ISSN:
1432-1912
Keywords:
α-and β-Adrenoceptors
;
Methoxamine
;
Isoprenaline
;
cAMP
;
Papaverine
;
Rabbit Papillary Muscle
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary In the isolated papillary muscle of the rabbit the time course of the effects of selective β-and α-adrenoceptor stimulation by isoprenaline and methoxamine, respectively, on the contractile force and on the level of 3′,5′-cyclic AMP (cAMP) was determined. 1. Isoprenaline (3×10−7 M) increased significantly the content of cAMP at 15 sec and elevated it to the maximal level-about twice the control value-at 30 sec after its administration, while the developed tension of the papillary muscle was also increased significantly at 15 sec and reached gradually its maximum at 90 sec. 2. Compared with isoprenaline methoxamine (10−4 M) increased the developed tension very slowly: the maximal response was reached after 20 min. The level of cAMP, on the other hand, was changed neither before nor during the induction of the positive inotropic effect of methoxamine. 3. The phosphodiesterase inhibitor papaverine (10−5 M) inhibited the PDE activity of the papillary muscle by about 40% after an incubation of 1 hr, and increased the level of cAMP significantly. The effects of isoprenaline on the contractile force and on the level of cAMP were considerably enhanced by papaverine: the content of cAMP was increased by isoprenaline (3×10−7 M) to about 3 times the control value and also its positive inotropic effect was significantly greater than in controls without papaverine. On the other hand, the positive inotropic effect of methoxamine (10−4 M) was not affected by papaverine (10−5 M). Further-more, in the papillary muscle treated with papaverine the level of cAMP was significantly reduced by methoxamine: the papaverine-induced increase of cAMP was abolished by methoxamine. 4. The present results are compatible with the hypothesis that cAMP is involved as a mediator in the positive inotropic effect induced by β-adrenoceptor stimulation, and indicate further that the stimulation of α-adrenoceptors evokes its positive inotropic effect through a mechanism other than that elicited by β-adrenoceptor stimulation, i.e., independent of cAMP.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00499982
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