Changes in fat cell morphology during lactation in the mouse

Abstract

A.BSTRACTA comparison was made of changes in the morphology of fat cells in the intact mammary gland, de-epithelialized mammary fat pad, and the parametrial fat pad of female C3H mice during lactation. Mammary fat pad not in contact with actively secretory epithelium shows partial loss of fat during lactation (systemic effect) while in the presence of such epithelium there is much greater loss of fat (systemic plus local effect). In the same animal the parametrial fat pad shows greater depletion during lactation than the de-epithelialized mammary fat pad. The extent of fat depletion is dependent on the number of nursing young and the duration of lactation. In the intact mammary gland and parametrial fat pad, marked change ,in fat cell structure is not seen in pregnancy except possibly at the very end; after weaning, replenishment of lactation-depleted fat cells is conspicuous by 48 hours. The basic ultrastructure of mammary fat cells and the kinds of changes they undergo during depletion do not differ from those described for other mammalian adipose tissues.In the female mouse the epithelial component of the mammary gland lies embedded .in a pad of white adipose tissue that occupies most of the mass of the gland i n the non-pregnant state. Although changes in the mammary epithelium during pregnancy and lactation have been described extensively (e.g., Cole, '33; Turner and Gomez, '33), little attention has been given to the interactions of the parenchyma with the adipose stroma. Hass ('3:3) felt that the growing and active parenchyma of pregnancy and lactation exerted a local effect directly on the surrounding fat cells and caused their depletion, but he did not consider the degree to which depletion might be induced by systemic factors. A local interaction is also suggested by the observation that transplanted mammary parenchyma grows only if placed i n adipose tissue sites (Faulkin and DeOme, '58; DeOme et al., '59; Hoshino, '62; Slavin, '66).The questions raised by such observations warrant systematic study. In this paper we have attempted to analyze the question of a possible local action of mamm ry parenchyma on the surrounding fat cel B s during lactation by examining mor-ANAT. REC., 177: 533-548.

Cytoplasmic lipid droplet accumulation in developing mammary epithelial cells: roles of adipophilin and lipid metabolism

“…Our observations that relative perilipin protein and mRNA levels decrease with a time course similar to that of CLD accumulation in differentiating secretory cells suggest that the two processes may be functionally related. Indeed, earlier studies documented that depletion of lipid in mammary adipose cells during late pregnancy and lactation is dependent on the presence of an epithelial component (49). In this context, it is interesting that steady-state levels of perilipin protein and mRNA begin to decrease at mid pregnancy, well before alveoli are significant cellular components of the mammary gland.…”

“…In this context, it is interesting that steady-state levels of perilipin protein and mRNA begin to decrease at mid pregnancy, well before alveoli are significant cellular components of the mammary gland. Thus, it is unlikely that declines in perilipin expression are attributable simply to displacement of the adipose compartment by alveoli (49). At present, the factors regulating adipose lipid depletion and the reduction of perilipin expression are not well defined, but both systemic hormones and/or epithelium-derived paracrine factors are possible contributors.…”

“…The lipid content of the mammary gland adipose stores begins to be depleted in late pregnancy and is significantly depleted in response to lactation (49,50). It has been postulated that this depletion of adipose lipid is attributable to shunting of fatty acids into secretory epithelial cells for milk lipid synthesis (51).…”

Differential expression of the growth hormone receptor and growth hormone-binding protein in epithelia and stroma of the mouse mammary gland at various physiological stages

“…During gestation and early lactation, intense epithelial cell proliferation leading to increased ductal branching and lobulo-alveolar development causes the inter-ductal spaces to be filled with secretory lobules (Imagawa et al 1986). As the alveoli enlarge and differentiate into milk-producing and -secreting structures, the stromal mass decreases (Sakakura 1991) due to lipid depletion from mammary adipocytes (Elias et al 1973). After lactation, secretory epithelial cells are gradually lost by apoptosis and the mammary gland undergoes involution (Walker et al 1989, Strange et al 1992.…”

Classic Studies of Mammary Development and Milk Secretion: 1945 – 1980

“…Peter Wooding at Babraham had produced superior images showing the secretion of the milk fat globule [14]. One of the finest electron microscopists of the time, Dorothy Pitelka, was head of the electron microscope laboratory in the Department of Zoology at Berkeley, and began to publish astonishing images beginning in 1960 [12,16]. Perhaps her best work, reprinted in this issue, is a study of cell contacts in the developing and lactating mammary gland [17].…”