Stress-like responses to common procedures in rats: effect of the estrous cycle

The objective of this study was to assess cardiovascular and behavioral responses of Sprague-Dawley female rats subjected to or witnessing common husbandry and experimental procedures at various points during the estrous cycle. Heart rate (HR) and mean arterial blood pressure (MAP) were determined using radiotelemetry for 2 h before and 3 h after: cage change, restraint and subcutaneous (s.c.) injection, restraint and tail-vein injection, witnessing decapitation of other rats, smelling urine and feces from stressed rats, and smelling dried rat blood. Home cage behaviors (sleeping, awake, moving, rearing, and grooming) were scored once each minute for 15 min before and 45 min after the incidents. Being subjected to cage change, restraint and injections, and odors significantly increased HR and MAP 60-120 beats per min and 10-20 mm Hg over baseline respectively for 45 to 90 min. Witnessing these procedures also significantly increased HR and MAP but the magnitude was reduced by 20% to 30% compared to that seen in rats subjected to the procedures. Witnessing decapitation of other rats induced cardiovascular responses which were not different from those of rats witnessing other procedures. The cardiovascular responses were not enhanced during proestrus-estrus compared to metestrus-diestrus. There were also no significant effects of the estrous cycle on home cage behavior after these procedures. We conclude that cycling female rats show stress-like effects when they are subjected to or witness common husbandry and experimental procedures, but there is little to no effect of the estrous cycle.