Biomedical subjects

W W Dickhoff

Publications and source records attributed to W W Dickhoff.

54 records · Page 3Linked to original sources

PubMed1987

Nuclear receptors for L-triiodothyronine in trout erythrocytes.

We have developed an in vitro assay to evaluate saturable specific binding of triiodothyronine (T3) by erythrocyte (RBC) nuclei isolated from rainbow trout. Our results indicate that the nuclei contain a T3-saturable protein which binds T3 with temperature, and pH dependency, high T3 affinity (Ka = 1.6 X 10(9) M-1), and relative thyroid hormone (TH) analog affinities (TRIAC greater than T3 greater than T4 greater than rT3 greater than T2) which are characteristic of TH receptors in other vertebrates. Our estimate of the maximal T3 binding capacity (MBC) of nuclei isolated from heterogeneous populations of RBCs at different maturational stages (MBC = 3.6 fM/mg DNA; 13 sites/nucleus) was 10-100 times lower than would be expected of a TH-responsive tissue. Differential cell counts revealed that 1% of the RBCs in our trout were immature (pro-RBCs). Pro-RBCs, in contrast to mature RBCs, contain abundant heterochromatin, mitochondria, and polyribosomes, and synthesize hemoglobin. Evaluation of binding data for RBC nuclei taken from trout in which erythropoiesis was stimulated by prior bleeding indicated that MBC was directly proportional to the absolute number of pro-RBC nuclei in the incubation. Our maximum estimate of MBC for pro-RBC nuclei (458 fmol/mg DNA; 1781 sites/nucleus) falls within the range of MBC values reported for other vertebrate TH-responsive tissues. These data indicate that RBCs of rainbow trout contain a nuclear protein (putative receptor) which binds T3 with characteristics similar to the TH receptor of higher vertebrates, and that nuclear T3 binding may be diminished during RBC maturation.

Animals↗

PubMed1985

The effects of estradiol and triiodothyronine on protein synthesis by hepatocytes of juvenile coho salmon (Oncorhynchus kisutch).

A method was developed for studying the in vitro metabolism of radiolabeled amino acids by dispersed salmon hepatocytes. Radioactivity accumulated in trichloroacetic acid (TCA)-precipitable and -soluble fractions of cells and in TCA-precipitable fractions of incubation medium was measured. Estradiol (E2) or triiodothyronine (T3) stimulated the amount of radioactivity in the TCA-precipitable fraction of cells in a dose-dependent manner. T3 caused an increase in TCA-soluble radioactivity of cells that were incubated with [14C]serine, [14C]glycine or the nonmetabolizable amino acid [14C]cycloleucine. E2 had either no effect or caused a decrease in TCA-soluble radioactivity in cells that were incubated with [14C]serine or [14C]glycine. E2 increased TCA-soluble radioactivity in cells that were incubated with [14C]cycloleucine. E2 but not T3 caused an increase in TCA-precipitable radioactivity in the medium from incubation of hepatocytes with metabolizable radioactive amino acids. These results suggest that protein metabolism by salmon hepatocytes is stimulated by both E2 and T3 with differing kinetic patterns.

Animals↗

PubMed1985

Changes in the hemoglobin system of the coho salmon Oncorhynchus kisutch during smoltification and triiodothyronine and propylthiouracil treatment.

Three electrophoretically separable forms of blood hemoglobin were found in fry of coho salmon (Oncorhynchus kisutch). Ten hemoglobin forms were found in juvenile and adult salmon. Treatment of yearling salmon with triiodothyronine (T3) at 12 ppm in the diet accelerated the increase in concentration of adult forms of hemoglobin, while treatment with T3 at 4 ppm had no effect. Dietary propylthiouracil (1.5 or 5 mg/g) reduced the increases in adult forms of hemoglobin during smoltification. These results implicate thyroid hormones in the expression of adult forms of hemoglobin during the parr to smolt transformation of juvenile salmon.

Aging↗

PubMed1984

Increases in plasma melatonin titers accompanying seawater adaptation of coho salmon (Oncorhynchus kisutch).

Plasma melatonin (MT) concentrations were measured in coho salmon using a radioimmunoassay validated for that species. Plasma MT remained constant in juvenile salmon during the parr to smolt transformation in fresh water. However, upon seawater entry plasma MT concentrations increased significantly, peaked at approximately 24 hr, then returned to levels observed for the fish in fresh water.

Adaptation, Physiological↗

PubMed1984

A study of triiodothyronine-catecholamine interactions: their effect on plasma fatty acids in Pacific hagfish Eptatretus stouti.

Plasma circulating levels of fatty acids (PFA) were measured in intact and in triiodothyronine (T3)-treated Pacific hagfish Eptatretus stouti. Intraperitoneal injection of both pharmacological (200 ng/g) and physiological (1 ng/g) doses of T3 caused an elevation of PFA 24 and 48 hr after treatment. The implantation of capsules containing the antithyroid compound, 6-propylthiouracil (6-PTU) decreased PFA levels. Twenty-four hr after T3-injection the norepinephrine (NE) content of plasma declined, whereas epinephrine (E) titres increased. Forty-eight hr after T3-treatment the mean titres of dopamine (D) and NE were lower than in the control group of hagfish. The treatment of hagfish with E in either pharmacological (2-3 micrograms/g) or physiological (2-3 ng/g) doses did not cause any elevation of PFA during the 72 hr following injection. In the same experiment the high dose of E induced long-lasting hyperglycemia, whereas the low dose had no substantial effect on glycemic levels. The data provide evidence that in hagfish, unlike in higher animals, the observed lipolytic effect of administered T3 is not mediated through the potentiation of the fat mobilizing action of catecholamines.

Animals↗

PubMed1984

The effect of insulin on amino acid metabolism and glycogen content in isolated liver cells of juvenile coho salmon, Oncorhynchus kisutch.

Amino acid transport and [14C]leucine incorporation into liver proteins as well as the secretion of proteins into incubation medium were studied in liver cells isolated from coho salmon (Oncorhynchus kisutch) parr. Pink salmon (Oncorhynchus gorbuscha) or mammalian (bovine) insulin caused a significant increase in TCA-precipitable radioactivity from both cells and incubation medium. The effects appeared at insulin concentration of 10(-8) M with a maximal response at 5 X 10(-8) M. The radioactivity of the TCA-soluble fraction was not changed by insulin. Insulin increased the amount of the non-metabolized amino acid [14C]cycloleucine, in the TCA-soluble fraction of hepatocytes. The glycogen content of hepatocytes was increased in the presence of insulin at 10(-9) M but was not changed from the control value in the presence of insulin at 10(-8) M.

Amino Acids↗

PubMed1983

Plasma thyroid hormones in cyclostomes: do they have a role in regulation of glycemic levels?

Plasma levels of thyroxine (T4) and triiodothyronine (T3) were measured by radioimmunoassay in intact Pacific lamprey (Entosphenus tridentatus) undergoing the period of natural fasting and in Pacific hagfish (Eptatretus stouti) maintained unfed in the laboratory. Plasma T3 levels in both lamprey and hagfish were always severalfold lower than T4 levels. The influence of thyroid hormones on glycemic level was studied following intraperitoneal injection of T4 or T3 (13-20 micrograms/100 g body wt), as well as after implantation of sealed Silastic capsules containing the goitrogen, 6-propylthiouracil (6-PTU), or after intraperitoneal injections of an antithyroglobulin serum (ATgS) exhibiting both anti-T4 and anti-T3 activities. Measured plasma T4 and T3 levels after hormonal injection were extremely high and could be considered pharmacological. The 6-PTU treatment decreased plasma levels of both T4 and T3 within several weeks. The glycemic levels in lampreys and hagfish after thyroid hormone treatment were lower than in control animals, whereas in animals treated with either 6-PTU or ATgS, hyperglycemic levels prevailed. It is concluded that thyroid hormones, possibly acting with other hormones, may participate in the maintenance of glycemic levels in cyclostomes and that their action is to reduce glycemic levels.

Animals↗

PubMed1982

Comparison of thyroid hormone binding to heptic nuclei of the rat and a teleost (Oncorhynchus kisutch).

A modified T3 binding assay was used with coho salmon liver nuclei. Purified nuclei were incubated with [125I]T3 (or [125I]T4), nonradioactive thyroid hormone, or thyroid hormone analog. Bound hormone was separated from hormone by use of polyethylene glycol. Salmon liver nuclei specifically bound T3 with a high affinity [Ka = 1.031 +/- 0.174 x 10(9) M-1 (mean +/- SE); n = 12] which was 50% of the affinity measured with rat liver nuclei using the same assay. Salmon nuclear T3-binding capacity was 0.127 +/- 0.035 pmol T3/mg DNA (n = 7). Rat liver nuclear capacity for T3 binding was 3.4-fold greater than in salmon liver nuclei. T3 binding to salmon liver nuclei was greater than to nuclei from salmon brain; T3 binding to salmon spleen nuclei was low. Binding competition studies with hormone analogs indicated that binding to the salmon nuclei was dependent on molecular structure. These data indicate that the T3 binding to salmon nuclei may be due to T3 receptor activity. Analysis of Scatchard plots showed that the affinity of salmon hepatic nuclei for T3 is 10-fold greater than the affinity for T4. Reciprocal binding competition experiments with T3 and T4 indicate that both hormones bind to the same site. This suggests that in salmon, as in mammals, the liver nuclei predominantly bind thyroid hormones at T3-binding sites. Hepatic nuclei of human, rat, chick embryo, amphibian larva, and salmon have similar affinities for thyroid hormones and similar relative affinities for several thyroid hormone analogs, suggesting that the receptor molecule has been highly conserved during evolution.

Animals↗

PubMed1981