Isotocin Regulates Growth Hormone but Not Prolactin Release From the Pituitary of Ricefield Eels

Abstract

The neurohypophyseal hormone oxytocin (Oxt) has been shown to stimulate prolactin (Prl) synthesis and release from the adenohypophysis in rats. However, little is known about the functional roles of Oxt-like neuropeptides in the adenohypophysis of non-mammalian vertebrates. In this study, cDNAs encoding ricefield eel oxytocin-like receptors (Oxtlr), namely isotocin (Ist) receptor 1 (Istr1) and 2 (Istr2), were isolated and specific antisera were generated, respectively. RT-PCR and Western blot analysis detected the presence of both Istr1 and Istr2 in the brain and pituitary, but differential expression in some peripheral tissues, including the liver and kidney, where only Istr1 was detected. In the pituitary, immunoreactive Istr1 and Istr2 were differentially distributed, with the former mainly in adenohypophyseal cell layers adjacent to the neurohypophysis, whereas the latter in peripheral areas of the adenohypophysis. Double immunofluorescent images showed that immunostaining of Istr1, but not Istr2 was localized to growth hormone (Gh) cells, but neither of them was expressed in Prl cells. Ist inhibited Gh release in primary pituitary cells of ricefield eels and increased Gh contents in the pituitary gland of ricefield eels at 6 h after in vivo administration. Ist inhibition of Gh release is probably mediated by cAMP, PKC/DAG, and IP3/Ca2+ pathways. In contrast, Ist did not affect either prl gene expression or Prl contents in primary pituitary cells. Results of this study demonstrated that Ist may not be involved in the regulation of Prl, but inhibit Gh release via Istr1 rather than Istr2 in ricefield eels, and provided evidence for the direct regulation of Gh cells by oxytocin-like neuropeptides in the pituitary of non-mammalian vertebrates.

Neurohypophysial Hormones Associated with Osmotic Challenges in the Brain and Pituitary of the Euryhaline Black Porgy, Acanthopagrus schlegelii

“…The it may regulate osmoregulation via itr1, but not itr2 in eels [70]. The itr1 and itr2 immunoreactive cells are localized in different areas of the eel's pituitary [70]. Based on the current interesting data, in the future, we should further extend the studies of osmotic stress to other types of itr and avtr in black porgy.…”

“…The itr1 and itr2 mRNA and proteins are also expressed in rice field eels [8]. The it may regulate osmoregulation via itr1, but not itr2 in eels [70]. The itr1 and itr2 immunoreactive cells are localized in different areas of the eel's pituitary [70].…”

Hypo-Osmoregulatory Roles of Vasotocinergic and Isotocinergic Systems in the Intestines of Two European Sea Bass Lineages

“…Among ITR receptors, itr1 is the main paralog in both intestinal regions with a 50 to 80 higher expression than itr2 in the anterior and posterior intestines. itr1 was also more expressed than itr2 in the intestines of ricefield eels [ 45 ].…”

A Type IIb, but Not Type IIa, GnRH Receptor Mediates GnRH-Induced Release of Growth Hormone in the Ricefield Eel

“…DMSO (0.1%) vehicle was used for all control cultures. At the end of treatment, culture medium was harvested for measurement of Gh release, and the remaining cells in each well were homogenized individually in RIPA lysis buffer (Beyotime, Shanghai, China) for measurement of cell content of Gh by using a competitive enzyme-linked immunosorbent assay (ELISA), which was established and validated in our laboratory to assay Gh contents in pituitary homogenates and culture medium of pituitary cells of ricefield eels ( 39 ). Total production of Gh in individual wells was deduced pro rata based on the protein data for Gh release and cell content.…”

“…After acclimatization for 3 days, the ricefield eels were anesthetized with tricaine methanesulphonate (MS222, 0.5 g/L), and received intraperitoneal injections of either GnRH1 or GnRH3 or 0.65% NaCl (vehicle control, 16 or 17 fish per treatment in a tank) GnRH1 or GnRH3 was administered at doses of 0.01 and 0.1 μg/g body weight. The pituitary glands of ricefield eels were dissected out at 12 h after injection and homogenized individually in 200 μL of RIPA lysis buffer (Beyotime) for measurement of cell content of Gh with the competitive ELISA method ( 39 ). The gonads were also collected and histologically examined for the sex of individual experimental fish.…”