Alterations in rat cardiac myosin isozymes induced by whole-body irradiation are prevented by 3,5,3'-L-triiodothyronine.
Changes in cardiac myosin isozymes and serum thyroid hormone levels were investigated in rats following 10 Gy whole-body gamma irradiation. The percent beta-myosin heavy chain increased from 21.3 +/- 1.8 to 28.1 +/- 6.8 (NS) at 3-day postirradiation, 37.7 +/- 1.9 (P less than .001) at 6-day postirradiation, and 43.8 +/- 3.3 (P less than .001) at 9-day postirradiation. Along with the change in myosin isozymes was a significant 53% decrease (P less than .001) in the serum thyroxine (T4) level by day 3 postirradiation, remaining depressed through day 9 postirradiation. The serum 3,5,3'-triiodothyronine (T3) level, however, was normal until day 9, when significant depression was also observed. In contrast, the thyroid-stimulating hormone (TSH) level was significantly increased by fourfold at day 3, returning to near normal values by day 9 postirradiation. Daily injections of physiological doses of T3 (0.3 microgram/100 g body weight) prevented the change in the myosin isozymes following whole-body irradiation. Daily pharmacological injections of T3 (3.0 micrograms/100 g body weight) to the irradiated rats produced a further decrease in the percent beta-myosin heavy chain (below control values) indicating tissue hyperthyroidism. Thus, this study suggests that the change in myosin isozymes following whole-body irradiation is caused by an alteration in thyroid hormone activity.
Litten
R Z
RZ
Department of Physiology, Armed Forces Radiobiology Research Institute, Bethesda, MD.
Fein
H G
HG
Gainey
G T
GT
Walden
T L
TL
Smallridge
R C
RC
D000818:Animals; D006321:Heart / Q000187:drug effects / Q000528:radiation effects*; D006980:Hyperthyroidism / Q000201:enzymology / Q000378:metabolism; D008297:Male; D009206:Myocardium / Q000201:enzymology*; D015879:Myosin Subfragments / Q000378:metabolism; D009218:Myosins / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013963:Thyroid Hormones / Q000097:blood / Q000378:metabolism*; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood / Q000494:pharmacology*; D014916:Whole-Body Irradiation
D015879:Myosin Subfragments; D013963:Thyroid Hormones; D014284:Triiodothyronine; D013972:Thyrotropin; D009218:Myosins; D013974:Thyroxine