ISSN:
1432-1912
Keywords:
Vascular Smooth Muscle
;
Adrenergic Alpha-Receptors
;
Vasopressin
;
Potassium Depolarization
;
Noradrenaline
Source:
Springer Online Journal Archives 1860-2000
Topics:
Medicine
Notes:
Summary 1. Determinations of the maximum tension development of the helical strip of rat aorta showed that the maximal response to vasopressin amounted to 75% and that to potassium-induced depolarization to 93% of the contraction caused by noradrenaline (=100%). 2. When phentolamine (1.2-6.2×10−6 g/ml) was added to the bath 15 min before the determination of dose-response curves for noradrenaline, there was a concentration-dependent shift of the curve to the right; the slope of the curve, the ED50 and the concentration of noradrenaline required for maximum activation of the muscle increased. However, when phentolamine (1.2 to 6.2×10−6 g/ml) was administered after the development of a maximum response to noradrenaline, the muscle relaxed nearly completely. In the presence of phenoxybenzamine (3×10−6 g/ml) noradrenaline failed to cause contractions. 3. The dose-response curve for vasopressin was sigmoid. The presence of phentolamine did not affect the ED50 (at 1.6×10−3 IU/ml) or the peak of the curve (at 1.2×10−2 IU/ml). The administration of vasopressin to depolarized muscles always caused a contractile response. When the muscle was activated repeatedly by vasopressin, tachyphylaxis occurred. 4. Block of the adrenergic alpha-receptors influenced the contractile response to depolarization far less than that to noradrenaline. 5. In accordance with earlier studies, the present results lead to the conclusion that the contraction of the vascular smooth muscle in response to noradrenaline, vasopressin, or depolarization, respectively, involves different mechanisms.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00997025
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