HYPOXIA EFFECTS ON HYPOTHALAMIC CORTICOTROPIN-RELEASING HORMONE AND ANTERIOR-PITUITARY CAMP

AIM: To study the effects of acute and chronic hypoxia on hypothalamus -anterior pituitary-adrenocortex axis. METHODS: Rats and pikas were ex posed to different altitude and periods. Animals were injected with CR H, Arg and NE in the third ventricle of the brain of rats. RESULTS: An terior pituitary cAMP and plasma corticosterone levels of rats obvious ly increased during 1 h of hypoxia. cAMP was increased from 2.23 +/- 0 .13 of control group to 7.7 +/- 0.7 of 5 km and 13.4 +/- 1.9 nmol/g we t tissue of 8 km, respectively. icv CRH, Arg and NE all activated HPA axis. The effects of CRH were most potent. CRH 2 mu L 0.75 nmol icv in creased anterior pituitary of cAMP from 3.5 +/- 0.4 of control to 22.4 +/- 2.2 nmol/kg wet tissue. Stimulating altitude of 5000 m resulted i n a 16.9 % decrease in corticosterone level (P < 0.05), 8000 m resulte d in a 47.5 % decrease (P < 0.01) after hypoxia for 25 d. Hypoxia did not activate HPA axis in pikas. CONCLUSION: 1) Hypoxia stress activate s the secretion of corticotrophin (ACTH) via cAMP; 2) Adrenocotical fu nction of rats decays during chronic hypoxia; 3) Arg and NE regulate t he secretion of plasma corticosterone and synthesis of pituitary cAMP at the hypothalamus level; 4) Hypoxia tolerance of the pika was high.