Effect of glucose on the insulin production and insulin binding of Tetrahymena

As the unicellular ciliate, Tetrahymena has insulin receptors and produces insulin itself, which can regulate its glucose metabolism and other cell functions, in the present experiments the feed-back, the effect of glucose on the insulin binding and insulin production was studied. The cells were kept partly in tryptone-yeast medium, partly in Losina salt solution. The duration of treatment (in 0.1, 1.0, 10.0 mg/ml glucose) in the binding study was 10 min, in the hormone production study 30 min. FITC-insulin binding was significantly decreased only by 0.1 mg/ml glucose treatment in medium and by 10 mg/ml glucose in salt. The insulin production was significantly lower only in cells treated with 10 mg/ml glucose in medium. The insulin binding in salt was always higher and the insulin production always lower, than in medium. Earlier results demonstrated that the hormonal system (presence of hormones, receptors and signal pathways) of higher ranked animals can be deduced to a unicellular level, however, the feed-back mechanism is not really present here, only the traces can be observed in these protozoa.

The hormonal system of the unicellular Tetrahymena: a review with evolutionary aspects

The unicellular ciliate, Tetrahymena has receptors for hormones of the higher ranked animals, these hormones (e.g. insulin, triiodothyronine, ACTH, histamine, etc.) are also produced by it and it has signal pathways and second messengers for signal transmission. These components are chemically and functionally very similar to that of mammalian ones. The exogenously given hormones regulate different functions, as movement, phagocytosis, chemotaxis, cell growth, secretion, excretion and the cells' own hormone production. The receptors are extremely sensitive, certain hormones are sensed (and response is provoked) at 10-21 M concentration, which makes likely that the function could work by the effect of hormones produced by the Tetrahymena itself. The signal reception is selective, it can differentiate between closely related hormones. The review is listing the hormones produced by the Tetrahymena, the receptors which can receive signals and the signal pathways and second messengers as well, as the known effects of mammalian hormones to the life functions of Tetrahymena. The possible and justified role of hormonal system in the Tetrahymena as a single cell and inside the Tetrahymena population, as a community is discussed. The unicellular hormonal system and mammalian endocrine system are compared and evolutionary conclusions are drawn.

Thyrotropin (TSH) regulates triiodothyronine (T3) production in the unicellular Tetrahymena

The aim of the experiments was to study the regulation of triiodothyronine (T3) production in the unicellular Tetrahymena. Untreated and troph-hormone treated specimen were prepared and in different timepoints T3 content was measured and compared by immunocytochemical flow cytometry. 0.1 or 0.001 IU TSH in tryptone-yeast medium stimulated T3 synthesis at 10, 20, 30 min, but does not stimulate after 1 h. The overlapping gonadotropic hormone (GTH) also did it, however only at 10 min. In Losina salt solution (physiological for Tetrahymena) the effect was weaker, however outer amino acid source was not absolutely needed for the production of the hormone. The results show that the TSH regulation of thyroid hormone synthesis (storage, secretion) and troph-hormone overlap can be deduced to a unicellular level. This may allow the hypothesis that the endocrine mechanisms proved at a low level of phylogeny are preserved for the higher ranked organisms.

Effect of different concentrations of serotonin, histamine and insulin on the hormone (serotonin and ACTH) production of Tetrahymena in nutrient-free physiological milieu

Cell populations of Tetrahymena pyriformisGL were kept in nutrient-free (Losina) milieu and treated with different (10(-6)-10(-21)M) concentrations of serotonin, histamine or insulin for 30 min. Following that the hormone (serotonin and adrenocorticotropin (ACTH) content of the cells were measured by immunocytochemical flow cytometric method. Serotonin reduced histamine when applied in 10(-12) and 10(-15)M concentrations, while elevated ACTH levels when applied in 10(-6), 10(-9) and 10(-21)M concentrations. Histamine reduced serotonin concentration at 10(-9)-10(-21)M concentrations and increased ACTH in 10(-6)M. Insulin elevated both hormones' content in each concentration except at 10(-12)M. The results demonstrate that (1) in nutrient-free conditions the hormonal effects differ from that of nutrient-rich (tryptone+yeast) condition; (2) there is an optimal hormone concentration, which causes the strongest effect and this is different for each hormones; (3) the hormone receptors of Tetrahymena are very sensitive; as they react to zeptomolar concentrations. Such small concentration is even more effective than higher ones. Since hormones must become highly diluted in the natural environment of Tetrahymena, it seems that such low concentrations are the actual physiological concentrations.

Investigations on the triiodothyronine (T3)-specificity of thyrotropic (TSH) and gonadotropic (HCG) hormone in the unicellular Tetrahymena

In a previous experiment thyrotropin (TSH) increased the triiodothyronine (T3) production of Tetrahymena and chorionic gonadotropin (HCG) moderately overlapped the effect. At present the production of three amino acid type (histamine, serotonin, epinephrine) and one peptide (endorphin) hormones were studied under the effect of TSH or HCG, in tryptone-yeast (TY) or salt (Losina-Losinsky) medium. The duration of the effect was 10 min. TSH significantly (with almost 20%) decreased epinephrine production in TY medium and HCG similarly decreased epinephrine and increased histamine level. In salt solution TSH as well as HCG decreased the level of serotonin. The results show that at this low level of phylogeny TSH effect is not completely thyroxine-specific, however it is not general. HCG overlaps TSH effect on epinephrine and serotonin production, however its effect is broader. The experiments also demonstrate that the effect of pituitary trop-hormones can be bidirectional in Tetrahymena, as histamine level was increased and epinephrine level was decreased by HCG, in the same cells.

Hormonal effects on Tetrahymena: change in case of combined treatment

In order to approach their natural conditions, populations of Tetrahymena were kept in Losina-Losinky's salt solution for 1 h, than in the tryptone+yeast medium. During this time they were treated with histamine, serotonin or insulin, or with the combinations of these hormones. Effect of the combined treatments on the production of serotonin (5HT), or adrenocorticotropic hormone (ACTH) or triiodothyronine (T₃) by the cells was compared to the effect of single-hormone treatments. Significant differences were seen between the results obtained following the single or combined treatments. There was no summation of the effects, however an elevation or diminution of the hormone production was observed after the combined treatment, as compared with the untreated controls or with the use of one of the hormones in the samples. The experiments demonstrate that there is a hormonal regulation between the Tetrahymena cells and the hormones influence each other's effect.