Date of Award

8-1979

Document Type

Thesis

Degree Name

Master of Science

Department

Biology

First Advisor

Dr. David W.Towle

Abstract

The interacting effects of tetraiodothyronine (T4) and epi- nephrine on Na++K+-dependent ATPase, hexokinase, and pyruvate kinase in cardiac tissue of white rats were investigated in an attempt to elucidate the hormonal regulation of heart metabolism. Previous evidence has shown that 90% of the increase in oxygen consumption exhibited by hyperthyroid rats was due to an activation of Na++K+- dependent ATPase. In addition, hypothyroidism in sheep was re­ ported to lower cardiac Na++K+-dependent ATPase activity as well as 8-adrenergic binding sites for epinephrine. As T4 and epinephrine enhance carbohydrate metabolism, hexokinase and pyruvate kinase, two essentially irreversible glycolytic enzymes, were also assayed.

All animals were initially made hypothyroid by the addition of propylthiouracil to their drinking water. Hyperthyroidism was achieved through daily injections of T4 and epinephrine action on the heart was blocked by dl-timolol maleate.

No significant interacting effects of T4 and epinephrine were demonstrated on the activity of Na++K+-dependent ATPase. However, significant interacting effects of the two hormones were exhibited on hexokinase and pyruvate kinase activities. The simultaneous deficiency of T4 and epinephrine appeared to result in enhanced activities of both hexokinase and pyruvate kinase. The high activities of hexokinase and pyruvate kinase in these epinephrine- blocked hypothyroid rats may be attributed to low blood glucose levels which forced the combustion of lipids and amino acids or stimulated the release of glucocorticoids.

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