Abstract
We examined the presence of hormone-sensitive lipase (HSL) in mammary glands of virgin, pregnant (12, 20, and 21 days), and lactating (1 and 4 days postpartum) rats. Immunohistochemistry with antibody against rat HSL revealed positive HSL in the cytoplasm of both alveolar epithelial cells and adipocytes. In virgin rats, immunoreactive HSL was observed in mammary adipocytes, whereas diffuse staining was found in the epithelial cells. Positive staining for HSL was seen in the two types of cells in pregnant and lactating rats. However, as pregnancy advanced, the staining intensity of immunoreactive HSL increased in the epithelial cells parallel to their proliferation, attaining the maximum during lactation. An immunoreactive protein of 84 kDa and a HSL mRNA of 3.3. kb were found in the rat mammary gland as in white adipose tissue. Both HSL protein and activity were lower in mammary glands from 20 and 21 day pregnant rats than from those of virgin rats, although they returned to virgin values on days 1 and 4 of lactation. Mammary gland HSL activity correlated negatively to plasma insulin levels. Immunoreactive HSL and HSL activity were found in lactating rats' milk. The observed changes indicate an active role of HSL in mammary gland lipid metabolism.
Highlights
We examined the presence of hormone-sensitive lipase (HSL) in mammary glands of virgin, pregnant (12, 20, and 21 days), and lactating (1 and 4 days postpartum) rats
We have demonstrated the presence of HSL in mammary gland adipocytes and epithelial cells from nonpregnant, pregnant, and lactating rats, observing variations in HSL activity and expression during pregnancy and lactation
The presence of HSL in alveolar epithelial cells has previously been reported in lactating rat mammary tissue [37, 38], this is the first time that its presence has been reported in mammary gland adipocytes
Summary
We examined the presence of hormone-sensitive lipase (HSL) in mammary glands of virgin, pregnant (12, 20, and 21 days), and lactating (1 and 4 days postpartum) rats. The lactating mouse mammary gland secretes 5 ml of milk per day containing ف30% fat [3] To develop this transitory capacity for handling such a large amount of lipids, the morphology of the mammary tissue changes during pregnancy and lactation. In mammary glands there is an extensive proliferation of alveolar structures into the adipocytes, accompanied by differentiation of epithelial cells [4], which show cytoplasmic lipid droplets [5] surrounded by the protein adipophilin [6]. Net catabolic changes taking place in adipose tissue during late pregnancy are manifested by an enhanced hormone-sensitive lipase (HSL) activity and decreased LPL activity [8], which result in an increase in maternal plasma lipids both in humans [9, 10] and in rats [11, 12]. Dephosphorylation is affected primarily by protein phosphatases, which are activated by insulin [27]
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