Evaluation of skeletal muscle relaxant activity of methanolic extract of Hibiscus rosa sinensis leaves in albino rats.
Skeletal muscle relaxants are drugs that reduce the muscle tone. They act peripherally at the neuromuscular junction (neuromuscular blockers)/muscle fiber itself or centrally in the cerebrospinal axis to reduce muscle tone or cause paralysis. The neuromuscular blocking agents as adjuncts during general anesthesia to provide muscle relaxation for surgery, while centrally acting agents are used for painful muscle spasms and spastic neurological conditions.  However, these drugs cause several adverse effects. Thus, looking for an effective alternative has always been a priority in this regard.
Hibiscus rosa sinensis (family - Malvaceae) is a perennial shrub available throughout India. Various parts of this plant such as leaves, flowers, and roots have been known to possess medicinal properties such as aphrodisiac, menorrhagic, and oral contraceptive. 
Pharmacological studies have demonstrated that H. rosa sinensis exhibits wide range of properties antinociceptive, anti-inflammatory,  antioxidant, wound healing,  anticonvulsant,  antidiabetic, hypolipidemic, [6-8] anxiolytic, and central nervous system depressant,  promotes hair growth, and prevents graying of hair,  gastroprotective,  and antibacterial.  The studies evaluating the skeletal muscle relaxant activity of H. rosa sinensis leaves are limited. The main purpose of the study was to evaluate skeletal muscle relaxant activity of H. rosa sinensis leaves.
MATERIALS AND METHODS
Collection of Plant Material
Leaves of H. rosa sinensis were obtained from local market, and the identification was done.
Preparation of Extract
The leaves were shade dried and pulverized to a fine powder. Methanolic extract of leaves was prepared using Soxhlet apparatus using methanol as solvent. The extract was dried under vacuum. The percentage of yield was 8% w/w stored at room temperature and protected from sunlight.
Adult albino rats of either sex weighing between 200 and 250 g were used in this study. Animals were obtained from NIN, Hyderabad, India. The animals were stabilized for 1 week at a temperature 25 [+ or -] 1[degrees]C and 60 [+ or -] 5% relative humidity and 12 h dark-light cycles. They have been given a standard pellet diet and water ad libitum. All the experiments were conducted with prior permission taken from the Institutional Animal Ethics Committee.
Drugs and Chemicals
Diazepam (Lupin Laboratories Ltd., India) and other chemicals were analytical grade.
The rats were randomly allocated into four groups (n = 6) and treated as follows:
* Group I: Control received vehicle only (normal saline 10 ml/kg)
* Group II: Standard received 10 mg/kg diazepam
* Group III: Test rats received methanolic extract of H. rosa sinensis leaves (MEHRL) 200 mg/kg
* Group IV: Test rats received MEHRL 400 mg/kg.
All the drugs were administered orally.
Skeletal Muscle Relaxant Activity (Motor Coordination) 
The muscle relaxant activity was assessed with the help of rotarod. Rats were divided in to four groups consisting of six animals each. The animals retained on rotarod (25 rpm) for 5 min were included in the study. Rats were placed on the rotarod; falloff time from rotarod before and 30 min after drug administration was noted.
The difference in the falloff time from rotarod between control and treated rats was taken as index of muscle relaxation.
The spontaneous locomotor activity was assessed with the help of a photoactometer.  It consists of six built-in light source, photo sensor, and a digital counter to indicate locomotor activity. The device operates on photoelectric cells which are connected to the circuit with the counter when the beam of light falling on photocells is cut off by the animal, and a count is recorded.
To see the locomotor activity, the photoactometer was turned on and each rat was placed individually in the cage for 5 min. The basal activity score for all the animals was noted. All the drugs were administered orally after 1 h, and the activity score for 5 min was observed. The difference in the activity score before and after drug administration was noted. The percentage decrease in motor activity was calculated.
Results were expressed as mean [+ or -] standard deviation. Statistical analysis was performed using one-way analysis of variance followed by Dunnett's test. P < 0.05 was considered statistically significant.
Rotarod (Test for Muscle Relaxation)
The test doses MEHRL 200 mg/kg and 400 mg/kg showed significant dose-dependent reduction in motor coordination, that is, 36% and 48%, respectively. The standard drug showed 68.6% reduction in motor coordination [Table 1].
MEHRL (200 mg/kg and 400 mg/kg) showed significant (P < 0.001) skeletal muscle relaxant activity.
Actophotometer: (Test for Locomotor Activity)
The percentage of reduction in the locomotor activity after 1 h was 62% and 69% at the doses of 200 mg/kg and 400 mg/kg MEHRL, respectively, and the standard drug showed 84.5% reduction when compared to control.
MEHRL (200 mg/kg and 400 mg/kg) showed statistically significant (P < 0.001) reduction in locomotor activity [Table 2].
In recent years, the herbal medicines have been extensively used in various diseases due to their safety profile. The objective of the present study was to evaluate the effect of MEHRL on muscle relaxant activity in experimental animals. Actophotometer is used for evaluating the locomotor activity and antianxiety activity in rodents and rotarod for muscle relaxant activity. MEHRL significantly reduced motor coordination and locomotor activity in experimental animals. A decrease in locomotor activity indicates sedative action. Diazepam used as standard here at 10 mg/kg orally showed significant muscle relaxant activity in comparison with control as well as extract. Diazepam has low muscle relaxant sedation ratio, and sedation limits the dose used for muscle relaxation. 
Previous neuropharmacological studies on H. rosa sinensis roots showed significant skeletal muscle relaxant and sedative effect.  Our study also collaborates to these findings.
The MEHRL containing flavonoids (hibiscitin) phenolic content as well as terpenoid compounds such as betasitosterol and campesterol  is probably responsible for the actions.
The major limitation of the study is that phytochemical analysis was not done to identify the exact constituents. Further, extensive phytochemical analysis and research are necessary to identify the exact constituents and elucidation of its possible mechanism of action underlying the muscle relaxant activity of MEHRL.
MEHRL showed significant muscle relaxant activity in a dose-dependent manner.
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Sudha Madhuri A, Roopa C R
Department of Pharmacology, Navodaya Medical College, Raichur, Karnataka, India
Correspondence to: Sudha Madhuri A, E-mail: firstname.lastname@example.org
Received: December 12, 2018; Accepted: January 02, 2019
Source of Support: Nil, Conflict of Interest: None declared.
Table 1: Effect of MEHRL on muscle coordination on the rotarod apparatus Groups Fall of time (s) Before After Group I - control NS 311.66[+ or -]2.18 313.5[+ or -]3.06 (10 mg/kg) Group II - standard 328.5[+ or -]2.84 103.16[+ or -]2.38 (*) (10 mg/kg) diazepam Group III - MEHRL 318.33[+ or -]1.86 203.5[+ or -]2.26 (*) (200 mg/kg) Group IV - MEHRL 335.66[+ or -]2.32 174.66[+ or -]1.84 (*) (400 mg/kg) Groups % reduction Group I - control NS - (10 mg/kg) Group II - standard 68.596 (10 mg/kg) diazepam Group III - MEHRL 36.072 (200 mg/kg) Group IV - MEHRL 47.965 (400 mg/kg) Results expressed as mean[+ or -]SD. P<0.001 (*) compared to control. SD: Standard deviation, MEHRL: Methanolic extract of Hibiscus rosa sinensis leaves Table 2: Effect of MEHRL on the locomotor activity in the actophotometer Groups Actophotometer score % reduction 5 min before 60 min after administration administration Group I - control 177.6[+ or -]2.96 173.16[+ or -]1.08 NS (10 mg/kg) Group II - standard 185.33[+ or -]2.06 30.66[+ or -]2.26 (*) (10 mg/kg) diazepam Group III - MEHRL 198.5[+ or -]1.02 75.33[+ or -]2.84 (*) (200 mg/kg) Group IV - MEHRL 173.66[+ or -]2.18 53.55[+ or -]1.92 (*) (400 mg/kg) Groups % reduction Group I - control - NS (10 mg/kg) Group II - standard 84.45 (10 mg/kg) diazepam Group III - MEHRL 62 (200 mg/kg) Group IV - MEHRL 69.16 (400 mg/kg) Results expressed as mean[+ or -]SD. P<0.001 *compared to control. SD: Standard deviation, MEHRL: Methanolic extract of Hibiscus rosa sinensis leaves
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|Title Annotation:||RESEARCH ARTICLE|
|Author:||Sudha Madhuri, A; Roopa, C R|
|Publication:||National Journal of Physiology, Pharmacy and Pharmacology|
|Date:||Mar 1, 2019|
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