If a drug is to be used intelligent for the prevention, treatment, or diagnosis of disease, it is nessary to have adequate information on its physiologic effects on both the healthy, and diseased organism.
Much pharmacologic literature deals with the effects of drugs on healthy laboratory animals. Since many diseases of human beings can be reproduced in animals, the abundant results of experimental pharmacology often have predictive value for human therapeutics. Such results must always be checked, however, by careful clinical investigation.
Although all tissues of the body may be exposed to virtually the same concentration of a drug, it is common experience that some tissues are affected much more than others. This selectivity of drug action is of great interest, since it offers the oportunity for influencing a disturbed function without greatly altering normal processes. It also provides important tools for learning more about normal function.
What is the basics of drug selectivity? The simples explanation would be that a drug acts selectived on a tissue in which it is highly concentrated. This happens to be the case in a few instances. For example, the mercurial diuretics are more concentrated in the renal tubule in which they exert their effect. Often, however, such a simple explanation does not suffice.
Receptor concept. Many facts concerning the selective effect of drugs are compatible whith the hypothesis of specific chemical-combining sites within body cells. These hypothetic receptors must be at a submicroscopic level since histologic apperarence of a tissue is often not sufficient to predict its drug responce. For example, the uterine smooth muscle of the guinea pig is highly susceptible to histamine and will contract when exposed to even an extremely low concentration of this drug. On the other hand, the uterus of the rat is hardly susceptiple even to relatively high concentration of histamine.
