1911 Encyclopædia Britannica/Strophanthus

STROPHANTHUS, a genus of plants of the natural order Apocynaceae, deriving its name from the long twisted thread- like segments of the corolla, which in one species attain a length of 12 or 14 inches. The genus comprises about 30 species, mainly tropical African, extending into South Africa, with a few species in Asia, from farther India to the Philippines and China. Several of the African species furnish the natives with the principal ingredient in their arrow poisons. The inée or onaye poison of the Gaboon, the kombé of equatorial North Africa, the arquah of the banks of the Niger and the wanika of Zanzibar are all derived from members of this genus. The exact species used in each case cannot be said to be accurately known. There is no doubt, however, that S. hispidus and S. kombé are those most frequently employed.

Both S. hispidus and S. kombé have hairy seeds with a slender thread-like appendage, terminating in a feathery tuft of long silken hairs, the seeds of the former being coated with short appressed brown hairs, and those of the latter with white hairs; but in the species used at Delagoa Bay and called “umtsuli” the thread-like appendage of the seed is absent. The natives pound the seeds into an oily mass, which assumes a red colour, portions of this mass being smeared on the arrow immediately behind the barb.

Under the name of strophanti semina, the dried ripe seeds of Strophanthus kombé, freed from awns, are official in the British and many other pharmacopeias. The seeds must be mature. They are about 3/5 in. long, 1/6 in. broad, greenish fawn, covered with flattened silky hairs, and oval-acuminate in shape. They are almost odourless, but have an intensely bitter taste. The chief constituent is a white microcrystalline glucoside, known as strophanthin, freely soluble in water and alcohol, but not in chloroform or ether, and melting at about 173° C. It constitutes about 50% of the mature cotyledons of the seed, the proportion rising as maturity is reached. It is very similar to, but not identical with, onabaïn. It is split up by acids into strophanthidin and a methyl-ether of a peculiar sugar. The seeds also contain an active principle, inein, a body known as kombic acid, fat, resin and starch. The resin is contained in the husk, and occurs in the alcoholic tincture of strophanthus, its presence tending to cause digestive disturbance and diarrhoea. When the seeds are treated with sulphuric acid and heat is applied, a violet-coloration is produced. A section of the seed yields a green colour with cold sulphuric acid.

The British Pharmacopeia contains two preparations of this important and valuable drug, a dry extract and a tincture. The former is hardly ever prescribed. The official tincture is much inferior to that originally recommended by Sir Thomas Fraser, who introduced the drug into medical practice, in being much too weak, and in being prepared with alcohol instead of ether, which differs from alcohol in not dissolving the resin contained in the husks. It is therefore advisable to order the tincture of the British Pharmacopeia of 1885, or to prescribe the current tincture in double the official dose and combined with cardamoms, ginger or capsicum, in order to counteract the irritant properties of the resin which it contains.

Strophanthin itself may be injected hypodermically in doses of 1/300 to 1/60 grain. Unfortunately the injections usually cause some temporary local irritation. This method of exhibiting strophanthus is the only one of any avail when a result is wanted at once or even within several hours. Precisely the same observation applies to digitalis, the other great cardiac tonic.

Pharmacology.—The drug has no external actions. Taken internally it tends, after the repetition of large doses, to produce some gastric irritation. This is unquestionably less, however, than that produced by digitalis, and is probably due not at all to the active principle but entirely to the resin contained in the seed-husk. As ordinarily administered, the drug acts on the heart before influencing any other organ or tissue. Often indeed no other action can be observed. This is readily explained by the fact that the drug is carried by the coronary arteries to the cardiac muscle before it reaches any other part of the systemic circulation.

It is almost certain that strophanthus acts directly on no other cardiac structure than the muscle-fibre. No action can certainly be demonstrated either upon the terminals of the vagus nerves nor upon the intra-cardiac nervous ganglia. The muscular force is increased in a very marked degree. A secondary consequence of this is that the diastole is prolonged, and the pulse thus rendered less frequent. If the heart is beating irregularly the drug tends to make it more regular. The action is similar to that of digitalis—and fifty years ago both these drugs would thus have been regarded, as indeed digitalis was, as cardiac sedatives. As the cardiac muscle receives its blood supply only during diastole, it follows that strophanthus, while increasing the force of each beat, yet lengthens the period during which the muscle rests and is fed—thus being, in a paradoxical sense, a sedative as well as a stimulant. In fatal cases of strophanthus poisoning death is brought about by the arrest of the heart in systole, i.e. in a state of tetanic spasm from over-stimulation. This of course is a striking exception to the natural rule that death finds the heart in a state of relaxation and inability to contract. Strophanthus markedly raises the blood-pressure, but this action is proportional to and almost entirely due to the increased force of the heart; not, as in the case of digitalis, to constriction of the arterioles.

Its action on the heart causes strophanthus to exert a powerful diuretic action, especially in cases of dropsy of cardiac origin. It is a less powerful diuretic than digitalis as a rule. The drug has no action on the nervous system, but in toxic doses it powerfully affects the voluntary striped muscles. This action may be correlated with that exerted upon the cardiac muscle, which is striped, though not voluntary, and contrasted with its want of action upon the muscular fibre of the arteries, which is involuntary and non-striped.

The drug, like onabaïn, has a slight anaesthetic action when locally applied to the eyeball, and also causes contraction of the pupil.

Strophanthin is one of the most active and lethal of all known substances. One-hundredth of a grain will kill a mammal weighing four pounds, and one-third of a grain will kill a man of average weight. Serum containing one part of strophanthin in ten millions will arrest the frog’s heart in systole.

Strophanthus is used therapeutically only as a cardiac stimulant. When given by the mouth it acts somewhat more rapidly than digitalis, being more soluble; but it is of course far less speedy in action than ether, ammonia or such a pseudo-stimulant as ethyl alcohol. In mitral disease of the heart especially strophanthus is an invaluable drug. It frequently succeeds when digitalis has failed ; occasionally it fails where digitalis succeeds. It has the great advantage over digitalis of being non-cumulative, and can be administered continually for many weeks or even months at a time. It is never to be given in acute Bright’s disease, but is frequently of use in chronic Bright’s disease, where digitalis, owing to its influence on the already over-contracted arterioles, is absolutely contra-indicated.