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

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Abstract
1 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. 2 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. 3 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. 4 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.