THROMBOXANE A(2) MIMETIC U-46619 INDUCES SYSTEMIC AND PULMONARY-HYPERTENSION AND DELAYED TACHYPNEA IN THE GOAT

Cardiorespiratory variables were measured continuously in five conscio us goats before and after the infusion of U-46619 at a dose of either 2, 4, or 6 mu g . kg(-1) . 5 min(-1). Infusion of U-46619 led to immed iate increases in pulmonary arterial blood pressure (ABP) that were su stained for up to 15 min after the end of the infusion. Systemic ABP a lso increased, but the relative increase from control was less than th e pulmonary presser response. At the highest dose, U-46619 elicited a delayed tachypneic response that was greatest several minutes after th e infusion was stopped. U-46619 was also infused simultaneously with s odium nitroprusside to clamp ABP pressure at baseline levels to determ ine whether stimulation of baroreceptors might contribute to the laten cy of the tachypneic response. Although sodium nitroprusside infusion prevented the increase in ABP, the increase in breathing frequency was still delayed 3-4 min from the start of the infusion. We conclude tha t U-46619 elicits pulmonary and systemic arterial hypertension in the conscious goat. At the higher dose U-46619 also elicits a delayed tach ypnea that remains delayed even if ABP is normal.