This section is from the book "Materia Medica Pharmacy, Pharmacology And Therapeutics", by W. Hale White. Also available from Amazon: Materia Medica Pharmacy, Pharmacology And Therapeutics..
Gastro intestinal tract. - Pilocarpine is very quickly absorbed, and soon produces a great increase in the amount of salivary secretion. The mouth seems warm, and there may be a feeling of tenseness about the salivary glands. The saliva contains an abundance of salts and ptyalin, and can convert starch into sugar. Its increase is due to a direct stimulation of the terminal filaments of the chorda tympani and of the other nerves which end in the cells of the salivary glands, so that stimulation of these nerves can add very little to the flow produced by the drug - in fact, not more than can be accounted for by vascular alterations. This action is antagonized immediately by atropine, as that paralyzes the endings of these nerves. To a slight extent pilocarpine excites the secretion of the gastric juice, intestinal fluid, and pancreatic secretion. The unstriped muscle of the stomach and intestine is stimulated, and thus the drug may purge. The bile is unaffected. Large doses, especially of pilocarpus, may produce vomiting.
Circulation. - Pilocarpine has no effect on the blood, but it is a cardiac depressant. The pulse-rate, it is true, may be, and in the human being always is, a little accelerated at first, but soon both it and the blood-pressure fall. This slowing of the pulse is at once set aside by atropine, but is not prevented by section of the vagus, therefore pilocarpine acts on the heart itself, probably stimulating the terminations of the vagus. The bloodvessels are at first dilated.
Respiration. - The drug has no effect on this. The amount of bronchial secretion is increased.
Skin.-Pilocarpus, through its alkaloid pilocarpine, produces a very profuse secretion of sweat. It is the most powerful diaphoretic drug we have. A single dose may cause the flow of fifteen fluid ounces 450. c.c of sweat. It is said that the proportion of urea and chlorides in the sweat is greatly increased. This profuse diaphoresis is due to the action of the pilocarpine on the cells of the sweat-glands, or the terminations of the nerves in them, and is stopped by atropine. The skin may flush, but this is not the cause of the diaphoresis. Under a course of pilocarpus the hair grows more actively, but it becomes very coarse and dark.
Kidneys. - If the sweating is profuse, the secretion of urine is lessened. Pilocarpine is excreted unchanged in the urine.
Temperature. - There may be a slight rise at first, but soon the temperature falls considerably. This is probably due in large part to the evaporation of the perspiration.
Eye. - Whether applied locally to the eye or given internally, pilocarpine produces great contraction of the pupil, due to stimulation of the ends of the third nerve in the eye, and this is antagonized by atropine. It also causes increased tension of the eye-ball, and an approximation of the nearest and farthest points of distinct vision.
Other actions. - It stimulates the uterus, and has in very rare cases produced abortion. It increases the secretion of milk, of tears, of nasal mucus, and, according to some authors, that of cerumen. It causes the spleen and bladder to contract.
It will be noticed that it has two main actions. (1) It stimulates the secretions - viz., those of the salivary glands, stomach, intestines, skin, kidney, bronchial mucous membrane, nose, lachrymal glands and ear. In those that have been investigated, and probably in all, it acts locally. It has not been decided in every case whether the cells of the glands or the nerve terminations in them are affected. (2) It stimulates the nerve terminations of involuntary muscles - viz., in the eye, the intestines, the stomach, the uterus, the spleen, the heart, the bladder, and it acts on the muscular coat of the vessels, although these, if affected, are usually dilated. The most important effects are the diaphoresis, the salivation, and the myosis. It is consequently antagonistic in its action to atropine. Children bear large doses of it well. Pilocarpine is much more used than pilocarpus, as it is more prompt and more certain in its action, and is less likely to cause indigestion.
Jaborine has an action similar to that of atropine; the amount of it in pilocarpus varies, hence the varying effects of different specimens of the leaves, but there is never enough totally to counteract the pilocarpine.
Pilocarpine has been used locally to promote the growth of hair. An ointment (Pilocarpine hydrochlorate,
Pilocarpine has been employed for many conditions, but its great use is as a diaphoretic in Bright's disease. For this purpose 1/6 of a gr., .01 gm. or more of the hydrochlorate is injected subcutaneously in the evening. The sweating is aided by wrapping the patient, who should be naked, in several warm blankets, giving him hot drinks, and putting a hot water bottle to his feet. After the sweating has ceased, he should be dried and left in a dry blanket. As it is such a powerful cardiac depressant, it must be given with great caution when the heart is diseased. Occasionally it is employed locally in affections of the eye. Patients suffering from deafness due to disease of the auditory nerve or its terminations are sometimes relieved by pilocarpine. It is often given internally for deafness due to otitis media sicca. Injected subcutaneously, it has been given successfully as an antidote to belladonna poisoning.