Originating in the 19th century, the discipline makes drug development possible.1
Pharmacology is one of the cornerstones of the drug discovery process. The medicinal chemist may create the candidate compound, but the pharmacologist is the one who tests it for physiologic activity. A promising compound is investigated by many other scientists—toxicologists, microbiologists, clinicians—but only after the pharmacologist has documented a potential therapeutic effect. This article briefly presents the historical development of pharmacology and some of the basic methods used.
Etymologically, pharmacology is the science of drugs (Greek pharmakos, medicine or drug; and logos, study). In actual use, however, its meaning is limited to the study of the actions of drugs. Pharmacology has been defined as “an experimental science which has for its purpose the study of changes brought about in living organisms by chemically acting substances (with the exception of foods), whether used for therapeutic purposes or not.”
Pharmacology studies the effects of drugs and how they exert their effects. There is a distinction between what a drug does and how it acts. Thus, amoxicillin cures a strep throat, and cimetidine promotes the healing of duodenal ulcers. Pharmacology asks “How”? Amoxicillin inhibits the synthesis of cell wall mucopeptide by the bacteria that cause the infection, and cimetidine inhibits gastric acid secretion by its antagonist action on histamine H2 receptors.
The main tasks of pharmacologists in the search for and development of new medicines are
- screening for desired activity,
- determining mode of action, and
- quantifying drug activity when chemical methods are not available.
Synthetic organic chemistry was born in 1828, when Friedrich Wohler synthesized urea from inorganic substances and thus demolished the vital force theory. The birth date of pharmacology is not as clear-cut. In the early 19thcentury, physiologists performed many pharmacologic studies. Thus, François Magendie studied the action of nux vomica (a strychnine-containing plant drug) on dogs, and showed that the spinal cord was the site of its convulsant action. His work was presented to the Paris Academy in 1809. In1842, Claude Bernard discovered that the arrow poison curare acts at the neuromuscular junction to interrupt the stimulation of muscle by nerve impulses.
Nevertheless, pharmacology is held to have emerged as a separate science only when the first university chair was established. According to Walter Sneader, this occurred in 1847, when Rudolf Buchheim was appointed professor of pharmacology at the University of Dorpat in Estonia (then a part of Russia). Lacking outside funding, Buchheim built a laboratory at his own expense in the basement of his home. Although Buchheim is credited with turning the purely descriptive and empirical study of medicines into an experimental science, his reputation is overshadowed by that of his student, Oswald Schmiedeberg.
Oswald Schmiedeberg (1838–1921) is generally recognized as the founder of modern pharmacology. The son of a Latvian forester, Schmiedeberg obtained his medical doctorate in 1866 with a thesis on the measurement of chloroform in blood. He worked at Dorpat under Buchheim, succeeding him in 1869. In 1872, he became professor of pharmacology at the University of Strassburg, receiving generous government support in the form of a magnificent institute of pharmacology. He studied the pharmacology of chloroform and chloralhydrate. In 1869, Schmiedeberg showed that muscarine evoked the same effect on the heart as electrical stimulation of the vagus nerve. In 1878, he published a classic text, Outline of Pharmacology, and in 1885, he introduced urethane as a hypnotic.
In his 46 years at Strassburg, Schmiedeberg trained most of the men who became professors at other German universities and in several foreign countries. He was largely responsible for the preeminence of the German pharmaceutical industry up to World War II.
In the United States, the first chair in pharmacology was established at the University of Michigan in 1890 under John Jacob Abel, an American who had trained under Schmiedeberg. In 1893, Abel went to Johns Hopkins University in Baltimore, where he had a long and brilliant career. His major accomplishments include the isolation of epinephrine from adrenal gland extracts (1897–1898), isolation of histamine from pituitary extract (1919), and preparation of pure crystalline insulin (1926). His student Reid Hunt discovered acetylcholine in adrenal extracts in 1906.
Today, there is a pharmacology department in every college of medicine or pharmacy.
Pharmacology depends largely on experiments conducted in laboratory animals, but even the human animal may be used as a test subject.Friedrich Serturner, the German pharmacist who isolated the first alkaloid from opium in 1805, administered a whopping dose (100 mg) to himself and three friends. All experienced the symptoms of severe opium poisoning for several days. The alkaloid was named morphine, for Morpheus, the Greek god of sleep.
An interesting example of the use of humans for testing occurred in the 1940s.Although digitalis had been a standard medication for heart disease for more than a century, there were still no reliable methods for evaluating its potency. Biological assays (bioassays) were performed on frogs, pigeons, and cats, but none were totally satisfactory.
In 1942, a group of cardiologists published “a method for bioassay of digitalis in humans”. The assay was based on quantitative changes in the electrocardiogram (ECG) of patients in the cardiac clinics of two New York City hospitals. It was hard to find patients whose ECGs could be standardized. Of 97 patients in whom calibration of the ECG was tried, only 18 proved to be satisfactory assay subjects. Fortunately, chemical research on the active glycosides of digitalis, and development of analytical methods, soon rendered all digitalis bioassays obsolete.
Although humans are no longer used as ad hoc laboratory animals, they are essential in clinical pharmacology. When a new drug compound has gone through sufficient preclinical testing to show potential therapeutic action and reasonable safety on short-term administration, and the data have been reviewed by the FDA, the compound is administered to a small number of human volunteers under closely controlled and monitored conditions. These Phase I clinical trials provide information about dosage and the most common side effects to be expected.
The animals most frequently used in pharmacologic studies are mammals. Mice are preferred because of their small size, ease of breeding, and short generation time. Rats, guinea pigs, rabbits, and dogs are also used; each has special characteristics that make it optimal for certain types of tests.
Experimental pharmacology uses animals in various ways. Intact animals are essential for the acute, subacute, and chronic toxicity tests that a new drug substance must undergo, and for important special tests such as teratology and carcinogenicity. Pharmacology per se tends to use excised (isolated) organs or tissues and animals that are surgically prepared in various ways to aid in the detection and study of target activities.
Early in the development of pharmacologic techniques, it was found that an isolated organ or tissue remained functional for several hours in a bath containing a physiologic solution of salts through which oxygen was bubbled. Henrick Magnus (1802–1870) first applied this method to a strip of small intestine, Jean-François Heymans (1904) worked with the mammalian heart, and Claude Bernard experimented with isolated nerve–muscle preparations.
The organ or tissue is so suspended that the contraction or relaxation of the muscle is mechanically transmitted to a stylet. The stylet writes on a drum covered with smoked paper rotated by clockwork at a constant speed. This device, called a kymograph, graphically records motion or pressure. The effects of drug substances added to the bath can thus be visualized. The kymograph is a relatively crude device. In modern laboratories, organ and tissue movements are transmitted by force transducers to polygraph machines, which produce similar tracings. Or the polygraph is replaced by computerized equipment that issues a digital record.
The surgical preparation of animals is illustrated by the following examples. As early as 1849, the German anatomist Arnold Berthold transplanted testicular tissue into a capon (a castrated rooster) and showed that this induced growth of the comb. This basic method was used in the 20th century to isolate and study the male sex hormones.
Similarly, in 1924, Americans Edgar Allen and Edward Doisy used ovariectomized rats to test the action of estrogenic hormones. To study anti-inflammatory agents, rats can be made arthritic by injection of an oily suspension of killed bacteria (Freund’s adjuvant).
Drugs affecting gastric secretion may be studied in animals by forming a Heidenhain pouch—a small sac of the stomach, vagally denervated and closed off from the main cavity, but with an opening through the abdominal wall.
Screening of candidate compounds and mode-of-action studies may focus on specific tissues, organs, or systems or on actions, such as antihistaminic or anticonvulsant. As knowledge of human biochemistry and molecular biology advances, pharmacology zeroes in more often on enzymatic action and receptors.
Captopril (Capoten), developed by M. Ondetti and co-workers at Squibb in the 1970s, exemplifies a molecule that was rationally designed to fit the active site of an enzyme—angiotensin converting enzyme (ACE). This drug, and subsequent ACE inhibitors, reduces blood pressure.
Knowledge of cell receptors is now on the cutting edge of pharmacology and drug discovery. The concept was first proposed about a hundred years ago by Paul Ehrlich, the great bacteriologist and chemist who synthesized salvarsan (also known as “606”) for the treatment of syphilis. On the basis of his research on bacterial toxins, Ehrlich postulated that the body’s cells possess a great many “receptors” by which they combine with the food substances in the body fluids. He theorized that the metabolic products of certain bacteria combine with the receptors of some cells, thus injuring the cells. Ehrlich visualized receptors as unsatisfied chemical side chains. This is not far from the modern idea of receptors as domains in enzymes or other proteins, with which drugs of appropriate structure can combine.
Illustrating the importance of receptor research are drugs that act on the adrenergic (sympathetic) nervous system. This system has both - and β-receptors. Propranolol (Inderal) was the first specific β-adrenergic receptor blocking agent. Marketed in 1964, it ended a long drought in new heart medicines and soon became a major therapy for angina pectoris, cardiac arrhythmias, hypertension, and essential tremor. However, all β-adrenergic receptors are not identical, and propranolol is nonselective. Second-generation drugs such as atenolol (Tenormin) and metoprolol (Lopressor), developed in the late 1970s, have a preferential effect on βl receptors, which are chiefly located in heart muscle. At higher doses, they also inhibit β2 receptors, which are found mainly in the bronchial and vascular musculature. We also have blockers of the α-adrenoreceptors, such as prazosin (Minipress; early 1980s), and α1-blockers, such as terazosin (Hytrin; 1987). And there are α/β-blockers: Labetolol (Normodyne) and carvedilol (Coreg), developed in the mid-1990s, exhibit selective α1 and non selective β-blocking action.
The methods and approaches touched on in this article are merely a sampling. Pharmacology is similar to medicinal chemistry in that it has developed a vast array of techniques, both general and specialized. Building on its past, the ongoing progress of pharmacology supports its critical role in modern drug discovery and augurs well for the future.
- Oldham, F. K.; Kelsey, F. E.; Geiling, E. M. K. Essentials of Pharmacology; Lippincott: Philadelphia, 1955.
- Sneader, W. Drug Discovery: The Evolution of Modern Medicines; Wiley: New York, 1985.
- Holmstedt, B.; Liljestrand, G. Readings in Pharmacology; MacMillan: New York, 1963.
- Leake, C. D. An Historical Account of Pharmacology to the Twentieth Century; Charles C. Thomas: Springfield, IL, 1975.
1Stanley Scheindlin, D.Sc., received his degrees in pharmaceutical chemistry and is retired after more than 40 years in the industry. He has published in research journals and specialty publications in pharmacy.