PII S0031-9384(97)00002-4 Plasma Galanin Immunoreactivity in the Rat after Swimming MARTIN MILOT AND FRANC ¸ OIS TRUDEAU 1 De ´partement des Sciences de l’Activite ´ Physique, Universite ´ du Que ´bec a ` Trois-Rivie `res, Trois-Rivie `res (Que ´bec) G9A 5H7 Canada Received 29 July 1996; Accepted 30 January 1997 MILOT, M. AND F. TRUDEAU. Plasma galanin immunoreactivity in the rat after swimming. PHYSIOL BEHAV 62(4) 697–700, 1997.—The purpose of our experiment was to study plasma immunoreactive galanin in the rat after swimming. Four groups of rats were used. At rest, one group was studied after an intravenous injection of D-glucose while another group received a corresponding saline injection. The two remaining groups, treated respectively with glucose and saline, were investigated after a 30-min swimming session. After 30 min of rest in their respective cages, or after swimming, the animals were anesthetized for immediate blood sampling. The main observation was that plasma galanin was higher after swimming than after rest only in glucose-treated rats, in the vena cava (11.82  2.90 vs. 5.05  1.65 pM) and the portal vein (15.75  3.74 vs. 6.58  1.75 pM). Both saline- and glucose-treated groups had a significant increase of plasma norepinephrine from rest to swimming in the vena cava. A decrease of plasma insulin was observed in the portal vein of exercised glucose-treated rats, while plasma glucose was higher in the portal vein of this group. In conclusion, after swimming, plasma galanin level was increased only in glucose-treated rats. A significant correlation was also observed between plasma galanin and glucose (r = 0.69, p  0.01), suggesting that the presence of glucose is necessary to induce galanin liberation during exercise. © 1997 Elsevier Science Inc. Galanin Exercise Rat Glucose Norepinephrine Insulin Swimming GALANIN is is a peptidic neuromodulator found in many areas of mammalians, particularly in the nervous and digestive systems (3). Hypothalamic galanin was shown to influence feeding behavior, particularly by increasing fat consumption (16). In the spinal cord, galanin could be involved in the mechanisms of pain control, whereas in the hippocampus it was associated with mechanisms of the memory (3). In the peripheral nervous system, galanin was released during stimulation of pancreatic sympathetic nerve fibers in the dog (1). In the rat, it was observed that galanin is localized in peripheral sympathetic nerves endings since a treatment with 6-hydroxydopamine depleted galanin as well as norepinephrine in pancreatic nerves (18). This observation supported the hypothesis that galanin seems to be coreleased from the pancreatic nerve with norepinephrine (8). During exercise in the fed animal, norepineph- rine released by sympathetic nerve endings in the pancreas is responsible for inhibition of insulin release (11). Since galanin seems to be coreleased with norepinephrine during electrical stim- ulation of the pancreatic nerve (8), it is logical to hypothesize a potential role for galanin in the control of insulin secretion during exercise. The purpose of the present study was to document potential variations of plasma galanin associated with exercise in the rat. Exercise is a physiological stimulus known to increase sympa- thetic nervous activity if sufficiently intense or prolonged (11). It is then one of our hypotheses that the association of galanin and the peripheral sympathetic nervous system in some tissues like the pancreas could potentially lead to a parallel increase of galanin and norepinephrine release during a sympathetic stimulation, accom- panied by an elevation of their plasma levels. Previous studies have shown optimized galanin release in glucose-treated animals, probably because galanin seems to be involved in the control of insulin inhibition (1,7). We therefore investigated the levels of plasma galanin in exercised glucose-treated rats (1,7). METHOD Design Forty male Sprague Dawley rats (Anilab, Quebec City, Quebec, Canada) with a mean b.w. of 390.7  50.2 g were divided into four groups. Two groups were studied after an intravenous glucose treatment described later in the text: one at rest (n = 13); and the other after an exercise session (n = 13). The remaining two groups were studied after an intravenous saline injection, at rest (n = 7) or after exercise (n = 7), respectively. Experimental Procedures One week before the experiment began, the animals were submitted to three swimming sessions of 10, 15 and 20 min, respectively, to reduce the stress of the forthcoming experimental 1 Requests for reprints should be addressed to Franc ¸ois Trudeau, Ph.D., De ´p. des Sciences de l’Activite ´ Physique, 3351, boul. des Forges, C.P. 500, Trois-Rivie `res (Que ´bec), G9A 5H7 Canada. E-mail: Francois_Trudeau@uqtr.uquebec.ca Physiology & Behavior, Vol. 62, No. 4, pp. 697–700, 1997 © 1997 Elsevier Science Inc. All rights reserved. Printed in the U.S.A. 0031-9384/97 $17.00 + .00 697