CARDIOVASCULAR-RESPONSES AND CENTRAL CATECHOLAMINES IN STREPTOZOCIN-DIABETIC RATS

Brain catecholamine levels, spinal cord levels of the norepinephrine m etabolite methoxy-hydroxy-phenylglycol (MHPG), and heart rate were mea sured in nondiabetic and streptozocin-diabetic rats after sham surgery or bilateral carotid ligation. Although carotid ligation increased he art rate in both diabetic and nondiabetic rats, in diabetic animals th e response did not differ from the response to sham surgery. Carotid l igation increased epinephrine concentrations in the medulla/pons of di abetic animals but was not associated with alterations in other centra l catecholamines. In all diabetic rats spinal ratios of MHPG/norepinep hrine (an index of noradrenergic activity) were higher than in nondiab etics, and the change in heart rate (post-surgical-pre-surgical rate) correlated inversely with hypothalamic dopamine (R = -0.60). In sham-o perated diabetic rats there were high inverse correlations of the chan ge in heart rate with medullary epinephrine and of pre- and post-surgi cal heart rate with spinal MHPG/NE (R = -0.87 to -0.95). Central catec holamines and heart rate were not correlated in nondiabetic animals an d correlated only weakly when nondiabetic and diabetic animals were po oled. Correlations in diabetic animals were usually abolished or reduc ed by carotid ligation. These findings suggest a link between central catecholamines and heart rate in diabetic rats subjected to surgical s tress. Whether catecholaminergic neurons contribute to abnormal chrono tropic responses in diabetic rats or respond to stimuli that affect bo th heart rate and neural function remains to be determined.