Effects of Methionine Enkephalin (Met-Enkephalin) on Regional Blood Flow and Vascular Resistance: Radioactive Microsphere Techniques

Ever since Hughes et al. (1975) discovered opioid-like peptides from the brain extract of rat, many advancements in the field of neurophysiology and pharmacology have been made. Methionine enkephalin ([met5]enkephalin), a simple pentapeptide, has been implicated in many physiological functions such as pain perception, appetite, hormone-release, thermoregulation, gastrointestinal function, and cardiovascular function (Martin, 1983). Although the cardiovascular effects of [met5]enkephalin depend on many factors, the level of anesthesia (Schaz et al., 1980; Eulie and Rhee, 1984), the sites of peptide injection (Wei et al., 1980; Petty and DeJong, 1983) and the animal species have been shown to be important factors.