Enhanced Vasoconstriction Mediated by α(1)-Adrenergic Mechanisms in Small Femoral Arteries in Newborn Llama and Sheep Gestated at Low and High Altitudes

The authors previously demonstrated that newborn llama (NBLL) express high levels of α(1) adrenergic receptors, which provide a potent vasoconstriction response when compared with newborn sheep (NBSH) gestated at sea level. However, data regarding the impact of chronic gestational hypobaric hypoxia on α-adrenergic vasoconstriction in the neonatal life has not been studied. We evaluated if gestation under chronic hypobaric hypoxia modifies α(1)-adrenergic vasoconstrictor function in NBLL and NBSH. We compared the vasoconstrictor response induced by potassium and α-adrenergic stimuli in isolated small femoral arteries of NBLL and NBSH gestated at high altitude (HA; 3,600 m) or low altitude (LA; 580 m). The maximal contraction (R(MAX)) and potency (EC(50)) to potassium, noradrenaline (NA), and phenylephrine (PHE) were larger in HA-NBLL than LA-NBLL. R(MAX) to potassium, NA, and PHE were lower in HA-NBSH when compared with LA-NBSH and potency results were similar. Competitive blockade with prazosin showed that RNLL LA/HA have a similar pA(2). In contrast, NBSH had increased pA(2) values in HA when compared with LA. Finally, small femoral arteries denudated or treated with LNAME in LA and HA lacked NO or endothelium participation in response to PHE stimulation. In contrast, NBSH displayed that denudation or blockade with LNAME support NO or endothelium participation in response to PHE activation. In conclusion, HA chronic hypoxia enhances α(1) adrenergic receptor activity in small femoral arteries in NBLL to a higher degree than NBSH, implying a higher vasoconstriction function.