Sodium potassium dependent ATPase in hypophysectomized rats: response to growth hormone, triiodothyronine, and...

Groups of hypophysectomized rats were treated with pharmacologic doses of growth hormone, triiodothyronine or cortisone acetate alone or with a combination of growth hormone plus triiodothyronine or growth hormone plus cortisone. After a 7 day period of treatment the hydrolysis of ATP in the presence of ouabain (mg ATPase) and in the absence of ouabain (total ATPase) was determined. Ouabain-suppressible sodium, potassium-dependent ATPase or (Na+ + K+) ATPase was calculated as the difference in the rate of hydrolysis in the presence and absence of ouabain. The activity of the Mg ATPase was significantly reduced in brain after treatment with growth hormone regardless of whether other hormone. In liver there was a significant increase in (Na+ + K+) ATPase in growth hormone, triiodothyronine, or (Na+ + K+) ATPase but there was no effect of triiodothyronine or cortisone and no interaction with the effect of growth hormone. In liver there was a significant increase in (Na+ + K+) ATPase in growth hormone, triiodothyronine, or cortisone-treated animals but Mg ATPase was unaffected by hormone treatment except for the group receiving both growth hormone and cortisone. In kidney homogenates both growth hormone and triiodothyronine significantly increased the activity of the (Na+ + K+) ATPase. There was no effect of cortisone. These data suggest that growth hormone and triiodothyronine may both be calorigenic through their effect on the sodium pumping mechanism in the call membrane.