Butyl benzyl phthalate, an endocrine disrupter, inhibits pulsatile luteinizing hormone secretion under an insulin-induced hypoglycaemic state in ovariectomized rats

Alteration of sex hormone levels and steroidogenic pathway by several low molecular weight phthalates and their metabolites in male zebrafish (Danio rerio) and/or human adrenal cell (H295R) line

Low molecular weight phthalates, such as diethyl phthalate (DEP), benzyl butyl phthalate (BBzP), or diisobutyl phthalate (DiBP), are suspected to disrupt endocrine system. However, their adverse effects on sex steroid hormones and underlying mechanisms are not well-documented. The aim of this study is to investigate the effects of major low molecular weight phthalates (LMWPs), i.e., DEP, BBzP, and DiBP, and their hydrolytic metabolites, on sex steroid hormone system, employing male zebrafish and/or a human adrenocortical carcinoma (H295R) cell. In male zebrafish, 14-day exposure to DEP, BBzP, or DiBP significantly decreased testosterone (T) concentrations. All test compounds significantly up-regulated cyp19a gene expression, and down-regulated star and 3β hsd genes in the male fish. In H295R cell, all test compounds except monoisobutyl phthalate (MiBP) reduced T concentrations and increased E2/T ratio. Gene expression changes in H295R cell, e.g., significant down-regulation of StAR gene and up-regulation of CYP19A gene, supported depressed synthesis of sex hormones in the adrenal cell. Our results show that not only DEP, BBzP, and DiBP, but also their hydrolytic metabolites disrupt sex hormone balances through modulating key steroidogenic genes in the human adrenal cells and in zebrafish.

Effects of p-nonylphenol and 4-tert-octylphenol on the anterior pituitary functions in adult ovariectomized rats

p-Nonylphenol (NP) and 4-tert-octylphenol (OP) are known to mimic the action of estrogens as endocrine disruptors. However, their acute effects on the pituitary and the hypothalamus functions in vivo have been uncertain. We therefore determined their effects on the anterior pituitary, in particular, gonadotropin secretion. Two weeks after ovariectomy, the rats were given a subcutaneous injection of 10 mg NP, 10 mg OP, 10 mg bisphenol A, 1 microg 17beta-estradiol, or sesame oil alone as control. Twenty-four hours after the treatment, the expression of progesterone receptor mRNA in the anterior pituitary and the level of luteinizing hormone (LH), follicle-stimulating hormone, and prolactin were determined. The expression of progesterone receptor mRNA in the anterior pituitary was significantly increased by either NP, OP, bisphenol A, or estradiol, but bisphenol A was less effective. The level of LH was significantly decreased by either NP or OP, but not by bisphenol A and estradiol. Only estradiol significantly increased the level of prolactin. The level of follicle-stimulating hormone was unchanged by any of the treatments. To check the effects of NP and OP on pulsatile LH secretion, blood samplings were done at 6-min intervals for 3 h. Twenty-four hours after treatment in ovariectomized adult rats, we found that the injection of NP significantly decreased the amplitude of LH pulses and the mean LH concentrations, but not the frequency of LH pulses. The injection of OP significantly decreased the mean LH concentrations without affecting the frequency and amplitude of the LH pulses. Finally, the rats given an injection of NP or sesame oil were intravenously injected with 50 ng of gonadotropin-releasing hormone (GnRH) to check whether NP affected the LH secretory responsiveness of the anterior pituitary to GnRH. We found that the responsiveness to GnRH in NP-injected rats was significantly attenuated compared to the sesame oil-injected rats. The present study suggests that NP, even with a single injection, suppresses the pulsatile LH secretion in adult ovariectomized rats, probably by affecting the anterior pituitary level.

Determination of three phthalate metabolites in human urine using on-line solid-phase extraction-liquid chromatography-tandem mass spectrometry

An on-line solid-phase extraction-liquid chromatography-tandem mass spectrometry (on-line SPE-HPLC-MS/MS) method was developed for the analysis of metabolites of three phthalate esters in human urine at the low nanogram per milliliter level. The recoveries were above 84.3% and relative standard deviations varied from 0.8 to 4.8%. The compounds along with their deuterated internal standards were detected in the negative ion mode by selective reaction monitoring and the accuracy of the method was improved by isotope dilution. Monobutyl phthalate was detected with median level of 22.5 ng/ml. The median levels for monobenzyl phthalate and monoethylhexyl phthalate were less than the limit of quantitation (LOQ). The on-line SPE-HPLC-MS/MS method allowed the possibility of determining these metabolites within a short time, with increased sensitivity and by using decreased amounts of sample and solvent.