Effects of triiodo-L-thyronine (T3)-induced hyperthyroidism on the cardiovascular alpha-adrenoceptor system in young and older rats.
We have compared the vasopressor response of alpha-adrenoceptor agonists in young (2 month-old) and older (12 month-old) pithed rats both in the presence and absence of triiodo-L-thyronine (T3)-induced hyperthyroidism. There was no age-related changes in the pressor response to either the alpha 1-selective agonist phenylephrine or the alpha 2-selective agonists clonidine and UK-14,304. However, T3-induced hyperthyroidism caused a selective reduction in postjunctional alpha 2-adrenoceptor-mediated pressor responses but not alpha 1-adrenoceptor-mediated ones in both age groups. In contrast to vascular alpha-adrenoceptors, there was an age-related decrease in the number of myocardial alpha 1-adrenoceptor sites measured by specific binding of [3H]prazosin. With thyroid hormone treatment, the density of ventricular alpha 1 receptors was found to be further reduced even in the older rats. These results suggest that thyroid hormone and aging have different influences on the cardiovascular alpha-adrenoceptor system and that these two physiological variables are independently interrelated.
Tsujimoto
G
G
Department of Pharmacology, Yamanashi Medical College, Japan.
Hashimoto
K
K
D000375:Aging / Q000378:metabolism*; D000818:Animals; D000959:Antihypertensive Agents / Q000494:pharmacology; D001794:Blood Pressure / Q000187:drug effects; D000068438:Brimonidine Tartrate; D002319:Cardiovascular System / Q000378:metabolism*; D003655:Decerebrate State; D006980:Hyperthyroidism / Q000139:chemically induced / Q000503:physiopathology*; D008297:Male; D009206:Myocardium / Q000378:metabolism; D011224:Prazosin / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000378:metabolism*; D014284:Triiodothyronine / Q000494:pharmacology*
D000959:Antihypertensive Agents; D011810:Quinoxalines; D011942:Receptors, Adrenergic, alpha; D014284:Triiodothyronine; D000068438:Brimonidine Tartrate; D011224:Prazosin