Kai-Lee Wang

Differential effects of nonylphenol on testosterone secretion in rat Leydig cells

Nonylphenol (NP), a final metabolite of nonylphenol polyethoxylate, has been reported to interfere with male reproduction. However, its mechanisms are not fully understood. In the present study, we examined the effects of NP on steroidogenesis of testosterone in rat Leydig cells. The testosterone concentrations in rat plasma were examined after intravenous injection of NP (100 microg/kg) at different time intervals. In addition, rat Leydig cells were challenged with different concentrations of NP (4.25-127.5 microM) to evaluate its influences on testosterone steroidogenesis. Administration of NP showed a decrease of hCG-induced plasma testosterone. Moreover, in vitro experiments revealed that NP (127.5 microM) alone stimulated testosterone release through increase of both protein levels and activities of the StAR and P450(SCC). In contrast, NP inhibited hCG-induced testosterone release in rat Leydig cells. The inhibitory effect was also observed after incubation of the Leydig cells in the presence of different precursors. These results suggested that NP had differential effects on testosterone synthesis.

Effects of Oral Nonylphenol on Testosterone Production in Rat Leydig Cells

Nonylphenol (NP) is the final metabolite of nonyphenol polyethoxylate (NPE), a non-ionic surfactant which is frequently incorporated into detergent and pesticide formulation. This metabolite has a structure mimicking 17β-estradiol and has been reported to have xenoestrogenic effects, to affect the endocrine system. However, its effects on testosterone release are still obscure. In the present study, we investigated the influence of NP by oral gavage or delivering via spray on testosterone release in vivo. Rat Leydig cells were prepared by enzymatic dispersion and then percoll density gradient centrifugation. Testosterone levels in the media were measured by radioimmunoassay. The data showed that oral administration of NP (100μg/kg) once per day for 30 days inhibited steroidogenesis of testosterone in rat Leydig cells. On the contrary, administration of NP via spray did not affect steroidogenesis of testosterone. In the in vivo experiments, administration of NP by oral ingestion decreased plasma testosterone concentrations in response to human chorionic gonadotropin (hCG, 5 IU/ml). Furthermore, oral NP induced a significant inhibition on the release of testosterone in vitro in response to hCG, 8-bromo-cyclic adenosine monophosphate (8-Br-cAMP), and forskolin. Moreover, administration of NP also caused a decrease on testosterone release in response to androstenedione. The in vitro experiments revealed that oral NP at a dose of 100μg/kg/day suppressed testosterone biosynthesis by inhibiting the activity of 17β-hydroxysteroid dehydrogenase (17β-HSD) and cyclic AMP pathway in Leydig cells. These results suggested that oral administration of NP inhibited steroidogenesis of testosterone in rat Leydig cells, at least in part, due to an inhibitors effect on the cAMP pathway and 17β-HSD activity.

Effects of acrolein on aldosterone release from zona glomerulosa cells in male rats

A positive correlation between smoking and hypertension has been well established. Acrolein is a major toxic volatile compound found in cigarette smoke. Human exposure to low levels of acrolein is unavoidable due to its production in daily activities, such as smoke from industrial, hot oil cooking vapors, and exhaust fumes from vehicles. The toxicity and the action mechanism of acrolein to induce apoptosis have been extensively studied, but the effects of acrolein on hypertension are still unknown. The present study aimed to examine the effects of acrolein on aldosterone release both in vivo and in vitro. Male rats were divided into three groups, and intraperitoneally injected with normal saline, or acrolein (2mg/kg) for 1 (group A-1) or 3 (group A-3) days, respectively. After sacrificing, rat blood samples were obtained to measure plasma aldosterone and angiotensin II (Ang II) levels. Zona glomerulosa (ZG) cells were prepared from rat adrenal cortex, and were incubated with or without stimulants. We found that the serum aldosterone was increased by 1.2-fold (p<0.05) in A-3 group as compared to control group. Basal aldosterone release from ZG cells in A-3 group was also increased significantly. Moreover, acrolein enhanced the stimulatory effects of Ang II and 8-bromo-cyclic AMP on aldosterone secretion from ZG cells prepared in both A-1 and A-3 groups. Furthermore, the enzyme activity of P450scc, the rate-limiting step of aldosterone synthesis, was elevated after acrolein injection. Plasma level of Ang II was increased in both A-1 and A-3 groups. These results suggested that acrolein exposure increased aldosterone production, at least in part, through elevating the level of plasma Ang II and stimulating steroidogenesis pathways.

Adaptation of Testosterone Production in Response to Low-Dose Effects of Nonylphenol

Nonylphenol (NP) is a non-ionic surfactant that is used widely as an industrial detergent. We have found that NP impairs male reproductive functions in vitro. However, the in vivo effects of NP on testosterone release at environmentally relevant doses remain unclear. Male rats were exposed to a low-dose of NP by oral gavage at 10 and 100 μg/kg body weight daily for 3-7 days. After 7 days of NP exposure, plasma testosterone level was significantly higher in higher NP exposure group than in the vehicle group. Higher basal testosterone release was found in the Leydig cells obtained from the rats treated with NP for 7 days. Additionally, evoked testosterone release was also higher after treating Leydig cells with human chorionicgonadotropin, 8-bromo-adenosine cyclic monophosphate, or forskolin. The expression of steroidogenic acute regulatory protein (StAR) was also increased by 40% in oral NP group. In contrast, the stimulatory effects were absent in Leydig cells treated with various steroid precursors. The stimulatory effects of NP were abolished after administration with intracellular calcium, EGFR and ERK blockers, which were well known to stimulate StAR activation. These results suggest that NP at an environmentally relevant dose could stimulate plasma testosterone level.

Effect of Swimming on the Production of Aldosterone in Rats

It has been demonstrated that exercise is one of the stresses known to increase the aldosterone secretion. Both potassium and angiotensin II (Ang II) levels are shown to be correlated with aldosterone production during exercise, but the mechanism is still unclear. In an in vivo study, male rats were catheterized via right jugular vein (RJV), and divided into four groups namely water immersion, swimming, lactate infusion (13 mg/kg/min) and pyruvate infusion (13 mg/kg/min) groups. Each group was treated for 10 min. Blood samples were collected at 0, 10, 15, 30, 60 and 120 min from RJV after administration. In an in vitro study, rat zona glomerulosa (ZG) cells were challenged by lactate (1–10 mM) in the presence or absence of Ang II (10−8 M) for 60 min. The levels of aldosterone in plasma and medium were measured by radioimmunoassay. Cell lysates were analyzed by immunoblotting assay. After exercise and lactate infusion, plasma levels of aldosterone and lactate were significantly higher than those in the control group. Swimming for 10 min significantly increased the plasma Ang II levels in male rats. Administration of lactate plus Ang II significantly increased aldosterone production and enhanced protein expression of steroidogenic acute regulatory protein (StAR) in ZG cells. These results demonstrated that acute exercise led to the increase of both aldosterone and Ang II secretion, which is associated with lactate action on ZG cells and might be dependent on the activity of renin-angiotensin system.