Influence of beta-adrenoceptor-mediated relaxation on alpha-adrenoceptor-mediated contraction of rat pulmonary artery to adrenaline or noradrenaline.
Concentration-response (contraction) curves to either adrenaline or noradrenaline were obtained on isolated ring preparations of pulmonary artery from rats. In preparations from young rats the curve for adrenaline was bell-shaped, unless beta-adrenoceptors were blocked with propranolol (1 X 10(-6) M). The maximum contraction to adrenaline was less in the absence than in the presence of propranolol. In preparations from aged rats the adrenaline curve was no longer bell-shaped, even in the absence of propranolol. This reflected a decrease in the beta-adrenoceptor-mediated relaxant responses of preparations from aged rats, seen as a separation between the concentration-response (relaxation) curves to adrenaline on preparations (phenoxybenzamine-treated, KCl-contracted) from young and aged rats. In preparations from young rats the noradrenaline curve was not bell-shaped, but if the preparations were from young rats treated with thyroxine (T4), then a bell-shaped curve for noradrenaline was obtained, unless beta-adrenoceptors were blocked by propranolol. These data could be explained by an increase in beta-adrenoceptor-mediated relaxant responses of preparations from T4-treated rats, seen as a separation in the concentration-response (relaxation) curves to noradrenaline on preparations from control and T4-treated rats, respectively. Thus alpha-adrenoceptor-mediated contractile responses of rat pulmonary artery preparations, to adrenaline or noradrenaline, can be attenuated by activation of beta-adrenoceptors, mediating relaxation, and the extent of this attenuation changes under the influence of factors, such as ageing or T4-treatment, which modify beta-adrenoceptor-mediated relaxation in this blood vessel type.
D000375:Aging; D000818:Animals; D004305:Dose-Response Relationship, Drug; D004837:Epinephrine / Q000494:pharmacology*; D066298:In Vitro Techniques; D008297:Male; D009638:Norepinephrine / Q000494:pharmacology*; D011433:Propranolol / Q000494:pharmacology; D011651:Pulmonary Artery / Q000187:drug effects* / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000502:physiology*; D011943:Receptors, Adrenergic, beta / Q000502:physiology*; D013974:Thyroxine / Q000494:pharmacology; D014661:Vasoconstriction / Q000187:drug effects*
D011942:Receptors, Adrenergic, alpha; D011943:Receptors, Adrenergic, beta; D011433:Propranolol; D013974:Thyroxine; D009638:Norepinephrine; D004837:Epinephrine