In this study we have applied the technique of hypothalamo-pituitary disconnection (HPD) to the fetal sheep at 108–112 days of gestation. The pituitary is surgically disconnected from the hypothalamus by the removal of the neural component of the median eminence above the level of the portal circulation. This procedure results in the complete disconnection of the pituitary from the hypothalamus. After HPD, the lactotroph response to the dopamine antagonist chlorpromazine was significantly reduced (p < 0.005) indicating the functional isolation of the pituitary gland from the hypothalamus. The increase in plasma prolactin in response to exogenous thyrotrophin-releasing factor was maintained following HPD. HPD resulted in the complete atrophy of the pars nervosa. At 132–135 days of gestation after HPD there was no change in the volume or appearance of the pars distalis; small infarcts were observed in the pars distalis of some HPD fetuses, but these occupied less than 1% of the volume of the anterior lobe of the pituitary. There was a significant increase (p < 0.05) in the volume of the pars intermedia after HPD. Gestation was prolonged for at least 8 days beyond normal term following HPD, indicating that the processes integral to the initiation of parturition at term had been disrupted. We conclude that HPD provides a good in vivo model for the investigation of the activity of the isolated pituitary gland, and for the examination of the role of neuroendocrine mechanisms in fetal sheep development in the latter third of gestation.
We have investigated the effect of bilateral adrenalectomy at 116–119 days’ gestation on the levels of the messenger (m) RNA for proopiomelanocortin (POMC) in the anterior pituitary of the fetal sheep and in the ovine placentome during late gestation (134–136 days’ gestation). After fetal adrenalectomy there was a significant (p < 0.001) and sustained increase in circulating ACTH concentrations in the adrenalectomised group (1,838 ± 155 ng/l at 130–136 days) when compared with the intact control group (131 ± 25 ng/l at 130–136 days). The mean levels of POMCmRNA relative to 18S RNA were also significantly higher (p < 0.001) in the adrenalectomised fetal sheep pituitaries (2.8 ± 0.12; n = 4) than in the intact/control fetal sheep pituitaries (1.31 ± 0.13; n = 4). In contrast to the findings in the anterior pituitary, POMCmRNA was not detected in RNA extracted from the placentomes of either the adrenalectomised or intact fetal sheep. There was also a significant arteriovenous difference in ACTH concentrations in the umbilical circulation in both adrenalectomised and intact fetal sheep at 134–136 days’ gestation. This study demonstrates therefore that the fetal adrenals act to suppress POMCmRNA levels in late gestation and also that the increase in circulating ACTH after adrenalectomy originates from the pituitary and not the placentome.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.