Received March 25, 2004
Revised April 26, 2004
Accepted after revision May 27, 2004

¹ Slovak Academy of Sciences
² Fundacao Faculdade Federal de Ciencias Medicas, Porto Alegre,
³ Wright State University School of Medicine
⁴ Wright State University School of Medicine,

^* To whom correspondence should be addressed. E-mail: iveta.bernatova{at}savba.sk.

	Abstract

Studies used oxytocin knockout (OTKO) mice to investigate the role of the oxytocine in regulation of blood pressure, heart rate and stress reactivity (blood pressure and plasma corticosterone). Male OTKO and Control wild type mice with carotid arterial catheters were exposed to intermittent shaker stress for 7 days (2-min stressors, 45 times/day). Mean arterial pressure (MAP) and heart rate (HR) were recorded continuously (24h) before stress (Basal), stress days 1, 3, 7 (S1, S3, S7) and one day post-stress (Recovery). Plasma corticosterone (Cort) was measured before stress and 30 min after the last stress on day 7. 24-h MAP and HR were lower in OTKO than Controls (p<0.0001 and p<0.005, respectively) with a significant diurnal rhythm. Chronic stress (S1 and S3) produced an increase in 24-h MAP in OTKO mice, but not in Controls. There were no stress-related changes in 24-h HR values between Controls and OTKO. The immediate pressor responses were analyzed during the dark and light periods (19.00h and 08.00h). During the dark period, stress-induced pressor responses were observed only in OTKO (S1 and S3). In the light period, stress-induced MAP increases were seen on all days in OTKO and on days S1 and S3 in Controls. There were no differences in baseline Cort between the groups; however, OTKO mice showed a reduced response to chronic stress (+298% vs. +411%, OTKO vs. Controls, p<0.005). In conclusion, OT deficiency alters the endocrine and pressor responses to chronic stress, suggesting that the endogenous OT system is important in regulating the stress-induced pressor response.

Key Words: Blood pressure, Circadian rhythm, Stress