open access

Vol 72, No 3 (2021)
Original paper
Submitted: 2021-02-15
Accepted: 2021-03-25
Early publication date: 2021-04-13
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Exogenous orexin-A downregulates luteinizing hormone secretory activity in prepubertal female rats

Lidia Martyńska1, Alina Gajewska2, Magdalena Chmielowska1, Małgorzata Kalisz1, Anna Litwiniuk1, Wojciech Bik1, Bogusława Baranowska3
DOI: 10.5603/EP.a2021.0041
·
Pubmed: 34010439
·
Endokrynol Pol 2021;72(3):238-242.
Affiliations
  1. Department of Neuroendocrinology, Centre of Postgraduate Medical Education, Warsaw, Poland
  2. Department of Animal Physiology, The Kielanowski Institute of Animal Physiology and Nutrition, Polish Academy of Sciences, Jabłonna, Poland
  3. Department of Neurology, Faculty of Medical Sciences, Medical University of Warsaw, Cegłowska 80, 01- 809 Warsaw, Poland

open access

Vol 72, No 3 (2021)
Original Paper
Submitted: 2021-02-15
Accepted: 2021-03-25
Early publication date: 2021-04-13

Abstract

Introduction: Orexin-A is a neuropeptide synthesized in the lateral hypothalamus. Orexin-A immunoreactive fibres overlap distribution with GnRH neurons. In adult rats, orexin A is known to affect LH secretion via GnRH release modulation. Because data concerning the impact of orexin-A on the hypothalamo-pituitary axis activity are limited, we focused on the involvement of orexin-A and receptors of NPY in the modulation of LH release and LH subunit b (Lhb) mRNA expression in prepubertal female rats.

Material and methods: Forty immature female Wistar rats were divided into 4 groups and received 2 intracerebroventricular (icv) microinjections of: 1 — artificial cerebrospinal fluid (CSF) (controls); 2 — CSF followed by orexin A; 3 — selective NPY receptor antagonist (BIBP) followed by CSF; 4 — BIBP followed by orexin A. One hour after the last microinjection, all rats were decapitated. Trunk blood was collected, and serum was stored at –20°C for the LH RIA examination. The adenohypophysis was immediately excised, flash-frozen, and kept at –80°C for RNA extraction. Real-time PCR amplification was carried out, and relative Lhb gene expression was calculated.

Results: In comparison to the CSF-treated controls with a mean LH serum concentration of 0.40 ± 0.02 ng/mL, the mean LH serum level was diminished both after orexin-A (0.27 ± 0.01 ng/mL) and after BIBP (0.30 ± 0.02 ng/mL) icv microinjections. In the presence of BIBP, orexin-A more effectively inhibited LH release (0.20 ± 0.01 ng/mL) when compared to the BIBP-treated group. Orexin-A and BIBP exerted a consistent inhibitory effect on Lhb mRNA expression levels in the anterior pituitary gland. In comparison to the CSF-treated controls, orexin-A, and BIBP-treated females responded with, respectively, 35% and 40% reduction of Lhb mRNA expression. Orexin-A and BIBP co-administration evoked a further reduction of Lhb gene transcriptional activity.

Conclusions: Orexin-A exerts a down-regulatory effect on LH synthesis and release in immature female rats. Considering that Y1R-oriented down-regulation of endogenous NPY activity did not reverse the suppressive effect of exogenous orexin-A, it might be suggested that NPY and orexin A systems can operate independently to affect gonadotropin activity in the anterior pituitary of the immature female rats. 

Abstract

Introduction: Orexin-A is a neuropeptide synthesized in the lateral hypothalamus. Orexin-A immunoreactive fibres overlap distribution with GnRH neurons. In adult rats, orexin A is known to affect LH secretion via GnRH release modulation. Because data concerning the impact of orexin-A on the hypothalamo-pituitary axis activity are limited, we focused on the involvement of orexin-A and receptors of NPY in the modulation of LH release and LH subunit b (Lhb) mRNA expression in prepubertal female rats.

Material and methods: Forty immature female Wistar rats were divided into 4 groups and received 2 intracerebroventricular (icv) microinjections of: 1 — artificial cerebrospinal fluid (CSF) (controls); 2 — CSF followed by orexin A; 3 — selective NPY receptor antagonist (BIBP) followed by CSF; 4 — BIBP followed by orexin A. One hour after the last microinjection, all rats were decapitated. Trunk blood was collected, and serum was stored at –20°C for the LH RIA examination. The adenohypophysis was immediately excised, flash-frozen, and kept at –80°C for RNA extraction. Real-time PCR amplification was carried out, and relative Lhb gene expression was calculated.

Results: In comparison to the CSF-treated controls with a mean LH serum concentration of 0.40 ± 0.02 ng/mL, the mean LH serum level was diminished both after orexin-A (0.27 ± 0.01 ng/mL) and after BIBP (0.30 ± 0.02 ng/mL) icv microinjections. In the presence of BIBP, orexin-A more effectively inhibited LH release (0.20 ± 0.01 ng/mL) when compared to the BIBP-treated group. Orexin-A and BIBP exerted a consistent inhibitory effect on Lhb mRNA expression levels in the anterior pituitary gland. In comparison to the CSF-treated controls, orexin-A, and BIBP-treated females responded with, respectively, 35% and 40% reduction of Lhb mRNA expression. Orexin-A and BIBP co-administration evoked a further reduction of Lhb gene transcriptional activity.

Conclusions: Orexin-A exerts a down-regulatory effect on LH synthesis and release in immature female rats. Considering that Y1R-oriented down-regulation of endogenous NPY activity did not reverse the suppressive effect of exogenous orexin-A, it might be suggested that NPY and orexin A systems can operate independently to affect gonadotropin activity in the anterior pituitary of the immature female rats. 

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Keywords

orexin-A; LH; Lhb mRNA; NPY Y1 receptor antagonist; prepubertal female rats

About this article
Title

Exogenous orexin-A downregulates luteinizing hormone secretory activity in prepubertal female rats

Journal

Endokrynologia Polska

Issue

Vol 72, No 3 (2021)

Article type

Original paper

Pages

238-242

Early publication date

2021-04-13

Page views

655

Article views/downloads

258

DOI

10.5603/EP.a2021.0041

Pubmed

34010439

Bibliographic record

Endokrynol Pol 2021;72(3):238-242.

Keywords

orexin-A
LH
Lhb mRNA
NPY Y1 receptor antagonist
prepubertal female rats

Authors

Lidia Martyńska
Alina Gajewska
Magdalena Chmielowska
Małgorzata Kalisz
Anna Litwiniuk
Wojciech Bik
Bogusława Baranowska

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