Prolactin and LH release in response to LH-RH and TRH in ewes during dioestrus, pregnancy and post partum

Wright, Patrick; Jenkin, Graham; Heap, R. B.

doi:10.1530/jrf.0.0620447

Cited by 19 publications

(4 citation statements)

References 20 publications

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“…Seasonal or photoperiod-induced changes may re flect changes in secretion of several putative hypothalamic prolactin-releasing and inhibiting hormones including The role of TRH in mediating seasonal changes in pro lactin is unclear. Exogenous TRH elevates prolactin secre tion in sheep [4, 21,22], and both prolactin and thyroid-sti mulating hormone are elevated in sheep exposed to long photoperiods [12], These observations suggest that in creased TRH secretion could mediate both effects. However, active immunoneutralization of TRH in ewes does not prevent seasonal rhythms of prolactin secretion al though it reduces mean prolactin concentrations [5].…”

mentioning

confidence: 82%

Effect of Photoperiod and Morphine on Plasma Prolactin Concentrations and Thyrotropin-Releasing Hormone Secretion in the Ewe

Leshin

Jackson²

1987

Neuroendocrinology

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This study investigated the effects of daily photoperiod length and morphine on thyrotropin-releasing hormone (TRH) and prolactin secretion in sheep. Two groups of adult ewes were kept under either 16hL:8 h D or 8 h L:16 h D photoperiods for approximately 60 days. Then the photoperiods were reversed and approximately 60 days later push-pull cannulae were implanted into the hypothalamic stalk-median eminence. After a 7-day recovery period, the ewes were subjected to hypothalamic perfusion and blood was collected at 15-min intervals from the jugular vein. Perfusates also were collected into 15-min fractions. The first 3 h of perfusion served as an equilibrium period. During the next 2 h, saline was infused into one jugular vein. This was followed by a 2-hour morphine infusion (1 mg·kg^–1 • h^–1). Data from 13 ewes were analyzed for effect of photoperiod and drug on TRH concentrations in the perfusates and prolactin in the serum. Prolactin was significantly (p < 0.01) higher under 16 h L:8 h D than 8 h L:16 h D and was greatly increased (p < 0.001) by morphine infusion. TRH only tended to be higher (p = 0.05) under 16 h L:8 h D than under 8 h L:16 h D, but morphine infusion induced a rapid and highly significant (p < 0.01) increase in TRH secretion. There were no photoperiod and drug interactions for either TRH or prolactin. These results suggest that increased prolactin secretion induced by long-day photoperiods is not mediated by TRH, whereas the morphine-induced increase in prolactin secretion appears to be due at least partially to increased TRH secretion.

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mentioning

confidence: 82%

Effect of Photoperiod and Morphine on Plasma Prolactin Concentrations and Thyrotropin-Releasing Hormone Secretion in the Ewe

Leshin

Jackson²

1987

Neuroendocrinology

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“…Plasma gonadotrophin concentrations (LH and FSH) decrease to a nadir in late gestation (Chamley et al, 1974a;Jenkin et al, 1977). Furthermore, the release of LH and FSH in response to the administration of gonadotrophin releasing hormone (GnRH) is suppressed to minimal values in late gestation (Chamley et al, 1974a,b;Jenkin and Heap, 1974;Jenkin et al, 1977), while the release of prolactin in response to thyrotrophin releasing hormone is increased (Wright et al, 1981). In contrast to the cycle, this suppression of gonadotrophin release is not associated with high plasma concentrations of inhibin, as Findlay et al (1991) demonstrated that immunoreactive inhibin concentrations decline from values equivalent to those observed during the cycle from day 40 of gestation to barely detectable concentrations by late gestation.…”

Section: Feedback Role Of Inhibin In Pregnant Ewesmentioning

confidence: 99%

Inhibin and activin in embryonic and fetal development in ruminants

Jenkin¹,

McFARLANE²,

de³

2019

Proc

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Inhibin, activin and follistatin are protein hormones with diverse physiological roles. The involvement of inhibin in the regulation of pituitary FSH production and secretion in adult males and non-pregnant females is well established. However, it is unlikely that inhibin plays a similar role in pregnancy in ruminants. Inhibin and activin molecules show a high degree of structural similarity to potent growth and differentiation factors of the transforming growth factor 13(TGF-f3) superfamily of peptides and their localization in a range of embryonic and fetal tissues indicates that they may thus play a role in development. Furthermore, the demonstration that follistatin is also present in a number of embryonic and fetal tissues and fluids has further implications for the actions of activin to which it binds. The role of inhibin, activin and follistatin in early development has yet to be established since gene knockout experiments have so far proved inconclusive. During mid-and late gestation, high concentrations of inhibin are found in the testes and plasma of male fetuses of sheep and cattle. Inhibin may play a role in regulating pituitary FSH release in late pregnancy, but the very high concentrations of this hormone in ovine fetal testes and in male fetal plasma compared with that observed in the fetal ovary and female fetal plasma has yet to be explained. The recent observation of high concentrations of inhibin, activin and follistatin in amniotic fluid surrounding the fetus is intriguing. Excretion via urine or lung liquid is partly responsible for the presence of these proteins in amniotic fluid. The fetal membranes and the placenta are also possible sources. It remains to be established whether these proteins constitute an inactive pool of secreted hormone or whether they have other actions in this fetal compartment.

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“…Plasma folliclestimulating hormone (FSH) and prolactin were measured by previously published methods (Parrott & Davies 1977;Wright et al 1978Wright et al , 1981. The coefficients of variation within and between assays were < 14 and < 16%, respectively, for all hormones.…”

Section: Analyticalmentioning

confidence: 99%

Estimation of pituitary secretion rate during the reproductive cycle of sheep

et al. 1990

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S U M M A R YA technique has been developed for the measurement of pituitary hormone secretion rates in conscious sheep. The technique involves the continuous and simultaneous sampling of blood from the carotid artery and jugular vein and the measurement of cephalic blood flow by an indicator dilution technique. Veno-arterial differences in hormone concentrations multiplied by cephalic blood flow gave average secretion rates which were measured after single or repeated large doses of luteinizing hormone releasing hormone (LHRH) and thyrotrophin-releasing hormone (TRH) at various times in the reproductive cycle.

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Prolactin and LH release in response to LH-RH and TRH in ewes during dioestrus, pregnancy and post partum

Abstract: Summary. With

Cited by 19 publications

References 20 publications

Effect of Photoperiod and Morphine on Plasma Prolactin Concentrations and Thyrotropin-Releasing Hormone Secretion in the Ewe

Effect of Photoperiod and Morphine on Plasma Prolactin Concentrations and Thyrotropin-Releasing Hormone Secretion in the Ewe

Inhibin and activin in embryonic and fetal development in ruminants

Estimation of pituitary secretion rate during the reproductive cycle of sheep

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