Effects of autonomic drugs on cat colonic muscle

The cat colon was divided in vitro into four equal segments, and one transverse and one longitudinal strip (1.5 cm x 2.5 mm) was taken from each. Transverse strips contracted rhythmically, each strip generating 0.9-1.2 g force. Longitudinal strips contracted irregularly, each strip generating 11.9-16.8 g force. Acetylcholine (10(-7) to 10(-5) M) and physostigmine (10(-8) to 10(-5) M) increased frequencies in longitudinal (P less than 0.05) but not in transverse strips (P greater than 0.05) and increased amplitudes in both (P less than 0.05). Atropine (10(-8) to 10(-6) M) reduced frequencies and amplitudes in longitudinal strips (P less than 0.05) but only amplitudes in transverse strips (P less than 0.05). Phenylephrine (10(-7) to 10(-5) M) and norepinephrine (10(-7) to 10(-5) M) increased amplitudes in transverse strips (P less than 0.05) but decreased frequencies and amplitudes in longitudinal strips (P less than 0.05). Isoproterenol (10(-7) to 10(-5) M) decreased frequencies an amplitudes in both transverse and longitudinal strips (P less than 0.05). Dopamine (10(-7) to 10(-5) M) decreased amplitudes in longitudinal strips (P less than 0.05). Tetrodotoxin (10(-7) M increased amplitudes in transverse (P less than 0.05) but not in longitudinal strips (P greater than 0.05). Both layers are affected by cholinergic and adrenergic drugs. Muscarinic receptors are excitatory in both. alpha-Adrenergic stimulations result in excitation in circular muscle and inhibition in longitudinal muscle. Circular muscle is dominated by an inhibitory neural tone.