Cardiovascular responses and central catecholamines in streptozocin-diabetic rats.
Brain catecholamine levels, spinal cord levels of the norepinephrine metabolite methoxy-hydroxy-phenylglycol (MHPG), and heart rate were measured in nondiabetic and streptozocin-diabetic rats after sham surgery or bilateral carotid ligation. Although carotid ligation increased heart rate in both diabetic and nondiabetic rats, in diabetic animals the response did not differ from the response to sham surgery. Carotid ligation increased epinephrine concentrations in the medulla/pons of diabetic animals but was not associated with alterations in other central catecholamines. In all diabetic rats spinal ratios of MHPG/norepinephrine (an index of noradrenergic activity) were higher than in nondiabetics, and the change in heart rate (post-surgical-pre-surgical rate) correlated inversely with hypothalamic dopamine (R = -0.60). In sham-operated diabetic rats there were high inverse correlations of the change in heart rate with medullary epinephrine and of pre- and post-surgical heart rate with spinal MHPG/NE (R = -0.87 to -0.95). Central catecholamines and heart rate were not correlated in nondiabetic animals and correlated only weakly when nondiabetic and diabetic animals were pooled. Correlations in diabetic animals were usually abolished or reduced by carotid ligation. These findings suggest a link between central catecholamines and heart rate in diabetic rats subjected to surgical stress. Whether catecholaminergic neurons contribute to abnormal chronotropic responses in diabetic rats or respond to stimuli that affect both heart rate and neural function remains to be determined.