Cellular and functional interactions between gonadotrophs and lactotrophs in pituitary cell cultures

Abstract

Lactotroph secretory activity is regulated by hypothalamic stimulating and inhibiting factors as well as peripheral endocrine hormones. In addition to this important control domain, the pituitary gland displays an intrinsic regulatory ability through autocrine and paracrine signals. To evaluate the role of gonadotrophs in the regulation of prolactin (PRL) secretion, a comparative study was performed applying two regulatory agents that operate through different physiological mechanisms: gonadotropin-releasing hormone (GnRH), which releases regulatory factors co-localized in secretory granules of gonadotrophs, stimulating PRL secretion from lactotrophs; and angiotensin II (AII), with direct effects on lactotroph secretion through specific receptors. In these studies performed in regular and purified primary pituitary cell cultures from female rats, the lactotrophs comprised the largest population of cells (about 51%), whereas gonadotrophs represented only a small fraction (3%) of the total pituitary cell count. In regular cell cultures treatments with AII and GnRH showed a similar secretory behavior, increasing PRL output 73% and 63%, respectively. The stimulation with GnRH and AII of cell cultures with purified lactotrophs and gonadotrophs provided comparable results, but the response of lactotrophs was significantly higher (106% and 138%, respectively) than that recorded in regular cell cultures. Simultaneous AII treatment with an antipeptide antagonist to AII receptor (AII-antipep) completely blocked the PRL release induced by AII. The co-incubation of cells with GnRH and AII-antipep suppressed the peak of PRL release caused by GnRH, confirming that AII is a paracrine agent released by gonadotrophs stimulated with GnRH. The different secretory behavior of lactotrophs treated with AII and GnRH in both regular and purified cell cultures is indicative of the degree of functional interactions between different pituitary cell types. The present study supplies morphological and functional information on the cell-to-cell interactions, which plays an important role in the intrinsic regulatory control of PRL secretion.

Preserved inhibitory effect of recurrent hypoglycaemia on the male gonadotrophic axis

“…Moreover, the adaptation of PRL to recurrent hypoglycaemia leads us to suspect that gonadotrophins and PRL are differentially regulated following separate mechanisms. Consequently, it is precluded that the observed effects on LH and PRL are based on a concurrent control by hypothalamic GnRH 24 or PRL‐releasing peptide 25 . This fits with the data of Bogacka et al ., who found that GnRH did not affect PRL secretion in vitro 26 .…”

Antagonic effects of oestradiol in interaction with IGF-1 on proliferation of lactotroph cells in vitro

“…Bar 1 lm stimulating the pituitary glycoprotein alpha-subunit of the luteinizing hormone (Atkin et al 1993), which was shown to foster the lactotroph differentiation and proliferation in the rat pituitary (Van Bael and Denef 1996). Other cellular and functional interactions between gonadotrophs and lactotrophs in cell culture were previously reported in this laboratory (De Paul et al 2000).…”

Ultrastructural immunolocalization of IGF-1 and insulin receptors in rat pituitary culture: evidence of a functional interaction between gonadotroph and lactotroph cells

“…Moreover, evidence has been presented that other factors synthesized by gonadotrophs can influence the lactotroph population: angiotensin II stimulating PRL synthesis (De Paul et al 2000); epidermal growth factor (Childs and Armstrong 2001) and fibroblast growth factor (Schechter et al 1995) promoting lactotroph cell proliferation Oomizu et al 2000Oomizu et al , 2004. Further studies are necessary to identify the factors that are released by the gonadotrophs and that participate in this paracrine mechanism.…”