ISSN:
1432-1912
Keywords:
Chemical sympathectomy
;
Inotropic catecholamine effect
;
Myocardial adrenoceptors
;
Blockade of extraneuronal uptake
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary The positive inotropic effects of (−)-noradrenaline and (±)-isoprenaline were studied on guinea-pig papillary muscles after chemical sympathectomy with 6-hydroxydopamine. 1. Pretreatment with 6-hydroxydopamine increased the sensitivity of the papillary muscle to (−)-noradrenaline from a normal EC50 of about 2×10−6 mol/l to 1.5×10−8 mol/l (−)-noradrenaline. The sensitivity to (±)-isoprenaline was not significantly altered. 2. The positive inotropic effect of (−)-noradrenaline was antagonized by (±)-propranolol (10−7, 3×10−6 mol/l) and (±)-practolol (7×10−5 mol/l) with a decrease in slope. In the presence of hydrocortisone (10−4 mol/l), phenoxybenzamine (5×10−6 mol/l) or phentolamine (10−7, 3×10−6 mol/l) (±)-propranolol caused a nearly parallel shift of the concentration-effect curves to the right. Inhibition of monoamine oxidase by pargyline (10−5 mol/l) and of catechol-O-methyl-transferase (COMT) by U-0521 (10−5 mol/l) did not interfere with the (−)-noradrenaline—(±)-propranolol antagonism. 3. The positive inotropic effect of (±)-isoprenaline was antagonized by (±)-propranolol (10−7, 3×10−6 mol/l) with only a slight decrease in slone of the concentration-effect curves. When phentolamine (3×10−6 mol/l) was added to (±)-propranolol, there was no significant further effect. Inhibition of COMT by U-0521 (10−5 mol/l) was without influence on the (±)-isoprenaline—(±)-propranolol antagonism. 4. The results suggest the existence of differences in the mechanism of the positive inotropic effects of (−)-noradrenaline and (±)-isoprenaline at postsynaptic sites. Compartmentalization of two types of adrenoceptors, differing in their affinity to (−)-noradrenaline and (±)-isoprenaline, offers the most probable explanation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00507220
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