Blunting of pulmonary but not systemic vasodilator responses to dobutaminein newborn lambs

Little is known about the changes in systemic and pulmonary vascular respon ses to dobutamine that occur during postnatal development. To address this question, vascular pressures and cardiac output were measured in anesthetiz ed 1- to 2-d-old (n = 6), 7- to 10-d-old (n = 7), and 6- to 8-wk-old lambs (n = 6) while dobutamine was infused incrementally in the dose range of 0.5 -40 mu g.kg(-1).min(-1). Dobutamine reduced pulmonary vascular resistance i n the three age groups (all p < 0.005). However, although this reduction re ached a plateau over the infusion range of 15-40 mu g.kg(-1).min(-1) at all ages, its magnitude was less (p < 0.02) in 1- to 2-d-old lambs (24 +/- 2%) than in 7- to 10-d-old (41 +/- 7%) or 6- to 8-wk-old lambs (42 +/- 6%). Ov er the same infusion range, dobutamine produced a fall in systemic vascular resistance (all p < 0.005) that was proportionally similar in 1- to 2-d-ol d (51 +/- 3%), 7- to 10-d-old (48 +/- 3%), and 6- to 8-wk-old lambs (42 +/- 6%). In separate subgroups of 1- to 2-d-old lambs, pulmonary and systemic responses to dobutamine were not affected by pretreatment with selective al pha(1)-, beta(1)-, or beta(2)-adrenoceptor antagonists. Taken together, the se findings suggest that the pulmonary but not systemic vasodilator respons e to dobutamine in lambs is blunted in the initial days after birth, and th at this pulmonary effect is not directly related to the adrenoceptor-stimul ating properties of dobutamine.