Journal of Clinical Endocrinology & Metabolism, Vol 62, 595-600, Copyright © 1986 by Endocrine Society

ARTICLES

Responses of growth hormone (GH) and somatomedin-C to GH-releasing hormone in healthy aging men

EP Pavlov, SM Harman, GR Merriam, MC Gelato and MR Blackman

Although controversy exists regarding the effects of aging on GH secretory responses to indirect stimulation, in the only prior study of GH-releasing hormone (GHRH)-mediated GH secretion decreased GH responsivity occurred in healthy men after age 40 yr. We measured serum GH before and up to 180 min after and somatomedin-C (SM-C) levels before and 24 h after single morning bolus iv injections of GHRH-(1-44)- NH2 (1 microgram/kg) in 50 healthy fasted men, aged 21-86 yr, from the Baltimore Longitudinal Study of Aging. Only subjects with a body mass index (BMI; kilograms per m2) between 20.0 and 29.0 were studied. Basal serum GH levels were undetectable (less than 0.7 ng/ml) in all but 2 men. Neither the frequency of GH responses (P greater than 0.8), the magnitude of response (P greater than 0.2), nor the timing (P greater than 0.05) of the peak GH responses to GHRH were significantly altered with age. Although BMI values did not vary significantly with age in our study group, there was a significant negative correlation (r = - 0.37; P less than 0.01) of peak GH with BMI. Regression analysis revealed a slight but significant increase in the level of fasting blood sugar with age, but no significant correlation between fasting blood sugar and peak GH levels. Serum levels of SM-C were significantly lower in older men both before (P less than 0.001) and 24 h after (P less than 0.02) GHRH injection. Repeated measures analysis of variance revealed significant (P less than 0.001) responses of SM-C to endogenous GH elevations produced by GHRH at all ages, but no age- dependent alterations in the magnitudes of these responses (P greater than 0.7). Our findings suggest that increasing age in adult men has little effect on the secretory responsiveness of pituitary somatotropes to GHRH. However, the finding of lower serum levels of SM-C with intact SM-C responsivity to endogenous GH is compatible with prior observations of an age-related decrease in the total daily spontaneous secretion of GH.

This article has been cited by other articles:

				M. G. S. Frutos, L. Cacicedo, C. F. Mendez, D. Vicent, M. Gonzalez, and F. Sanchez-Franco Pituitary Alterations Involved in the Decline of Growth Hormone Gene Expression in the Pituitary of Aging Rats J. Gerontol. A Biol. Sci. Med. Sci., June 1, 2007; 62(6): 585 - 597. [Abstract] [Full Text] [PDF]

				S M. HARMAN What Do Hormones Have to Do with Aging? What Does Aging Have to Do with Hormones? Ann. N.Y. Acad. Sci., June 1, 2004; 1019(1): 299 - 308. [Abstract] [Full Text] [PDF]

				S. Nakamura, M. Mizuno, H. Katakami, A. C. Gore, and E. Terasawa 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) J. Clin. Endocrinol. Metab., February 1, 2003; 88(2): 827 - 833. [Abstract] [Full Text] [PDF]

				M. J. Woller, G. Everson-Binotto, E. Nichols, A. Acheson, K. L. Keen, C. Y. Bowers, and E. Terasawa Aging-Related Changes in Release of Growth Hormone and Luteinizing Hormone in Female Rhesus Monkeys J. Clin. Endocrinol. Metab., November 1, 2002; 87(11): 5160 - 5167. [Abstract] [Full Text] [PDF]

				J. Manetta, J. F. Brun, L. Maimoun, A. Callis, C. Prefaut, and J. Mercier Effect of training on the GH/IGF-I axis during exercise in middle-aged men: relationship to glucose homeostasis Am J Physiol Endocrinol Metab, November 1, 2002; 283(5): E929 - E936. [Abstract] [Full Text] [PDF]

				R. N. Dhir, W. Dworakowski, and B. H. Shapiro Middle-Age Alterations in the Sexually Dimorphic Plasma Growth Hormone Profiles: Involvement of Growth Hormone-Releasing Factor and Effects on Cytochrome P450 Expression Drug Metab. Dispos., February 1, 2002; 30(2): 141 - 147. [Abstract] [Full Text] [PDF]

				J. A. Gusenoff, S. M. Harman, J. D. Veldhuis, J. J. Jayme, C. St. Clair, T. Munzer, C. Christmas, K. G. O'Connor, T. E. Stevens, M. F. Bellantoni, et al. Cortisol and GH secretory dynamics, and their interrelationships, in healthy aged women and men Am J Physiol Endocrinol Metab, April 1, 2001; 280(4): E616 - E625. [Abstract] [Full Text] [PDF]

				M. Russell-Aulet, E. V. Dimaraki, C. A. Jaffe, R. DeMott-Friberg, and A. L. Barkan Aging-Related Growth Hormone (GH) Decrease Is a Selective Hypothalamic GH-Releasing Hormone Pulse Amplitude Mediated Phenomenon J. Gerontol. A Biol. Sci. Med. Sci., January 1, 2001; 56(2): 124M - 129. [Abstract] [Full Text]

				A. Giustina and J. D. Veldhuis Pathophysiology of the Neuroregulation of Growth Hormone Secretion in Experimental Animals and the Human Endocr. Rev., December 1, 1998; 19(6): 717 - 797. [Abstract] [Full Text]

				E. C. degli Uberti, M. R. Ambrosio, S. G. Cella, A. R. Margutti, G. Trasforini, A. E. Rigamonti, E. Petrone, and E. E. Muller Defective Hypothalamic Growth Hormone (GH)-Releasing Hormone Activity May Contribute to Declining GH Secretion with Age in Man J. Clin. Endocrinol. Metab., September 1, 1997; 82(9): 2885 - 2888. [Abstract] [Full Text] [PDF]