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Aging-Related Changes in in Vivo Release of Growth Hormone-Releasing Hormone and Somatostatin from the Stalk-Median Eminence in Female Rhesus Monkeys (Macaca mulatta)

Wisconsin National Primate Research Center (S.N., M.M., E.T.) and Department of Pediatrics (E.T.), University of Wisconsin-Madison, Madison, Wisconsin 53715; Department of Neurobiology and Geriatrics (A.C.G.), Mount Sinai School of Medicine, New York, New York 10029; and Department of Internal Medicine (H.K.), Miyazaki Medical College, Miyazaki 889-1692, Japan

Address all correspondence and requests for reprints to: Ei Terasawa, Ph.D., Wisconsin National Primate Research Center, 1223 Capitol Court, Madison, Wisconsin 53715-1299. E-mail: terasawa{at}primate.wisc.edu.

GH release decreases with aging in primates. However, it is unclear whether the age-related decrease in GH release is due to a decrease in stimulatory GHRH or an increase in inhibitory somatostatin (SS) from the hypothalamus. In the present study, we measured the release of GHRH and SS in the stalk-median eminence of conscious aged (n = 7, 27.0 ± 0.7 yr old) and young adult female monkeys (n = 12, 5.0 ± 0.3 yr old) using the push-pull perfusion method. Mean GHRH levels during morning (0600–1200 h) and evening (1800–2400 h) in aged monkeys were 3- to 4-fold lower than in young monkeys. Pulse analysis indicated that pulse frequency, pulse amplitude, and baseline GHRH release in aged monkeys were much lower than in young adults. In contrast, mean SS levels in aged monkeys during mornings and evenings were 2-fold higher than in young monkeys. Pulse analyses indicated that amplitude and baseline levels of SS were significantly higher in aged monkeys than in young adults. There were no significant changes in the pulse frequency of SS release. Therefore, the aging-related decrease in GH release is due to a substantial decrease in GHRH release and an increase in SS release from the hypothalamus.

This work (publication no. 42-009 from the Wisconsin Regional Primate Research Center) was supported by NIH Grants AG17942 and RR00167 (to E.T.) and AG16765 (to A.C.G.).

Present address for S.N.: Department of Veterinary Pathology, Nippon Veterinary and Animal Science University, Musashino, Tokyo, Japan.

Present address for M.M.: Department of Integrative Physiology, Kyushu University, Fukuoka, Japan.

Abbreviations: PPP, Push-pull perfusion; S-ME, stalk-median eminence; SS, somatostatin.

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