In both sexes, decline in testosterone levels leads to bone density loss and decline in muscle mass. Conversely, high levels of testosterone have been linked to higher risk for prostate cancer. In both sexes, low levels of testosterone have been correlated with lower coital frequency and loss of sexual desire. Since testosterone levels decrease gradually over time, the sharp decrease in sexual interest, among menopausal women, does not seem to be solely attributable to declining testosterone levels. Studies have shown that testosterone administration improves mood and well-being in both sexes, but especially among men. PROLACTIN (PRL), Prolactin is a protein hormone produced in the anterior pituitary by the pituitary mammotropic cells.Its secretion is controlled by an inhibitory influence from the hypothalamus that is thought to be dopamine. Prolactin has many effects including regulating lactation and stimulating proliferation of oligodendrocyte
precursor cells . It stimulates the mammary glands to produce milk ( lactation ). Increased serum concentrations of prolactin during pregnancy cause enlargement of the mammary glands of the breasts and prepare the production of milk. However, the high levels of progesterone during pregnancy suppress the production of milk. Milk production normally starts when the levels of progesterone fall by the end of pregnancy and a suckling stimulus is present. Sometimes, newborn babies (males as well as females) secrete a milky substance from their nipples known as witch's milk . This is in part caused by maternal prolactin and other hormone. Prolactin provides the body with sexual gratification after sexual acts : The hormone counteracts the effect of dopamine , which is responsible for sexual arousal . This is thought to cause the sexual refractory period .  The amount of prolactin can be an indicator for the amount of sexual satisfaction and relaxation. Unusually high amounts are suspected to be responsible for impotence and loss of libido (see hyperprolactinemia symptoms ). Prolactin also has a number of other effects including contributing to surfactant synthesis of the fetal lungs at the end of the pregnancy and immune tolerance of the fetus by the maternal organism during pregnancy; it also decreases normal levels of sex hormones — estrogen in women and testosterone in men. It is this inhibition of sex steroids that is responsible for loss of the menstrual cycle in lactating women as well as lactation-associated osteoporosis. Prolactin also enhances luteinizing hormone -receptors in Leydig cells , resulting in testosterone secretion, which leads to spermatogenesis. Prolactin levels peak during sleep, and in the early morning. Levels can rise after exercise, meals, sexual intercourse, minor surgical procedures, or following epileptic seizures. Hypersecretion of prolactin is more common than hyposecretion. Hyperprolactinemia is the most frequent abnormality of the anterior pituitary tumors. Clinical signs include
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