AbstractInsulin stimulates hexose transport, intermediary metabolism, and cell growth and development. These effects are well‐documented in skeletal but not smooth muscle.31P NMR spectroscopy was performed on rabbit urinary bladders (n=4) to characterize insulin's actions on smooth muscle. The bladder and its vasculature were surgically isolated from the animal and perfused with a PSS/red blood cell perfusate. After a control steady state was achieved (approx 1−2 h), insulin (0.100 mU/ml) was added to the perfusate. Relative levels of intracellular phosphorylated compounds, pH, and free Mg2+were measured and compared to control values. Also, extracellular pH and fractional volume were assessed using phenylphosphonate, a31P NMR extracellular pH and volume indicator. Insulin induced significant increases in PCr (16 ± 9%) at the expense ofPi, intracellular pH ( Δ 0.24 + 0.07 ), and fractional extracellular volume (49 ± 1%). Intracellular free Mg2+and extracellular pH did not change. These results indicate thatin situsmooth muscle is sensitive to physiological levels of insulin. In fact, insulin improves the energy state of smooth muscle cells and the overall tissue perfusion. © 1989 Academic Pre