Apocynum. N. F. IV (U. S. P. VIII). Canadian Hemp. Black Indian Hemp. Dogsbane. Chanvre du Canada, Fr. Canadische Hanfwurzel, G.—"The dried rhizome and roots of Apocynum cannabinum Linné (Fam. Apocynaceae), without the presence of more than 5 per cent. of stems or other foreign matter." N. F. IV. Although latterly apocynum has fallen into disuse, some physicians have insisted that the A. cannabinum is a valuable remedy and that its unfavorable reputation has arisen from the use of other species. The drug of commerce in recent years has consisted of several species of Apocynum. A number of physicians in the United States have come to the conclusion that the absorption of Apocynum in the gastro-intestinal tract is uncertain and irregular, which led to its being deleted from the Pharmacopoeia. It has been admitted into the N. F.
There are several indigenous species of this genus of very similar general aspect, the rhizome and roots of two of them being collected, viz.: Apocynum cannabinum, L., and A. androsaemifolium, L. Both plants abound in a milky juice, and have a tough, fibrous bark, which, by maceration, affords a substitute for hemp; hence the common name. It is used by the Indians of California for making all manner of cordage and for weaving.
In A. cannabinum the stems and branches are upright or ascending, terminated by erect and close, many-flowered cymes, which are usually shorter than the nearly sessile leaves, and the corolla has nearly erect lobes, with the tube not longer than the lanceolate divisions of the calyx. In A. androsaemifolium the branches are divergently forked, the leaves are slender petioled, the cymes loose and spreading, the open bell-shaped corolla with revolute lobes and a tube much longer than the ovate-pointed divisions of the calyx. A. cannabinum, of which there are a number of well recognized varieties, grows in gravelly or sandy soil mostly near streams, while A. androsaemifolium grows in dry thickets and open woods. According to E. A. Manheimer, the root of the latter is distinguished from A. cannabinum by the thick-walled stone cells, which are arranged in an interrupted circle near the middle of the bark. (A. J. P., Nov., 1881. See also A. J. P., 1888.) Holm has contributed an article on the structure of A. cannabinum. [Merck's Rep,, 1910, p. 277.)
It is described in the N. F. as: "Cylindrical, somewhat branched, of varying length, from 3 to 10 mm. in thickness; externally reddish-brown to grayish-brown, longitudinally wrinkled and occasionally with transverse fissures having vertical sides extending through the bark; fracture short; internally, bark light brown, from 1.5 to 3 mm. in thickness, wood faintly radiate and with large tracheae, a small pith occurring in pieces of the rhizome. Almost inodorous; taste starchy, afterwards becoming bitter and somewhat acrid. Under the microscope sections of Apocynum show numerous laticiferous vessels in both the bark and pith. The stems of Apocynum have a comparatively thin fibrous bark, a light brown porous wood and a large, hollow pith. The powder is light brown, starch grains numerous, from 0.003 to 0.015 mm. in diameter, spherical, ellipsoidal, ovate, pyriform, or more or less irregular, sometimes more or less altered, swollen, and with a hyaline central cleft; numerous fragments of strongly lignified wood fibers, associated with tracheae mostly having bordered pores, occasionally with spiral thickenings; fragments of cork layer few, the walls being of a reddish-brown color; an occasional fragment with laticiferous tissues; stone cells few or absent (Apocynum androsaemifolium Linne). Apocynum yields not more than 5 per cent. of ash." N. F. IV. The fresh root, when wounded, emits a milky juice, which concretes into a substance resembling caoutchouc. The stems of Apocynum have a comparatively thin, fibrous bark, a light brown porous wood and a large, hollow pith. In the dried state, the rhizome and roots are brittle and readily pulverized, affording a powder which is light brown, containing numerous starch grains which are from 0.003 to 0.015 mm. in diameter, spherical, ellipsoidal, ovate, pyriform, or more or less irregular, sometimes more or less altered, swollen, and with a hyaline central cleft. It also contains numerous fragments of strongly lignified wood fibers which are associated with tracheae having bordered pores or occasionally with spiral thickenings, a few fragments of cork, the walls being of a reddish-brown color, and an occasional fragment with laticiferous tissues. Stone cells are not present in A. cannabinum, but are common in A. androsaemifolium.
The nature of the active principle of apocynum is as yet somewhat uncertain. Finnemore, in 1908, obtained from the A. cannabinum a crystalline substance to which the name of cynotoxin was applied. The following year Moore (J. Chem. Soc., 1909, xcv) separated from the A. androsaemifolium a glucoside having the formula C14H18O3, to which he applied the name of apocynamarin. These two principles which appear to be identical, possess the characteristic physiological effects of the crude drug. Taub and Fickewirth (A. G. P., cliii, p. 239) believe that neither of these principles is chemically pure and that the activity of the plant is due to an intensely bitter principle which is not of glucosidal nature and to which they apply the name of cymarin. This latter substance has been studied pharmacologically by Impens and has also been used practically by Allard (D. M. W., 1913, xxxix, p. 783) and others, and appears to exert the characteristic effects of the drug. Cymarin is given in oral single dose of one two-hundredth of a grain (0.003 Gm.); daily dose, one-sixtieth to one-thirtieth of a grain (0.001-0.002 Gm.) intravenous or intramuscular dose, one one-hundred and twenty-eighth to one sixty-fourth of a grain (0.0005-0.001 Gm.).
Von Oefele (Journ. Pharm. Elsass-Lothr., 1891, 325) described apocynteine, an alkaloid obtained from A. venetum;it is said to be a cardiac sedative.
Apocynum belongs physiologically to the digitalis group of cardiac tonics. Like digitalis it slows the pulse by stimulating cardiac inhibition, increases the vigor and tone of the heart muscle, and in overdose causes systolic spasm of the frog's heart, increases vasomotor tone and the activity of the kidney. It differs from digitalis only in the relative degree of its different effects. It appears to be the most powerful of the whole group in its effect upon inhibition, the slowing of the pulse being so extreme that despite marked constriction of the blood vessels the pressure is often lowered instead of elevated. According to Dale and Laidlaw [Proceedings of the Royal Society of Medicine, Dec., 1909), its action upon the vasomotor system is also relatively strong. It appears to be more irritant to mucous membranes than either digitalis or strophanthus, and therefore is prone to cause nausea and catharsis. Perhaps this local stimulant effect is also the explanation of its very powerful diuretic action, although Dale and Laidlaw believe that the effect upon the kidneys is due chiefly to a relative dilatation of the renal arteries.
Apocynum is useful in medicine as a diuretic and as a cardiac tonic. For the former purpose it is especially of service in dropsies due to heart failure, but has been also highly recommended in the ascites of hepatic cirrhosis; indeed, so powerful are its hydragogue properties that it has been dubbed the "vegetable trocar." As a tonic to the heart it is useful in the same classes of chronic heart disease in which digitalis is of service. The N. F., however, adds the following caution: "It has been stated that the absorption of Apocynum in the gastro-intestinal tract is uncertain and irregular. To avoid an accumulation of the drug or toxic action, the physician should carefully guard the dosage and determine in each case the tolerance of the patient.'' Its irritant action upon the intestinal tract also militates strongly against its clinical usefulness; many patients are quite unable to take the drug because of the occurrence of emesis or purgation. Dose, five to fifteen grains (0.32-1.0 Gm.).