Section A. Physiology. Hormonal control of lactogenesis

Denamur, R

doi:10.1017/s0022029900019348

Cited by 96 publications

(43 citation statements)

References 292 publications

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“…2), are in agreement with previous reports (Amenomori et al 1970;Denamur 1971;Bast and Melampy 1972;Linkie and Niswender 1972;Morishinge et al 1973;Nicholas and Hartmann 1981a) and with the changes observed in chronically cannulated rats (Fig. 1).…”

Section: Discussionsupporting

confidence: 93%

“…Gala and Westphal (l965a) reported a fall in the concentration of corticosteroid binding globulin (CBG) between late pregnancy and early lactation in the rat, and suggested that the increase in biologically active corticosteroid may induce lactogenesis in this species. However, there is still disagreement whether the concentration of corticosteroids in the plasma increases during the final 4-5 days before term in the rat (Kuhn 1969;Denamur 1971;Martin et al 1977), and thus the involvement of corticosteroids in the lactogenic mechanism is uncertain.…”

Section: Introductionmentioning

confidence: 99%

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Progressive Changes in Plasma Progesterone, Prolactin and Corticosteroid Levels During Late Pregnancy and the Initiation of Lactose Synthesis in the Rat

Nicholas¹,

Hartmann²

1981

Aust. Jnl. Of Bio. Sci.

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The relationship between progesterone, prolactin, corticosteroids and corticosteroid binding globulin . (CBO) activity in plasma and the initiation of lactation were studied in normal parturient rats, and rats either ovariohysterectomized or Caesarean-sectioned on day 19 of gestation. In chronically cannulated rats the decline in plasma progesterone to low values « 10 p.g/l) in normal parturient rats 20 h before term and in Caesarean-sectioned rats 10--14 h after surgery was closely related to an increase in plasma prolactin. However, in ovariohysterectomized rats the levels of progesterone declined abruptly to 20 p.g/l within 30 min of surgery and prolactin remained low (5 p.g/l) for 4-8 h and then gradually increased during the subsequent 16-18 h. Lactose concentrations in mammary tissue of rats killed at 0, 12, 18. 24, 36 and 48 h after surgery was low « 0·14 mg/g tissue) up to 12 h, and increased to reach maximum values at 36 hand 48 h after surgery in ovariohysterectomized and Caesarean-sectioned rats respectively.The concentration of corticosteroids and CBO capacity in the plasma was 250--550 p.g/l and 250-480 p.g corticosterone bound per litre, respectively, in rats killed during the last 4 days of,gestation. However, both the concentration of corticosteroids and the CBO capacity, within the individual cannulated rats, remained relatively constant during late gestation.These findings support the proposal that progesterone withdrawal is the lactogenic trigger ana suggest the sequential involvement of prolactin. An increase in the concentration of free corticosteroids in late pregnancy and a related stimulatory role in the lactogenic mechanism were not established.

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Section: Discussionsupporting

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Progressive Changes in Plasma Progesterone, Prolactin and Corticosteroid Levels During Late Pregnancy and the Initiation of Lactose Synthesis in the Rat

Nicholas¹,

Hartmann²

1981

Aust. Jnl. Of Bio. Sci.

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“…Kuhn (1969) and Denamur (1971) have suggested that progesterone acts as a repressor of milk biosynthesis before the onset of lactation. In the rabbit, the initial decline in the concentration of plasma progesterone occurs by day 21 of pregnancy (Denamur, 1971;Challis et al, 1973) which coincides with the first lactogenic stimulus. There do not appear to be any reports of changes in the plasma concentration of prolactin in the rabbit during lactogenesis, but it seems likely that prolactin is involved as well as cortisol.…”

Section: Discussionmentioning

confidence: 99%

“…of tissue and the ratio ofRNA/DNA also increased between day 15 and day 24 of pregnancy. Denamur (1969) has demonstrated that the major increase in the concentration of RNA/g wet wt. of tissue during this period occurred on day 21 of pregnancy.…”

Section: Enzyme Analysismentioning

confidence: 99%

Metabolic adaptations during lactogenesis. Lactose synthesis in rabbit mammary tissue during pregnancy and lactation

Mellenberger

Bauman

1974

Biochemical Journal

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1. Mammary tissue, obtained from rabbits at various stages of pregnancy and lactation, was used for tissue-slice incubations to measure the rate of lactose biosynthesis and for relevant enzymic activity measurements. A biphasic adaptation in the rate of lactose synthesis and in the RNA concentration was noted during lactogenesis. 2. The first increase in the rate oflactose biosynthesis occurred between days 15 and 24 ofpregnancy. A second substantial increase was noted immediately postpartum. The overall rate of lactose biosynthesis increased 12-fold from day 24 of pregnancy to day 15 of lactation postpartum, and then decreased from 15 to 22 days post partum. 3. The RNA concentration/g wet wt. of tissue and the ratio of RNA/DNA closely represented the biphasic ability of the mammary-tissue slice to synthesize lactose. 4. Increases in the activities of UDP-glucose 4-epimerase (EC 5.1.3.2) and lactose synthase (EC 2.4

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“…During the course of pregnancy, the plasma concentrations of these hormones fluctuates SO that the balance is gradually shifted in favor of milk synthesis and secretion. Foremost in importance amongst the lactogenic hormones is prolactin, which is absolutely essential for milk synthesis in the rabbit [8]. A radioreceptor assay for total lactogenic activity in plasma revealed that an initial increase occurred the first few days of pregnancy.…”

Section: (A-a)mentioning

confidence: 99%

Studies on the Synthesis of Casein Messenger RNA during Pregnancy in the Rabbit

Shuster

Houdebiné²,

Gaye³

1976

European Journal of Biochemistry

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The quantity of casein mRNA in the rabbit mammary gland was assayed during the course of pregnancy, by translation of casein mRNA in a reticulocyte lysate and by hybridization to DNA complementary to purified casein mRNA. Both methods indicated that the major increases in the concentration of casein mRNA in both polysomal and total cellular RNA occurred between the 18th and 25th day of pregnancy. The change in casein mRNA concentration during this period coincided with a sharp rise in casein synthesis in mammary gland explants suggesting that the levels of casein mRNA determine the rate of casein synthesis in the mammary gland.The sensitivity of the hybridization assay made it possible to detect the presence of casein mRNA in virgin animals and during the very early stages of pregnancy. At day 5, casein mRNA was found associated with polysomes indicating that there was probably some casein synthesis at this early stage of gestation. These results suggest that the hormones controlling lactogenesis in the rabbit may function by augmenting the rate of casein mRNA synthesis rather than initiating transcription of previously inactive genes.Previous studies on the growth of the mammary gland in pregnant rabbits have shown that significant increases in both wet weight and nucleic acid content occur between days 16 and 24 or pregnancy [I-51. It is also during this period that lactose synthetase activity is detected in the mammary gland and the synthesis and secretion of milk is first observed [5 -71.When considered in combination, these results suggested that the genes directing the synthesis of milk proteins were not actively transcribed until mid-pregnancy. At that time, they would presumably be switched on in response to a combination of the same hormonal influences which were responsible for the growth and maturation of the mammary gland [2,8 -111. In this report, we have tested this assumption by examining the content of casein mRNA in rabbit mammary gland during the entire course of pregnancy. We have used both the method of translation in a reticulocyte-lysate and hybridization to cDNA to assay for the presence of casein mRNA. In agreement with the results of recent experiments in the rat [12], we have found casein mRNA appearing in the rabbit mammary gland well before the onset of lactogenesis. Furthermore, the sensitivity of the hybridization technique has enabled us to detect casein mRNA in the mammary gland of virgin animals, indicating that there is a low level of transcription of casein genes in undeveloped tissue. We will present evidence that the casein mRNA detected in mammary glands during the first few days of pregnancy is found associated with a polysomal fraction indicating that it is translated even during the very early stages of gestation. MATERIALS AND METHODS AnimalsPrimiparous rabbits were used. The day of coitus was counted as day 0 of pregnancy. Animals were sacrified by exsanguination and the mammary glands were immediately excised and frozen at -30 "C. Four animals were used in each group...

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Section A. Physiology. Hormonal control of lactogenesis

Cited by 96 publications

References 292 publications

Progressive Changes in Plasma Progesterone, Prolactin and Corticosteroid Levels During Late Pregnancy and the Initiation of Lactose Synthesis in the Rat

Progressive Changes in Plasma Progesterone, Prolactin and Corticosteroid Levels During Late Pregnancy and the Initiation of Lactose Synthesis in the Rat

Metabolic adaptations during lactogenesis. Lactose synthesis in rabbit mammary tissue during pregnancy and lactation

Studies on the Synthesis of Casein Messenger RNA during Pregnancy in the Rabbit

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