PURINE NUCLEOSIDE AND NUCLEOTIDE INTERACTIONS ON NORMAL AND SUBSENSITIVE ALPHA ADRENORECEPTOR RESPONSIVENESS IN GUINEA-PIG VAS-DEFERENS

  • 1 January 1978
    • journal article
    • research article
    • Vol. 205  (1) , 104-117
Abstract
Adenosine and AMP augment contractile responses to norepinephrine (NE) in isolated guinea pig vas deferens. Dipyridamole slightly enhances, while theophylline antagonizes, adenosine effects on responses to NE. ATP and the nonhydrolyzable analog, adenosine 5''-(.beta.,.gamma.-imido)triphosphate (AppNp) depress responses to NE. Adenine and ADP are ineffective in influencing .alpha. adrenoreceptor responsiveness. Repetitive stimulation of isolated vas deferens with maximal concentrations of NE markedly reduce the contractile response to test concentrations of 6 .mu.M NE. Spontaneous resensitization of responses to NE to control levels occurs within 25-35 min after the end of desensitization treatment. Adenine nucleosides and nucleotides promote a more rapid rate of .alpha. adenoreceptor resensitization, with a potency order: AMP > adenosine > ADP. Adenine and ATP did not influence the rate of .alpha. adrenoreceptor resensitization. The adenine nucleotides ADP, ATP and the analog AppNp elicit concentration-dependent contractions of guinea pig vas deferens. Theophylline antagonizes this contractile activity to adenine nucleotides. AMP, adenosine and adenine are devoid of agonistic activity. In the presence of NE, however, AMP and adenosine produce contractile responses of isolated vas deferens strips, and the agonistic activity of ADP, ATP and AppNp is profoundly enhanced. Agonistic actions of purines in the presence of NE are antagonized by phentolamine much more effectively than by theophylline. The results suggest the existence of a purinergic receptor mediating excitatory responses of guinea pig vas deferens. There appears to be mutual interaction between purinergic and .alpha. adrenoreceptor mechanisms. That adenyl derivatives are capable of augmenting subsensitive .alpha. adrenoreceptor responsiveness suggests that adenine nucleosides or nucleotides, released during sympathetic transmission, may be required for maintenance of normal .alpha. adrenoreceptor sensitivity.

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