Thyroid Thermogenesis in Adult Rat Hepatocytes in Primary Monolayer Culture Direct Action of Thyroid Hormone In Vitro

We have studied the effect of 3,5,3 't r i iodothyronine (Ts) on the respiration of adul t rat hepatocytes in pr imary monolayer culture p repared f rom hypothyroid rat liver. After addit ion of T3 to the culture medium at a concentration of 2 x 10 -7 M, oxygen consumption of the cultured cells increased detectably at 24 h and was maximal at 72-96 h, relative to control cultures (38.0 -+ 1.8 vs. 25.0 1.5 g.1/h, mg protein). The thyroid-responsive enzymes, Na + + K+-activated adenosine t r iphosphatase (NaK-ATPase) and ot-glycerophosphate dehydrogenase (GPD), each exhibited increased activity in response to Ta, in parallel with the change in oxygen consumption, whereas the activity of Mg-dependent ATPase was unaffected. These responses to T3 were dose dependen t over similar concentration ranges, the half-maximal response for each occurr ing at ca 8 x 10 -l~ M. In thyroidt reated cells, the observed increase in respirat ion was almost completely (90%) inhibited after addi t ion o f ouabain (10 -3 M) to the culture medium. It was found also that a 4-h exposure o f the cul tured hepatocytes to Tn was sufficient to elicit a significant thermogenic response, measured at a t ime (48 h later) when T3 was no longer present in the medium. The response to T3 occurred in fully def ined culture medium and was independen t of the presence or absence o f hypothyroid rat serum, corticosterone, or insulin, and cellular ATP was unaffected by Ts in concentrations up to 2 x 10 -~ M. The findings document that adul t rat hepatocytes in pr imary monolayer cul ture respond directly to thyroid hormone; the increases in respirat ion and NaK-ATPase activity elicited by T3 were cotemporal and apparent ly coordinate. I N T R O D U C T I O N A d m i n i s t r a t i o n o f t h y r o i d h o r m o n e in vivo elici ts a t h e r m o g e n i c r e s p o n s e ( m e a s u r e d as i n c r e a s e d o x y g e n c o n s u m p t i o n ) wh ich can be a s c r i b e d to its a c t i on o n spec i f ic t a r g e t t i ssues ( B a r k e r , 1951). A m o n g these t issues is the l iver , wh ich has b e e n u t i l i zed e x t e n s i v e l y in s tud ies o f t he b i o c h e m i c a l basis o f t h y r o i d J. GEN. PHYSIOL. ~) The Rockefeller University Press 9 0022-1295/79/03/0369/15 $1.00 369 Volume 73 March 1979 369-383 on Jne 6, 2017 D ow nladed fom Published March 1, 1979