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Adrenal Responsiveness and the Timing of Parturition in Hypothalamo‐Pituitary Disconnected Ovine Foetuses With and Without Constant Adrenocorticotrophin Infusion
Author(s) -
Kirsten R. Poore,
Ben Canny,
I. R. Young
Publication year - 1999
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1046/j.1365-2826.1999.00340.x
Subject(s) - endocrinology , medicine , basal (medicine) , gestation , adrenocorticotropic hormone , fetus , hydrocortisone , hormone , pituitary gland , pregnancy , gestational age , biology , insulin , genetics
Ovine parturition results from an increase in foetal cortisol secretion in late gestation which is dependant on an intact hypothalamo‐pituitary connection. The cortisol surge and parturition fails in hypothalamo‐pituitary disconnected (HPD) foetuses but, paradoxically, immunoreactive (ir)‐ACTH concentrations and secretory dynamics appear normal. This study compares the occurrence and timing of labour, basal ir‐ACTH and cortisol concentrations and adrenal responsiveness in HPD foetuses (HPD/ACTH) receiving constant ACTH (1–24) infusion (43 ng/h/kg) from surgery (114±1 days gestational age (GA)) with those of saline‐infused HPD or intact foetuses (HPD/SAL and INT/SAL). HPD/ACTH foetuses initiated labour at 147±2 days GA, which was not significantly different from INT/SAL foetuses (149±1 day GA). HPD/SAL foetuses were killed electively at 146±3 days GA with no signs of labour. Foetal ir‐ACTH concentrations in all groups were indistinguishable, but only HPD/ACTH and INT/SAL foetuses had a significant cortisol surge. Adrenal responsiveness to ACTH (1–24) (1 μg/kg) was greater in HPD/ACTH foetuses than in HPD/SAL or INT/SAL foetuses at all GAs studied. Adrenal responsiveness in HPD/SAL foetuses exceeded that in INT/SAL foetuses at 120 and 130 days GA but did not change with GA. In summary, the basal cortisol and parturition defect in HPD foetuses was reversed by low‐dose ACTH (1–24) infusion. Basal cortisol concentrations were unrelated to adrenal responsiveness. HPD/SAL foetuses had hyper‐responsive adrenals compared to those of INT/SAL foetuses until 130 days GA, suggesting that the foetal hypothalamus exerts a negative influence on adrenal cortisol responses before 130 days GA, after which time stimulatory influences predominate.