Life Sciences, Vol. 52, pp. 361-370 Pergamon Press Printed in the USA ROLE OF SOMATOSTATIN IN THE ACUTE IMMOBILIZATION STRESS-INDUCED GH DECREASE I N RAT. A. Benyassi 1, A. Gavald& 2, A. Armario 2 and S. Arancibia 1 Laboratory of Endocrinological Neurobiology. UA 1197 of CNRS, University of Montpellier -2 (USTL). Place Eugene Bataillon, 34095, Montpellier Cedex 5, France (1) and Department of Cellular Biology & Physiology, University Autonoma of Barcelona, 08193 Bellaterra, Barcelona, Spain (2). (Received in final form November 23, 1992) Summarv In the present work we have investigated to what extent somatostatin (SRIF) release from median eminence (ME) is affected by stress immobilization (IMO) in unanesthetized rats stereotaxically implanted with a push-pull cannula (PPC). One week after implantation, the ME was perfused with artificial cerebrospinal fluid for 1 hour in basal, stress and recovery conditions respectively. Samples were collected every 15 min and SRIF was measured by RIA. In another group of animals, a jugular cannula was inserted the day before and plasma samples were taken off simultaneously with the ME perfusate for GH and SRIF analysis respectively. SRIF release from the ME is rapidly (15 min) and significantly increased (58 + 11 vs 28 + 5 pg/15 min ; n=7; P < 0.01 ) in rats bearing only PPC. Intriguingly, animals bearing a jugular catheter plus a PPC showed no increase in SRIF release during the first 15 min of IMO in spite of a striking decrease of plasma GH ( 27.2 + 3.8 vs 3.6 + 1.3 ng/ml ; n=6; P < 0.001 ) observed at this time. However, in spite that the animals responded with a significant increase in SRIF, the response was later and more reduced than in animals without jugular cannula. Since our two rat groups -as result of jugular cannula surgery 24 hours before- showed differences such as a food intake, body weight gain, plasma GH levels and basal SRIF release, we think that these differences could explain the modifications in the regulatory mechanisms involved in GH control under acute stress. It is well established that growth hormone (GH) secretion results from the interaction between two hypothalamic hormones acting at the pituitary level: somatostatin (SRIF), that exerts an inhibitory role on growth hormone secretion ( 1 ) and somatocrinin (GHRH), that is stimulatory ( 2 ). This work was presented under abstract form in the XX e Colloque de la Societ~ de Neuroendocrinologie Exp~rimentale, Abstract N°27, Gen~ve, 18-20 Septembre 1991. 0024-3205/93 $6.00 + .00 Copyright © 1992 Pergamon Press Ltd. All rights reserved.