Oxytocin stimulates secretory processes in lactating rabbit mammary epithelial cells

Abstract

Oxytocin plays a major role in lactation mainly by its action on milk ejection via the contraction of myoepithelial cells. The effect of oxytocin on milk production and the presence of oxytocin receptors on different epithelial cells suggest that this hormone may play a role in mammary epithelial cells. To determine precisely the various roles of oxytocin, we studied localization of oxytocin receptors in lactating rabbit and rat mammary tissue and the influence of oxytocin on secretory processes in lactating rabbit mammary epithelial cells. Immunolocalization of oxytocin receptors on mammary epithelial cells by immunofluorescence and in mammary tissue by immunogold in addition to in situ hybridization showed that lactating rat and rabbit mammary epithelial cells expressed oxytocin receptors. Moreover, oxytocin bound specifically to epithelial cells. To determine whether oxytocin had an effect on lactating rabbit mammary epithelial cells, isolated mammary fragments were incubated in the presence or absence of 10 −6 i.u. ml −1 of oxytocin. After 1 min of incubation with oxytocin, the morphology of epithelial cells and the localization of caseins and proteins associated with the secretory traffic suggested a striking acceleration of the transport leading to exocytosis, whereas the contraction of myoepithelial cells was only detectable after 7 min. Addition of 10 −8 g ml −1 of atosiban before the addition of oxytocin prevented the oxytocin effect on secretory processes and on myoepithelial cell contraction. Addition of 10 −6 i.u. ml −1 of vasopressin to the incubation medium did not mimic the stimulating effect of oxytocin on secretory traffic. These results show that lactating rabbit and rat mammary epithelial cells express oxytocin receptors and that oxytocin binds to these receptors. They strongly suggest that oxytocin has a dual effect on lactating mammary tissue: an acceleration of the intracellular transfer of caseins in mammary epithelial cells followed by the contraction of myoepithelial cells.

Physiology of milk secretion

“…As OT receptors are also present in MECs [66], this hormone may also exert direct effects on the secretory activity of MECs (Fig. 3D) [50,60]. Milk is then expelled out of the alveoli into the ducts and lactiferous sinuses.…”

“…Indeed, independently of activating casein gene expression, PRL exerts a secretagogue effect on the last steps of apical transport and possibly the exocytosis of caseins through the production of arachidonic acid [49]. On the other hand, after binding to its cognate receptor in MECs, OT has been shown increase the number of SVs and to accelerate their transport towards the APM [50].…”

Mammary gland secretion: hormonal coordination of endocytosis and exocytosis

“…A question arises as to whether lactogenic hormones play a role in the specific mechanism of exocytosis. This seems to be the case for oxytocin that, through its oxytocin receptors, acts directly on MECs (Lollivier et al, 2006). Within one minute, oxytocin was shown to induce an increase in the intracellular transport of caseins to the lumen of acini.…”

“…The lactogenic hormones released at each suckling or milking not only control the gene expression of milk proteins but also maintain cellular architecture and stimulate the mechanisms of MEC intracellular transport by secretagogue effects (Ollivier-Bousquet and Devinoy, 2005 and references therein; Lollivier et al, 2006). In addition, some blood-borne hormones are carried to the milk across MECs (Ollivier-Bousquet, 1993).…”

Efek Ekstrak Air Buah Pepaya (Carica papaya L.) Muda terhadap Gambaran Histologi Kelenjar Mamma Mencit Laktasi

“…Oksitosin juga dapat memberikan efek yang serupa dengan mempercepat pengosongan lumen alveoli melalui kontraksi mioepitel dan meningkatkan kecepatan sekresi protein dalam sel sekretorius yang melapisi dinding alveoli. 13 Tujuan penelitian ini untuk menilai efek ekstrak air buah pepaya muda terhadap gambaran histologi kelenjar mamma laktasi. Gambaran histologi berupa peningkatan produksi air susu melalui penghitungan jumlah dan pengukuran diameter rata-rata alveoli kelenjar mamma laktasi pada induk mencit, serta menilai perbandingannya dengan sediaan luteotropin.…”