Immunoreactive β-endorphin/lipotrophin in the chronically cannulated ovine foetus: response to bilateral foetal adrenalectomy

Abstract

Abstract. Adrenocorticotrophin (ACTH) is derived from a 'stem' hormone of approximately 31 000 daltons. In man, cleavage of this hormone can produce equimolar amounts of ACTH and β-lipotrophin (β-LPH) in the plasma. Further cleavage of β-LPH in either the pituitary or plasma can release β-endorphin (β-EP). The plasma concentrations of both ACTH and β-EP can be increased by stressful stimuli, adrenalectomy, pituitary-adrenal disorders, or decreased with glucocorticoid treatment. This study investigated the presence of β-EP/LPH in the intact and adrenalectomized (adrX) ovine foetus. Three ovine foetuses were bilaterally adrX at the time of implantation of cannulae into the carotid artery and jugular vein (106–120 days gestation). The foetuses of 9 ewes were chronically cannulated (95–115 days gestation) to serve as controls. Gestation length was 147 ± 5 days. Plasma β-EP/LPH was measured using a heterologous modification of a human β-EP RIA. The assay system had molar cross-reactivity of about 20% with ovine β-LPH, thus results are expressed as β-EP/LPH-like immunoreactivity (IR-β-EP/LPH). In the intact unstressed foetus the plasma IR-β-EP/LPH concentration was relatively constant throughout gestation 228.9 ± 12.0 pg/ml (mean ± sem, n = 35) except for the last 48 h prior to either parturition, abortion or in utero foetal death when concentrations were seen to rise to 357 ± 56.8 pg/ml (n = 10) in 5 out of 6 sheep. During gestation the IR-β-EP/LPH in amniotic fluid was less than in foetal plasma the mean being 130.5 ± 14.8 (n = 10). IR-β-EP/LPH in maternal plasma was similar to that in foetal plasma. In the adrX foetus data has been arbitrarily divided into 3 age groups 90–121, 122–135 and > 136 days gestation, the IR-β-EP/LPH concentrations being 202.7 ± 16.3 (n = 9), 404.6 ± 54.8 (n = 13) and 2566 ± 681 (n = 5) pg/ml, respectively. The elevated IR-β-EP/LPH seen after 122 days does not appear to be reflected in either foetal urine or amniotic fluid. It can be suggested that the pituitary feedback systems controlling both IR-ACTH and IR-β-EP/LPH start to mature or change after 122 days gestation. In summary these findings show the presence of an immunoassayable substance with β-EP/LPH-like reactivity in the plasma of the ovine foetus, and that this IR-β-EP/LPH can often increase prior to parturition, abortion of foetal death. After 122 days gestation IR-β-EP/LPH increases in adrX foetuses, suggesting that after this time feedback control systems with some product of the foetal adrenal first begin to appear.