Pituitary function

Inhibin and Activin. Inhibin, a water-soluble, gonadal factor known for over 50 years to inhibit pituitary function, has been isolated and identified (127—130). Inhibin is a glycoprotein hormone that preferentially inhibits the secretion of FSH. It consists of an a-chain subunit, mol wt 14,000, linked by disulfide bonds to a P-chain subunit, mol wt 18,000. There exist two forms of the P-chain subunit, P-A and P-B. The smaller subunit combines with either the P-A or P-B subunit to form inhibin-A or inhibin-B, respectively. 

Therapeutic Function Diagnostic aid (pituitary function) Chemical Name 2-methyl-1,2-di-3-pyridyl-1-propanone Common Name —... 

Contraceptives. Figure 1 Regulation of hypothalamic and pituitary function by ovarian steroid hormones. 

Routinely assess acromegaly complications, including blood pressure, glucose tolerance, fasting lipid profile, cardiac evaluations (if clinically indicated), colonoscopy, dual-energy x-ray absorptiometry (DEXA) scan (hypogonadal only), evaluation of residual pituitary function, and evaluation of sleep apnea. 

B13. van den Berghe, G., de Zegher, F., and Lauwers, P., Dopamine suppresses pituitary function in infants and children. Crit. Care Med. 22,1747-1753 (1994). 

Overview of Hypothalamic-Pituitary Function at Time of Gonadotropin Surge... 

Lessons in SERM Behavior from Effects of Tamoxifen on Rat Pituitary Function... 

Fink G (2000) Neuroendocrine regulation of pituitary function general principles. In Conn PM, Freeman ME (eds) Neuroendocrinology in physiology and medicine. Humana, Totowa, NJ, pp 107-134... 

Reduced G-6-PDH activity entails in intact rats a longer starvation period, thus suggesting an influence of pituitary function on maintenance of normal G-6-PDH level, or on the utilization of G-6-P by the oxidative pathway. 

Cooper RL, Goldman JM, Rehnberg GL. 1986. Pituitary function following treatment with reproductive toxins. Environ Health Perspect 70 77-184,86... 

GnRH is also used (in both human and veterinary medicine) to improve conception rates by enhancing basal hypothalamic-pituitary function. The preparations utilized clinically are manufactured by direct chemical synthesis and are usually administered by s.c. injection or, sometimes, by i.v. injection. Occasionally it has also been administered intranasally. Frequent injection is often required, particularly if administration is via the i.v. route, as the peptide s plasma half-life is of the order of a few minutes (it is hydrolysed in the plasma and excreted in the urine). 

Mechanism of Action A hormone and antineoplastic agent that suppresses the release of luteinizing hormone from the anterior pituitary gland by inhibiting pituitary function. Therapeutic Effect Shrinks tumors. Also increases appetite by an unknown mechanism. 

Serotonin has an effect on the hypothalamic control of pituitary function (see chapter 5), in central thermoregulation (attributed to the 5-HTj receptor), and in pain perception (probably the S-HTj receptor), where increased serotonergic function potentiates opiate analgesia. The administration of 5-HT reuptake inhibitors like fluoxetine increases the anorectic effect of 5-hydroxytryptamine and induces a selective suppression of nonprotein caloric intake in rats. The involvement of serotonin in endogenous psychiatric depression has been mentioned. 

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. 

Hypothalamo-pituitary function Anterior pituitary hormones Posterior pituitary hormones Adrenal cortex Adrenal medulla Thyroid Pancreas INTRODUCTION... 

Changes in serum proteins and other effects on endocrine function (see above) must be taken into account when thyroid, adrenal, or pituitary function is being evaluated. Increases in sedimentation rate are thought to be due to increased levels of fibrinogen. 

Castracane VD, Allen-Rowlands CF, Hamilton MG, et al. 1982. The effect of polychlorinated biphenyl (PBB) on testes, adrenal, and pituitary function in the rat. Proc Soc Exp Biol Med 169 343-347. 

When markedly impaired growth is noted in patients treated with glucocorticoids long-term or in pulses, it is necessary to assess pituitary function and the anatomy of the pituitary gland. Children who receive glucocorticoid pulse therapy may develop an empty sella more frequently than is usually recognized. 

The most serious adverse effect of protirelin is pituitary apoplexy (pituitary hemorrhage or infarction, characterized by severe headache, visual loss, and often by pituitary failure, hypotension, and coma). This complication has been described in 15 cases after pituitary function testing... 

Masago A, Ueda Y, Kanai H, Nagai H, Umemura S. Pituitary apoplexy after pituitary function test a report of two cases and review of the literature. Surg Neurol 1995 43(2) 158-64. 

It is likely that in this case long-standing suppression of pituitary function secondary to negative feedback from exogenous hormone ingestion (including liothyronine) resulted in pituitary atrophy. 

Thyroid function tests are often altered by somatropin because of increased conversion of T4 to T3, but this is clinically insignificant at low doses (SEDA-21, 453). One child with Prader-Willi syndrome had a fall in serum thyroxine concentration during somatropin therapy and needed thyroxine replacement (33). Hypothyroidism developed in 11 of 46 growth hormone-deficient children treated with somatropin (34). Prior abnormalities in hypothalamic-pituitary function and alterations in thyroid hormone metabolism, probably both, contributed to the high incidence of hypothyroidism, which was similar to that in previous studies. 

Diagnosis of Endocrine Disorders. Hormones or their antagonists can be administered to determine the presence of excess endocrine function or endocrine hypofunction. For example, hormones or their synthetic analogs can be administered that either increase or decrease pituitary secretion to determine if pituitary function is normal. Likewise, antagonists to specific hormones can be administered to see if symptoms are caused by excessive hormone production. Specific examples of how hormones are used to diagnose endocrine abnormalities are presented in subsequent chapters. 

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