Role of Vasopressin in the Cardiovascular Response to Stimulation of the Locus Coeruleus*

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Abstract
Hypothalamic vasopressin synthesizing nuclei (paraventricular and supraoptic) send vasopressin-containing projections to a number of neural target areas thought to be involved in cardiovascular regulation. One area known to receive vasopressinergic projections from the paraventricular nucleus is the pontine nucleus locus coeruleus. To examine the possible functional participation of vasopressin in central cardiovascular regulation, we examined mean arterial pressure (millimeters of Hg) and heart rate (beats per min) responses to electrical stimulation of the locus coeruleus in conscious, unrestrained vasopressin-deficient Brattleboro rats homozygous for diabetes insipidus (DI rats) and long Evans (LE) rats. Rats received chronic arterial and venous catheters and bipolar stimulating electrodes 3-5 days before experiment. Stimulation of the locus coeruleus (100 .mu.A, 10-40 Hz) produced frequency-dependent increases in mean arterial pressure (millimeters of Hg) and heart rate (beats per min) responses to electrical stimulation of the locus coeruleus in conscious, unrestrained vasopressin-deficient Brattleboro rats homozygous for diabetes insipidus (DI rats) and long Evans (LE) rats. Rats received chronic arterial and venous catheters and bipolar stimulating electrodes 3-5 days before experiment. Stimulation of the locus coeruleus (100 .mu.A, 10-40 Hz) produced frequency-dependent increases in mean arterial pressure and heart rate in LE and DI, but the responses were significantly less in the latter group. The deficiency in mean arterial pressure and heart rate responses to locus coeruleus stimulation in DI rats was found to be centrally mediated in that responses to peripherally administered phenylephrine were the same as those for LE rats. Ganglionic blockade significantly attenuated responses to locus coeruleus stimulation in LE rats but had little effect in DI rats. Pretreatment of DI rats with chronic intracerebroventricular infusion of vasopressin (osmotic minipump) at a dose that had no effect peripherally increased the mean arterial pressure and heart rate responses to locus coeruleus stimulation. Our results suggest that vasopressin acts in the region of the locus coeruleus to exert a central action on sympathetic outflow.