The Hypothalamo-Pituitary- Adrenal Axis

Table 10.1 Factors Influencing Evaluation of Endocrine Function in Aging Physiologic Metabolism Body Composition Nutrition Exercise Stress Inter-endocrine Relations Secretory Rate Transport to target site Hormone Metabolism  Activity T 4  T 3 T  DHT Number & Affinity Of Receptors

Hypophysiotropic hormones CRH: corticotropic releasing hormone GHRH: growth hormone releasing hormone GHIH: growth hormone inhibitory hormone Somatostatin PRH: prolactin releasing hormone GnRH: gonadotropin releasing hormone TRH thyrotropin (TSH)-releasing hormone Pituitary Hormones ACTH: adrenocorticotropin hormone LH: lutenizing hormone FSH: follicle stimulating hormone PL: prolactin TSH: thyroid stimulating hormone GH: growth hormone **Please see Figures in text** Figure 10.1

Figure 10.2

Figure 10.3 Diagram of a section of the adrenals illustrating the various zones and hormones

Reminder CRH: corticotropic releasing hormone ACTH: adrenocorticotropic hormone Figure 10.6

Actions Of Glucocorticoids Actions of Adrenaline/Noradrenaline Target cellular

Figure 10.5 Schematic diagram of corticosteroid action in target cell

Gene expression & new protein synthesis Relatively long latency of onset Medium & long term cell program Organization of cell networks for complex functions Activation/repression of pre- existing cell proteins Rapid onset of action Rapid adaptation to changes in the milieu Dynamic modifications of long term cell programs

Figure 10.7 Diagrammatic representation of the anterior pituitary

Figure 10.8 Diagrammatic representation of the posterior pituitary

Changes with Aging in the Hypothalamo-Pituitary-Adrenal Axis No significant changes in healthy, non-stressed, elderly The few changes that occur are rapidly compensated for (e.g. decreased secretion of GCs from the adrenal cortex) but also less rapid metabolism in the liver & less urine excretion Therefore the circulating levels remain constant Also, normal ACTH & cortisol responses to CRH administration Some alterations of the circadian rhythm

Cortisol, norepinephrine, and epinephrine STRESS

Old rats Young rats Figure 10.4 Corticosterone titers in young (3-5 mo) and aged (24-28 mo) rats

Exposure to Stress Generates: Specific responses: vary with the stimulus (specialized responses) and generate different responses with each different stimulus. Nonspecific responses: (also called non- specialized) are always the same –regardless of the stimulus –mediated through stimulation of neural, endocrine, and immune axis