Effect of dietary protein level during pregnancy and 2 weeks of lactation on mammary gland growth in rats

Pyska, H.; Styczynski, H.

doi:10.1017/s0022029900020756

Journal of Dairy Research

1979

DOI: 10.1017/s0022029900020756

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Effect of dietary protein level during pregnancy and 2 weeks of lactation on mammary gland growth in rats

H. Pyska

H. Styczynski

Abstract: In a previous paper (Pyska & Styczyriski, 1979) it was shown that protein level in the diet of a rat influences the development of its mammary gland during the animal's growth to sexual maturity. Rats fed a semi-synthetic diet containing 15% protein had better-developed mammary glands than rats on a diet containing 10% protein. The aim of the study now reported was to investigate the effect of the protein level in the diet on the development of the mammary gland during pregnancy and 14 d of lactation.

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Cited by 6 publications

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Functional differentiation of virgin mouse mammary epithelium in explant culture is dependent upon extracellular proline

Smith

1987

Journal Cellular Physiology

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Depletion of proline from insulin, hydrocortisone, and prolactin-containing medium prior to incubating virgin mouse mammary explants prevents both DNA synthesis and functional differentiation in the mammary epithelial cells; however, DNA synthesis in the mammary stroma and total incorporation of radioactive amino acids into total protein appears to continue without hindrance. Removal of glycine instead of proline had no deleterious effect on either DNA replication in the hormone-stimulated epithelium or in its functional differentiation. Functional differentiation was determined by the induction of casein and alpha-lactalbumin synthesis in the insulin, hydrocortisone, and prolactin (IFPrl)-treated explant cultures. As a control, the induction of mouse mammary tumor virus (MMTV) gene expression, a corticosteroid-regulated function, was also measured. Neither the absence of proline or glycine prevented the glucocorticoid stimulation of MMTV gene expression. In contrast to mammary tissue from virgin mice, explants from nonpregnant primiparous mice responded fully to IFPrl stimulation with respect to DNA, casein, and alpha-lactalbumin synthesis in medium depleted of proline. These data suggest that the uncommitted epithelium of virgin mouse mammary glands requires the presence of exogenous proline in order to respond to lactogenic hormonal signals. We have demonstrated earlier that DNA synthesis is a prerequisite of functional differentiation in virgin mouse mammary explants (Smith and Vonderhaar, 1981, Dev. Biol., 88:167-179; Vonderhaar and Smith, 1982, J. Cell Sci, 53:97-114), although cytological differentiation proceeded unencumbered in explants prevented from synthesizing DNA. Here, without proline, neither cytological nor functional differentiation can be induced; this suggests that proline provides an essential metabolic interlock in the acquisition of lactogenic hormone responsiveness in uncommitted mouse mammary tissue.

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Functional differentiation of virgin mouse mammary epithelium in explant culture is dependent upon extracellular proline

Smith

1987

Journal Cellular Physiology

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Effects of fasting during mid pregnancy or early lactation on mammary development and milk yield in mice

Knight

Peaker

1982

Journal of Dairy Research

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SUMMARYMice were fasted during pregnancy or early lactation and the effects on mammary development and milk yield studied on d 13 and d 18 of pregnancy and on d 7 of lactation. Fasting during pregnancy reduced body weight and mammary weight on d 13 of pregnancy but not on d 18. Mammary concentrations and total contents of DNA and RNA ([DNA], [RNA], DNAt, RNAt) were increased or unchanged on d 13 but significantly decreased on d 18. Fasting had no effect on fetal number or weight at either stage of pregnancy. Fasting on d 1 of lactation reduced mammary weight, DNAt and RNAt (but not [DNA] or [RNA]) and the incorporation of tritiated thymidine into DNA on d 2 of lactation. Mammary gland weight and composition on d 7 of lactation were not significantly affected by fasting for 24 h on d 1 of lactation or for 40 h on d 11–13 of pregnancy, except that DNAt was decreased slightly by the latter treatment.Milk yield (litter weight gain) was depressed markedly during fasting on d 1 of lactation, but thereafter recovered so that it was the same as controls between d 3 and 13 of lactation; after d 13 it fell once more. A 40 h fast on d 11–13 of pregnancy had no effect on milk yield. Thus, although normal mammary development was inhibited by starvation, the gland was subsequently able to compensate so that milk yield was not reduced.

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Mammary sensitivity to protein restriction and re-alimentation

1996

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The present study tested the influence of protein undernutrition and re-alimentation on mammary gland size and secretory cell activity in lactating rats. During gestation, female Sprague-Dawley rats were offered a high-protein diet (215 g crude protein (N x 625; CP)/kg DM; H); litters were standardized to twelve pups at parturition. During lactation, two diets were offered ad libitum, diet H and a lowprotein diet (90 g CP/kg DM; L). Lactational dietary treatments were the supply ad libitum of either diet H (HHH) or diet L (LLL) for the first 12 d of lactation, or diet L transferring to diet H on either day 6 (LHH) or 9 (LLH) of lactation. On days 1,6,9 and 12 of lactation, rats from each group (n 2 6) were used to estimate mammary dry mass, fat, protein, DNA and RNA; the activities of lactose synthetase (EC 2.4.1.22) enzyme and Na+, K+-ATPase (EC 3.6.1.37) were also measured. Rats offered a diet considered protein sufficient (H) from day 1 of lactation showed a decrease in mammary dry mass and fat but an increase in DNA, RNA and protein on day 6, after which there was no further change, except for mammary protein which continued to increase. However, rats offered diet L showed a steady loss in mammary mass and fat throughout the 12 d lactation period and no change in mammary DNA, RNA or protein. Rats previously protein restricted for either the first 6 or 9 d of lactation had their mammary dry mass and mammary fat loss halted and showed a rapid increase in mammary DNA, RNA and protein on re-alimentation. Lactose production in group HHH, as measured by lactose synthetase activity, was similar on days 1 and 6 of lactation, after which a significant increase was seen. Proteinrestricted rats showed no change in lactose synthetase activity during the 12 d experimental period. Changing from diet L to diet H led to a significant increase in lactose synthetase activity to levels comparable with those offered diet H from day 1. These results show that rats offered a protein-restricted diet during lactation suffer mammary underdevelopment, but this may be rapidly reversed by realimentation with a high-protein diet.

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Effect of dietary protein level during pregnancy and 2 weeks of lactation on mammary gland growth in rats

Cited by 6 publications

References 9 publications

Functional differentiation of virgin mouse mammary epithelium in explant culture is dependent upon extracellular proline

Functional differentiation of virgin mouse mammary epithelium in explant culture is dependent upon extracellular proline

Effects of fasting during mid pregnancy or early lactation on mammary development and milk yield in mice

Mammary sensitivity to protein restriction and re-alimentation

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