Hypothalamic-pituitary-gonadal axis female

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 50-9 The regulatory feedback loop of the hypothalamic-pituitary-gonadal axis. Neural and sensory input from the brain elicits the release of Gn-RH. Gn-RH in turn stimulates the synthesis and release of the gonadotropins FSH and LH, which act on the gonads (ovary and testes) to elicit the ripening and ovulation of the ovary and steroidogenesis (estradiol and progesterone) in the female and spermatogenesis and testosterone production in the male. Inhibin formed by the ovaries and testes along with estradiol and testosterone negatively feeds back to the hypothalamic-pituitary axis to modulate Gn-RH, FSH, and LH release.

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.

Hyperprolactinemia can lead to hypogonadism secondary to prolactin s inhibitory effects on the hypothalamic-pituitary-gonadal hormonal axis. A 35-year-old female with psychosis and history of 7years of treatment with different antipsychotics presented with hypogonadism and radiological evidence of a pituitary microadenoma while on amisulpride and aripiprazole [53 ]. The authors did not relate the microadenoma to the hyperprolactinema and commented on the difficulty of treating these disorders. 

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