Diabetic hypertensive leptin receptor-deficient db/db mice develop cardioregulatory autonomic dysfunction

Leptin receptor-deficient db/db mice develop human type 2 diabetes mellitus, hypertension, and obesity with disrupted circadian blood pressure (BP) rhythm. Whether leptin is the sole mechanism mediating autonomic imbalance and hypertension is unclear. To explore this notion further, we measured BP by radiotelemetry combined with fast Fourier transformation and assessed autonomic function pharmacologically before and after renin-angiotensin system blockade with enalapril. The resting period BP (117+/-3 versus 108+/-1.0 mm Hg) and heart rate (HR; 488+/-12 versus 436+/-8 bpm) were higher in db/db mice compared with db/+ mice. BP and HR amplitudes were lower in db/db mice compared with db/+ mice. BP response to trimetaphan (-43+/-5 versus -27+/-3 mm Hg) and HR response to metoprolol (-59+/-12 versus -5+/-4 bpm) were greater in db/db mice than in db/+ mice. The HR response to atropine was blunted in db/db mice (59+/-17 versus 144+/-24 bpm), as were baroreflex sensitivity and HR variability. Enalapril improved autonomic regulation in db/db mice. Stimulation of central alpha-2 adrenoreceptors enhanced both parasympathetic HR control and baroreflex sensitivity in db/db mice. We suggest that functional, rather than structural, alpha-2 adrenoceptor changes and the renin-angiotensin system are involved in the increased sympathetic and decreased parasympathetic tones in db/db mice. Our data suggest that db/db mice exhibit features found in humans with type 2 diabetic autonomic neuropathy and could serve as a model for this complication.