This section is from the book "A Text-Book Of Pharmacology, Therapeutics And Materia Medica", by T. Lauder Brunton. Also available from Amazon: A text-book of pharmacology, therapeutics and materia medica.
An alkaloid or mixture of alkaloids obtained from cevadilla; not quite pure, B.P. An alkaloid or mixture of alkaloids prepared from the seeds of Asagrcea officinalis, U.S.P.
Preparation. - A concentrated tincture of the seeds is poured into cold water in order to precipitate the albumin. From the filtered solution veratrine is precipitated by ammonia, and purified byre-solution in dilute hydrochloric acid, decolorisation by animal charcoal, and reprecipitation by ammonia.
Solubility. - Insoluble in water; soluble in spirit, in ether, and in diluted acids, leaving traces of an insoluble brown resinoid matter.
Impurities. - Mineral matter, and sometimes traces of the other alkaloids of cevadilla.
Test. - Heated with access of air it melts into a yellow liquid, and at length burns away, leaving no residue.
Dose.- 1/12-1/8 gr.
(8 gr. to 1 oz.) for external use.
(1 part in 50).
(1 part in 25).
Action. - Large doses of veratrine cause violent sneezing, and great gastro-intestinal irritation, vomiting, purging, and symptoms of collapse, the pulse being rapid, small, and irregular; and often involuntary muscular tremors come on. A peculiar creeping and prickling sensation in the skin generally accompanies these symptoms.
Externally, applied to the unbroken skin, it has no marked action, but if rubbed in with some fat it passes through the epidermis and acts on the true skin, and causes first irritation and then paralysis of the ends of the sensory nerves, producing a prickling and creeping sensation, succeeded by numbness. It is somewhat like aconitine in this respect. This effect is produced whether applied locally or taken internally.
Its irritating action on the sensory nerves is also observed if it be inhaled into the nose, when it causes violent sneezing, which also occurs after absorption from the stomach.
Internally. - It has no marked action on the brain. It has probably no action on the spinal cord. By some experimenters it is stated that convulsions are produced in frogs, but, from numerous experiments which I performed, I doubt the accuracy of this statement.
Muscles. - The contractile power is increased, but the elasticity very much diminished. The period of contraction is very much prolonged, but neither the latent period nor the ascent of the curve is affected in character; the height of the curve is slightly increased, and the descent of the curve very much prolonged, so that it does not reach the abscissa for several revolutions of the cylinder. This contraction is not a state of partial rigor, since during its continuance the development of heat is increased to a marked degree; neither is it a true tetanus, since the rheoscopic frog only gives a single contraction when its nerve is laid on the poisoned muscle. It is a prolonged contraction. To this alteration in the muscles is due the peculiar behaviour of frogs when poisoned by veratrine. The frog jumps readily on stimulation, but after its spring it lies on the table with legs extended for a long time; then it draws the limbs up slowly, for both the flexors and extensors are contracted, and the contraction has to pass off from the extensors before the flexors can act. When it has drawn its limbs up, it remains still for a time, to allow the contraction to pass off from the flexors, after which it springs again. Thus the frog performs the normal movements with very long intervals between them. These movements have probably been mistaken for convulsions. Temperature affects the veratrine curve in a remarkable manner. As the muscle is cooled down, the curve becomes more and more like the normal, and if the temperature be much raised (keeping below the heat of rigor caloris), the effect also disappears; thus extremes of heat and cold remove the veratrine effect on the muscle-curve. The effect of veratrine on the muscle is also removed by potash (p. 130).
Muscles previously exhausted by over-exertion have their powers restored by veratrine.
Motor nerves have their excitability increased at first; afterwards their peripheral ends are paralysed. Sensory nerves have their peripheral ends first stimulated (causing pricking, &c), and then paralysed (cf. Aconite, p. 832).
Circulation. - The effect of veratrine on the heart-muscle of the frog is very similar to that on voluntary muscle; hence the contractions of the heart become slower, and each systole lasts a long time, till finally the heart stops in complete systole. The effect of veratrine on the heart is also removed by heat and by potash (Ringer). In mammals, small doses injected into the circulation quicken the pulse and raise the blood-pressure; moderate and large doses slow the heart and lower the blood-pressure. Small doses quicken the respiration; large ones slow it, producing long pauses like those which occur after section of the vagi, and finally paralyse it. These effects are probably due to stimulation at first, and afterwards to paralysis of the ends of the vagus in the lung, and to paralysis of the respiratory centre. The temperature is lowered.
Uses. - Locally, it is used like aconitine for neuralgia, in the form of the ointment rubbed over the affected part.
Internally, it is sometimes used in rheumatic arthritis, and in sthenic febrile affections, as pneumonia; but its action is uncertain, and its use dangerous; hence it is seldom employed. Possibly one cause of the uncertainty of its action is the high temperature accompanying febrile affections, by which its action is altered. A similar reason may hold good for aconite, which varies considerably in its action on febrile disorders (cf. Digitalis, p. 998).