Development of the hypothalamic-pituitary-axis in the ovine fetus: Ontogeny of action of ovine corticotropin-releasing factor

R. J. MacIsaac, R. J. Bell, J. G. McDougall, G. W. Tregear, X. Wang, E. M. Wintour

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In samples from twenty chronically cannulated ovine fetuses the plasma immunoreactive adrenocorticotrophin (ACTH) concentrations were 12.5 ± 3.2(8), 15.2 ± 4.1(9) and 21.2 ± 5.6(8) pg/ml at periods, prior to parturition, of -30 to -35, -25 to -29 and -20 to -24 days respectively. Values are mean ±SEM (number of samples). These values were not significantly different from each other but were significantly lower (P < 0.02) than values in the next two age groups -36.0 ± 4.9(7) pg/ml at -19 to -15 days, and 39.6 ± 6.6(11) pg/ml at -14 to -9 days. A further significant increase (P < 0.05) occurred in the -8 to -3 day period, ACTH being 53.9 ± 5.4(12) pg/ml. On day of delivery two samples had values of 325 and 360 pg/ml. A single injection, intravenously of 1.0 μg ovine corticotrophin-releasing factor (O-CRF), caused a significant increase in fetal plasma ACTH concentrations in fetuses of -6 to -23 days prior to delivery but not in fetuses -24 to -35 days prior to parturition. The maximum values of ACTH after O-CRF were significantly greater in fetuses -2 to 0 days prior to parturition than in younger fetuses (P < 0.01). In 6 experiments in 4 fetuses (parturition -1 to -13 days) the effect of 1.0 μg O-CRF persisted for at least 2.5 h. The results support the hypothesis that the pituitary release of ACTH changes sensitivity to hypothalamic O-CRF at least twice during the last fifth of gestation; an increasing sensitivity is seen as term approaches.

Original languageEnglish
Pages (from-to)329-338
Number of pages10
JournalJournal of Developmental Physiology
Issue number5
Publication statusPublished - 1 Dec 1985

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