Hypotensive Potential of Desmodium Adscendens on Cardiovascular Functions

Backgrounds: Desmodium adscendens is one of the medicinal herbs used in the management of some medical conditions in recent times. The current study investigates the effects of aqueous leave extract of Desmodium adscendens on the serum levels of Sodium, Chloride, Potassium, and Bicarbonate ions, and the implication on cardiovascular function in healthy wistar rats. Method: Twenty-four (24) wistar rats grouped into four (n=6) were used for the research. Group 1 served as control, while Groups 2, 3, and 4 were treated orally with low, median and high doses of the extract of D adscendens for four weeks, after which blood was collected separately from each group and the serum level of the electrolyte determined by appropriate methods and comparison made with the control group and among the groups. Results: There was significant decrease (P < 0.05) in serum concentration of Sodium, Chloride and Bicarbonate ions, and significant increase in Potassium ion concentration. Conclusions: The significant decrease in serum concentration of Na + , Cl - , HCO3 - and significant decrease indicate that the extract has the potential to lower blood pressure, and that may be attributed to the active phytochemical constituents present in the leave. Therefore D. adscendens leaf has beneficial hypotensive potential on cardiovascular functions.


Sodium ion
The most available cation in the extracellular fluid is sodium.
It plays a very important role in regulating water balance in the body. Its normal serum level ranges from 130 to 145 mmol/L. Antidiuretic hormone (ADH), also known as arginine vasopressin is a non-peptide hormone that regulates renal handling of free water. Alteration of the amount of water reabsorbed by the kidney has an important effect on serum sodium concentration. ADH is secreted by the neurons in the supra-optic and paraventricular nuclei of the hypothalamus, and its release is stimulated by hypovolemia, thirst, increased serum osmolality, and angiotensin II [4]. In the renin-angiotensin-aldosterone system, renin from the juxtaglomerumar apparatus of the kidney catalyzes the conversion of angiotensinogen in the liver to angiotensin I, which is further converted to angiotensin II (in the lungs) by Angiotensin converting Enzyme (ACE) [5]. Angiotensin II, which is a vasoconstrictor enhances optimal perfusion pressure to end organs, especially when plasma volume is decreased. It also induces the release of aldosterone, ADH and cortisol. Aldosterone is a hormone released from the adrenal cortex of the kidneys with mineralocorticoidal actions, which affects the distal tubular reabsorption and retention of sodium rather than water [6].

Potassium ions
Potassium represents an important ion of the human body. About 98% of the body's potassium pool is present in the intracellular compartment, leading to a steep potassium concentration gradient across cellular membranes, indicating why potassium is particularly important to maintain the cellular membrane potential. It regulates the heartbeat and function of muscles. Normal serum potassium level = 3.5-5.0 m Eq/L. Potassium, along with sodium is involved with regulation of water and acid-base balance in blood and tissue [7]. In mammals, the osmotic pressure and water distribution maintenance is the primary function of electrolytes like sodium and potassium. In addition, they play a role in maintenance of pH, in oxidation reduction reactions, in heart muscle functioning and as co-factors for enzymes [6]. The body has two mechanisms to restore potassium balance when the serum potassium level goes up: by shifting the plasma potassium into cells, and by renal elimination [8].

Chloride ion
The chloride ion is the principal extracellular anion in humans with a concentration of about 95-110 mmol/L. It is passively absorbed from the upper small intestine and primarily regulated by the renal proximal tubules, where it is exchanged for bicarbonate ions. and passively follows sodium and water through during renal tubular reabsorption by the nephron [8]. Homeostatic mechanisms indirectly regulate Chloride ion through changes in sodium and bicarbonate. Being an anion, Sodium will balance out positive charges in the extracellular fluid, and by passively following sodium, it helps to maintain extracellular osmolality.

Bicarbonate ion
Bicarbonate ion is an intermediate form in the deprotonation of carbonic acid. It is a polyatomic anion with the chemical formula HCO 3 -. It serves a crucial biochemical role in the physiological pH buffering system [8]. Bicarbonate (HCO −

3
) is a vital component of the pH buffering system [9] of the human body (maintaining acidbase homeostasis). 70%-75% of CO2 in the body is converted into carbonic acid (H2CO3), which is the conjugate acid of HCO − 3 and can quickly turn into it.
With carbonic acid as the central intermediate species, bicarbonate, in conjunction with water, hydrogen ions, and carbon dioxide -forms the buffering system, which is maintained at the volatile equilibrium [9] required to provide prompt resistance to pH changes in both the acidic and basic directions. This is especially important for protecting tissues of the central nervous system, where pH changes too far outside of the normal range in either direction could prove disastrous. A higher serum bicarbonate concentration is associated with higher left ventricular mass, higher aortic pulse pressure and a higher risk of heart failure among nonusers of diuretics [10].

Phytochemical analysis
The ethanolic leaf extract of Desmodium adscendens was subjected to phytochemical analysis. 2g of the crude extract was weighed and dissolved in 20 ml of distilled. The solution was screened for the presence and absence of alkaloids, flavonoids, tannins, saponins, glycosides, reducing agents, polyphenols, anthraquinones, and phlobatanins following standard methods [11].

Experimental Animals
A total of forty 24 adult male albino Wistar rats weighing between 120-160g were used for this experiment. The animals were obtained from the faculty of Basic medical science animal house, University of Calabar. The rats were maintained on standard rat feed (growers feed) and tap water available all through the period of experiment. The animals were maintained at an ambient temperature between 28 -30 0 C, humidity of 55 ± 5%, and standard

Preparation of Extract
Two (2) grams of the aqueous leaves extract of Desmodium adscendens was dissolved in 10ml of distilled water as follows; 2 g = 10 ml of water (200 mg = 1 ml). If 200 mg = 1 ml, therefore, 300 mg = 1.5 ml, 450mg = 2.25 ml, and 600 mg = 3 ml of water. Volume per animal was determined as follows; for the low dose treated group, 300mg of extract was dissolved in 1.5 ml of water. A rat in the low dose group with a body weight 120g received 36mg of the extract.
If 300 mg of extract was dissolved in 1.5 ml of water, 36 mg of the extract will be dissolved in 0.18 ml of water. Therefore, an animal in the low dose group with a body weight of 120g will receive 0.18 ml of the extract daily all through the treatment period. Same was applicable to all the experimental animals all the extract treated groups. Extract administration was done orally with the aid of an orogastric cannula and treatment lasted for four (4) weeks.

Experimental design
At the end of the acclimatization period, the animals were randomly assigned into four (4) groups, n=6, as follows:

Collection of blood samples
At the end of treatment period, animals from all the experimental groups were sedated and made unconscious using chloroform anaesthesia. Blood samples from each rat was collected via cardiac puncture [11] into EDTA and plain sample bottles for the estimation of haematological and biochemical parameters [12].

Potassium ion concentration (K + )
There was significant increase in potassium ion concentration in the groups given medium and high doses of extract when compared with the control (5.43 ±0.08 mmol/L) and low dose (5.60 ±0.06 mmol/L) groups. The group treated with high dose of the extract also showed significant increase in K + concentration (6.97 ±0.07 mmol/L) over the group given median dose. There was however no significant different in potassium ion concentration in the group given low dose of extract when compared with the control group ( Figure 2).    words, small increases in plasma sodium may be in part directly responsible for the elevated blood pressure, and vice versa [13]. So, Desmodium adscendens, which causes decrease in serum sodium concentration, will cause a drop in blood pressure. Evidence from monogenic syndromes, dietary and animal studies on renal Cl − balance, and Cl − transporters in vascular tissues point to a critical role for Cl − in mechanisms that contribute to blood pressure regulation. Monogenic syndromes associated with Cl − transporters manifest high and low blood pressure phenotypes. In Gordon's syndrome, hypertension occurs as a consequence of increased Cl − reabsorption in the thiazide-sensitive segment of the distal renal tubule [14]. Therefore, any agent that reduces serum concentration of Chloride ion will reduce blood pressure.
Another likely mechanism may relate to non-cardiac and nonrenal roles for Cl − . Cl − channels are present in the surface and transverse tubular membranes of mammalian skeletal muscle and Cl − moves into muscle during t-tubular action potentials or with K + -induced depolarization of the sarcolemma. Extracellular Cl − has been shown to be protective against fatigue, with implications for survival and cardiovascular risk, involving high-intensity contractions in both fast-and slow-twitch mammalian muscle possibly by preventing excessive depolarisation with exerciseinduced decline in trans-sarcolemmal K + gradient [15]. The treated groups had significant increase in serum potassium ion levels. This is beneficial, as high potassium helps to lower the arterial blood pressure by stabilizing the resting membrane potential. Potassium helps lower blood pressure by balancing out the negative effects of salt. The kidneys use a delicate balance of sodium and potassium to pull fluid across a wall of cell from the blood stream for excretion [16]. Serum bicarbonate (HCO3 -) level was significantly decreased in the extract-treated groups in this study. The decrease may imply that the pH of the blood went up. However, this is not to pose any serious problem as the serum chloride concentration also went down. Cl − is the major extracellular strong ion and it's key to maintenance of acid-base homeostasis. Cl − levels are inversely related to bicarbonate, which acts as the major acid-base buffer in humans. Cl − was identified as the primary factor influencing the occurrence of metabolic alkalosis and non-anion gap metabolic acidosis in critical illness. This decrease in HCO3 could be attributed to increased renal excretion of bicarbonate [17,18].

Conclusion
Desmodium adscendens extract has the potential to reduce high blood pressure in normotensive and hypertensive patients by increasing serum level of potassium ion and also reducing serum level of sodium, chloride and bicarbonate ions. This potential may be attributed to its phytochemical constituents of flavonoid, alkaloids, tannins, saponins, glycosides, reducing sugar, polyphenols, anthraquinones, and phlobatanins.