Journal of the Autonomic Nervous System ELSEVIER Journal of the Autonomic Nervous System 56 (1995) 26-30 Massage-like stroking of the abdomen lowers blood pressure in anesthetized rats: influence of oxytocin o Mieko Kurosawa *, Thomas Lundeberg, Greta Agren, Irene Lund, Kerstin Uvniis-Moberg Department of Physiology and Pharmacology, Karolinska Instituter, S-171 77 Stockholm, Sweden Received 27 February 1995; revised 12 June 1995; accepted 12 June 1995 Abstract The aim of this study was to determine how massage-like stroking of the abdomen in rats influences arterial blood pressure. The participation of oxytocinergic mechanisms in this effect was also investigated. The ventral and/or lateral sides of the abdomen were stroked at a speed of 20 cm/s with a frequency of 0.017-0.67 Hz in pentobarbital anesthetized, artificially ventilated rats. Arterial blood pressure was recorded with a pressure transducer via a catheter in the carotid artery. Stroking of the ventral, or both ventral and lateral sides of the abdomen for 1 rain with a frequency of 0.67 Hz caused a marked decrease in arterial blood pressure (approx. 50 mmHg). After cessation of the stimulation blood pressure returned to the control level within 1 min. The maximum decrease in blood pressure was achieved at frequencies of 0.083 Hz or more. Stroking only the lateral sides of the abdomen elicited a significantly smaller decrease in blood pressure (approx, 30 mmHg decrease) than stroking the ventral side. The decrease in blood pressure caused by stroking was not altered by s.c. administration of an oxytocin antagonist (1-deamino-2-o-Tyr-(Oet)-4-Thr-8-Orn-oxytocin, 1 mg/kg) directed against the uterine receptor. In contrast, the administration of 0.1 mg/kg of oxytocin diminished the effect, which was antagonized by a simultaneous injection of the oxytocin antagonist. These results indicate that the massage-like stroking of the abdomen decreases blood pressure in anesthetized rats. This effect does not involve intrinsic oxytocinergic transmission. However, since exogenously applied oxytocin was found to diminish the effect of stroking, oxytocin may exert an inhibitory modulatory effect on this reflex arc. Keywords: Massage; Stroking; Blood pressure; Oxytocin; Oxytocin antagonist; Abdomen; Rat 1. Introduction Somatic afferent stimulation can modify various auto- nomic functions, including blood pressure [15], heart rate [9,15], adrenal catecholamine secretion [2,11], gastro-in- testinal motility [7,10] and vesical contractility [16,17], by means of a reflex action. Studies on these somato-auto- nomic reflex responses have emphasized that the responses depend on both the type of somatic afferent stimulation (e.g., noxious or innocuous mechanical stimulation) and the segments of the skin stimulated in the respective autonomic functions. Kanetake has shown that rhythmic massage-like stroking of the abdominal area elicits a sedative response in con- * Corresponding author. Present address: Department of Physiology, International University of Health and Welfare, 2600-1 Kitakanemaru, Ohtawara, Tochigi-324, Japan. Fax: (81-287) 22-3191. 0165-1838/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSDI 0165-1838(95)00056-9 scious rats [8]. Recently, we have reported that the same type of stroking increases the withdrawal latency to heat and to mechanical stimuli. The increase in withdrawal latency to heat could be blocked by an oxytocin antagonist directed against the uterine receptor, indicating that this effect involves oxytocinergic mechanisms [1]. In the present study we have investigated the influence on blood pressure by the stroking of the abdomen in anesthetized rats. We also investigated the role of oxy- tocinergic mechanisms in this response. 2. Materials and methods 2.1. Animals and general preparation Experiments were performed on 28 male Sprague-Daw- ley rats (280-430 g) anesthetized with pentobarbital (60- 70 mg/kg, i.p.). The trachea was catheterized, and the