AJP - Regulatory, Integrative and Comparative Physiology, Vol 273, Issue 4 1346-R1351, Copyright © 1997 by American Physiological Society
Insulin-like growth factor I is suppressed in socially subordinate male baboons
R. M. Sapolsky and E. M. Spencer
Department of Biological Sciences, Stanford University, California 94305, USA.
Insulin-like growth factor (IGF) I is a potent growth-promoting and
anabolic hormone with major roles in cellular growth and differentiation,
protein metabolism and muscle physiology, wound healing, erythropoiesis,
and immune stimulation. Few, if any, studies have examined social or
psychological factors that could give rise to individual differences in
IGF-I levels. As part of a long-term psychoendocrine study of a population
of male baboons living freely in a national reserve in East Africa, we
examined the relationship between social rank and IGF-I concentrations. We
observed that social subordinance was associated with a relative
suppression of IGF-I concentrations; no rank-related differences in
concentrations of IGF-II or IGF-binding protein were observed. Extensive
psychoendocrine literature suggests that the individual differences in
IGF-I profiles were a consequence, rather than a cause, of the rank
difference. We were able to rule out a number of possible proximal
explanations for the rank-IGF-I correlation: 1) the correlation was not a
function of age (which involves both an adolescent spurt in IGF-I
concentrations as well as a decline in concentrations in aged individuals);
2) the IGF-I suppression in subordinate individuals could not be explained
by the basal hypercortisolism typical of such subordinate animals; and 3)
neither differences in the quality or quantity of food consumed, in basal
testosterone concentrations, nor in genetics could explain the rank
difference. Although the mediating mechanisms responsible for this rank
difference were not discernible in this study, the magnitude of difference
in IGF-I levels among baboons of differing ranks might be of physiological
significance.
