The effects of ACTH on adrenal steroidogenesis and blood corticosteroid levels in the echidna (Tachyglossus aculeatus)

Abstract 1. 1. The effects of short-term (S.T., 30 min) and long-term (L.T., 4 days) administration of ACTH on peripheral blood corticosteroid levels and on in vitro steroidogenesis were investigated. 2. 2. Control levels of cortisol, corticosterone and aldosterone were 58 ± 12, 130 ± 26 and 10 ± 6 (SEM) ng/100 ml respectively. 3. 3. Corticosterone was 70% higher after S.T. and 150% higher after L.T., when cortisol was 800% higher. 4. 4. Adrenal homogenates from control echidnas converted [ 14 C]progesterone predominantly to 11-deoxycorticosterone (45%) and 11-deoxycortisol (12%). 5. 5. After L.T. the principal product was corticosterone (25%), but S.T. had no effect. 6. 6. In control echidnas the K m , and V for 11β-hydroxylation of 11-deoxycorticosterone were 20 μM and 2.8 ρmol/min/mg respectively. After L.T. V increased to 10 ρmol/min/mg.