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Endocrine Disruptors and Male Infertility
Published in Rajesh K. Naz, Endocrine Disruptors, 2004
Suresh C. Sikka, Muammer Kendirci, Rajesh Naz
Steroid hormones do not appear to be stored intracellularly within membranous secretory granules. For example, testosterone is synthesized by the Leydig cells of the testis and released on activation of the LH receptor. Thus, compounds that block the LH receptor or the activation of the 3′,5′-cyclic AMP-dependent cascade involved in testosterone biosynthesis can rapidly alter the secretion of this hormone. The release of many protein hormones is dependent on the activation of second messenger pathways, such as cAMP, phosphatidylinositol 4, 5-bisphosphate (PIP2), inositol 1, 4, 5-trisphosphate (IP3), tyrosine kinase, and Ca++. Interference with these processes consequently will alter the serum levels (availability) of many hormones. Several metal cations have been shown to disrupt pituitary hormone release, presumably by interfering with Ca++ flux.63
Phosphatidylinositol and inositolphosphatide metabolism in hypertrophied rat heart
Published in H. Saito, Y. Yamori, M. Minami, S.H. Parvez, New Advances in SHR Research –, 2020
Hideaki Kawaguchi, Akira Kitabatake
Inositol 1, 4, 5-trisphosphate kinase activity. The assay for IP3 kinase activity was performed according to published methods (Irvinet al., 1986). Assays were performed at 37°C in a final volume of 200 ml and initiated by the addition of 100 mg of cytosolic protein. The reaction buffer contained 1 mM of [3H]inositol 1,4,5-trisphosphate (a preliminary experiment revealed a Vmax of 2.2 nmol/min/mg cytosolic protein, and a Km of 1 mM), 50 mM Tris-malate pH7.0, 10 mM ATP, 20 mM MgCl2, 5 mM 2, 3-diphosphoglycerate (2, 3-DPG; this concentration of 2, 3-DPG inhibited the dephosphorylation of IP3 and IP4 by 98%), 10 mM Ca2+. Ca2+ concentration in buffer was determined by prebiously reported method (Renard and Poggioli, 1987). Incubation was carried out for 2 min at 37°C. The reaction was terminated by the addition of 0.5 ml of 15% ice-cold trichloroacetic acid (TCA) and 0.1 ml of 5% bovine serum albumin (BSA), after which TCA was removed by four diethylether washes and the mixture neutralized with NH3. Inositol monophosphate, IP2, IP3 and IP4. were separated by elution from AG 1-X 8 columns in formate form (100-200 mesh; Bio-Rad) by a gradient of ammonium formate (0.2-1.2 M) plus 0.1 M formic acid (Downes et al., 1986; Merritt et al., 1986). For a more detailed analysis, including the separation of inositol phosphate isomers, samples were filtered and separated by high performance-liquid chromatography (Whatman Partisil 10 SAX anion-exchange column with a guard column) with a gradient of ammonium formate and phosphate (Batty et al., 1985; Hawkins et al., 1986).
Oxytocin modulates steroidogenesis-associated genes and estradiol levels in the placenta
Published in Systems Biology in Reproductive Medicine, 2023
Sung-Min An, Min Jae Kim, Jea Sic Jeong, So Young Kim, Da Som Kim, Beum-Soo An, Seung Chul Kim
Oxytocin (OXT) is a neurohypophyseal hormone synthesized by the hypothalamus and several peripheral tissues such as the corpus luteum, gonad, uterus, and placenta (Soloff et al. 1977; Swann et al. 1984; Sugahara et al. 1985; Watson et al. 1999). OXT is secreted by magnocellular neurons and is stored in the posterior pituitary until it is released into the bloodstream (Thackare et al. 2006; Johnson 2018). The released OXT acts directly via axon terminals on OXT receptors (OXTRs) in the CNS (e.g., the nucleus accumbens) (Knobloch and Grinevich 2014). Activation of OXTRs triggers the coupling of Gaq/11 and phospholipase C (PLC), which catalyzes the hydrolysis of diacylglycerol (DAG), phosphatidylinositol-4, and 5-bisphosphate (PIP2) to inositol-1, 4, 5-trisphosphate (IP3). Subsequently, inositol triphosphate causes an increase in Ca2+ influx from both intracellular and extracellular stores, whereas DAG facilitates the activation of protein kinase type C, which phosphorylates target proteins (Koehbach et al. 2013).