Heart rate-dependent stiffening of large arteries in intact and sympathectomized rats

In the anesthetized rat, acute increases in heart rate are accompanied by a reduction in arterial distensibility, which is a significant phenomenon in elastic-type vessels such as the common carotid but much less evident in m uscle-type vessels such as the femoral artery. Because the sympathetic nerv ous system importantly reduces arterial distensibility, the present study a imed to determine whether sympathetic influences (1) are involved in the he art rate-dependent changes in arterial distensibility and (2) exert differe ntial effects on elastic-type versus muscle-type arteries, To address this issue, 9 sympathectomized (6-hydroxydopamine) and 10 vehicle-treated, 12-we ek-old, pentobarbitone-anesthetized Wistar-Kyoto rats were subjected to atr ial pacing via a transjugular catheter at 5 different randomly sequenced ra tes (280, 310, 340, 370, and 400 bpm). After each step, spontaneous sinus r hythm was allowed to return to normal, Common carotid and femoral artery di ameters were measured by an echo Doppler device (NIUS 01), and blood pressu re was measured via catheter inserted into the contralateral vessel, Arteri al distensibility was calculated over the systolic-diastolic pressure range according to the Langewouters formula, In the common carotid artery, progr essive increases in heart rate determined progressive and marked reductions of distensibility (range, 15% to 43%) in sympathectomized and intact rats. In the femoral artery, the stiffening effect of tachycardia was present in sympathectomized rats (range, 21% to 42%), at variance with the inconsiste nt changes observed in intact rats, In conclusion, our experiments support the notions (1) that in predominantly elastic-type arteries, the stiffening effect of tachycardia is exerted independently of sympathetic modulation o f the vessel wall properties and (2) that in predominantly muscle-type arte ries, removal of sympathetic influences unmasks the stiffening effect of ta chycardia.