Prolactin induces apoptosis of lactotropes

RADL DANIELA; RAMIREZ DELIA; DE LAURENTIIS ANDREA; ZÁRATE SANDRA; JAITA GABRIELA; ZALDIVAR VERÓNICA; EIJO GUADALUPE; SEILICOVICH ADRIANA; PISERA DANIEL

Toronto

Congreso; 89th Annual Meeting of the Endocrine Society; 2007

Prolactin (PRL) is a 23-kDa polypeptide hormone mainly synthesized and secreted by the anterior pituitary. PRL is frecuently associated with proliferation and differentiation of several tissues such as mammary gland, ovary, prostate and immune cells. However, PRL may also exert a proapoptotic action in different cell types. In rats, PRL increases the number of corpora lutea apoptotic cells in the morning of proestrus (1). In addition, the antiangiogenic action of the 16-kDa PRL isoform involves apoptosis of endothelial cells (2). Since it has been demostrated that PRL markedly inhibits the proliferation of lactotropes of female mice (3), we investigated the effects of PRL in the induction of apoptosis in anterior pituitary cells and lactotropes. Primary cultures of anterior pituitary cells from female rats were incubated with PRL (0-500 ng/ml, 16 h). PRL decreased cell viability (MTS) in a dose dependent manner (OD, Control: 0.52 ± 0.01; 10 ng/ml: 0.53 ± 0.01; 100 ng/ml: 0.29 ± 0.02, p<0.01; 500 ng/ml: 0.03 ± 0.01, p<0.01; Dunnet). PRL also increased the number of apoptotic anterior pituitary cells (TUNEL) in a dose dependent manner (Control: 3.5 %; 10 ng/ml: 3.1 %; 100 ng/ml: 13.0 %, p<0.01; 500 ng/ml: 64.4 %, p<0.01; c2) as well as the number of apoptotic lactotropes, identified by immunofluorescence (Control: 3.1 %; 10 ng/ml: 3.7 %; 100 ng/ml: 20.6 %, p<0.01; 500 ng/ml: 62,0 %, p<0.01; c2). Since estrogens sensitize anterior pituitary cells to propapototic factors such as TNF-a, FasL and LPS (4), we evaluated the action of estradiol in the apoptotic effect of PRL. Anterior pituitary cells from ovariectomized rats were incubated with estradiol (E2, 10-9 M, 48 h) or vehicle and then PRL was added (0-500 ng/ml, 16 h). PRL decreased cell viability (MTS) when cells were incubated either with E2  (OD; Control: 0.76 ± 0.02; 100 ng/ml: 0.47 ± 0.07, p<0.01; 500 ng/ml: 0.12 ± 0.08, p<0.01; Dunnet) or with vehicle (Control: 0.77 ± 0.02; 100 ng/ml: 0.52 ± 0.05, p<0.01; 500 ng/ml: 0.18 ± 0.11, p<0.01; Dunnet). These observations indicate that PRL induces apoptosis of anterior pituitary cells and lactotropes in an estrogen independent manner. The proestrus PRL surge could be involved in the apoptosis of lactotropes that occurs during this estrous cycle stage, participating in the anterior pituitary cell renewal process. 1) Gaytán F, et al., Cyclic changes in the responsiveness of regressing corpora lutea to the luteolytic effects of prolactin in rats. Reproduction (2001) 122: 411–417. 2) Clapp C, et al., Vasoinhibins: endogenous regulators of angiogenesis and vascular function.. TRENDS in Endocrinology and Metabolism (2006) 17 (8): 301-307 3) Schuff K. G, et al., Lack of prolactin receptor signaling in mice result in lactotroph proliferation and prolactinomas by dopamine-dependent and -independent mechanisms. J. Clin. Invest (2002) 110: 973–981. 4) Candolfi M, et al., Anterior pituitary cell renewal during the estrous cycle. Front Horm Res( 2006) 35: 9-21.