VASODEPRESSOR ACTION OF PROSTAGLANDINS A₂ AND E₂ IN THE SPONTANEOUSLY HYPERTENSIVE RAT (SH RAT): EVIDENCE FOR AN ACTION MEDIATED BY THE VAGUS

¹ Department of Pathology, University of Tennessee Medical Units, Department of Pathology, Baptist Memorial Hospital, Memphis, Tennessee

The depressor prostaglandin A₂ (PGA₂) and prostaglandin E₂, when injected intravenously as a bolus in serially doubled doses up to 1.25 µg/kg followed by two additional doses of 1.25 µg/kg 10 minutes apart, caused a unique prolonged depression of the arterial pressure of the anesthetized spontaneously hypertensive rat of Okamoto and Aoki. The second and third 1.25 µg/kg doses of PGA₂, evoked a potentiation of the acute depressor effect. The arterial pressure reached its lowest level in different groups an average of 46 to 62 minutes after the first 1.25 µg/kg dose. The pulse rate dropped significantly only when PGA₂ was injected into the spontaneously hypertensive male rat. Cutting the vagi when the pressure was down caused a prompt rise in pressure, usually above the initial value. Cutting the vagi or efferent vagal blockage with atropine before the dose schedule of PGA₂ prevented the delayed drop in arterial pressure. Appropriate control animals failed to display the delayed depressor effect. The results seem to indicate an indirect type of depressor effect mediated by the vagus. Assuming a vagusmediated effect, it was not demonstrated whether the effect originated centrally or peripherally, such as from chemical changes of baroreceptors or other reflexogenic receptors in the heart and pulmonary vasculature.