The cardiovascular system

I Plants in tropical West Africa with an action on the cardiovascular system

In the particular field of cardiovascular drugs, plants still provide the basis of treatment, even in orthodox pharmacy. However, some of the plants accepted by most Pharmacopoeias, such as Digitalis, Convallaria, Adonis, Helleborus and Crataegus, which act mainly on the heart, and Hydrastis, Veratrum, Amni visnagi, Viscutn album and Aesculus hippocastanum, which act more specifically on the blood vessels, do not grow in West Africa. On the other hand, the possibilities of many plants that are locally available have not yet been fully investigated. Also, some of the currently used cardiotonics have a high toxicity; less toxic but yet active constituents might be found amongst the West African plants. As mentioned in the general introduction only a limited number of local uses have been indicated.

Most herbalists will know that many plants in this group (several formerly used as arrow poisons1 or even in ordeals) are very toxic and will avoid using them. A few healers, however, may, in view of the fact that they are also emetics, purgatives or diuretics, be tempted to make use of them. But these plants should be employed only after complete extraction and with very exact dosages of the active constituents, and then only by physicians in possession of a full clinical diagnosis. In this, these plants differ from many others, which may be given as a decoction, an infusion or in dried or powder form.

Cardiovascular activities are mainly controlled by the ANS. The ANS can be divided into two main divisions. One, which through the influence of noradrenaline on the corresponding nerve endings has a stimulating effect on the heart and produces vasoconstriction, is called the adrenergic or sympathetic division. The other, which through the influence of acetylcholine slows down the heartbeat and produces a fall in blood pressure and vasodilatation, is called the cholinergic or parasympathetic division. Both these divisions can stimulate or antagonize (block) the autonomic ganglia (Fig. 1.1, p.7).

The actions of acetylcholine at the peripheral cholinergic nerve endings are known as its muscarinic actions, because they are mimicked by muscarine (a mushroom alkaloid).

Stimulation of the preganglionic nerve fibres to the ganglia results in liberation of acetylcholine (physiological neurotransmitter in autonomic ganglia). This action is almost immediately counterbalanced by cholinesterase, which destroys acetylcholine through hydrolysis. The cholinergic actions on the ganglia are referred to as the nicotinic actions of acetylcholine because the effects of acetylcholine on the ganglia are similar to those produced by nicotine. There is initial stimulation and then blockade of the ganglion cells (Turner and Richens, 1978).

Changes in the force of contraction of the myocardium are called inotropic effects while changes in the heart rate are called chronotropic effects. The myocardium, which contains the fi receptors for noradrenaline, responds to this by increasing the frequency and amplitude of the heartbeat (Lechat et al., 1978).

The plants which act on the cardiovascular system can be divided into three groups:

(a) Cardiotonics. Cardiotonic drugs act on the force, the rate and the rhythm of the heartbeat. They have a stimulating effect on the cardiac muscle and thus increase the contractile force (inotropic effect), decrease the heart rate and regularize the heartbeat (chronotropic effect). By increasing the renal bloodflow, cardiotonics can have a diuretic action. They often produce nausea and vomiting as they irritate the gastric mucosa, and are sometimes used in small doses for their expectorant action, which precedes the vomiting. By increasing the pulse rate, cardiotonics can also increase the blood pressure.

(b) Cardiac depressants. These drugs have a depressant effect on the heart muscle and some are particularly suited to the treatment of arrhythmias (anti-arrhythmic drugs). By slowing the cardiac rhythm they often have an antihypertensive action, either through vasodilatation of the coronary arteries or through direct control by the nervous system.

(c) Vascular agents. These are plant constituents which act primarily on the blood vessels.

(a) Cardiotonics

Today the plant cardiotonics are generally used in orthodox pharmacy as isolated active principles. Many of the plants formerly used in Africa as arrow poisons have been shown to contain cardenolides and to be valuable in minute doses in treating heart conditions. Cardenolides are steroid heterosides. Their aglycones (or genins) are responsible for the specific action but do not act by themselves as they are insoluble and have a low power of fixation on the heart muscle (Mcllroy, 1950, p. 79). The fixation on the tissues of the isolated frog heart could be attributed for certain components like flavotannins from Paullinia pinnata (see below) to the formation of a complex with calcium on the surface of the heart tissues (Bowden, 1962; Broadbent, 1962).

Table 2.1. Apocynaceae in tropical West Africa

In the leaves of the members of the Apocynaceae free ursolic acid is frequently found (Alstonia boonei, Rauvolfia vomitoria, Pleioceras barteri, Thevetia neriifolia, etc.), whereas in the coagulum of the latex the triterpenic alcohols /3-amyrin are often present. As most of the plants contain a very great number of alkaloids or heterosides, only the main constituents and their most important uses have been indicated.

It appears from the table that only the Plumeroideae contain indole alkaloids and steroid alkaloids, whilst the Echitoideae and Cerberoideae contain cardiac glycosides. However, from studies of the way in which the constituents are built up it appears that the Apocynaceae are able, starting from a steroid nucleus, to produce either cardiac heterosides or steroid alkaloids, thus bringing the members of this family nearer than they might appear at first sight (Goutarel, 1964; Paris and Delaveau, 1966). On the other hand, Paris and Delaveau (1966) mention the fact that the same 'specific' chemical constituents are sometimes found in families which are far apart in their morphological classification. Thus in West Africa cardiac glycosides are found not only in plants of the Apocynaceae and Asclepiadaceae but also in members of the Liliaceae ( Urginea indica), Moraceae (Antiaris africana), Tileaceae (Corchorus olitorius), Sterculiaceae (Mansonia altissima) and even Compositae (Vernonia colorata). Similarly, indole alkaloids are also found in Rubiaceae (Mitragyna inermis,M. macrophylla, Corynanthepachyceras, Pausinystaliajohimbe, etc.), and steroid alkaloids also occur in some Solanum species (Solanum nigrum, S. lycopersicum (Oliver-Bever, 1968).

Plant

Part used

Active constituent(s)

Chemical group

Recognized or possible medicinal action"

Subfamily Plumeroideae

Carisseae

Carissa edulis Vahl

Hunteria ebumea Pichon Picralima nitida Stapf

Roots

Seeds Seeds

Carissin Burnamine

Akuammine, akuammiline, akuammidine, akuammigine, etc.

Cardenolide

Indole alkaloids Indole alkaloids

Oncolytic (sarcoma 180) (Abbot era/., 1966) Hypotensive Hypotensive, local anaesthetic, sympatholytic

Tabernaemontaneae' Tabemaemontana crassa Benth. syn. (Cortopharyngia durissima Stapf)

Roots, bark

Seeds

Isovoacangine, conopharyngine, conodurine, conoduramine Voacamidine, tabersonine, coronaridine

Indole alkaloids

Sympathomimetic

{Table continued)

{Table continued)

Table 2.1. (Continued)

Plant

Part used

Tabernaemontana pachysiphon Stapfsyn. (Conopharyngia pachysiphon Stapf)

Hedranthera barteri (Hook.) Pichón, syn. (Callichilia barteri Stapf, C. monopodiales (Schum.) Stapf)

Voacanga africana Stapf

Roots

Roots, stems

Roots, stems

Leaves

Stembark and rootbark

Voacanga bracteata Stapf

Alstonieae Alstonia boonei de Wild. syn. (A. congensisChev. & Aubrev.) c.

Catharanthus roseus (L.) Don. syn. (.Lochnera rosea Reichb. ) c.

Stembark and rootbark

Bark

Leaves Roots, twigs

Active constituent(s)

Recognized or possible Chemical group medicinal action"

Pachysiphine

Voacangine Callichine, vobtusine

Aminosteroid glycoside Indole alkaloid Indole alkaloids

Callichine

Indole alkaloids

? Ursolic acid Voacamine, voacangine, voacristine, voacorine, voacamidine, vobasine, vobtusine, etc.

Voacamine, voacangine, voacorine, epivoacorine

Triterpene Indole alkaloids

Indole alkaloids

Echitamine, echitamidine, alstonine, reserpine Amyrin, lupeol, ursolic acid Catharan thine, lochnerine, vindoline

Vincristine, vinblastine Reserpine, ajmalicine

Indole alkaloids

Triterpenes Indole alkaloids

Indole alkaloids Indole alkaloids

Hypotensive (Heg-nauer, 1962-8, vol. 3, p. 129) Cardiotonic (Patel and Rowson, 1964) Cardiotoxic (Patel and Rowson, 1964) Cardiotonic Cardiotonic, sympatholytic, hypotensive

Same as V. africana

Hypotensive? (Raymond-Hamet, 1934,1941) Hypoglycaemic

Oncolytic (Hodgkin's disease, leukaemia) Hypotensive, tranquillizer

Holarrhena floribunda (Don.) Dur. & Schinz. syn. (H. africana, H. wulfsbergii)

Stembark and rootbark

Bark Leaves

Allamanda cathartica L. c.

Seeds, stems, roots

Plumería rubra c.

Rauvolfieae Rauvolfia vomitoria Afzel.

Leaves Latex, leaves and bark Bark

Rootbark and stembark

Funtumia africana (Benth.) Stapf

Pleioceras barteri Baill. syn. (Wrightia parviflora Stapf.)

Bark, leaves

Rootbark, seeds

Leaves

Conessine, conkurchine

Holarrhenine

Holarrhimine, holaphyllamine, holaphylline

Plumeriede = plumeroside, allamandin

Ursolic acid Plumieric acid, plumieride Fulvoplumierin

Steroid alkaloids Steroid alkaloids

Glycoside of iridoid lactone

Glycoside of cinnamic acid lactone

Antibiotic (Entamoeba histolytica, Trichomonas)

Hypotensive, local anaesthetic, spasmolytic

Cardiotonic, antitumour agent, cardiotoxic

Local anaesthetic, cardiotonic

Bacteriostatic

Reserpine, rescinnamine, raumitorine

Reserpiline, rauvanine Ajmaline, rauvanine Ajmalicine

Funtumine

Alkaloids

Ursolic acid

Indole alkaloids

Indole alkaloids

Steroid alkaloid

? Steroid alkaloid

Triterpene

Tranquillizer Sedative Hypotensive Hypotensive Anti-arrhythmic Raynaud's disease vasodilating Hemisynthesis of corticosteroids Local use, emmena-gogue, abortifacient Produces sodium retention like desoxy-corticosterone (Ker-haro and Adam, 1974, P-157)

(Table continued)

Table 2.1. (Continued)

Plant

Part used

Active constituent(s)

Chemical group

Recognized or possible medicinal action"

Malouetia heudelotii DC. Bark

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Responses

  • violanda
    Does rawolfia vomitoria contain a cardenolide?
    2 years ago
  • celso lorenzo
    Does rauwolfia vomitoria contain cardenolide?
    2 years ago

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