Ts. Mcdowell et al., BAROREFLEX DYSFUNCTION IN DIABETES-MELLITUS .1. SELECTIVE IMPAIRMENT OF PARASYMPATHETIC CONTROL OF HEART-RATE, The American journal of physiology, 266(1), 1994, pp. 80000235-80000243
The purpose of this study was to determine the effect of diabetes mell
itus on baroreflex control of heart rate. Diabetes (blood glucose = 37
8 +/- 21 mg/dl) was induced in rabbits by alloxan (n = 9). Alloxantrea
ted rabbits that remained normoglycemic (n = 9) and rabbits given sali
ne instead of alloxan (n = 5) served as controls. Baroreflex control o
f heart rate was evaluated in conscious rabbits by measuring changes i
n heart rate during phenylephrine-induced increases and nitroglycerin-
induced decreases in arterial pressure. In diabetic rabbits, the gain
of the baroreflex-mediated bradycardia in response to increased pressu
re decreased significantly from -1.8 +/- 0.3 beats.min-1.mmHg-1 before
alloxan (n = 9) to -0.9 +/- 0.1 and -0.9 +/- 0.3 beats.min-1.mmHg-1 a
fter 12 and 24 wk of diabetes, respectively (n = 8; P < 0.05). There w
as no significant change in baroreflex gain in either alloxan-treated
or saline-treated normoglycemic rabbits. Baroreflex-mediated bradycard
ia was not influenced significantly after P-adrenergic blockade with p
ropranolol (1 mg/kg) and was still impaired in diabetic vs. control ra
bbits after propranolol. The gain of the baroreflex-mediated tachycard
ia in response to decreased pressure was not altered in any of the thr
ee groups. Propranolol significantly decreased but did not abolish bar
oreflex-mediated tachycardia. Neither the vagal nor the sympathetic co
mponent of the tachycardia was altered significantly by diabetes. We c
onclude that in diabetic rabbits 1) baroreflex-mediated bradycardia is
impaired, whereas reflex tachycardia is preserved; 2) the impairment
of baroreflex-mediated bradycardia is caused by a defect in parasympat
hetic control; and 3) the preservation of baroreflex-mediated tachycar
dia reflects preservation of both sympathetic activation and parasympa
thetic withdrawal. We speculate that selective impairment of parasympa
thetic activation may contribute to the increased incidence of arrhyth
mias and sudden death in diabetes.