The role of growth hormone signaling in the control of aging

BARTKE A ; HEIMAN M ; TURYN D; DOMINICI FP; KOPCHICK JJ

“The Neuroendocrine Immune Network in Ageing”,

Springerlink

Año: 2004; p. 123 - 137

Growth hormone plasma levels gradually decline during adult life. It is apparent from the relevant literature that role of GH changes in different stages of life. Excess GH during adulthood in animals and man shortens their lifespan. Tradeoffs must exist between growth, reproduction and longevity. Low GH levels may have a role in protecting the organism from cancer and other age-related diseases. Subnormal GH levels affect body composition, muscle and brain function, and are suspected of contributing to the deterioration of quality of life in the elderly. However, the risks and benefits of anti-ageing therapy with GH are not well understood and the concept of GH replacement during “somatopause” is controversial [49]   It seems very intriguing that GH has an influence on lifespan. Being an anabolic hormone, excess GH must promote metabolic processes that are deleterious for longevity. Growth hormone is the member of the growth and lactogenic hormone (GLH) family, which include multiple isoforms of GH, prolactin (PRL) and placental lactogenic hormones (PL). These hormones have overlapping functions and are of fundamental importance in governing the growth, development and bodily functions of higher animals for their life-cycle. On the basis of the immunological effects of GLH hormones it was postulated that they function as competence hormones for the immune system, and likely for all other tissues and organs in higher animals [50, 51] Because of overlapping functions between GH and PRL, GH or PRL deficiency alone rarely causes severe problems due to compensation by the other hormone, if it is present at normal levels. However, joint and complete deficiency has not been adequately demonstrated to date [52]. Our experiments in hypophysectomized rats indicated that animals lacking both hormones die of bone marrow and immune failure and of cachexia within 6 weeks [53]. These observations indicate that PRL alone is capable of maintaining vital bodily functions in hypophysectomized rats. Redundancy exists within the GLH family and these hormones are indispensable for the growth, development and functional maintenance of the body throughout the entire lifespan of higher animals [50-53]. Consequently, it is reasonable to suggest that GLH, rather than GH alone, should be viewed as functional unit, when it comes to the assessment of biological functions and of the impact on health and longevity.