Haemodynamic responses to conflict stress in borderline hypertensive rats

Chronic exposure to a shock-shock conflict paradigm (2 h/day, 5 days/week for 12 weeks [1]) produces hypertension in the borderline hypertensive rat (BHR), a cross between the spontaneously hypertensive rat (SHR) and the Wistar-Kyoto rat (WKY). The purpose of the present study was to characterize the regional haemodynamic responses which take place during conflict-stress. A pulsed Doppler flowmeter and miniature probes implanted on the left renal and superior mesenteric arteries and the abdominal aorta were used to record changes in regional flow velocity. Recording of mean arterial pressure (MAP) allowed changes in regional resistance to be calculated. The first conflict session produced intense splanchnic and renal vasoconstriction and hindquarter vasodilation. Pressor responses were moderate. A second group of BHRs was studied during conflict sessions 17-18, prior to the development of hypertension. This group exhibited faster habituation to the stress than the group studied during the first conflict session: MAP and mesenteric resistance returned more rapidly towards pre-stress levels. Relative to naive control rats, this group exhibited a larger peak MAP and less tachycardia in response to a neutral stressor (air-jet stress) and a smaller reduction in renal resistance in response to ganglionic blockade. These data suggest that in this model, pressure load per se is moderate. More attention should be directed towards the role of trophic effects of the neurohumoral factors responsible for the pronounced constriction of splanchnic and renal vasculature in producing hypertension.