Action Mechanisms of Secretagogue Drugs

A large number of agents with laxative or diarrheal effects have been shown to influence intestinal fluid and electrolyte transfer. They inhibit the absorption of electrolytes and water and they can also cause an accumulation of fluid within the intestinal lumen. Depending on the administered dose or concentration of the agent and on the particular experimental conditions, inhibition of absorption may result, either on its own or accompanied by secretion. In order to characterize the pharmacodynamic properties of these agents to influence intestinal fluid transfer, they have been named secretagogue (Gaginella et al. 1977a), antiabsorptive and hydragogue (Rummel et al. 1975), or hydrophoric agents (Gaginella and Bass 1978). In this chapter the term “secretagogue” is used, since this expression seems to be the most widely accepted one. It is a phenomenological term without implications with regard to the action mechanisms. This restriction appears reasonable, particularly if one takes into account that, owing to the cytologic heterogeneity of the intestinal epithelium, different types of cells might be involved to different degrees in secretion. Confusion with the term “active secretion”, i.e., active transport of electrolytes and fluid from the blood to the intestinal lumen should be avoided (see Sect. B). Table 1 gives a list of diarrheal agents with secretagogue effects.