Ventricular and aortic myosin in hypothyroid and hyperthyroid broad breasted white turkeys.

Hyperthyroidism, and alternatively hypothyroidism, were induced in spontaneously hypertensive broad-breasted white turkeys (BBWT) to see if these conditions influenced the pattern of Ca++-activated ATPase activity and isomyosin synthesis in the cardiac muscle. Nine animals were given thyroxine 500 micrograms p.o., 9 animals propylthiouracil 150 mg p.o., 6 animals placebo p.o. All animals were treated daily from the 27th to the 33rd week of age. The ventricular myosin Ca++-activated ATPase activity was assayed in all the animals; aortic smooth-muscle myosin light chains were analysed by mono- and two-dimensional gel electrophoresis, and myosin heavy chains by proteolytic mapping. No significant difference was found between the three groups in the ventricular myosin Ca++-activated ATPase activity. As for aortic myosin, a similar peptide map of heavy chains but a different phosphorylative level of the LC1 light chain was found in the three groups of animals. It is concluded that a thyroid-hormone modulation of contractile proteins in vascular smooth muscle, but not in cardiac muscle, exists in the broad-breasted white turkey.