Obese Zucker rats, though still normotensive, already have impaired chronotropic baroreflexes.

We compared reflex chronotropic responses to intravenously-infused drugs in 3 groups of age-matched female rats, namely: Sprague-Dawley, lean Zucker, and obese Zucker. Initial baselines for mean arterial pressure and heart rate did not differ between rat groups. However, baroreflex sensitivity was evidently attenuated in obese Zucker rats because their heart rate responses to infused phenylephrine or sodium nitroprusside were consistently weaker than those of other rats. Should these rats eventually become hypertensive, their blunted baroreflexes could contribute importantly to initiate the blood pressure elevation.