ABSTRACT
Opioids are best known for their ability to relieve pain, an action that is quite novel and unique.1,2 Local anesthetics block the transmission of nerve impulses, leading to the complete loss of sensation. In contrast, opiates interfere with the suffering component of pain, leaving objective sensations intact. Thus, opioids act on the integrated sensation of pain. Patients receiving opioids often report that the pain is still present but that it no longer hurts. Although the ability to relieve pain is often considered their most important characteristic, opiates have many other actions, including the modulation of respiratory function, gastrointestinal transit, and a wide variety of effects on the endocrine system. Indeed, the highest concentrations of opioid peptides in the body are in the adrenal medulla, where they are co-released with epinephrine in periods of stress. Similarly, β-endorphin is generated from β-lipotropin, the same peptide precursor which generates ACTH, and both are secreted together from the pituitary. The past 30 years have yielded many important new insights into the opioid systems, which consist of a large family of endogenous peptides and their receptors.
