Chau-Heng Chien

Regulation of thyroid hormones on the production of testosterone in rats

The effects of a thyroidectomy and thyroxine (T4) replacement on the spontaneous and human chorionic gonadotropin (hCG)‐stimulated secretion of testosterone and the production of adenosine 3′,5′‐cyclic monophosphate (cAMP) in rat testes were studied. Thyroidectomy decreased the basal levels of plasma luteinizing hormone (LH) and testosterone, which delayed the maximal response of testosterone to gonadotropin‐releasing hormone (GnRH) and hCG in male rats. T4 replacement in thyroparathyroidectomized (Tx) rats restored the concentrations of plasma LH and testosterone to euthyroid levels. Thyroidectomy decreased the basal release of hypothalamic GnRH, pituitary LH, and testicular testosterone as well as the LH response to GnRH and testosterone response to hCG in vitro. T4 replacement in Tx rats restored the in vitro release of GnRH, GnRH‐stimulated LH release as well as hCG‐stimulated testosterone release. Administration of T4 in vitro restored the release of testosterone by rat testicular interstitial cells (TICs). The increase of testosterone release in response to forskolin and androstenedione was less in TICs from Tx rats than in that from sham Tx rats. Administration of nifedipine in vitro resulted in a decrease of testosterone release by TICs from sham Tx but not from Tx rats. The basal level of cAMP in TICs was decreased by thyroidectomy. The increased accumulation of cAMP in TICs following administration of forskolin was eliminated in Tx rats. T4 replacement in Tx restored the testosterone response to forskolin. But the testosterone response to androstenedione and the cAMP response to forskolin in TICs was not restored by T4 in Tx rats. These results suggest that the inhibitory effect of a thyroidectomy on the production of testosterone in rat TICs is in part due to: 1) the decreased basal secretion of pituitary LH and its response to GnRH; 2) the decreased response of TICs to gonadotropin; and 3) the diminished production of cAMP, influx of calcium, and activity of 17β‐HSD. T4 may enhance testosterone production by acting directly at the testicular interstitial cells of Tx rats. J. Cell. Biochem. 73:554–562, 1999.

Effects of long-term administration of octreotide on sodium retention and atrial natriuretic peptide in carbon tetrachloride-induced cirrhotic rats

BACKGROUND/AIMS To realize the roles of peripheral vasodilatation and atrial natriuretic peptide in the formation of cirrhotic ascites, the effects of long-term administration of octreotide on carbon tetrachloride-induced cirrhotic rats were evaluated. METHODS Urine sodium excretion, hemodynamics, plasma atrial natriuretic peptide levels, renin activities and aldosterone concentrations were compared between cirrhotic and control rats (protocol 1); and between octreotide- (65 micrograms/kg, twice daily for 10 days, subcutaneously) and placebo-treated (5% dextrose) cirrhotic rats (protocol 2). In an in vitro experiment, right atrial tissue of cirrhotic rats was incubated with different concentrations of octreotide to evaluate the release of atrial natriuretic peptide (protocol 3). RESULTS Cirrhotic rats had significantly lower urine sodium excretion and systemic vascular resistance, and significantly higher plasma atrial natriuretic peptide levels, renin activities and aldosterone concentrations than control rats. Compared with placebo-treated cirrhotic rats, octreotide caused increased urine sodium excretion (-10 +/- 4% vs. 13 +/- 8% from baseline values, p < 0.05) and systemic vascular resistance (2.6 +/- 0.1 vs. 3.3 +/- 0.3 mmHg.min.100 g.ml-1, p < 0.05); and decreased plasma atrial natriuretic peptide levels (166.7 +/- 24.8 vs. 234.0 +/- 19.2 pg/ ml, p < 0.05), renin activities (2.45 +/- 0.49 vs. 4.36 +/- 0.53 ng.ml-1.h-1, p < 0.01) and aldosterone concentrations (290.2 +/- 40.0 vs. 483.3 +/- 82.6 pg/ml, p < 0.05). In the in vitro experiment, right atrial release of atrial natriuretic peptide of cirrhotic rats was not significantly changed when incubated with different concentrations of octreotide. CONCLUSIONS Octreotide ameliorates renal sodium retention and suppresses plasma levels of atrial natriuretic peptide of ascitic cirrhotic rats with a novel mechanism via, at least partly, the modification of peripheral vascular resistance.

Non-genomic rapid inhibition of Na+/H+-exchange 1 and apoptotic immunosuppression in human T cells by glucocorticoids.

Glucocorticoids (GCs) have been employed as immunosuppressive agents for many years. However, it is still unclear how GCs instantly uncouple T cells from acute stressful inflammatory. In terms of time scale, the genomic activity of the classic GC receptor cannot fulfill this role under crisis; but a rapid non‐genomic response can. In a previous study, intracellular acidification was found to be due to a rapid non‐genomic inhibition of Na+/H+‐exchange 1 (NHE1) and this event led to the immunosuppression of T cell proliferation by progesterone. The aim of this study was to examine whether there is a rapid acidification response caused by an inhibition of NHE1 activity and to explore the differential non‐genomic effect on immunosuppression of hydrocortisone and dexamethasone. The IC50 values for NHE1‐dependent pHi recovery by hydrocortisone and dexamethasone are 250 and 1 nM, respectively. Co‐stimulation of GCs with phytohemagglutinin (PHA) is able to inhibit PHA‐induced IL‐2 secretion, IL‐4 secretion, and T‐cell proliferation. Furthermore, apoptosis in PHA‐activated T cells is not induced by hydrocortisone but by dexamethasone. The mechanism of immunosuppression on proliferation by dexamethasone was found to be different of hydrocortisone and seems to involve cytotoxicity against T cells. Moreover, apoptosis induced by dexamethasone and impermeable dexamethasone–bovine serum albumin suggests that the apoptotic immunosuppression occurs through both the plasma membrane and cytoplasmic sites. The rapid inhibitory responses triggered by GCs would seem to release T cells instantly when an acute stress‐related response is needed. Nonetheless, the apoptotic immunosuppression by dexamethasone is attributable to its severe cytotoxicity. J. Cell. Physiol. 223:679–686, 2010.

Interrelationship between Thyroxine and Estradiol on the Secretion of Thyrotropin-Releasing Hormone and Dopamine into Hypophysial Portal Blood in Ovariectomized-Thyroidectomized Rats

Effects of thyroxine (T4) on the secretion of thyrotropin-releasing hormone (TRH) and catecholamines into hypophysial portal blood and on the concentrations of arterial plasma thyroid-stimulating hormone (TSH) and prolactin (PRL) in ovariectomized and thyroidectomized (Ovx-Tx) rats were studied. Immediately after ovariectomy, rats were Tx or sham Tx. The Ovx-Tx rats were injected subcutaneously with estradiol benzoate (EB, 0.5 microgram/kg b.w.) or sesame oil, and T4 (20 micrograms/kg b.w.) or saline once daily for 2 weeks. The Ovx rats with intact thyroid gland were injected with saline and oil only. The hypophysial portal blood samples were collected and mixed with or without 2,3-dimercaptopropanol before extraction by methanol or perchloric acid, respectively. The femoral arterial blood was also collected. The concentrations of TRH in methanol-extracted portal plasma and that of TSH and PRL in arterial plasma were measured by radioimmunoassay. The concentrations of catecholamines in perchloric acid-extracted portal plasma samples were measured by radioenzymatic assay. Thyroidectomy in Ovx rats resulted in an increase in portal plasma TRH and arterial plasma TSH. Despite the presence or absence of estradiol, T4 replacement in Ovx-Tx rats decreased portal plasma TRH and arterial plasma TSH to euthyroid levels. Combination of the injection of T4 and EB in vivo caused significantly decreased levels of portal plasma dopamine and increased arterial plasma PRL compared with those in vehicle-injected Ovx-Tx animals. Concentrations of neither norepinephrine nor epinephrine in hypophysial portal plasma paralleled the altered concentrations of PRL or TSH in arterial plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Bacterial lipopolysaccharide activates protein kinase C, but not intracellular calcium elevation, in human peripheral T cells

The increase of intracellular free calcium concentration ([Ca2+]i) and protein kinase C (PKC) activity are two major early mitogenic signals to initiate proliferation of human peripheral T cells. Bacterial lipopolysaccharide (LPS) is nonmitogenic in human T cells. However, in the presence of monocytes, LPS becomes mitogenic to proliferate T cells. The aim of this study was to define the incompetency of LPS on two mitogenic signals in human peripheral T cells. T cells were isolated from human peripheral blood. [Ca2+]i and pHi were determined by loading the cells with the fluorescent dyes, Fura‐2 acetoxymethyl ester (Fura‐2/AM) and 2′,7′‐bis(2‐carboxyethyl)‐5‐(and 6)carboxyfluorescein acetoxymethyl ester (BCECF/AM). PKC activity was determined by protein kinase assay and cell proliferation was estimated from the incorporation of [3H]‐thymidine. The results indicated that (1) LPS (10 μg/ml) stimulated PKC activity significantly within 5 min, reached a plateau at 30 min, and maintained that level for at least 2 h; and (2) LPS stimulated cytoplasmic alkalinization but did not affect the levels of [Ca2+]i and [3H]‐thymidine incorporation into T cells. Moreover, the combination of calcium ionophore A23187 with LPS significantly stimulated [3H]‐thymidine incorporation into T cells. Thus, the results demonstrate that LPS failed to proliferate T cells, probably because of a lack of the machinery necessary to stimulate the mitogenic signal on [Ca2+]i elevation. J. Cell. Biochem. 76:404–410, 2000.

Comparison of Different Ascitic Fluid Collection Methods for the Diagnosis of Spontaneous Bacterial Peritonitis in Cirrhotic Rats

To test for the best method of collecting ascitic fluid for the diagnosis of spontaneous bacterial peritonitis, carbon tetrachloride was administered in 120 rats for 6-18 weeks to induce infected cirrhotic ascites. Only 58 cirrhotic rats survived with ascitic fluid ≥3 ml for cell counts and cultures. These rats were randomly divided into 4 groups to compare the methods of ascitic fluid collection: group A, paracentesis; group B, direct laparotomy; group C, rapid decapitation followed by laparotomy; and group D, the intubation method. In 13 rats in which paracentesis was performed, ascitic fluid ≥3 ml was only successfully withdrawn in 7 rats and the amount of ascitic fluid was much less than they really had. Among 52 cirrhotic rats from which ascitic fluid was successfully withdrawn, 10 had infected ascites and 42 had sterile ascites. Of 42 rats with sterile cirrhotic ascites, ascitic fluid red cell counts were significantly greater in group B (3.88±4.12xl0^5cells/mm^3) than in group A (0.14±0.31x10^5cells/mm^3, p＜0.01), C (0.18±0.l9xl0^5cells/mm^3, p＜0.01) orD (0.12±0.1410^5cells/mm^3, p＜0.01). Ascitic fluid neutrophil counts and ratio were significantly greater in group B(1667±2336cells/mm^3, 15.0±19.3%) than in group C (76±103cells/mm^3, 4.2±3.0%, p＜0.05)orD (36±33 cells/mm^3, 3.8±2.8%, p＜0.05). Of 42 rats with sterile cirrhotic ascites, ascitic fluid neutrophil counts were greater than 250 cells / mm^3 in 0, 6, 1 and 0 of group A, B, C and D (p ＜0.01), respectively; and greater than 500 cells/mm^3 in 0, 5, 0and 0 (p＜0.0l). In conclusion, rapid decapitation followed by laparotomy and the intubation method are the two best methods in collecting ascitic fluid for the rat model of spontaneous bacterial peritonitis. Since blood specimens obtained from rapid decapitation followed by laparotomy are not aseptic, the intubation method may be the best way for further experiments when simultaneous collection of aseptic blood and ascitic fluid specimens is needed.