Psychosomatic Medicine 30:760-773 (1968)
© 1968 American Psychosomatic Society

Plasma Growth Hormone Response to Avoidance Sessions in the Monkey

¹ Departments of Neuroendocrinology and Experimental Psychology, Walter Reed Army Institute of Research, Walter Reed Army Medical Center, Washington, D. C.

Plasma immunoreactive growth hormone levels usually rise during conditioned avoidance sessions in monkeys. The rise occurs promptly, being evident in the first sample obtained after avoidance onset (30 min.), and levels remain elevated during 2-hr. avoidance sessions. Preliminary experiments suggest that the elevations may persist during longer avoidance sessions, but the reliability of single 9: 00 A.M. fasting samples in assessing day-to-day changes in growth hormone levels is open to question because of the lability of this system.

This study of growth hormone levels is complicated by a high frequency of elevated "baseline" values. It was consistently observed, however, that when "baseline" growth hormone values were below 7 mµg./ml., levels subsequently rose during avoidance, while when "baseline" values were above 7 mµg./ml., levels subsequently fell during avoidance sessions.

Several lines of evidence are presented which suggest that psychological response to the venipuncture procedure may be a major determinant of "baseline" variability in growth hormone levels. The lability of this system appears to be such that venipuncture effects may occur within the period of a few minutes required for a single venipuncture. Our data so far indicate a normal "basal" plasma immunoreactive growth hormone level in the region of 2 to 3 mµg./ml. in the rhesus monkey.

The significance of the sensitivity of growth hormone secretion to psychological influences is discussed in relation to the study of growth hormone regulation in general.