RELAXATION OF GUINEA-PIG FUNDIC STRIP BY ADENOSINE, ADENOSINE-TRIPHOSPHATE AND ELECTRICAL-STIMULATION - LACK OF ANTAGONISM BY THEOPHYLLINE OR ATP TREATMENT

Theophylline relaxed isolated strips of guinea‐pig stomach fundus in a dose‐dependent manner; above 50 to 100 μm responses showed no fade for up to 90 min. Relaxant responses to adenosine, adenosine triphosphate (ATP), noradrenaline, and to electric field stimulation of non‐adrenergic inhibitory nerves were not affected in a significant manner in the presence of 50 μm theophylline. In tissues which showed complete fade of initial responses in the continued presence of 50 μm ATP, the effects of stimulation of non‐adrenergic inhibitory nerves remained unaltered, suggesting that the ATP receptor has no function in non‐adrenergic inhibitory transmission in this tissue. These findings are opposite to those of Okwuasaba, Hamilton & Cook (1977), who claimed that 50 μm theophylline almost fully inhibited relaxation induced by adenosine, ATP and nerve stimulation and that ATP‐induced fade also abolished sensitivity to inhibitory nerve stimulation. 1979 British Pharmacological Society