[Vascular reactivity in young genetically hypertensive rats of the Lyons strain]

The vascular sensitivity to noradrenaline (NA), phenylephrine (PE) and angiotensin II (AII) has been studied in 8 week-old male rats of the genetically hypertensive (LH) and normotensive (LN) Lyon strains. Vascular sensitivity was obtained from the blood pressure response-curves observed in urethane anesthetized rats having received ganglioplegics and atropine. A cocaine pretreatment allowed to assess the influence of a reuptake blockade on the responses to NA. The vascular sensitivity of NA, PE and AII was normal in LH rats, while the cocaine blocked reuptake process was less important in LH than in LN rats. When comparing these results to those, previously obtained on the activity of the sympathetic nervous system, it appeared that: in the young prehypertensive LH rat an increased sympathetic activity was associated with a normal vascular reactivity to NA. On the contrary, in old LH rats, with established hypertension, the sympathetic activity returned to normal while a vascular hypersensitivity to NA developed. Therefore it is concluded that the overall efficacy of the sympathetic nervous system is increased at all stages of the development of genetic hypertension in the Lyon strain.