Age-related changes in rat hepatic and renal thyroid hormone-sensitive enzymes--different responses to acute and chronic L-triiodothyronine stimulation.
Using young (5-6 weeks) and adult (12-14 months) male Sprague-Dawley rats, the responses of hepatic and renal cytosolic malic enzymes (ME) and mitochondrial alpha-glycerophosphate dehydrogenase (alpha-GPDH), have been assessed following acute and chronic L-triiodothyronine (T3) administration. In control (untreated) animals a significant reduction of renal ME as well as hepatic and renal alpha-GPDH activity with increased age were observed but renal ME activity was not age-related. Following acute T3 stimulation (200 micrograms T3/100 g body wt single injection), the levels of hepatic ME and alpha-GPDH as well as renal alpha-GPDH but not renal ME remained lower in the adult than in the younger group. After chronic T3 stimulation (15 micrograms T3/100 g body wt for 7 days) or 200 micrograms T3/100 g body wt for 4 days), the enzyme levels remained significantly lower in older animals for hepatic ME but were no longer different for hepatic and renal alpha-GPDH, while renal ME, which was not altered with age, had values that were the same as in the younger group. These studies have demonstrated that age-related changes in hepatic and renal T3-sensitive enzymes could not be attributed solely to T3 occupancy of nuclear receptor binding sites, but may be influenced by other factors depending upon the specific tissues and subcellular T3-sensitive enzymes being assessed.
Sawada
K
K
Thyroid Research Laboratory, Mount Sinai Institute, Ontario, Canada.
Hummel
B C
BC
Walfish
P G
PG
D000367:Age Factors; D000818:Animals; D003600:Cytosol / Q000201:enzymology; D005993:Glycerolphosphate Dehydrogenase / Q000378:metabolism*; D007668:Kidney / Q000201:enzymology*; D008099:Liver / Q000201:enzymology*; D008291:Malate Dehydrogenase / Q000378:metabolism*; D008297:Male; D008928:Mitochondria / Q000201:enzymology; D051381:Rats; D011919:Rats, Inbred Strains; D011988:Receptors, Thyroid Hormone / Q000502:physiology; D013997:Time Factors; D014284:Triiodothyronine / Q000502:physiology*
D011988:Receptors, Thyroid Hormone; D014284:Triiodothyronine; D005993:Glycerolphosphate Dehydrogenase; D008291:Malate Dehydrogenase