2000]. Moreover, age-related bone loss is directly correlated with peak bone mass and even a 5–10% reduction in peak BMD (equivalent to a reduction of BMD between 0.5 and 1 SD) can increase the incidence of future fractures
substantially [Matkovic et al. 1995; Matkovic, 1996]. In sum, whether genetic or environmental, processes that impact bone mass accrual mTOR inhibitor during development have the potential to increase the lifetime Inhibitors,research,lifescience,medical risk of osteoporosis and fractures [Carrie Fassler and Bonjour, 1995; Duntas, 2001]. Mechanisms potentially linking antipsychotics to bone metabolism Most APs block the dopamine D2 receptors [Richelson and Souder, 2000]. Dopamine released by tuberoinfundibulum neurons in the arcuate nucleus of the mediobasal hypothalamus activate dopamine D2 receptors on pituitary lactotrophs, tonically inhibiting prolactin release [Halbreich et al. 2003; Shibli-Rahhal and Schlechte, 2009]. Thus, during AP treatment, hyperprolactinemia often ensues, particularly since lactotrophs dopamine D2 receptors are highly sensitive to the D2-blocking activity of APs Inhibitors,research,lifescience,medical [Langer et al. 1977]. Amenorrhea due to prolactin-secreting pituitary Inhibitors,research,lifescience,medical adenomas is associated with low spinal bone mass [Shibli-Rahhal and Schlechte, 2009]. Hyperprolactinemia may inhibit the pulsatile secretion of gonadotropin-releasing hormone, thereby impairing gonadotropin secretion and causing
hypogonadism [Klibanski et al. 1980; Biller et al. 1992; Schlechte et al. 1992; Shibli-Rahhal and Schlechte, 2009]. Sex hormones play a Inhibitors,research,lifescience,medical critical role in bone metabolism and hypogonadism (e.g. menopause) is associated with a drastic reduction in bone mass [Phillip and Lazar, 2003]. Therefore, concerns have been raised that, similar to prolactin-secreting pituitary adenomas, AP-induced hyperprolactinemia may lead to bone loss by causing hypogonadism [Abraham et al. 2003]. However, the mechanism by which hyperprolactinemia leads to bone loss is likely not limited to its effects on the hypothalamic–pituitary–gonadal axis since eugonadal patients with hyperprolactinemia may exhibit bone loss and fail to completely recover bone Inhibitors,research,lifescience,medical mass after treatment [Schlechte et al.
1983; Greenspan et al. 1989]. Moreover, adolescents with prolactin-secreting adenomas exhibit significantly reduced BMD for age despite progressing through puberty normally [Colao et al. 1998, 2000]. Of note, prolactin appears to directly affect the skeleton through the prolactin receptor Megestrol Acetate expressed by osteoblasts [Clement-Lacroix et al. 1999; Seriwatanachai et al. 2008a, 2008b, 2009]. In fact, knockout mice lacking the prolactin receptor gene exhibit a dramatic reduction in bone formation and, consequently, low BMD [Clement-Lacroix et al. 1999]. Conversely, activation of the prolactin receptor inhibits osteoblast differentiation and matrix mineralization, with reduced alkaline phosphatase concentration [Coss et al. 2000; Seriwatanachai et al. 2009].
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