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EFFECT OF ISOPRENALINE AND PHENYLEPHRINE ON THE ADENOSINE 3′,5′‐MONOPHOSPHATE CONTENT AND MECHANICAL ACTIVITY OF COLD‐STORED AND FRESH TAENIA CAECUM FROM THE GUINEA‐PIG
Author(s) -
HONDA F.,
KATSUKI S.,
MIYAHARA J.T.,
SHIBATA S.
Publication year - 1977
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1977.tb07531.x
Subject(s) - isoprenaline , phenylephrine , chemistry , endocrinology , medicine , caecum , adenosine , papaverine , propranolol , guinea pig , biology , biochemistry , stimulation , blood pressure
1 Cold storage treatment of the guinea‐pig taenia caecum had a greater inhibitory effect on the isoprenaline‐induced relaxation than that induced by phenylephrine. Prolonged cold storage (12‐14 days) almost abolished the effect of isoprenaline but only reduced the phenylephrine effect. The ED 50 of cyclic adenosine 3′,5′‐monophosphate (cyclic AMP) that elicited muscle relaxation was not altered by the prolonged cold storage. 2 After cold storage treatment, tissue cyclic AMP content was decreased; however, isoprenaline still caused a dose‐dependent increase in the cyclic AMP level. The threshold dose of isoprenaline for cyclic AMP accumulation was the same in fresh and cold‐stored preparations. 3 In the fresh preparation, the onset of the isoprenaline (10 −6 M)‐induced relaxation preceded the increase in tissue cyclic AMP. 4 Isoprenaline, phenylephrine, adrenaline and noradrenaline at doses (ED 50 ) sufficient to induce muscle relaxation did not always increase the cyclic AMP level. 5 Similarly, the responses to papaverine and nitroglycerine were not accompanied by an increase in cyclic AMP. 6 The adenylate cyclase and phosphodiesterase (low and high Km ) activities of taenia caecum were not attenuated by the prolonged cold storage. 7 Propranolol inhibited both the isoprenaline‐induced relaxation and cyclic AMP accumulation; however, the pA 2 values were significantly different for the two events. 8 Based on these results, both the relaxation and cyclic AMP accumulation caused by isoprenaline are mediated by activation of β‐adrenoceptors but are independent phenomena.