Mammary Growth During Pregnancy in Hypophysectomized or Bromocriptine-Treated Goats

Buttle, H. L.; Cowie, A. T.; Jones, Edward; Turvey, A.

doi:10.1677/joe.0.0800343

Cited by 36 publications

(27 citation statements)

References 30 publications

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“…In this connection, there is substantial evidence that placental lactogen is an important hormone in sheep (Martal andDjiane 1975, 1977;Kelly et al 1976) and goats (Kelly et al 1976; Buttle et al 1979). It is pertinent that the blood concentration of prolactin of pregnant sheep, goats and cows is low until shortly before parturition (Johke et al 1971;Fell et al 1972;Lamming et al 1974).…”

Section: Discussionmentioning

confidence: 99%

The Importance of Prolactin for Initiation. of Lactation in the Pregnant Ewe

Gow¹,

McDowell²,

Jenkin³

1983

Aust. Jnl. Of Bio. Sci.

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A single injection of ergocryptine (0, 5 mg/kg liveweight) given to ewes O· 5-20 days prepartum or two injections (0' 5 mg/kg liveweight per injection) given c. 30 and 10 days prepartum reduced concentrations of plasma prolactin to negligible « 5 ng/ml) values for 4 weeks after parturition, but did not affect concentrations of growth hormone and placental lactogen.Milking of treated ewes had no effect on concentrations of plasma prolactin during the first 4 weeks of lactation, but concentrations of growth hormone were increased during the 10-20 min period after milking. The half-life of prolactin in plasma was estimated as 21 min.In spite of the dramatic effect of ergocryptine on plasma prolactin all treated ewes secreted copious quantities of milk of normal composition. Mean daily yields of ewes treated with ergocryptine were not significantly different (P > 0'05) from those of untreated control ewes, but the mean ± s.e.m. of total milk production over the first 3 weeks of lactation for ergocryptine-treated ewes was significantly lower (P < 0'05) than that of control ewes (9·5±1·11 v. 14·1±1·20 kg milk).The results suggest that prolactin is not an essential component of the lactogenic and galactopoietic complexes of hormones in the ewe.

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Section: Discussionmentioning

confidence: 99%

The Importance of Prolactin for Initiation. of Lactation in the Pregnant Ewe

Gow¹,

McDowell²,

Jenkin³

1983

Aust. Jnl. Of Bio. Sci.

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“…Relaxin synergizes with pituitary and ovarian hormones to stimulate growth in young ovariectomized-hypophysectomized rats (Harness & Anderson, 1977) but inhibits steroidinduced mammary development in virgin goats (Cowie et al, 1965) Anderson, 1975a) or only partly inhibited (e.g. goats: Buttle, Cowie, Jones & Turvey, 1979; sheep: Denamur & Martinet, 1961). Ovariectomy or fetectomy of pregnant rats and mice has no significant effect on mammogenesis, either, provided that the placentae remain intact; if the placentae are removed then mammogenesis ceases (Desjardins, Paape & Tucker, 1968).…”

Section: Systemic Endocrine Controlmentioning

confidence: 99%

Development of the mammary gland

Knight¹,

Peaker²

1982

Reproduction

139

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“…Several studies have shown that this PRL pulse is also essential for the initiation of lactation. Treatment at the end of pregnancy with the dopamine agonist bromocriptine (BRO) to suppress the peripartum PRL pulse results in a complete failure of milk production and the subsequent death of the neonates (Buttle et al 1979, Fletcher et al 1990. One of the possible mechanisms of this crucial PRL effect is the well-documented dependence of cyclin D1 synthesis in the mammary gland on PRL (Brockman et al 2002).…”

Section: Introductionmentioning

confidence: 99%

Has the mammary gland a protective mechanism against overexposure to triiodothyronine during the peripartum period? The prolactin pulse down-regulates mammary type I deiodinase responsiveness to norepinephrine

Anguiano¹,

Rojas-Huidobro²,

Delgado³

et al. 2004

Journal of Endocrinology

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Peripartum is a crucial period for mammary gland final differentiation and the onset of lactation. Although the 'trigger' for lactogenesis depends on several hormones, a key factor is the peripartum prolactin (PRL) pulse whose deletion results in a failure to initiate milk production. Other hormones having a critical role during this period but exerting a contrary effect are the thyronines. A transitory hypothyroidism occurs at peripartum in serum and several other extrathyroidal tissues, whereas the induction of hyperthyroidism during late pregnancy is associated with the absence of lactation after delivery. We analyzed the mammary gland during pregnancy and lactation for: (a) the type and amount of thyroid receptors (TRs), (b) the local triiodothyronine (T3) generation catalyzed by type I deiodinase (Dio1), (c) the Dio1 response to norepinephrine (NE) and (d) the effect on Dio1 and TRs of blocking the PRL pulse at peripartum. Our data showed that during pregnancy the mammary gland contains Dio1 in low amounts associated with the highest expression of TR 1; whereas during lactation the gland shows high levels of both Dio1 and TR 1. However, at peripartum, both TRs and Dio1 decrease, and Dio1 becomes refractory to NE. This refractoriness disappears when the PRL pulse is blocked by the dopamine agonist bromocriptine. This blockade is also accompanied by a significant decrease in cyclin D1 expression. Our data suggested that the peripartum PRL pulse is part of a protective mechanism against precocious differentiation and/or premature involution of the alveolar epithelium due to T3 overexposure.

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Mammary Growth During Pregnancy in Hypophysectomized or Bromocriptine-Treated Goats

Cited by 36 publications

References 30 publications

The Importance of Prolactin for Initiation. of Lactation in the Pregnant Ewe

The Importance of Prolactin for Initiation. of Lactation in the Pregnant Ewe

Development of the mammary gland

Has the mammary gland a protective mechanism against overexposure to triiodothyronine during the peripartum period? The prolactin pulse down-regulates mammary type I deiodinase responsiveness to norepinephrine

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