5. CORTICAL AND MEDULAR ADRENAL GLAND RESPONSE TO HYPOXEMIA (H) IN FETAL ILAMA

Abstract

The cardiovascular response to H in fetal llam (Lama glama) is characterized by an intense vascoconstriction of the carcass, kidneys and gut. In fetal sheep this response is partially mediated by catecholamines and arginine-vasopressim. A simultaneous increase in plasma ACTH and cortisol (F) is also observed. Since the llama has evolved at 4000 meters shove the sea level in a low O2 environment, we investigated whether nonadrenaline (Na) and F plasma concentrations increase after an acute episode of H at sea level in fetal llama. Catheters were placed into fetal and maternal femoral arteries and veins in 5 pregnant llamas in the last third of gestation, 7 days after their arrival to Santiago (586 m) from Parinacota (4500 m). Hypoxemia was induced by making the mother breath a mixture of N2 and air (fetal % Sat Hb decreased from 46.6±5.7 to 28.6 ± 1.7%). Plasma concentrations of F (RIA) and NA (fluorimetry) were measured in basal and H (10min) conditions. Na increassd from 2.3±1.4 to 42.2±14.0 ng/ml (mean ± SEM)during H. Basal F was 23.8 ± 24.9 ± 9.9 ng/ml during H. The results sjow a medullar but not a cortical response to an acute H in the fetal llama in the last third of gestation. The medulla responded with a 1800% increase in Na plasma concentrations during H. This result could explain the intense vasoconstriction observed during H in the fetal llama. The failure of Fto increase during H could be due to an insufficient fetal H, immature F synthetic pathway, refractoriness of the fetal adrenal cortex to ACTH or the presence of a factor inhibiting the ACTH trophic action on the fetal adrenal gland.FONDECYT 0820/86.