Selective adrenergic agonists and colon motility in monkeys

Sympathetic stimulation during and after laparotomy and other surgical procedures may be a factor inducing postoperative ileus. In experiments conducted in fasting monkeys, the effects of the selective sympathetic agonists alpha 1 (phenylephrine), alpha 2 (ST-91), beta 1 (dobutamine), and beta 2 (terbutaline) on colon contractile activity were measured. Strain gauges were implanted on the colon. Recordings were made for 1 hour (control) and then for an additional hour during continuous infusion by one of a range of doses of each drug (experimental). The drug doses were chosen to cover both physiologic and pharmacologic concentrations. All of the sympathetic agonists caused a dose-dependent decrease in the frequency of colon contractions. The beta-agonists did so at a concentration that is sufficiently low to support a hypothesis that beta-stimulation leading to inhibition of smooth-muscle contraction may play an important role in the genesis of postoperative ileus.