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Thyroxine treatment of aged or young rats demonstrates that vascular responses mediated by β‐adrenoceptor subtypes can be differentially regulated
Author(s) -
O'Donnell Stella R.,
Wanstall Janet C.
Publication year - 1986
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1986.tb09469.x
Subject(s) - isoprenaline , fenoterol , endocrinology , medicine , agonist , forskolin , aorta , terbutaline , saline , chemistry , receptor , asthma , stimulation
1 Responses to vascular relaxant drugs were obtained on KCl (15 mM)‐contracted isolated ring preparations of pulmonary artery and aorta from young (1–2 months old) and aged (> 16 months old) rats. These vessels contain both β 1 ‐ and β 2 ‐adrenoceptors. 2 Relaxant responses (i.e. relaxation expressed as a % of the KCl‐induced contraction) to isoprenaline, procaterol (β 2 ‐seleotive partial agonist), fenoterol (β 2 ‐selective) and noradrenaline (β 1 ‐selective) but not those to forskolin, 3‐isobutyl‐1‐methylxanthine, enprofylline or sodium nitrite, were smaller on preparations from aged rats than on those from young rats. 3 Thyroxine (T 4 )‐treatment (1 mg kg −1 s.c. thrice weekly for 3–5 weeks) of aged or young rats enhanced responses to isoprenaline and noradrenaline but reduced those to procaterol, when compared with preparations from age‐matched saline‐treated control rats. 4 The agonist order of potency, determined in young rats, was isoprenaline>noradrenaline>adrenaline in preparations from T 4 ‐treated rats compared with isoprenaline > adrenaline > noradrenaline in saline‐treated control rats. 5 It is concluded (a) that the age‐related decline in vascular responses to β‐adrenoceptor agonists involves β‐adrenoceptor mechanisms specifically and possibly β 2 ‐adrenoceptors more than β 1 ‐adrenoceptors; and (b) that T 4 ‐treatment of rats enhances β 1 ‐adrenoceptor‐mediated and reduces, or does not change, β 2 ‐adrenoceptor‐mediated responses of preparations of rat pulmonary artery and aorta. In preparations from control rats β 2 ‐adrenoceptors were functionally predominant but in preparations from T 4 ‐treated rats β 1 ‐adrenoceptors appeared to become functionally predominant.