Hormones of the Pituitary and Thyroid

Fail PA, Anderson S A, Friedman MA (1999) Response of the pituitary and thyroid to tropic hormones in Sprague-Dawley versus Fischer 344 male rats. Toxicol Sci 52 107-121 Kyung OY, Narayanan L, Mattie DR, Godfrey RJ, Todd PN, Sterner TR, Mahle DA, Lumpkin MH, Fisher JW (2002) The Pharmacokinetics of Perchlorate and Its Effect on the Hypothalamus-Pituitary-Thyroid Axis in the Male Rat. Toxicol Applied Pharmacol 182 148-159... 

Generalized resistance to thyroid hormone (GRTH) is a rare form of thyroid disorder and may be a heritable disorder characterized by reduced responsiveness of the pituitary and peripheral tissues to the action of thyroid hormones. Behavioral manifestations include hyperactivity, behavioral problems, and cognitive... 

In thyrotoxic Graves disease, there is an increase in the overall hormone production rate with a disproportionate increase in T3 relative to T4 (Table 20-1). Saturation of thyroid-binding globulin is increased due to the elevated levels of serum T4 and T3, which is reflected in an elevated T3 resin uptake. As a result, the concentrations of free T4, free T3, and the free T4 and T3 indices are increased to an even greater extent than are the measured serum total T4 and T3 concentrations. The TSH level is undetectable due to negative feedback by elevated levels of thyroid hormone at the pituitary. In... 

In another factor related to the thyroid gland, wide variation has been observed with respect to the thyroid-stimulating hormone (TSH) of the pituitary. D Angelo8 and co-workers, using tadpoles as a tool, have studied the thyroid and TSH activity of the serums of normal and diseased individuals. Both limb growth (metamorphosis) induced by thyroid hormone and the development of thyroid tissue induced by TSH were measured. 

TSH, or thyrotropin, is a glycosylated protein of two subunits, a and p. TSH stimulates the thyroid gland to produce thyroid hormones. Deficiencies are treated by giving thyroxine itself rather than TSH, but TSH is available for diagnostic purposes to differentiate between pituitary and thyroid gland failure as causes of hypothyroidism (see Chapter 65). 

Control of thyroid function via thyroid-pituitary feedback is also discussed in Chapter 37. Briefly, hypothalamic cells secrete thyrotropin-releasing hormone (TRH) (Figure 38-3). TRH is secreted into capillaries of the pituitary portal venous system, and in the pituitary gland, TRH stimulates the synthesis and release of thyrotropin (thyroid-stimulating hormoneTSH). TSH in turn stimulates an adenylyl cyclase-mediated mechanism in the thyroid cell to increase the synthesis and release of T4 and T3. These thyroid hormones act in a negative feedback fashion in the pituitary to block the action of TRH and in the hypothalamus to inhibit the synthesis and secretion of TRH. Other hormones or drugs may also affect the release of TRH or TSH. 

There are relationships between the adrenal cortical hormones and the thyroid and pituitary glands. Depression or the function of the adrenals produces thyroid deficiency, w hereas administration of thyroxine stimulates the ACTH-adrenal conical mechanism. 

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