1965; McNeill and Brody 1968) that the Txinduced super- ... mals similar to that reported by Brodie et al. ( 1966) for .... The authors thank Dr. G. Allan Robison,.
Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by University of British Columbia on 09/01/15 For personal use only.
Canadian Journa ogy and Pharmacology
VOLUME 47
NOVEMBER 1969
NUMBER I 1
The effect of triiodothyronine on cyclic AMP, phosphorylase, and adenyl cyclase in rat hearti JOHNH. MCNIEILL, LAWRENCE D. MUSCIIEK, AND THLCIDORE M. BRODY Departrnertt of P/zarn7ac.oIogRv, kfichigan State Llrriuersity, East Lansing, Miclzigavr 48823
Reccived May 12, 1969
MCNEII-L,J. H., MUSCHCK. L. D., AND BWCSDY, T. M . 1969. The effcct of triiodothyronine on cyclic AMP, phosphoryiasc, and adenyl cyclase in rat hcart. Can. J. PhysioB. kharmaco%.47, 913-986. Pretreatment with triiodothyronine (T3) greatly enhanced the epinephrine-ind~~ced increasc in rat cardiac phosphorylase a. Tvreatmcnt, however, did not increase the level of adenosine-3',5'-monophosphate (cyclic AMP) in rat heart. T3 trcattascnt also did not increase the activity of rat heart adenyl cyclase or change. the sensitivity of the enzyme to epinephrine when actikity was deterrnnined in vitso. It is suggested that if thyroid hormone affects the activity sf adenyl cyciase in vivo the effect is Best in the preparation of the enzyme for assay in vitro.
Previous reports frola this labratory (Hornbrook et al. 1965; MeNeil1 and Brody 1968) have indicated that rats pretreated with triiodothyroninc (T3) exhibit an increased responsc to atlscncrgic aminc induced cardiac phosphorylase activation as compared with control animals. In addition, T:j-pretreated animals had levels of phosphorylase a significant]y higher than saline-treated control animals. It has been skaggestcd (Hornbrook et al. 1965; McNeill and Brody 1968) that the Txinduced supersensitivity of cardiac phosphorylase to the adrenergic amines could result from an increasc in the activity or sensitivity of the enzyme adenyl cyclase in hearts of hyperthyroid animals similar to that reported by Brodie et al. ( 1966) for the fat pad of the rat. Therefore .the effect of T-retreatment on rat heart adenyl cyclase and phosphorylase after epinephrine was studied in control and Txpretreated animals. Methods Phssphory &use experiment.^ Female rats (Sprague-Dawley, 190-200 g ) were anesthetized with kexobarbital and infused with 'Supported by a grant from the Michigan Heart Association and by N.I.H. Grant WE-12646-81.
epinephrine for 5 min via ,a jtagular vein as previonslj. described (McNeiIl and Brody 1966). The heart.; were then rapidly excised and frozen in isopentane cooled in a mixture of alcohol - Dry Ice. A $80-mg portion of the apex of the heart was then assayed for phosphorylase as describcd previously (McNeiHB and Brody 1966). Animals pretreated with triiodothyronine (500 pg/kg per day for 3 days) were similarly infused, and cardiac phosphorylase was estimated. Since total phosphsrylase did not change, all results are expressed as percent phosphorylase a which is (phosphorylase activity without adenosine rnonoghosphate/phosphorylase activity with adenosine monophosphate) x 100. Adeny l Cyckuse Experiments A washed particulate preparation of rat heart (hlurad et ak. 1962) was used as the source of adenyi cyclase. The enzyme was prepared from both normal and hyperthyroid animals and activity was determined on the same day. Enzyme activity was determined by measuring the conversion of IT-labelled adenosine triphasphate to l'C-labelled adenosine-3',St-monspkosphate (cyclic AMP) as described by Kriskna ef a/. (19686). Enzyme activity is expressed as pieomoles '4CC-cyclicAMP produced per milligram protein per 4 min incubation. Protein was determined by the method of Lowry et ak. (1951). Cyclic A M P Experiment Cyclic AMP was determined in hearts obtained from anesthetized control and T-treated animals as described by Rall and Sutherland (1961 ) . The hearts were rapidly excised and frozen as described for phosphorylase.
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CANADlAN JOURNAL 06 PHYSIOLOGY AND
PEIAIPMACOLOGY. VOL.
47, I969
TABLE I The efTect of triiodothyronine (T3) treatment on heart weight, body size, and cardiac cyclic AMP Bevels
Can. J. Physiol. Pharmacol. Downloaded from www.nrcresearchpress.com by University of British Columbia on 09/01/15 For personal use only.
-
-
A
-
a-
-
Body weight
Treatment
(8)
None
225 L- 3 (10)
P
-
-
--
203 b- 3 (10)
Cyclic AMP
Heart weight (mg)
-
P
pMoles/g
