during exercise with and without pharmacological alpha(1)- and alpha(2)-receptor blockade

The mechanism behind exercise-induced decreases in plasma insulin concentrations was examined in eight healthy young men. In addition, the influence of specific alpha(1)- and alpha(2)-adrenoceptor blockade on glucose kinetics during exercise was studied. To test the hypothesis that exercise-induced decreases in insulin secretion are mediated via alpha(2)-adrenoceptors, all subjects exercised for 60 min on separate occasions under four conditions: with and without alpha(1)-receptor blockade (1 mg prazosin) and with and without or alpha(2)-receptor blockade (15 mg yohimbine). Glucose kinetics were measured using [3-(3)H]glucose. During exercise with alpha(2)-receptor blockade, the insulin concentration initially increased (first 20 min) then decreased, whereas it continually decreased in the corresponding control experiment. The C-peptide concentration did not change during exercise with alpha(2)-receptor blockade but decreased in the control experiment. During exercise with alpha(1)-receptor blockade and corresponding control experiments, insulin and C-peptide levels always decreased. With alpha(1)-receptor blockade, the glucose concentration increased (first 30 min) and then decreased, whereas it slightly decreased in all other experiments. In addition, with alpha(1)-receptor blockade, the glucose rate of appearance (Ra) increased rapidly (because of higher catecholamine concentrations in alpha(1)-receptor blockade versus control) and the glucose rate of disappearance (Rd) was higher compared with control. During exercise with alpha(2)-receptor blockade, the Ra and Rd were always lower compared with control. Therefore, we conclude that exercise-induced decreases in insulin secretion are mediated via alpha(2)-adrenoceptors and that blockade of alpha(1)- and alpha(2)-adrenoceptors during exercise elicits opposite responses in glucose Ra and Rd.

Cardiovascular effects of ephedrine, caffeine and yohimbine measured by thoracic electrical bioimpedance in obese women

Low caloric diet is a commonly accepted treatment in obesity. However, owing to moderate results, a pharmacological support has been proposed. As some efficacious drugs activate overall sympathetic activity, they might modify functions of the cardiovascular system. Three groups of subjects were studied: (1) nine obese women receiving only a standard hypocaloric diet; (2) nine obese women receiving a standard hypocaloric diet and ephedrine (2 x 25 mg) with caffeine (2 x 200 mg); (3) nine obese women receiving a standard hypocaloric diet and ephedrine (2 x 25 mg) with caffeine (2 x 200 mg) and yohimbine (2 x 5 mg). The cardiovascular state was evaluated by thoracic electrical bioimpedance, automatic sphygmomanometry and continuous ECG recording. In each patient, the haemodynamic study was performed twice: at rest, i.e. before treatment; and after 10 days of treatment. On the same days in each patient, the haemodynamic tests were performed during physical exercises (handgrip stress and cycloergometer exercise). Caffeine and ephedrine had no haemodynamic effect in resting patients. These two drugs led to an increase in ejection fraction during cycloergometer exercise. Addition of yohimbine increased diastolic pressure and heart rate but decreased ejection fraction and stroke index during rest. We also observed that addition of yohimbine decreased ejection fraction during the handgrip and cycloergometer exercise and increased cardiac load during dynamic exercise. Pharmacological supplement of ephedrine and caffeine to a low caloric diet modified the cardiovascular system weakly, but the addition of yohimbine to this regimen attenuated cardiac performance during rest and handgrip and increased cardiac work during dynamic exercise.

Anti-obesity effect of MPV-1743 A III, a novel imidazoline derivative, in genetic obesity

MPV-1743 A III ((+/-)-4-(5-fluoro-2,3-dihydro-1H-inden-2-yl)-1H-imidazole) is a novel imidazoline derivative. In this study, it was shown to bind with high affinity to alpha2-adrenoceptor subtypes alpha2A (IC50) = 0.66 +/- 0.06 nM), alpha2B (IC50) = 3.8 +/- 0.53 nM), alpha2C (IC50) = 3.1 +/- 0.61 nM) in the recombinant S115 cells and to alpha2D (IC50 = 0.94 +/- 0.10 nM) in the rat submandibular gland. MPV-1743 A III also showed remarkably high affinity to alpha1-adrenoceptors (IC50 = 150 +/- 12 nM) in the rat cerebral cortex and to imidazoline I2b-binding sites (IC50) = 150 +/- 5.0 nM) in the rat liver. The functional alpha2-adrenoceptor antagonistic effect of MPV-1743 A III was demonstrated by studying the ability of orally administered MPV-1743 A III to reverse and prevent the alpha2-adrenoceptor agonist detomidine-induced mydriasis in rat. The anti-obesity effect of MPV-1743 A III was investigated in genetically obese (fa/fa) Zucker rats in two different phases of obesity. Chronic treatment with MPV-1743 A III (0.3 3 mg/kg per day p.o. for 3 weeks) dose dependently decreased weight gain in early-phase obesity. In fully established obesity, GDP binding to mitochondria and expression of uncoupling protein mRNA were increased in brown adipose tissue by MPV-1743 A III indicating an activation of non-shivering thermogenesis. The present study shows that MPV- 1743 A III has a modest anti-obesity effect in the genetic rodent model of obesity. The relative importance of alpha2- and alpha1-adrenoceptors and imidazoline I2b-binding sites in mediating the effects of MPV-1743 A III needs further evaluation.

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.

Involvement of alpha 2-adrenoceptors in metabolic and hormonal responses to a mixed meal in beagle dogs

The effects of alpha 2-adrenoceptor blockade or activation on glucose, insulin, free fatty acids (FFA), and glycerol responses to a mixed meal were studied in the beagle dog. The alpha 2-adrenoceptor antagonist deriglidole (1 mg/kg po), administered 45 min before feeding, significantly reduced glycemia and increased insulin, FFA, and glycerol levels. Although the alpha 2-adrenoceptor agonist UK-14.304 (3 micrograms/kg sc), administered 15 min before feeding, had no effect per se, it completely blocked meal-induced insulin release, thus promoting a mild increase in glycemia, and prolonged the meal-induced FFA decrease. Deriglidole antagonized the reduction of insulin secretion and the hyperglycemia induced by UK-14.304. The meal-induced fall in FFA levels was still observed after deriglidole treatment and was markedly amplified when UK-14.304 was administered with deriglidole. These results suggest that, in the dog, insulin release and lipolysis are very sensitive to alpha 2-adrenoceptor stimulation. It is also suggested that the meal-evoked decrease in lipid mobilization results from an increase in alpha 2-adrenoceptor stimulation rather than from an increase in insulin secretion.

Evidence for activation of both adrenergic and cholinergic nervous pathways by yohimbine, an alpha 2-adrenoceptor antagonist

Adrenoceptors are involved in the control of the activity of the autonomic nervous system and especially the sympathetic nervous system. Activation of alpha 2-adrenoceptors decreases sympathetic tone whereas their blockade has an opposite effect. However, previous investigations have shown that yohimbine (a potent alpha 2-adrenoceptor antagonist) increases salivary secretion through activation of cholinergic pathways. The aim of the present experiment was to investigate the involvement of both the sympathetic and the parasympathetic system in several pharmacological effects of yohimbine. For this purpose, salivary secretion and various endocrino-metabolic parameters (noradrenaline and insulin secretions, lipomobilization) were evaluated in conscious fasting dogs before and after blockade of either the sympathetic (with the beta-adrenoceptor antagonist agent nadolol) or the parasympathetic (with the anticholinergic agent atropine) systems. Yohimbine alone (0.4 mg.kg-1, i.v.) increased within 5-15 minutes, plasma noradrenaline (600%), insulin levels (300%), free-fatty acids (79%) and salivary secretion (143%). Atropine (0.2 mg.kg-1, i.v.) suppressed yohimbine-induced salivary secretion (90%) but did not significantly modify the yohimbine induced changes in noradrenaline (312%), insulin (277%) and free-fatty acids (102%) plasma levels. Administration of nadolol (1 mg.kg-1, i.v.) did not change the magnitude of the increase in both noradrenaline plasma levels (550%) and salivary secretion (300%) induced by yohimbine. However, nadolol totally blunted the increase in insulin (15%) and free-fatty acids (4%) plasma levels. These results show that yohimbine-induced increase in salivary secretion is a cholinergic effect whereas the increase in insulin and free fatty acids can be explained by an increase in sympathetic tone.(ABSTRACT TRUNCATED AT 250 WORDS)

Alpha-adrenoceptors

Major advances have been made in our understanding of the molecular structure and function of the alpha-adrenoceptors. Many new subtypes of the alpha-adrenoceptor have been identified recently through biochemical and pharmacological techniques and several of these receptors have been cloned and expressed in a variety of vector systems. Currently, at least seven subtypes of the alpha-adrenoceptor have been identified and the molecular structure and biochemical functions of these subtypes are beginning to be understood. The alpha-adrenoceptors belong to the super family of receptors that are coupled to guanine nucleotide regulatory proteins (G-proteins). A variety of G-proteins are involved in the coupling of the various alpha-adrenoceptor subtypes to intracellular second messenger systems, which ultimately produce the end-organ response. The mechanisms by which the alpha-adrenoceptor subtypes recognize different G-proteins, as well as the molecular interactions between receptors and G-proteins, are the topics of current research. Furthermore, the physiological and pathophysiological role that alpha-adrenoceptors play in homeostasis and in a variety of disease states is also being elucidated. These major advances made in alpha-adrenoceptor classification, molecular structure, physiologic function, second messenger systems and therapeutic relevance are the subject of this review.

Effects of physiological and pharmacological variation of sympathetic nervous system activity on plasma non-esterified fatty acid concentrations in man

1. The consequence of the sympatholytic effect of clonidine (alpha 2-adrenoceptor agonist) was compared with the effect of a physiological inhibition of sympathetic nervous system activity (change from upright to supine position) on plasma catecholamine and non-esterified fatty acid (NEFA) concentrations in overnight fasting healthy men. 2. Clonidine (150 micrograms orally) administered in upright position induced a significant reduction of plasma noradrenaline and NEFA concentrations. A change from upright to supine position which provoked a more marked decrease in plasma noradrenaline concentrations induced a weak increase in plasma NEFA concentrations. 3. The modification of plasma NEFA and catecholamine concentrations brought about by standing up was studied after placebo or yohimbine (alpha 2-adrenoceptor antagonist) administration. With placebo, standing up promotes a 100% increase in plasma noradrenaline concentrations (measured 5 and 15 min after rising) and a weak transient decrease in plasma NEFA concentrations (5 min after rising). In the supine position, yohimbine increased plasma noradrenaline and NEFA concentrations by about 100% and 55% respectively. Standing after yohimbine administration promoted large increases in plasma noradrenaline and NEFA concentrations. 4. These results indicate that a reduction of sympathetic nervous activity is not associated with a decrease of plasma NEFA concentrations and argue for a role of alpha 2-adrenoceptors in the NEFA mobilization from adipose tissue after sympathetic nervous system activation in man.

Role of vascular alpha-2 adrenoceptors in regulating lipid mobilization from human adipose tissue

The role of alpha-2 adrenoceptors in lipid mobilization and blood flow was investigated in situ using microdialysis of subcutaneous adipose tissue in nonobese healthy subjects. The alpha-2 agonist clonidine caused dose-dependent biphasic response with increased glycerol levels at low clonidine concentrations and decreased glycerol levels at concentrations > 10(-7) mol/liter. Similar results were observed with epinephrine plus propranolol. Clonidine action was unaffected in the presence of labetalol (beta-/alpha-1 antagonist) but completely blunted by the presence of yohimbine (alpha-2 antagonist). The pseudolipolytic effect of clonidine was significantly more pronounced in gluteal as compared with abdominal adipose tissue. When clonidine was added together with the vasodilating agents nitroprusside or hydralazine, the pseudolipolytic effect was abolished and a dose-dependent decrease in dialysate glycerol was observed at all clonidine concentrations (10(-10)-10(-4) mol/liter). When ethanol was added to the perfusate to monitor blood flow, the escape of alcohol from the dialysate was accelerated by 30% with hydralazine or nitroprusside (P < 0.01) and 30% retarded (P < 0.05) by clonidine (10(-10) mol/liter). Thus, the results demonstrate an important role of blood flow for regulating lipid mobilization from adipose tissue in vivo. Alpha-2 adrenoceptor activation causes marked retention of lipids in adipose tissue due to vasoconstriction in combination with antilipoiysis.

Alpha 2-adrenoceptor antagonist potencies of two hydroxylated metabolites of yohimbine

1. The alpha 2-adrenoceptor antagonist capacities of two hydroxylated metabolites of yohimbine in man (10-OH-yohimbine and 11-OH-yohimbine) were investigated on the alpha 2-adrenoceptors of human platelets and adipocytes and compared to those of yohimbine. 2. Yohimbine and 11-OH-yohimbine exhibited similar alpha 2-adrenoceptor affinity in biological studies i.e. inhibition of adrenaline-induced platelet aggregation and inhibition of UK14304-induced antilipolysis in adipocytes. 3. Yohimbine and the two metabolites displaced [3H]-RX 821002 binding with equivalent affinities in platelet and adipocyte membranes with the following order of potency: yohimbine > 11-OH-yohimbine > 10-OH-yohimbine. However, when binding studies were carried out in binding buffer supplemented with 5% albumin, the apparent affinity of yohimbine was reduced about 10 fold and was similar to that of 11-OH-yohimbine. 4. Yohimbine and its metabolites were bound to different extents to plasma proteins, the bound fraction being 82%, 43% and 32% respectively for yohimbine, 11-OH-yohimbine and 10-OH-yohimbine. 5. These results show that the main hydroxylated metabolite of yohimbine in man (11-OH-yohimbine) possesses alpha 2-adrenoceptor antagonist properties. The discrepancies found in binding studies (i.e. 10 fold lower affinity of 11-OH-yohimbine than yohimbine for alpha 2-adrenoceptors but similar capacities in blocking biological alpha 2-adrenoceptor effects in cells) are attributable to the higher degree of binding of yohimbine to plasma protein.

Yohimbine pharmacokinetics and interaction with the sympathetic nervous system in normal volunteers

The pharmacokinetics of yohimbine and its effects on sympathoadrenal function were studied in 13 young, healthy, male volunteers after an IV bolus dose of 0.25 or 0.5 mg.kg-1. Pharmacokinetic analysis showed that distribution was rapid, with a half life between 0.4 and 18 min, and the elimination half life ranged between 0.25 and 2.5 h. The volume of distribution (Vss) was 74 l, (range 26 to 127 l). Only 0.5 to 1% of unchanged yohimbine was found in the urine, indicating that the major part of the drug was eliminated by hepatic clearance. Total plasma clearance was 117 l.h-1, which exceeds the hepatic plasma flow. This means that yohimbine is a high extraction drug with considerable extra-hepatic metabolism. Fractional urine sampling revealed that 0.5-1% of unchanged yohimbine was excreted in urine in a biphasic manner. The data also suggested the existence of a slower elimination phase, with a half life of 13 h. The venous plasma concentration of noradrenaline (NA) increased 3-fold within 15 min after the yohimbine injection while plasma adrenaline (A) and neuropeptide Y-like immunoreactivity (NPY-LI) remained unchanged. The plasma concentration-effect relationship of the changes in circulating NA followed counter-clockwise hysteresis. The results show that the hyperadrenergic state elicited by therapeutic doses of the alpha 2-adrenergic autoreceptor antagonist, yohimbine, is due to an interaction with NA but not to release of A or NPY in man.

Determination of yohimbine and its two hydroxylated metabolites in humans by high-performance liquid chromatography and mass spectral analysis

The existence of at least two metabolites of yohimbine (YO) in humans is demonstrated. Combined high-performance liquid chromatographic (HPLC), NMR and mass spectral analyses permitted them to be identified as hydroxylated metabolites at the C-10 and C-11 positions. A normal-phase HPLC method allowing the simultaneous determination of YO and its main metabolite, 11-hydroxyyohimbine (11-OHYO), in biological samples is described. This assay was performed using a LiChrosorb Si 60 column and a mobile phase consisting of 0.02 M sodium acetate (pH 5)-methanol (5:95, v/v) at a flow-rate of 1 ml/min. Detection was achieved by a fluorimetric method (excitation at 280 nm and emission at 320 nm). The extraction yields of YO, 10-OHYO and 11-OHYO from plasma were 91.8, 45.3 and 17.8%, respectively, and their respective within-day reproducibilities were 3.8, 1.4 and 5.9%. The between-day reproducibility for YO at the concentrations of 1 and 10 ng/ml were 8.9 and 6.4%, respectively. The accuracy of the method for YO at concentrations of 1 and 10 ng/ml were 5.1 and 2.3%, respectively. The limits of determination of YO, 10-OHYO and 11-OHYO were 0.1, 0.5 and 1 ng/ml, respectively. The method was used in bioavailability study of YO following oral and intravenous administration in humans.

Pharmacological prospects for α2-adrenoceptor antagonist therapy

The discovery of various alpha 2-adrenoceptor subtypes in numerous tissues and studies of alpha 2-adrenoceptor-mediated mechanisms has generated considerable interest in their physiological functions. It has also increased possibilities for the design of new pharmacological tools and for the study of the pharmacological impact of new drugs. Alpha 2-adrenoceptors are located pre- and postsynaptically both in the central noradrenergic pathways and on the autonomic nerve endings. It is difficult to dissociate alpha 2-adrenoceptor-mediated autoregulation, involving presynaptic receptors, from actions dependent on post- and extrajunctional alpha 2-adrenoceptor activation. A lot of alpha 2-adrenoceptors are subject to permanent tonic activation by the sympathetic nervous system. Max Lafontan and colleagues review the major actions of alpha 2-adrenoceptors and consider the sites of impact of alpha 2-antagonists that could initiate further research for putative applications of these drugs. Many of the possible targets for alpha 2-adrenoceptor antagonists have not yet been explored clinically.

Thermogenic and lipolytic effect of yohimbine in the dog

1. Lipid mobilization during a hypocaloric diet may be enhanced by a pharmacological approach using alpha 2-adrenoceptor antagonists since these drugs are known to increase sympathetic tone and stimulate lipolysis. Studies were undertaken in the dog in order to evaluate the effects of oral yohimbine administration (alpha 2-adrenoceptor antagonist) on heat production, metabolic, endocrinological and cardiovascular parameters. 2. Acute oral yohimbine (0.25 or 0.40 mg kg-1) provoked an increase in plasma non-esterified fatty acids. The drug increased sympathetic nervous system activity as indicated by the increased level of plasma noradrenaline. These effects persisted during the entire experimental period (4 h). The increase in plasma noradrenaline level was two fold higher with the higher dose of yohimbine (0.4 mg kg-1). The plasma adrenaline level was increased only with the higher dose. 3. Yohimbine transiently increased plasma insulin and the effect was dose-dependent. 4. Yohimbine (0.25 mg kg-1) enhanced heart rate and arterial blood pressure. 5. The effect of yohimbine on oxygen consumption, carbon dioxide and heat production was determined by indirect calorimetry. The drug (0.25 mg kg-1) increased O2 consumption and CO2 and heat production 30 min after its administration and the effect persisted over the experimental period. The respiratory quotient, rather low in the fasting animals, remained unchanged. 6. The present work indicates that thermogenesis and lipid mobilization are enhanced during fasting in the dog by alpha 2-adrenoceptor blockade. Yohimbine also induced a transient increase in plasma insulin level and increased heart rate and blood pressure. The lipid mobilization plus the action on thermogenesis observed after yohimbine draw attention to the putative interest of a2-antagonists in the pharmacological treatment of obesity during restricted calorie intake.

Absence of arterial hypertension despite chronic plasma noradrenaline elevation: evidence for down-regulation of alpha-adrenoceptors. A case report

A 44 year old-healthy female presented chronic and stable high levels of plasma noradrenaline (NA) without any major change in adrenaline. The diagnosis of phaeochromocytoma was discarded. These increased levels of NA offered an unique opportunity to investigate under in vivo conditions a putative regulation of alpha-adrenoceptors by this endogenous catecholamine. Infusion rates of exogenous NA up to 0.74 micrograms/kg per min were unable to induce any change in blood pressure (or heart rate) in the subject, In contrast, in normotensive controls, an increase in blood pressure (+ 15 mm Hg) was observed with 0.39 micrograms/kg per min. The magnitude of yohimbine-induced increase in plasma NA was similar in the subject and in the controls. Platelet alpha 2-adrenoceptors evaluated by specific [3H]-yohimbine binding showed a significantly lower level in the subject when compared to controls. The results show that a sustained increase in plasma NA is able to induce down-regulation of alpha-adrenoceptors. This down-regulation can explain the lack of arterial hypertension despite the increased sympathetic tone.

Anorectic effect of alpha 2-antagonists in dog: effect of acute and chronic treatment

Acute oral administration of alpha 2-antagonists (yohimbine, RX 821002, atipamezole: 1 mg/kg each) reduced dog food intake. Yohimbine reduced food intake over 20 hours, while the effect of the two other drugs lasted only 2 hours. Yohimbine (0.4 or 1 microgram/kg) gave the same results. At these doses, it promoted a lasting durable increase in plasma nonesterified fatty acids and catecholamines levels and a transient elevation of plasma insulin levels. The beta-antagonist nadolol (4 mg/kg per os) suppressed the yohimbine-induced lipid mobilization without modifying its anorectic effect. Chronic oral yohimbine (0.4 mg/kg/day during 14 days) reduced food intake and promoted a weight loss. Normal food intake was recovered two days after yohimbine withdrawal. No change was observed in the number of platelet alpha 2-adrenergic receptors. In addition to their lipid mobilizing action and sympathetic tone stimulation, alpha 2-antagonist compounds reduce food intake.

Metabolic regulation by alpha 1- and alpha 2-adrenoceptors

The role of alpha-adrenoceptors in the mediation of autonomic function, particularly in the control of the cardiovascular system, is widely known. However, alpha-adrenoceptors are also important in the regulation of a variety of metabolic processes that occur in the body either through direct action or by stimulation of the release of other mediators that control metabolic function. Thus, alpha 2-adrenoceptor activation by circulating or neuronally released catecholamines inhibits the release of insulin from pancreatic islet beta-cells and, by inhibiting this response, alpha 2-adrenoceptor antagonists have been shown to have an antihyperglycemic effect. The alpha-adrenoceptor-mediated regulation of the release of pituitary hormones is indirect, with alpha-adrenoceptors being located on peptidergic neurons in the hypothalamus that secrete releasing hormones into the hypophysial portal system to regulate the secretion of hormones from the anterior pituitary gland. Thus, the increase in cortisol secretion from the adrenal glands following a meal is produced, at least in part, by an alpha 1-adrenoceptor-mediated increase in vasopressin and CRF-41 secretion from neurons on the hypothalamus that stimulate the release of adrenocorticotrophic hormone secretion from the pituitary gland, which subsequently stimulates the synthesis and release of cortisol from the adrenal medulla. In addition to metabolic regulation by alpha 1- and alpha 2-adrenoceptors within the endocrine system, alpha-adrenoceptors are also a component of the system that regulates certain aspects of metabolism within autonomic effector cells, such as the control of smooth muscle cell division and growth during periods of continued alpha-adrenoceptor activation as a result of activation of second messenger systems.

Yohimbine increases human salivary secretion

The effect of oral yohimbine (14 mg) on salivary secretion was evaluated in healthy volunteers. Yohimbine significantly increased salivary secretion when compared with placebo. This effect was significant from 60 min until 180 min after administration under our experimental conditions. Yohimbine (or alpha 2-adrenoceptor blocking agents) could have a potential interest in the treatment of dry mouths.