Effects of delta-aminolaevulinic acid on contractile activity of rabbit duodenum

delta-Aminolaevulinic acid (ALA) inhibited spontaneous contractions and contractions induced by acetylcholine, barium chloride or ouabain in rabbit duodenum preparations suspended in Ringe-Locke solution. Concentrations of ALA between 25--100 micrograms/ml reduced amplitude of spontaneous contractions and at levels above 200 micrograms ALA/ml spontaneous contractions caused. Muscle tone was decreased in proportion to logarithm of AL concentration between 25 and 1000 micrograms/ml. Gut ALA levels were increased by the treatment and returned to control values after washing, and pharmacological effects were full reversed. Neither tetrodotoxin nor atropine affected the gut's response to ALA. The response still occurred in calcium-free, high-calcium, potassium-free and high-potassium bathing fluid. Effects of ouabain resembled those of ALA only when gut had been pretreated with atropine; pretreatment with tetrodotoxin induced slight contracture. The observed pharmacological effects of ALA must be by actions additional to sodium pump inhibition.