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. 1977 Jan;59(1):75-81.
doi: 10.1111/j.1476-5381.1977.tb06979.x.

Theophylline and phenylephrine effects on cardiac relaxation

B G Benfey

Theophylline and phenylephrine effects on cardiac relaxation

B G Benfey. Br J Pharmacol. 1977 Jan.

Abstract

In the driven isolated left atrium of the rabbit theophylline shortened relaxation time in a similar manner to isoprenaline and histamine. 2 Phenylephrine lengthened relaxation time in a similar manner to calcium. 3 Theophylline caused phenylephrine to shorten relaxation time, which was inhibited by a beta-adrenoceptor blocking drug, but theophylline did not potentiate the effect of phenylephrine on peak tension. 4 Theophylline separated drug effects on cardiac relaxation and contraction: in the presence of theophylline at a low calcium concentration, phenylephrine shortened relaxation time by beta-adrenoceptor stimulation and increased peak tension by alpha-adrenoceptor stimulation. At a high calcium concentration, theophylline potentiated the effect of isoprenaline, histamine and phenylephrine on relaxation time but inhibited the effect on peak tension.

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