Endocrinology, Vol 113, 1056-1061, Copyright © 1983 by Endocrine Society

ARTICLES

Characteristics of the post-somatostatin rebound in growth hormone secretion from perifused somatotrophs

JS Cowan, B Moor, A Chow and J Kraicer

Dispersed rat somatotrophs were perifused with repeated step SRIF signals of 10 or 60 min (100 ng/ml) separated by 45-min control periods. Effluent was assayed for rat GH (RIA). Maximum suppression of GH secretion (on signal) or complete recovery (off signal) occurred within 1 min. Repeated signals evoked identical normalized responses. GH release fell to 67 +/- (SE) 2% of control with 10-min SRIF signals and 59 +/- 4% of control with 60-min SRIF signals. After SRIF removal, major overshoots of GH secretion were observed, lasting 21 +/- 2 min (after 10-min or 60-min SRIF steps). Peak secretion rates and total secretion due to the overshoot were greater after longer SRIF signals, despite the constant duration of the overshoot. However, the extra secretion during overshoots after 60-min SRIF exposure contained only 23 +/- 3% of the secretion suppressed by SRIF, whereas the extra secretion after 10-min SRIF exposure contained 79 +/- 12% of the amount suppressed by the SRIF exposure, suggesting an intracellular feedback which slows accumulation of readily releasable GH after a period of SRIF exposure. During overshoot, peak secretion rates of twice the control rate (and 3.5 times the SRIF-inhibited rate) were observed. Similarities between these overshoots and in vivo bursts of GH secretion are noted.

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