Variations of the labelling index in vitro of rat mammary gland in pregnancy and early lactation

Changes in the tissue content of phosphoribosyl pyrophosphate (PPRibP), glucose 6-phosphate, ribose 5-phosphate (Rib5P), RNA and DNA, of the activity of PPRibP synthetase (EC 2.7.6.1) and the conversion of [1-14C]- and [6-14C]-glucose into 14CO2 were measured at mid-lactation in the normal and diabetic rat and in pregnancy, lactation and mammary involution in the normal rat. The PPRibP, glucose 6-phosphate and Rib5P contents increase during pregnancy and early lactation to reach a plateau value at mid-lactation, before falling sharply during weaning. The PPRibP content, PPRibP synthetase activity and flux of glucose through the oxidative pentose phosphate pathway (PPP) all change in parallel during the lactation cycle. Similarly, after 3 and 5 days duration of streptozotocin-induced diabetes, ending on day 10 of lactation, there were parallel declines in PPRibP content, PPRibP synthetase and PPP activity. The effect of streptozotocin was prevented by pretreatment with nicotinamide and partially reversed by insulin administration. Addition of insulin to lactating rat mammary-gland slices incubated in vitro significantly raised the PPRibP content (+47%) and the activity of the PPP (+40%); phenazine methosulphate, which gives a 2-fold increase in PPP activity, raised the PPRibP content of lactating mammary gland slices by approx. 3-fold. It is concluded that Rib5P, generated in the oxidative segment of the PPP, is an important determinant of PPRibP synthesis in the lactating rat mammary gland and that insulin plays a central role in the regulation of the bioavailability of this precursor of nucleotide and nucleic acid synthesis.

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THE IN VITRO METABOLISM OF MAMMARY GLAND SLICES IN THE PRESENCE OF POSTERIOR PITUITARY LOBE EXTRACTS RICH IN MELANOPHORE-DISPERSING ACTIVITY

Journal of Endocrinology ◽

10.1677/joe.0.0150366 ◽

1957 ◽

Vol 15 (4) ◽

pp. 366-373 ◽

Cited By ~ 1

Author(s):

T. R. BRADLEY ◽

G. M. MITCHELL

Keyword(s):

Mammary Gland ◽

Guinea Pigs ◽

Incubation Medium ◽

Mammary Glands ◽

Gas Evolution ◽

Early Lactation ◽

Posterior Pituitary ◽

Rats And Mice ◽

Posterior Pituitary Lobe

SUMMARY Slices cut from mammary glands of rats and mice during gestation and lactation were incubated in vitro in the presence of pig posterior pituitary lobe extracts rich in melanophore-dispersing ('B') activity. Slices taken in early lactation but not during gestation or late lactation showed increased net gas evolution compared with control slices. Similar tissue from rabbits and guinea-pigs did not give rise to this effect, nor did slices of other tissues taken from lactating rats. The increased net gas evolution was not observed in the absence of glucose from the incubation medium. Treatment of the 'B' extract with NaOH or hypophysectomy of the rats prior to use decreased the response.

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Expression of the mammary gland-specific tammar wallaby early lactation protein gene is maintained in vitro in the absence of prolactin

Molecular and Cellular Endocrinology ◽

10.1016/j.mce.2013.10.030 ◽

2014 ◽

Vol 382 (2) ◽

pp. 871-880 ◽

Cited By ~ 3

Author(s):

Elizabeth A. Pharo

Keyword(s):

Mammary Gland ◽

Protein Gene ◽

Tammar Wallaby ◽

Early Lactation

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Characterization and biological activity of relaxin in porcine milk

Reproduction ◽

10.1530/rep-10-0401 ◽

2011 ◽

Vol 141 (3) ◽

pp. 373-380 ◽

Cited By ~ 17

Author(s):

Amy-Lynn Frankshun ◽

Teh-Yuan Ho ◽

David C Reimer ◽

Joseph Chen ◽

Salamia Lasano ◽

...

Keyword(s):

Mammary Gland ◽

Milk Proteins ◽

Immunoblot Analysis ◽

Mammary Tissue ◽

Early Lactation ◽

Maternal Circulation ◽

A Site ◽

Porcine Milk ◽

Primary Form

A lactocrine mechanism for delivery of maternally derived relaxin (RLX) into the neonatal circulation as a consequence of nursing was proposed for the pig. Immunoreactive RLX was detected in colostrum and in the serum of newborn pigs only if they were allowed to nurse. Milk-borne RLX concentrations are highest during early lactation (9–19 ng/ml), declining to <2 ng/ml by postnatal day 14. Whether milk-borne RLX is bioactive is unknown. Evidence that RLX concentrations in milk are higher than in maternal circulation in several species suggests the mammary gland as a site of local RLX production. It is unknown whether the porcine mammary gland is a source of RLX. Therefore, objectives were to evaluate RLX bioactivity in porcine milk during the first 2 weeks of lactation, identify the form of RLX in porcine milk, and determine whether mammary tissue from early lactation is a source of milk-borne RLX. Milk RLX bioactivity was determined using anin vitrobioassay in which cAMP production by human embryonic kidney (HEK293T) cells transfected with the human RLX receptor (RXFP1) was measured. RLX bioactivity was highest at lactation day (LD) 0, decreasing to undetectable levels by LD 4. Immunoblot analysis of milk proteins revealed an 18 kDa band, indicating proRLX as the primary form of RLX in porcine milk. ProRLX protein and transcripts were detected in porcine mammary tissue on LD 0 and 7. Results support the lactocrine hypothesis by defining the nature and a potential source for bioactive proRLX in porcine colostrum/milk.

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Rapid inhibition of lipogenesis in vivo in lactating rat mammary gland by medium- or long-chain triacylglycerols and partial reversal by insulin

Biochemical Journal ◽

10.1042/bj1920361 ◽

1980 ◽

Vol 192 (1) ◽

pp. 361-364 ◽

Cited By ~ 17

Author(s):

L Agius ◽

D H Williamson

Keyword(s):

Mammary Gland ◽

Glucose Utilization ◽

Insulin Administration ◽

Hepatic Lipogenesis ◽

Medium Chain ◽

Rat Mammary Gland ◽

Long Chain ◽

Partial Reversal

An intragastric load of medium- or long-chain triacylglycerols inhibited lipogenesis in lactating rat mammary gland in vivo by 82 or 89% respectively. This inhibition was reversed partially by insulin administration. Long-chain triacylglycerols inhibited hepatic lipogenesis in vivo but medium-chain triacylglycerols increased it 2-fold. Glucose utilization in vitro by mammary gland acini from triacylglycerol-fed rat was normal.

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BREAKDOWN OF [3H]OXYTOCIN BY RAT TISSUES IN VITRO

Journal of Endocrinology ◽

10.1677/joe.0.0590305 ◽

1973 ◽

Vol 59 (2) ◽

pp. 305-312

Author(s):

SANDRA M. EGAN ◽

A. LIVINGSTON

Keyword(s):

Skeletal Muscle ◽

Mammary Gland ◽

Incubation Medium ◽

Rat Tissues ◽

Tissue Uptake ◽

Tissue Extracts ◽

Rat Mammary Gland

SUMMARY Tissue uptake of oxytocin by rat mammary gland, uterus, heart and skeletal muscle was demonstrated by incubation of these tissues with 3H-labelled oxytocin. Chromatography of tissue extracts showed that some breakdown of oxytocin had occurred after only 30 s. However, in all cases there was no breakdown of oxytocin in the corresponding incubation medium. This indicated that the breakdown of oxytocin occurred within the tissues.

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