Evolution with age of baroreflex sensitivity and its autonomic nervous components in conscious hypertensive rats of the Lyon strain.

1. Cardiac baroreflex sensitivity (BRS) and its sympathetic and vagal components were studied after atropine and propranolol administrations in conscious genetically hypertensive (LH), normotensive (LN) and low blood pressure (LL) rats of the Lyon strain at 5, 9, 13 and 70 weeks of age. 2. LH rats older than 9 weeks exhibit a lower BRS than age-matched LN and LL controls. 3. The vagal component of cardiac baroreflex is predominant. In LN rats, this component increases up to 9 weeks of age. 4. The sympathetic component of cardiac baroreflex is small and identical in the three strains and does not alter with age. 5. Thus, in normotensive rats, the increase in BRS during maturation reflects mainly the vagal component. The development of hypertension prevents this physiological increase in the sensitivity of the vagal component of cardiac baroreflex leading to a reduced BRS.