Comparison of intracerebroventricular and intracarotid infusions of PGE2 in conscious sheep

Abstract

Conscious sheep chronically prepared with nonocclusive indwelling vascular and cerebroventricular catheters were used to compare hemodynamic, hematologic, hormonal, and behavioral responses of intracarotid (ic) prostaglandin E2 (PGE2) to intracerebroventricular (ivt) PGE2. PGE2 had less potent hemodynamic effects when infused ivt than when infused ic. Intracarotid PGE2, 100 ng.kg-1.min-1, increased arterial pressure and heart rate 31 mmHg and 26 beats/min, respectively (P less than 0.01), whereas ivt PGE2, 300 ng.kg-1.min-1, did not alter heart rate and increased arterial pressure 9 mmHg (P less than 0.01). Both ic and ivt PGE2 increased packed cell volume 3% (P less than 0.01). Neither ic nor ivt PGE2 caused changes in plasma concentrations of epinephrine or norepinephrine. Despite ivt PGE2S less potent hemodynamic effects, ivt administration of PGE2 decreased plasma osmolality 2 mosmol/kg (P less than 0.05) and sodium concentration 2 meq/l (P less than 0.01) and increased plasma vasopressin concentration 2.5-fold (P less than 0.05). Intracerebroventricular PGE2 also caused some physical and behavioral changes that were not observed during ic PGE2 administration or during ivt infusion of vehicle. These changes included pupillary constriction, vocalization, and coughing. We conclude that PGE2 given ivt may not reach the same sites in the brain as does ic PGE2 or that ivt PGE2 may reach the same sites in different concentrations.