Hypothalamic-pituitary-gonadal

Thomas EJ, Walton PL, Thomas NM, Dowsett M (1994) The effects of ICI 182,780, a pure anti-oestrogen, on the hypothalamic- pituitary-gonadal axis and on endometrial proliferation in pre- menopausal women. Hum Reprod 9 1991-1996... 

There has been some concern that the recently observed decline in sperm quality may be related to exposure to environmental estrogens (Sharpe and Skakkebaek, 1993) and at the same time there has been speculation that these estrogenic compounds may exert inhibitory effects against prostate cancer (Kurzer, 2002). Theoretically, exposure to high levels of dietary estrogens could alter the hypothalamic-pituitary-gonadal axis in men, but dietary studies to date have not shown such an hormonal effects. 

Fig. 2. Gonadotrophin releasing hormone (GnRH) released in pulses by the hypothalamus stimulates pituitary production and secretion of luteinizing hormone (LH) and follicle stimulating hormone (FSH). The hypothalamic-pituitary—gonadal (H-P-G) axis is affected by a variety of external hormones and external factors.

Figure 17.2 The hypothalamic-pituitary-gonadal axis. Endocrine signaling cascades provide multiple sites for regulation and ensure optimum signaling.

Figure 20.1 Hypothalamic-pituitary-gonadal axis. Negative feedback is designated by (—), and positive feedback is designated by (+).

Rivier C, Rivest S. Effect of stress on the activity of the hypothalamic-pituitary-gonadal axis peripheral and central mechanisms. Biol Reprod 1991 45 523-532. 

Paul. Hypothalamic-pituitary-gonadal dysfunction in men using cimetidine. N. Eng. J. Med. 300 1012-1015,... 

EDSTAC, Endocrine Disruptor Screening and Testing Advisory Committee HPG, hypothalamic-pituitary-gonadal PND, postnatal day p.o., per oral (by mouth) s.c., subcutaneous T4, thyroxine TSH, thyroid stimulating 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 ).

Figure 33.2. Endocrine feedback loops of the mammalian hypothalamic-pituitary-gonadal (HPG) axis. (Adapted from La Barbera A. R. Differentiation and function of the female reproductive system. In Boekelheide, K., Chapin, R. E., Hoyer, P. B., and Harris, C. (Eds.). Comprehensive Toxicology, Vol. 10, Reproductive and Endocrine Toxicology, Elsevier, New York, 1997, pp. 255-272 and Creasy, D. M., and Foster, P. M. D. Male reproductive system. In Haschek, W. M., Rousseaux, C. G. and Wallig, M. A. (Eds.). Handbook of Toxicologic Pathology, 2nd ed., Academic Press, San Diego, 2002,pp. 785-846. E2, estradiol T, testosterone, DHT, dihydrotestosterone, FSH, follicle stimulating hormone LH, luteinizing hormone.

In terms of pharmacological management, often little can be done for those with an abnormality in the hypothalamic-pituitary-gonad axis. In some patients hormone replacement is required, and in patients with Turner s syndrome in vitro fertilization and hormone therapy can be offered. 

In prospective non-randomized non-blinded evaluation of the effects of a 12-week course of intrathecal opioids for the control of chronic non-cancer pain on the hypothalamic-pituitary-gonadal axis in 12 men, it was suppressed and serum testosterone concentrations fell (44). This effect not only reduces quality of life through sexual... 

Table 9.6 lists the major effects of chronic heavy drinking on body systems. As you can. see, alcohol can be highly toxic to the human body and cause extensive damage to it in a variety of ways. Two prominent body systems that alcohol harms are the brain and the liver. We will look at alcohol s chronic effects on these systems in more detail. Alcohol s chronic effects also extend to human reproductive fimetioning, which has to do with alcohol s altering the fimetioning of the hypothalamic-pituitary-gonadal endocrine axis and with fetal alcohol syndrome (FAS). 

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