Clonidine Lowers Blood Pressure by Reducing Vascular Resistance and Cardiac Output in Young, Healthy Males

Opposing Responses of the Calcium Channel Blocker Nicardipine to Vascular Stiffness in the Elastic and Muscular Arteries in Rabbits

AIM

The cardio-ankle vascular index (CAVI) consists of intrinsic and functional arterial stiffness mainly regulated by vasoactive compounds. A new stiffness index of the aorta (aBeta) and iliac-femoral arteries (ifBeta) was determined by applying the CAVI theory to the whole aorta and iliac-femoral arteries. We investigated the changes in aBeta and ifBeta in response to decreased blood pressure (BP) induced by the Ca2＋ channel blocker nicardipine to elucidate the involvement of Ca2＋ in aBeta and ifBeta.

METHODS

Pressure waves at the origin of the aorta (oA), distal end of the abdominal aorta (dA), and left femoral artery (fA) as well as flow waves at the oA were simultaneously recorded before and after the infusion of nicardipine (50 µg/kg/min) for 2 min in 12 male rabbits under pentobarbital anesthesia. Beta was calculated using the following formula: Beta=2ρ / PP×ln (SBP / DBP)×PWV2, where ρ, SBP, DBP, and PP denote blood density and systolic, diastolic, and pulse pressures, respectively. aBeta, ifBeta, and aortic-iliac-femoral Beta (aifBeta) were calculated using aPWV, ifPWV, and aifPWV, respectively.

RESULTS

SBP, mean arterial pressure (MAP), DBP, and total peripheral vascular resistance significantly decreased during the administration of nicardipine, whereas cardiac output significantly increased. aBeta and ifBeta significantly increased and decreased, respectively, whereas aifBeta did not change despite the decrease in BP. ifBeta and aBeta positively and negatively correlated with BP, respectively, whereas aifBeta did not correlate with SBP.

CONCLUSIONS

There were contradictory arterial responses to nicardipine between the elastic and muscular arteries. Unknown vasoconstriction mechanisms that are not involved in Ca2＋ influx may function in the aorta in response to decreased BP.

The first report of clonidine in vivo/in vitro effects on infertile women with polycystic ovary syndrome (in vivo/in vitro study)

The sympathetic nervous system (SNS) is hyperactive in women with polycystic ovary syndrome (PCOS). This study was designed in two sections: in vivo/in vitro with clonidine as the alpha-2 adrenoceptor (ADR-α₂) agonist for modulating this hyperactivity. Eighty women with PCO participated in this randomised clinical trial (in vivo). A clonidine (0.1 mg) tablet was given twice a day for two months. Polycystic ovary morphology (PCOM) and pregnancy rate were the main outcome measurements. In the candidates for in vitro fertilisation (IVF), clonidine was added to the culture medium during IVF for two study groups (PCO-clonidine/PCO-without) and two control groups (egg donors-clonidine/egg donors-without). Our results showed that the pregnancy rate significantly was higher in the study group (p = .002). The mRNA expression of ADR-α₁ and ADR-β₂ in PCO was higher than control group (p value <.001). But ADR-α₁ expression in PCO-clonidine group decreased (p value = .042), the same as ADR-α₂ expression. The intensity of this effect showed a pattern for ADR-α₁<ADR-β₂<ADR-α₂. Increase of antral follicle count (AFC) growth and pregnancy rate indicate the significant role of ADR-α₂ in PCOS. Clonidine reduced gene expression and protein levels, confirming the above results. These results would aid in pharmacological treatments, as well as assisted reproductive technologies (ARTs).Impact StatementWhat is already known on this subject? In women with PCOS, sympathetic nerve activity is higher than in healthy women. Clonidine is widely used as an alpha-2 presynaptic adrenoceptor (autoreceptor) agonist to modulate the output of the sympathetic nervous system (SNS). Our in vivo/in vitro results showed that the optimal dose of clonidine can increase the oocyte maturity and pregnancy rate in PCO women. This finding was also confirmed by the results in cumulus cell culture.What do the results of this study add? The results of administration of 0.2 mg of clonidine (in vivo) for oocyte maturation and pregnancy rate confirms the in vitro response in the cumulus cell culture of PCO women's follicle.What are the implications of these findings for clinical practice and/or further research? These findings can be used in pharmacological treatment of anovulation and assisted reproductive technology (ART).

Effects of Enhanced Intracranial Pressure on Blood Pressure and the Cardio-Ankle Vascular Index in Rabbits

Aim: Stroke is well known to lead to hypertension; nevertheless, the role of vascular function in hypertension remains unclear. In this study, we aimed to clarify the mechanism underlying increased arterial stiffness following stroke.

Methods: The cardio-ankle vascular index (CAVI) was measured in five New Zealand White rabbits. Under general anesthesia, intracranial pressure (ICP) was increased by injecting saline (15 mL) into the cisterna magna. ICP was monitored using a catheter inserted into the subarachnoid space via right frontal bone craniotomy. Blood pressure (BP), CAVI, and common carotid flow (CCF) were evaluated, and the responses of these parameters to increased ICP were analyzed.

Results: Saline injection into the cisterna magna increased the ICP by over 20 mmHg. Both BP and CAVI increased from 63.2±4.84 to 128.8±14.68 mmHg and from 4.02±0.28 to 4.9±0.53, respectively. Similarly, BP and CCF increased. When hexamethonium was administered before the increase in ICP, the increase in BP (132.2±9.41 mmHg with 10 mg/kg hexamethonium vs. 105.6±11.01 mmHg with 100 mg/kg hexamethonium) and CAVI (5.02±0.64 with 10 mg/kg hexamethonium vs. 4.82±0.42 with 100 mg/kg hexamethonium) were suppressed in a dose-dependent manner.

Conclusion: Increased ICP causes an increase in BP and CAVI, suggesting that enhanced stiffness of the muscular arteries contributes to high BP. Blocking the autonomic nervous system with hexamethonium suppresses the increase in BP and CAVI, indicating that these increases are mediated by activation of the autonomic nervous system.

Expression of ADR-α1, 2 and ADR-β2 in cumulus cell culture of infertile women with polycystic ovary syndrome and poor responder who are a candidate for IVF: the novel strategic role of clonidine in this expression

OBJECTIVE

Alpha and beta-adrenoceptors (ADR-α1, 2, and β2) play a regulatory role in the folliculogenesis and steroidogenesis in the ovarian follicles. This study aimed to measure these adrenoceptors mRNA and its protein levels in cumulus cells (CCs) culture of poor ovarian reserve (POR) and polycystic ovarian syndrome (PCOS) infertile women (IVF candidate) and the effect of clonidine treatment at CCs culture.

METHODS

This case/control study was conducted in 2017 includes a control (donation oocytes) and two studies (PCO and POR) groups. The ovulation induction drugs were prescribed in all groups. After the oocyte puncture, the follicular fluid was collected and CCs were isolated were cultured. RNA was extracted and cDNA was synthesized and designed the primer for the ADR-α1, 2 and ADR-β2 gene expression. The protein levels were investigated by Western Blot.

RESULTS

The results showed a high level of three adrenergic expressions in PCO women compared to the control group (p-value <.001), which can be reduced by clonidine. POR group showed a significant decrease in the gene expression of ADR-α1 (p-value = .004) and ADR-α2 (p-value = .003) compared to the control group and clonidine treatment had no effect.

CONCLUSION

The significant increase of three adrenoceptors gene expression and protein levels in CCs culture indicate to the hyperactivity of the ovarian sympathetic nervous system at the receptor levels in women with PCOS, and clonidine confirmed it by reducing this expression. In POR women, the reduction of ADR-α1, 2 expressions maybe lead to the aging process in the ovary.

Pharmacological Studies Pertaining to Smooth Muscle Relaxant, Platelet Aggregation Inhibitory and Hypotensive Effects of Ailanthus altissima

OBJECTIVE

This in vitro and in vivo study was conducted to rationalize some of traditional medicinal uses of Ailanthus altissima in gastrointestinal, respiratory, and cardiovascular systems.

MATERIALS

Crude extract of Ailanthus altissima (Aa.Cr) and its fractions were prepared and utilized in in vitro and in vivo studies. For in vitro studies, Aa.Cr was investigated on isolated rabbit jejunum, isolated tracheal strip, and isolated aorta of rat suspended in tissue organ bath. Platelet rich and platelet poor plasma were used to study platelet aggregation inhibitory activity. In vivo antidiarrheal effect of Aa.Cr was investigated on balb/c mice pretreated with castor oil to induce diarrhea and SD rats were used to study hypotensive activity.

RESULTS

Concentration dependent spasmolytic effects of Aa.Cr and its DCM fraction (Aa.DCM) were observed on spontaneous and spasmogen induced contractions in jejunum isolated from rabbit, but effect against high potassium (high-K+) induced contractions was more potent. Moreover Aa.Cr showed parallel shifting of calcium response curve to the right side. While its aqueous fraction (Aa.aq) caused spasmogenesis of isolated rabbit jejunum, this effect was blocked partially with prior administration of atropine (1μM). Concentration dependent protection against castor oil induced diarrhea was also observed. Relaxant effect was observed by the application of Aa.Cr and Aa.DCM against high-K+ and carbachol (CCh) induced contractions in tracheal strips isolated from SD rats, while Aa.Aq caused partial relaxation of high-K+ induced contractions, but no effect was observed against CCh induced contractions. Relaxation of rat aorta by the application of Aa.Cr and its fractions was also observed. Inhibition of force of contraction in rabbit atrium was also observed. Inhibition of platelet aggregation was observed against epinephrine and ADP induced aggregation.

CONCLUSION

Keeping in view the observed results, it is concluded that smooth muscle relaxant, platelet aggregation inhibitory and hypotensive effect may be due to the blockage of calcium channels.

Noradrenaline Modulates Visual Perception and Late Visually Evoked Activity

An identical sensory stimulus may or may not be incorporated into perceptual experience, depending on the behavioral and cognitive state of the organism. What determines whether a sensory stimulus will be perceived? While different behavioral and cognitive states may share a similar profile of electrophysiology, metabolism, and early sensory responses, neuromodulation is often different and therefore may constitute a key mechanism enabling perceptual awareness. Specifically, noradrenaline improves sensory responses, correlates with orienting toward behaviorally relevant stimuli, and is markedly reduced during sleep, while experience is largely "disconnected" from external events. Despite correlative evidence hinting at a relationship between noradrenaline and perception, causal evidence remains absent. Here, we pharmacologically down- and upregulated noradrenaline signaling in healthy volunteers using clonidine and reboxetine in double-blind placebo-controlled experiments, testing the effects on perceptual abilities and visually evoked electroencephalography (EEG) and fMRI responses. We found that detection sensitivity, discrimination accuracy, and subjective visibility change in accordance with noradrenaline (NE) levels, whereas decision bias (criterion) is not affected. Similarly, noradrenaline increases the consistency of EEG visually evoked potentials, while lower noradrenaline levels delay response components around 200 ms. Furthermore, blood-oxygen-level-dependent (BOLD) fMRI activations in high-order visual cortex selectively vary along with noradrenaline signaling. Taken together, these results point to noradrenaline as a key factor causally linking visual awareness to external world events. VIDEO ABSTRACT.

Thoracic Epidural Clonidine Attenuates Haemodynamic Responses Induced by Endobronchial Intubation

Laryngoscopy and endobronchial intubation usually cause transient hypertension and tachycardia. We investigated whether thoracic epidurally injected 3 μg/kg clonidine attenuates cardiovascular responses to intubation compared with 2 μg/kg fentanyl and 1 mg/kg lidocaine. Epidural catheterization was performed at the T6–T7 or T7–T8 intervertebral space, and saline or clonidine in saline was injected 20 min before anaesthetic induction. Anaesthesia was induced using 5 mg/kg thiopental sodium and 0.1 mg/kg vecuronium. Laryngoscopy and endobronchial intubation were performed 2 min later. Mean blood pressure and heart rate were measured throughout anaesthetic induction. In the control group and the fentanyl group, mean blood pressure and heart rate 3 min after endobronchial intubation were elevated significantly compared with baseline. In the clonidine group, however, mean blood pressure and heart rate did not increase compared with baseline. The control group had higher mean blood pressure and heart rate than the clonidine group 3 min after endobronchial intubation. Thoracic epidural clonidine may attenuate the haemodynamic response to endobronchial intubation.

Selective REM Sleep Deprivation Improves Expectation-Related Placebo Analgesia

The placebo effect is a neurobiological and psychophysiological process known to influence perceived pain relief. Optimization of placebo analgesia may contribute to the clinical efficacy and effectiveness of medication for acute and chronic pain management. We know that the placebo effect operates through two main mechanisms, expectations and learning, which is also influenced by sleep. Moreover, a recent study suggested that rapid eye movement (REM) sleep is associated with modulation of expectation-mediated placebo analgesia. We examined placebo analgesia following pharmacological REM sleep deprivation and we tested the hypothesis that relief expectations and placebo analgesia would be improved by experimental REM sleep deprivation in healthy volunteers. Following an adaptive night in a sleep laboratory, 26 healthy volunteers underwent classical experimental placebo analgesic conditioning in the evening combined with pharmacological REM sleep deprivation (clonidine: 13 volunteers or inert control pill: 13 volunteers). Medication was administered in a double-blind manner at bedtime, and placebo analgesia was tested in the morning. Results revealed that 1) placebo analgesia improved with REM sleep deprivation; 2) pain relief expectations did not differ between REM sleep deprivation and control groups; and 3) REM sleep moderated the relationship between pain relief expectations and placebo analgesia. These results support the putative role of REM sleep in modulating placebo analgesia. The mechanisms involved in these improvements in placebo analgesia and pain relief following selective REM sleep deprivation should be further investigated.

Effect of Clonidine (an antihypertensive drug) treatment on oxidative stress markers in the heart of spontaneously hypertensive rats

Hypertension is a risk factor for several cardiovascular diseases and oxidative stress suggested to be involved in the pathophysiology. Antihypertensive drug Clonidine action in ameliorating oxidative stress was not well studied. Therefore, this study investigate the effect of Clonidine on oxidative stress markers and nitric oxide (NO) in SHR and nitric oxide synthase inhibitor, N-nitro-L-arginine methyl ester (L-NAME) administered SHR. Male rats were divided into four groups [SHR, SHR+Clonidine (SHR-C), SHR+L-NAME, SHR+Clonidine+L-NAME(SHRC+L-NAME)]. Rats (SHRC) were administered with Clonidine (0.5 mg kg⁻¹ day⁻¹) from 4 weeks to 28 weeks in drinking water and L-NAME (25 mg kg⁻¹ day⁻¹) from 16 weeks to 28 weeks to SHRC+L-NAME. Systolic blood pressure (SBP) was measured. At the end of 28 weeks, all rats were sacrificed and in their heart homogenate, oxidative stress parameters and NO was assessed. Clonidine treatment significantly enhanced the total antioxidant status (TAS) (P < 0.001) and reduced the thibarbituric acid reactive substances (TBARS) (P < 0.001) and protein carbonyl content (PCO) (P < 0.05). These data suggest that oxidative stress is involved in the hypertensive organ damage and Clonidine not only lowers the SBP but also ameliorated the oxidative stress in the heart of SHR and SHR+L-NAME.

Efficacy of lignocaine with clonidine and adrenaline in minor oral surgical procedure

Use of vasoconstrictors in local anaesthesia is well known. The study was done on 30 patients who underwent removal of bilateral impacted third molars. The aim of the study was to compare the efficacy of lignocaine with clonidine and lignocaine with adrenaline in respect to onset, duration of anaesthesia, and postoperative analgesia along with hemodynamic stability (systolic blood pressure, diastolic blood pressure, mean arterial pressure, heart rate in intraoral nerve block. The patients were randomly selected of both sexes (male and female) between the age group of 18–40 years. Patients received 2 mL of 2% lignocaine with adrenaline (12.5 μg/mL) on one side and 2 mL of 2% lignocaine with clonidine (15 μg/mL) on the other side at two different appointments. 2 millilitres of drug was administered in both the test group and the control group. Statistically there was significant decrease in intraoperative and postoperative systolic blood pressure, diastolic blood pressure, mean arterial pressure, and heart rate in the lignocaine with clonidine group. The efficacy of clonidine based on visual analog scale was similar to adrenaline. No significant operative complications were observed.

Effects of the α₂-adrenergic agonist clonidine on the pharmacodynamics and pharmacokinetics of 3,4-methylenedioxymethamphetamine in healthy volunteers

The mechanism of action of 3,4-methylenedioxymethamphetamine (MDMA; ecstasy) involves the carrier-mediated and potentially vesicular release of monoamines. We assessed the effects of the sympatholytic α₂-adrenergic receptor agonist clonidine (150 μg p.o.), which inhibits the neuronal vesicular release of norepinephrine, on the cardiovascular and psychotropic response to MDMA (125 mg p.o.) in 16 healthy subjects. The study used a randomized, double-blind, placebo-controlled crossover design with four experimental sessions. The administration of clonidine 1 h before MDMA reduced the MDMA-induced increases in plasma norepinephrine concentrations and blood pressure but only to the extent that clonidine lowered norepinephrine levels and blood pressure compared with placebo. Thus, no interaction was found between the cardiovascular effects of the two drugs. Clonidine did not affect the psychotropic effects or pharmacokinetics of MDMA. The lack of an interaction of the effects of clonidine and MDMA indicates that vesicular release of norepinephrine, which is inhibited by clonidine, does not critically contribute to the effects of MDMA in humans. Although clonidine may be used in the treatment of stimulant-induced hypertensive reactions, the present findings do not support a role for α₂-adrenergic receptor agonists in the prevention of psychostimulant dependence.

Role of sympathetic responses on the hemodynamic consequences of rapid changes in posture in humans

Tolerance to +G(z) gravitational stress is reduced when +G(z) stress is preceded by exposure to hypogravity (fractional, 0, or negative G(z)). For example, there is an exaggerated fall in eye-level arterial pressure (ELAP) early on during +G(z) stress (head-up tilt; HUT) when this stress is immediately preceded by -G(z) stress (head-down tilt; HDT), termed the "push-pull effect." The aim of the present study was to test the hypothesis that sympathetic responses contribute to the push-pull effect. Young, healthy subjects (n = 7 males and 3 females) were subjected to 30 s of 30 degrees HUT from a horizontal position and to 30 s of 30 degrees HUT when HUT was immediately preceded by 20 s of -15 degrees HDT. Four bouts of HDT-HUT were alternated between five bouts of HUT in a counterbalanced design, and 1 min was allowed for recovery between tilts. This protocol was repeated during clonidine administration (2.5 microg/kg bolus over 30 min and then continuously at 0.36 microg x kg(-1) x h(-1)). Clonidine blunted the vasomotor responses to tilting, and this led to exaggerated changes in arterial pressure. Clonidine exerted little specific influence on the push-pull effect. Thus sympathetic responses appear neither to contribute to, nor protect against, the push-pull effect for the rate and duration of tilting imposed in the present study.

Value of Noninvasive Hemodynamics to Achieve Blood Pressure Control in Hypertensive Subjects

Abnormal hemodynamics play a central role in the development and perpetuation of high blood pressure. We hypothesized that hypertension therapy guided by noninvasive hemodynamics with impedance cardiography could aid primary care physicians in reducing blood pressure more effectively. Uncontrolled hypertensive patients on 1 to 3 medications were randomized by 3:2 ratio to either a standard arm or hemodynamic arm that used impedance cardiography (BioZ, CardioDynamics). Each patient completed 5 study visits with a 2-week washout period followed by 3 months of treatment. A total of 164 patients from 11 centers completed the study, 95 in the standard arm and 69 in the hemodynamic arm. At baseline and after washout, there were no differences between arms in number of medications or demographic, blood pressure, or hemodynamic characteristics. Systolic blood pressure reductions in the hemodynamic arm were greater from baseline (19 mm Hg versus 11 mm Hg; P <0.01) and after washout (25 mm Hg versus 19 mm Hg; P <0.05). Diastolic blood pressure reductions were also greater in the hemodynamic arm from baseline (12 mm Hg versus 5 mm Hg; P <0.001) and after washout (17 mm Hg versus 10 mm Hg; P <0.001). The hemodynamic arm achieved goal blood pressure (<140/90 mm Hg) more frequently (77% versus 57%; P <0.01) and a more aggressive blood pressure level (<130/85 mm Hg) more frequently (55% versus 27%; P <0.0001). These study results indicate that antihypertensive therapy guided by impedance cardiography in uncontrolled hypertensive patients on ≥1 medications is more effective than standard care.