STIMULATION OF RAT AND CAT HEART ADENYLATE-CYCLASE BY TRIIODOTHYRONINE IN PRESENCE OF 5'-GUANYLYLIMIDODIPHOSPHATE

  • 1 January 1976
    • journal article
    • research article
    • Vol. 35  (7) , 829-835
Abstract
Adenylate cyclase activity in particulate preparations from the myocardium of rats and cats was unaffected by 3,3'',5-triiodo-L-thyronine (L-T3) added in the absence of or together with, 5-guanylylimidodiphosphate (Gpp(NH)p), a potent activator of the enzyme. Preincubation of the heart particles with Gpp(NH)p made the cyclase sensitive to L-T3 which then caused, in concentrations of 10-8 M and higher, additional increases in enzyme activity up to about 50% above the Gpp(NH)p-stimulated level. Similar effects after Gpp(NH)p treatment were produced by low concentrations of 3,3'',5''-triiodo-L-thyronine (reverse T3) and 3,3'',5-triiodo-D-thyronine; diiodo-tyrosine, 3,5-diiodo-L-thyronine and 3''-isopropyl-3,5-diiodo-L-thyronine were without significant effect. The stimulatory action of L-T3 on cardiac adenylate cyclase pretreated with Gpp(NH)p may help to explain some of the effects of thyroid hormones on the heart that appear in the literature.