Induction of hepatic mitochondrial alpha-glycerophosphate dehydrogenase by L-triiodothyronine in Singi fish (Heteropneustes fossilis Bloch).
A single injection of L-triiodothyronine (T3) in different doses (0.25, 0.5, 5, 20 and 50 micrograms/g) increased the hepatic mitochondrial cytochrome-linked alpha-glycerophosphate dehydrogenase (alpha-GPD) activity and mitochondrial protein content of Singi fish, as observed on the 3rd day. A non-linear dose-response relationship with respect to enzyme activity was observed with different doses of T3. A low dose of 0.1 micrograms of T3 per g failed to cause any change in alpha-GPD activity and mitochondrial protein content of the liver. The enhancement of alpha-GPD activity over the control level with a low and a high dose of T3, viz., 0.5 and 5 micrograms/g, was followed from the 1st to the 7th day, when it was found that enzyme activity reached the maximum level on the 3rd day and then gradually declined to the control value on the 7th day. The percentage increase in enzyme activity with 5 micrograms/g was higher than that with 0.5 microgram/g from the 2nd to 5th day. Compared to the control, these two doses of T3 caused an increase in alpha-GPD activity from the 1st to the 6th day. Cycloheximide inhibited the T3-induced increase in alpha-GPD activity, mitochondrial and total protein content of liver. Immersion of Singi fishes in thiourea-containing (1 mg/ml) medium for 30 days showed a fall in hepatic alpha-GPD activity in comparison to the euthyroid control. A single injection of T3 (0.5 microgram/g) to the hypothyroid fish recovered alpha-GPD activity to more than the euthyroid control level. An increase in mitochondrial protein content in the T3-injected hypothyroid fish has been observed. DNA content of the fish liver remained unchanged in every experimental condition. The results thus showed the significant responsiveness of the fish liver to thyroid hormone.
D000818:Animals; D003513:Cycloheximide / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005399:Fishes; D005993:Glycerolphosphate Dehydrogenase / Q000032:analysis*; D007037:Hypothyroidism / Q000201:enzymology; D008930:Mitochondria, Liver / Q000201:enzymology*; D012016:Reference Values; D013890:Thiourea / Q000494:pharmacology; D014284:Triiodothyronine / Q000494:pharmacology*
D014284:Triiodothyronine; D003513:Cycloheximide; D005993:Glycerolphosphate Dehydrogenase; D013890:Thiourea