CAROTID-SINUS NERVE-SECTION AND THE INCREASE IN PLASMA-CORTISOL DURING ACUTE-HYPOXIA IN FETAL SHEEP

1. We studied the effects of acute isocapnic hypoxia on plasma concent rations of adrenocorticotrophic hormone (ACTH) and cortisol in sixteen sheep fetuses at 118-125 days of gestation(term is 147 days). Eight f etuses had their carotid sinus nerves cut (denervation); the remaining eight had these nerves left intact. 2. There were no differences in t he plasma concentrations of ACTH or cortisol between intact and denerv ated fetuses during normoxia. 3. Whilst plasma cortisol increased in e arly (after 15 min) and late (after 45 min) hypoxia in intact fetuses, the rise in cortisol in denervated fetuses was delayed, increasing si gnificantly only by late hypoxia. 4. In contrast, plasma ACTH concentr ations were increased in early and late hypoxia in both intact and den ervated fetuses. The rise was smaller in denervated fetuses, but was n ot significantly different from that in intact fetuses. 5. Our results indicate that, in the sheep fetus, carotid sinus nerve section delays the rise in plasma cortisol in response to acute hypoxia without affe cting the ACTH response. Further work is needed to establish the mecha nism underlying this effect of denervation.