Hypothalamic-pituitary axis

SANTELL R c, CHANG Y c, NAIR M G and HELFERICH w G (1997) Dietary genistein exerts estrogenic effects upon the uterus, mammary gland and the hypothalamic/pituitary axis in rats. . 1 Nutr. 127 (2) 263-9. 

FSH Follicle-stimulating hormone HPA Hypothalamic-pituitary axis... 

Shupnik MA (2002) Oestrogen receptor, receptor variants and oestrogen actions in the hypothalamic-pituitary axis. J Neuroendocrinol 14 85-94... 

The sympathetic nervous system (SNS) and the hypothalamic-pituitary axis work together as important modulators of the immune system after exposure to stressors. Norepinephrine (NE) and epinephrine (EPI) (catecholamines from the SNS) and neuroendocrine hormones modulate a range of immune cell activities, including cell proliferation, cytokine and antibody production, lytic activity, and migration. This chapter will focus on these two major pathways of brain-immune signaling, briefly summarizing the evidence for SNS and hypothalamic-pituitary-adrenal (HPA) modulation of immune function, their influence on immune-mediated diseases, immune modulation in aging, and early life influences on these pathways. 

HPA hypothalamic pituitary axis HPV human papilloma virus HR heart rate... 

Menaker Insects do have complex neuroendocrine systems, and animals had oscillators long before we had a hypothalamic—pituitary axis. 

Metyrapone is used in the differential diagnosis of both adrenocortical insufficiency and Cushing s syndrome (hypercortisolism). The drug tests the functional competence of the hypothalamic-pituitary axis when the adrenals are able to respond to corticotrophin that is, when primary adrenal insufficiency has been ruled out. 

Testicular failure may occur before puberty and present as delayed puberty and the eunuchoid phenotype, or after puberty, with the development of infertility, impotence, or decreased libido in otherwise fully virilized males. The source of hypogonadism can be testicular, as occurs in primary hypogonadism, or it may result from abnormalities of the hypothalamic-pituitary axis, as in secondary hypogonadism. 

Although it is the dominant organ of the neural system, the brain also has an endocrine function, enabling the all-important overlap between neural and endocrine control systems. The most obvious and classically recognized hormonal function of the brain arises from the peptide hormones of the hypothalamus. The hypothalamus is intimately connected with the pituitary, producing the hypothalamic-pituitary axis. The hypothalamus is part of the brain the pituitary, although located within the skull, is not part of the brain but is part of the endocrine system. Peptide hormones from the hypothalamus influence pituitary function and thus endocrine function throughout the body. 

Figure 5.2 The Hypothalamic Pituitary Axis The hypothalamus is part of the diencephalon within the brain. The pituitary, although located within the skull, is more correctly a part of the endocrine system than the nervous system. Together, the hypothalamus and pituitary form the interface between the nervous system and endocrine system and exert control over the majority of other hormone secreting organs. Releasing and inhibiting factors permit the hypothalamus to control the pituitary. Pituitary hormones are released into the general circulation, affecting metabolic function throughout the thorax and abdomen.

Given that the seat of hormonal modulation is in the limbic-hypothalamic-pituitary axis, endocrine changes serve as important correlates to major psychiatric disorders. These changes include basal hormone concentrations, as well as responses to pharmacological challenges. Equally important, endocrine disorders may present with psychiatric symptoms (e.g., manic symptoms in hyperthyroidism, severe depression in hypercortisol ism, psychotic symptoms associated with Cushing s syndrome). Commonly used neuroendocrine tests include the following. 

The authors suggested that ciclosporin had suppressed the hypothalamic-pituitary axis. 

The many effects of lithium on thyroid physiology and on the hypothalamic-pituitary axis and their clinical impact (goiter, hypothyroidism, and hyperthyroidism) have been reviewed (620). Lithium has a variety of effects on the hypothalamic-pituitary-thyroid axis, but it predominantly inhibits the release of thyroid hormone. It can also block the action of thyroid stimulating hormone (TSH) and enhance the peripheral degradation of thyroxine (620). Most patients have enough thyroid reserve to remain euthyroid during treatment, although some initially have modest rises in serum TSH that normalize over time. 

Franceschi M, Perego L, Cavagnini F, Cattaneo AG, Invitti C, Caviezel F, Strambi LF, Smirne S. Effects of long-term antiepileptic therapy on the hypothalamic-pituitary axis in man. Epilepsia 1984 25(l) 46-52. 

Thyroid hormone release is subject to the negative feedback strategy that is typical of endocrine systems controlled by the hypothalamic-pituitary axis. Increased circulating levels of the thyroid hormones (T4, T3) serve to limit their own production by inhibiting TRH release from the hypothalamus and TSH release from the anterior pituitary.30,35 This negative feedback control prevents peripheral levels of thyroid hormones from becoming excessively high. 

Adrenal glucocorticoid and androgen production is controlled predominantly by the hypothalamic-pituitary axis, whereas the production of aldosterone by the zona glomerulosa is predominantly regulated by the renin-angiotensin system and potassium concentration. The hypothalamus, pituitary, and adrenal form a neuroendocrine axis whose primary function is to regulate the production of both cortisol and some of the adrenal steroids (Figure 61.4). 

Prathiba J, Kumar KB, Karanth KS. Hyperactivity of hypothalamic pituitary axis in neonatal clomipramine model of depression. J Neural Trans (Bud) 1998 105 1335-1339. 

TCDD-exposed rats, suggesting that 2,3,7,8-TCDD inhibited the positive feedback action of 17 -estradiol at the hypothalamic-pituitary axis (Li et al. 1995a). In hypophysectomized rats, 2,3,7,8-TCDD exposure resulted in a reduction of ovulation Li et al. (1995a) suggests that this may be the result of a direct effect on the ovary, although the mechanism has not been elucidated. 

Fig. 6. Hormones of the hypothalamic-pituitary axis and the glands and target organs they regulate (ACTH = adrenocorticotropic hormone LH = luteinizing hormone FSH = follicle stimulating hormone TSH = thyroid stimulating hormone PRL = prolactin GH = growth hormone).

Fig. 1. Hormone secretion and control of the hypothalamic-pituitary-gonadal axis. Plus and minus signs indicate stimulation and inhibition respectively. In both male and female animals the dominant feedback effect of gonadal steroids on the hypothalamic-pituitary axis is inhibitory. The only major exception is in the female in which a rapid FSH-induced increase in the concentration of oestradiol triggers a large increase of the secretion of LH to induce ovulation. Note that LHRH secreted by the hypothalamus is carried directly to the pituitary gland without entering the peripheral circulation. Since the pituitary and gonadal hormones are secreted into the peripheral blood stream the functional response to hormone agonists or antagonists may be assessed by simple measurements of circulating hormone concentration ).

Exposure to pathobiological stressors causes the formation or release of mediators other than cytokines and ROS. These include stress-induced hormones and nitric oxide (NO). Stress responses stimulate the hypothalamic-pituitary axis causing the release of adrenocorticotropin, thereby elevating glucocorticoid levels. Glucocorti-... 

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