A.K. Medda

Effect of thyroxine and analogs on protein and nucleic acid contents of liver and muscle of Lata fish (Ophicephalus punctatus)

Injection of thyroxine (T4) induced a change, biphasic in nature, in the amounts of protein and RNA in liver and muscle of Lata fish (Ophicephalus punctatus). The lower doses of T4 (0.5 μg/g, three injections; or 1 μg/g, single injection) increased and the higher doses (2 or 4 μg/g, single injection) decreased the amounts of protein and RNA in liver and muscle on the fourth or fifth day after injection. The enhanced or reduced levels of liver protein and RNA with 1 or 4 μg of T4/g, respectively, continued up to the 12th day after injection. The muscle protein and RNA levels at 1 or 2 μg of T4/g were not different from the control values on the 12th day, whereas the reduced level of only muscle protein (not RNA) with 4 μg of T4/g remained unchanged up to the 12th day. A single injection of tetraiodothyroacetic acid (TETRAC, 1, 2, or 4 μg/g) increased the protein and RNA contents of liver and muscle in Lata fish. The increased levels of these substances continued up to the 12th day after injection, except in muscle at a dose of 1 μg/g. Triiodothyroacetic acid (TRIAC, 2 or 4 μg/g, single injection) also enhanced the amounts of protein and RNA in liver and muscle. This enhanced level of these cellular substances was also observed on the 12th day at a dose of only 4 μg of TRIAC/g. DNA contents of both liver and muscle remained unaltered at all doses of T4, TETRAC, and TRIAC used.

Effect of estrogen and testosterone on the protein and nucleic acid contents of liver, muscle, and gonad and plasma protein content of male and female (vitellogenic and nonvitellogenic) Singi fish, Heteropneustes fossilis bloch

Daily injections of estradiol dipropionate (0.5, 1, 2, and 4 μg/g, for 7 consecutive days) increased the hepatosomatic index, protein and RNA contents of liver, and protein content of plasma of male and female (vitellogenic and nonvitellogenic) Singi fish (Heteropneustes fossilis). The gonadosomatic index and protein and RNA contents of gonad (ovary or testes) and muscle remained unchanged in these male and female fish under such treatments. Testosterone propionate injections (0.5, 1, 2, and 4 μg/g, for 7 consecutive days) failed to cause any of these changes in male or female fish, except in the case of nonvitellogenic females where the muscle protein content increased after injections of 2 and 4 μg of testosterone per gram. The DNA content of liver, muscle, and ovary or testes was not affected by any of these hormones.

Effect of thyroid hormones and analogues on ammonia and urea excretion in Lata fish (Ophicephalus punctatus)

The influence of single intraperitoneal injection of thyroxine (T4), triiodothyronine (T3), tetraiodothyroacetic acid (TETRAC), and triiodothyroacetic acid (TRIAC) were studied on the nitrogen excretion (urea-N and NH3N) of Lata fish acclimatized at 25 or 30°. The actions of T4 and the iodinated analogs, studied at these temperatures on nitrogen excretion of these animals, appear to be temperature-specific. The NH3N as well as urea-N excretion of normal Lata fish was also found to be directly proportional to the environmental temperature (10 to 30°). Thyroxine (T4) injection at lower doses (0.5 or 1 μg/g) caused anabolic effect with respect to NH3N and urea-N excretions at 25°. With higher doses of T4 (2 μg/g or 4 μg/g) at 25° C, the results on nitrogen excretion were not significantly different from the control. At 30°, T4 (1, 2, or 4 μg/g) increased NH3N and urea-N excretion. Triiodothyronine (T3) with higher doses (2 or 4 μg/g) was effective in causing increased NH3N excretion at 25°. The responses of T3 with a dose of 4 μg/g with respect to nitrogen excretion was about at the same level as found with 10 μg/g of T4/g of body wt at this temperature. Tetraiodothyroacetic acid, or TETRAC, (1, 2, or 4 μg/g) enhanced NH3N excretion, but not urea-N excretion, at 25°. Triiodothyroacetic acid (TRIAC) even with 4 μg/g was ineffective in this respect, at 25°. Both TETRAC and TRIAC with 1, 2, or 4 μg/g at 30° significantly increased NH3N excretion. Compared to the controls, urea excretion remained unchanged with 1 μg of TRIAC/g at 30°. This nitrogen excretion (urea-N) was enhanced with higher doses of this analog (2 and 4 μg/g) at 30°. TETRAC with all doses used (1, 2, or 4 μg/g) increased urea-N excretion at this temperature. The results shown that TETRAC was more potent than TRIAC.

Effect of estradiol dipropionate and testosterone propionate on the glycogen, lipid, and water contents of liver, muscle, and gonad of male and female (vitellogenic and nonvitellogenic) Singi fish (Heteropneustes fossilis bloch)

Abstract Daily injections of estrogen given in doses of 0.5, 1, 2, or 4 μg/g for 7 consecutive days reduced the glycogen and enhanced the lipid and water contents of liver of male and female (vitellogenic and nonvitellogenic) Singi fish. All doses of estrogen produced similar reductions in glycogen and increases in lipid content of livers of male and nonvitellogenic female fish, but in vitellogenic females, the highest doses caused the strongest decreases in glycogen levels (dose dependent at 2 μg/g or less) and the strongest increases in lipid levels (dose dependent at 0.5 μg/g or less). The increase in water content was more marked with doses of 2 and 4 μg/g than with 0.5 and 1 μg/g in male and vitellogenic female fish. In nonvitellogenic females, all doses produced similar increases in water content. Testosterone injections (0.5, 1, 2, and 4 μg/g) given for 7 consecutive days significantly enhanced the glycogen content but not the lipid and water content of livers of male and female Singi fish. In male and nonvitellogenic female fish the highest doses caused the largest increases in glycogen content (dose dependent at 1 μg/g or less). In vitellogenic female fish the increase in liver glycogen was higher with 2 and 4 μg/g than with 0.5 and 1 μg/g. Both estrogen and testosterone failed to cause any significant alteration in glycogen, lipid, and water contents of muscle and gonad of male and female fish.

Demonstration of putative thyroid hormone receptor in the brain nuclei of Singi fish, Heteropneustes fossilis (Bloch)

A single injection of [125I]triiodothyronine (T3) with or without stable T3 in Singi fish, Heteropneustes fossilis (Bloch), showed that the fish brain has saturable binding sites and that the specific uptake is 60-70% higher than the nonspecific uptake. The distribution kinetics of [125I]T3 in the serum, whole brain, and brain nuclei after a single injection of the labeled hormone showed that the removal of [125I]T3 from the serum was very rapid with the t1/2 of about 3.3 hr and the incorporation of the hormone into the brain and brain nuclei were very slow and achieve a maximal value after 4-6 hr of postinjection. The binding of [125I]T3 to the isolated brain nuclei of Singi fish was further studied in vitro. Binding was linearly increased with the increasing concentration of the DNA (nuclei). The binding achieved equilibrium between 15 and 20 min at 27 degrees and was stable at least for 1 hr. The binding was reversible in the presence of excess unlabeled T3. Scatchard analysis showed only a single class of binding sites. The mean dissociation constant (Kd) is 2.15 +/- 0.45 x 10(-10) M and maximum binding capacity (MBC) is 0.044 +/- 0.024 pmol/mg DNA. The relative binding affinities of thyroid hormone analogs for T3 sites were as follows: TRIAC greater than T3 greater than TETRAC greater than T4 greater than reverse T3 greater than T2. These findings were similar to those for other animals. Therefore, the nuclear binding sites in Singi fish brain, as demonstrated, may be regarded as thyroid hormone receptors.

Effect of l-triiodothyronine on the mitochondrial α-glycerophosphate dehydrogenase activity, mitochondrial and total protein contents of brain of Singi fish (Heteropneustes fossilis bloch)

A single injection of various doses (0.25, 0.5, 5, 20 and 50 ?g/g) of l-triiodothyronine increased the mitochondrial cytochrome-linked ?-glycerophosphate dehydrogenase (EC 1.1.99.5) activity and mitochondrial protein content of brain of Singi fish on the 3rd day. l-Triiodothyronine at the dose of 0.1 ?g/g did not alter the ?-glycerophosphate dehydrogenase activity and mitochondrial protein content of brain. The total protein content of the brain also increased on the 3rd day with 0.5 ?g of l-triiodothyronine per g. Increased enzyme activity followed a dose-response relationship of a non-linear fashion. The enhancement of the ?-glycerophosphate dehydrogenase activity of fish brain with a dose of 0.5 ?g/g was found from the 1st day and it reached to a maximum level from the 3rd to the 5th day. The enzyme activity then sharply declined on the 6th or 7th day. Cycloheximide inhibited the l-triiodothyronine-induced increase in the ?-glycerophosphate dehydrogenase activity, mitochondrial and total protein content of fish brain. The present study thus reveals the responsiveness of fish brain to thyroid hormone, and ?-glycerophosphate dehydrogenase activity can be taken as a biochemical indices for the expression of thyroid hormone action in fish brain.

Alterations of ion-dependent ATPase activities in the brain of Singi fish, Heteropneustes fossilis (Bloch), by triiodothyronine

The activities of Na+K(+)- and Mg(2+)-ATPases in mitochondrial, microsomal, and cytosolic fractions of Singi fish (Heteropneustes fossilis Bloch) brain were investigated after injections of various doses (0.012, 0.025, 0.05, and 0.10 micrograms/g) of triiodothyronine (T3) for 3 consecutive days. Both ATPases were found in the mitochondrial and microsomal fractions. The cytosolic fraction showed only Mg(2+)-ATPase activity. Mitochondrial Na+K(+)-ATPase activity increased to almost the same level in fish treated with 0.025, 0.05, or 0.10 micrograms of T3/g, while the T3 dose of 0.012 micrograms/g was ineffective in this respect. Microsomal Na+K(+)-ATPase activity increased to about the same level with all of the doses of T3 used. No detectable amount of Na+K(+)-ATPase was found in the brain cytosolic fraction. Mitochondrial Mg(2+)-ATPase activity was enhanced with 0.025, 0.05, and 0.10 micrograms of T3/g. The last dose, however, produced a higher increase in activity than the other two doses. Surprisingly, microsomal and cytosolic Mg(2+)-ATPase activity was not increased by T3 treatment. Although T3 concentrations rose sharply after each T3 injection, the serum T3 level in T3-injected fish was not different from that in the control as observed on the fourth day. The T3-induced rise of Na+K(+)- and Mg(2+)-ATPase activities was inhibited by cycloheximide treatment. Immersion of Singi fishes in thiourea significantly reduced brain Na+K(+)-ATPase activity in microsomal and mitochondrial fractions but decreased Mg(2+)-ATPase activity only in the mitochondrial fraction. Three consecutive daily injections of T3 (0.10 micrograms/g) into the thiourea-treated fishes increased their ATPase activities even beyond the control level.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of NADP-dependent malic dehydrogenase activity in brain of Singi fish, Heteropneustes fossilis (Bloch), by 3,5,3'-triiodothyronine

For elucidation of thyroid hormone-induced responsiveness of fish brain, various doses (0.012, 0.025, 0.05, 0.1, 0.25, 0.5, 1, 2 and 4 ?g/g) of triiodothyronine (T(3)) were injected in Singi fish, Heteropneustes fossilis (Bloch), for 3 consecutive days and the changes in cytosolic NADP-dependent malic enzyme (ME, EC 1.1.1.40) activity in whole brain tissue were determined. Compared to the control, the ME activity increased with lower doses (0.012, 0.025 and 0.05 ?g/g) and decreased with higher doses (1, 2 and 4 ?g/g) of T(3), showing a biphasic nature of thyroid hormone action. The enzyme activity remained unaltered with 0.1, 0.25 and 0.5 ?g of T(3)/g in comparison to the control. Immersion of the fishes in cycloheximide-containing medium (0.5 mg/l) inhibited the T(3) (0.025 ?g/g)-induced rise in ME activity. On the other hand, the NAD-dependent cytosolic malate dehydrogenase (EC 1.1.1.37) activity and the total protein content of brain cytosol remained unaltered with all doses of T(3) used. The thyroid hormone specificity of cytosolic NADP-dependent malic enzyme in fish brain is thus documented.

Effect of thyroxine and thiourea on cholesterol, total lipid and glycogen contents of brain of Singi fish (Heteropneustes fossilis Bloch)

Three consecutive days injections of thyroxine of different doses (1, 2 and 4 ?g/g of body weight) caused significant increase in cholesterol content of cerebrum of Singi fish at 25 degrees C in comparison to the control. The cholesterol content of cerebellum, midbrain and medulla oblongata was enhanced significantly with higher doses of 2 and 4 ?g of thyroxine per g of body weight. The lipid and glycogen contents of whole brain were also found to increase with different doses of thyroxine after three consecutive days injections. These cellular constituents decreased with hypothyroid condition induced by thiourea treatment. The results indicate the thyroid hormonal regulation of lipid and carbohydrate metabolism in brain of Singi fish.

Inhibitory influence of thiourea on brain of Singi fish (Heteropneustes fossilis bloch) and subsequent recovery by L-triiodothyronine

Immersion of Singi fish in thiourea-containing medium (1 mg/ml) for 45 days significantly decreased the cranio-somatic index, weight of different parts of brain, viz. cerebrum, cerebellum, midbrain and medulla oblongata, and also protein and RNA contents of these different regions. The DNA content of these substructures remained unchanged. In other sets of experiment, thiourea treatment for 33 days caused reduction in mitochondrial cytochrome-linked ?-glycerophosphate dehydrogenase (EC 1.1.99.5) activity, and total protein and RNA contents of whole brain, while the amount of mitochondrial protein and total DNA content of whole brain did not undergo significant variation. A single injection of l-triiodothyronine (0.5 ?g/g) enhanced this enzyme activity, mitochondrial protein amount and total protein and RNA contents of whole brain of thiourea-treated fish to almost such levels as obtained by l-triiodothyronine injection in normal (control) Singi fish within 3 days. The CSI in normal fish increased by triiodothyronine injection. In thiourea-treated fish, the reduction of CSI was restored to just control level by triiodothyronine. The results are, therefore, discussed as additional supportive evidence of the responsiveness of fish brain to thyroid hormone.