Tilapia Prolactin Cells are Thermosensitive Osmoreceptors

Prolactin (PRL) cells within the rostral pars distalis (RPD) of the euryhaline teleost tilapia, Oreochromis mossambicus, rapidly respond to a hyposmotic stimulus by releasing two distinct PRL isoforms, PRL188 and PRL177. Here, we describe how environmentally relevant temperatures affect the release and mRNA levels of PRL188 and PRL177 from RPDs and dispersed PRL cells. When applied under isosmotic conditions (330 mOsm/kg), a 6 °C rise in temperature stimulated the release of PRL188 and PRL177 from both RPDs and dispersed PRL cells under perifusion. When exposed to this same change in temperature, ~50% of dispersed PRL cells gradually increased in volume by ~8%, a response partially inhibited by the water channel blocker, HgCl2. Following their response to increased temperature, PRL cells remained responsive to a hyposmotic stimulus (280 mOsm/kg). The mRNA expression of transient potential vanilloid 4, a Ca2+-channel involved in hyposomotically-induced PRL release, was elevated in response to a rise in temperature in dispersed PRL cells and RPDs at 6 and 24 h, respectively; prl188 and prl177 mRNAs were unaffected. Our findings indicate that thermosensitive PRL release is mediated, at least partially, through a cell-volume dependent pathway similar to how osmoreceptive PRL release is achieved.

Microcystin-LR: Effects on Freshwater Catfish Heteropneustes fossilis Prolactin Cells

Background: Previous studies have been reported on the toxicity of Microcystin-LR, which is produced by cyanobacterial growth in fish, such as Heteropneustes fossilis (H. fossilis). However, no studies have been conducted on the effects of Microcystin-LR on the prolactin cells of H. fossilis. Methods: H. fossilis fish were intraperitoneally injected with Microcystin-LR (2.5μg/25g) and sacrificed after 1, 3, 5, 10 and 15 days. The blood samples were analyzed for the calcium levels. Histological slides of the pituitary prolactin cells were stained with Herlant’s tetrachrome and Heidenhan’s azan techniques, and examined under light microscopy. Results: The prolactin cells exposed to Microcystin-LR exhibited no structural changes on day 1. However, hyperactive prolactin cells exhibited cellular degranulation from day 3 to day 5. On days 10 and 15, degenerated and vacuolated prolactin cells were also observed. The nuclear volume of prolactin cells exposed to MC-LR increased progressively from day 3 to day 10 but on day 15 the nuclear volume returned to normal. The serum calcium level of MC-LR injected specimens showed hypocalcemia from day 3 to day 10. On day 15, the level became normal. Conclusions: Our results indicated that the serum calcium levels and prolactin cells were altered after exposure to microcystin-LR.

Sex-specific changes in postnatal GH and PRL secretion in somatotrope LEPR-null mice

The developing pituitary is a rapidly changing environment that is constantly meeting the physiological demands of the growing organism. During early postnatal development, the anterior pituitary is refining patterns of anterior hormone secretion in response to numerous genetic factors. Our laboratory previously developed a somatotrope leptin receptor (LEPR) deletion mouse model that had decreased lean body mass, disrupted metabolism, decreased GH stores and was GH deficient as an adult. To understand how deletion of LEPR in somatotropes altered GH, we turned our attention to postnatal development. The current study examines GH, PRL, TSH, ACTH, LH and FSH secretion during postnatal days 4, 5, 8, 10 and 15 and compares age and sex differences. The LEPR mutants have dysregulation of GH (P < 0.03) and a reduced developmental prolactin peak in males (P < 0.04) and females (P < 0.002). There were no differences in weight between groups, and the postnatal leptin surge appeared to be normal. Percentages of immunolabeled GH cells were reduced in mutants compared with controls in all age groups by 35–61% in males and 41–44% in females. In addition, we measured pituitary expression of pituitary transcription factors, POU1F1 and PROP1. POU1F1 was reduced in mutant females at PND 10 (P < 0.009) and PND 15 (P < 0.02) but increased in males at PND 10 (P < 0.01). PROP1 was unchanged in female mutants but showed developmental increases at PND 5 (P < 0.02) and PND 15 (P < 0.01). These studies show that the dysfunction caused by LEPR deletion in somatotropes begins as early as neonatal development and involves developing GH and prolactin cells (somatolactotropes).

ALK7 expression in prolactinoma is associated with reduced prolactin and increased proliferation

Prolactinoma represents the most frequent hormone-secreting pituitary tumours. These tumours appear in a benign form, but some of them can reach an invasive and aggressive stage through an unknown mechanism. Discovering markers to identify prolactinoma proliferative and invading character is therefore crucial to develop new diagnostic/prognostic strategies. Interestingly, members of the TGFβ-Activin/BMP signalling pathways have emerged as important actors of pituitary development and adult function, but their role in prolactinomas remains to be precisely determined. Here, using a heterotopic allograft model derived from a rat prolactinoma, we report that the Activins orphan type I receptor ALK7 is ectopically expressed in prolactinomas-cells. Through immunohistological approaches, we further confirm that normal prolactin-producing cells lack ALK7-expression. Using a series of human tumour samples, we show that ALK7 expression in prolactinomas cells is evolutionary conserved between rat and human. More interestingly, our results highlight that tumours showing a robust expression of ALK7 present an increased proliferation as address by Ki67 expression and retrospective analysis of clinical data from 38 patients, presenting ALK7 as an appealing marker of prolactinoma aggressiveness. Beside this observation, our work pinpoints that the expression of prolactin is highly heterogeneous in prolactinoma cells. We further confirm the contribution of ALK7 in these observations and the existence of highly immunoreactive prolactin cells lacking ALK7 expression. Taken together, our observations suggest that Activin signalling mediated through ALK7 could therefore contribute to the hormonal heterogeneity and increased proliferation of prolactinomas.

Assessment of the effects of bisphenol-A as a disruptor on ionic regulation in Danio rerio zebrafish through a study of their chloride and prolactin cells

Bisphenol A (BPA) is one of the chemicals produced in the largest volume in the world. It is commonly used as a component of plastics and food containers and can act as a xenoestrogen in humans. In view of the risk of exposure to it from the environment and diet, and basically as a water pollutant, the objective of our study was to assess possible effects on ionic regulation after exposure to BPA by means of a histopathological and morphometric study of the chloride and prolactin cells in zebrafish (Danio rerio) as an experimental model. Twenty-five male 16-week old zebrafish (Danio rerio) were allocated randomly into 5 study groups (n=5/group); a control group, and four groups, exposed for 2 weeks to a concentration of (1, 10, 100 and 1000 μg/L) of BPA, respectively. After 2 weeks, the animals were sacrificed and samples of their gills and pituitary gland were immediately taken for their subsequent histopathological analysis. Our results showed how, in the first study groups, lesions appeared in chloride cells, generating compensatory modifications in the prolactin cells, which were enough to maintain stability in the ionic exchange. As the exposure concentration increased, more serious histological modifications occurred. In the groups with the highest concentration (100 and 1000 μg/L), the lesions were so severe that the prolactin cells underwent some degenerative processes, which probably prevented the compensatory action at gill level.

Autocrine Positive Feedback Regulation of Prolactin Release From Tilapia Prolactin Cells and Its Modulation by Extracellular Osmolality

Prolactin (PRL) is a vertebrate hormone with diverse actions in osmoregulation, metabolism, reproduction, and in growth and development. Osmoregulation is fundamental to maintaining the functional structure of the macromolecules that conduct the business of life. In teleost fish, PRL plays a critical role in osmoregulation in fresh water. Appropriately, PRL cells of the tilapia are directly osmosensitive, with PRL secretion increasing as extracellular osmolality falls. Using a model system that employs dispersed PRL cells from the euryhaline teleost fish, Oreochromis mossambicus, we investigated the autocrine regulation of PRL cell function. Unknown was whether these PRL cells might also be sensitive to autocrine feedback and whether possible autocrine regulation might interact with the well-established regulation by physiologically relevant changes in extracellular osmolality. In the cell-perfusion system, ovine PRL and two isoforms of tilapia PRL (tPRL), tPRL177 and tPRL188, stimulated the release of tPRLs from the dispersed PRL cells. These effects were significant within 5–10 minutes and lasted the entire course of exposure, ceasing within 5–10 minutes of removal of tested PRLs from the perifusion medium. The magnitude of response varied between tPRL177 and tPRL188 and was modulated by extracellular osmolality. On the other hand, the gene expression of tPRLs was mainly unchanged or suppressed by static incubations of PRL cells with added PRLs. By demonstrating the regulatory complexity driven by positive autocrine feedback and its interaction with osmotic stimuli, these findings expand upon the knowledge that pituitary PRL cells are regulated complexly through multiple factors and interactions.