Ganglioneuritis is common in rats with enteric neuropathy due to buserelin treatment

Gonadotropin-Releasing Hormone and Its Role in the Enteric Nervous System

Gonadotropin-releasing hormone (GnRH), follicle-stimulating hormone, and luteinizing hormone orchestrate the reproduction cycle and regulate the sex steroid secretion from the gonads. In mammals, GnRH1 is secreted as a hormone from the hypothalamus, whereas both GnRH1 and GnRH2 are present as neurotransmitters/peptides in various tissues, where the peptides exert many different effects. mRNA coding for GnRH1 and GnRH2 have been described in the human gastrointestinal tract, and GnRH has been found in both submucosal and myenteric neurons. mRNA coding for GnRH and the fully expressed peptide have been found in rat enteric neurons by some researchers but not by others. mRNA coding for GnRH receptors, but not the fully expressed receptor, has been found in one rat study. GnRH influences gastrointestinal motility and secretion. GnRH analogs are clinically used in the treatment of sex hormone-dependent diseases, i.e., endometriosis and malignancies, and as pretreatment for in vitro fertilization. Reduced numbers of enteric neurons and IgM antibodies against GnRH and progonadoliberin-2 (precursor of GnRH2) have been observed after such treatment, with the clinical picture of gastrointestinal dysmotility. Similarly, a rat model of enteric neurodegeneration has been developed after administration of the GnRH analog buserelin. Serum IgM antibodies against GnRH1, progonadoliberin-2, and GnRH receptors have been described in patients with signs and symptoms of gastrointestinal dysmotility and/or autonomic dysfunction, such as irritable bowel syndrome, enteric dysmotility, diabetes mellitus, and primary Sjögren's syndrome. Thus, apart from regulation of reproduction and sex hormone secretion, GnRH also constitutes a part of enteric nervous system (ENS) and its functions during physiological and pathological conditions. This review aimed to describe the role of GnRH in the ENS.

Long‑term follow‑up of buserelin‑induced enteric neuropathy in rats

A few patients have been shown to develop severe abdominal pain and gastrointestinal dysmotility during treatment with gonadotropin‑releasing hormone (GnRH) analogs. A rat model of enteric neuropathy has been developed by administration of the GnRH analog buserelin to rats. Loss of enteric neurons and ganglioneuritis throughout the gastrointestinal tract has been described, without other histopathological changes. The aim of the present study was to investigate the long‑term effects of this rat model on body weight, and on morphology and inflammatory changes in the gastrointestinal tract. Rats were administered subcutaneous injections of buserelin or saline once daily for 5 days and allowed to recover for 3 weeks. This regimen was repeated four times. The rats were weighed weekly and were sacrificed 16 weeks after the fourth treatment. The bowel wall was measured by morphometry, and the presence of enteric neurons, mast cells, eosinophils and T‑lymphocytes was evaluated. Buserelin‑treated rats were shown to have a lower body weight at sacrifice, as compared with the controls (P<0.05). Compared with controls, buserelin treatment caused loss of myenteric neurons in the ileum and colon (P<0.01), a thinner circular muscle layer in ileum (P<0.05) and longitudinal muscle layer in colon (P<0.05), increased number of eosinophils in the submucosa of the ileum (P<0.05), and an increased number of T‑lymphocytes in the submucosa and circular muscle layer of the fundus (P<0.01 and P<0.05, respectively) and circular muscle layer of the colon (P<0.05). Mast cells were equally distributed in the two groups. Thus, long‑term follow‑up of buserelin‑induced enteric neuropathy reveals reduced body weight, loss of myenteric neurons, thinning of muscle layers, and increased numbers of eosinophils and T‑lymphocytes in the gastrointestinal tract.

Gonadotropin-Releasing Hormone and Its Physiological and Pathophysiological Roles in Relation to the Structure and Function of the Gastrointestinal Tract

<b><i>Background:</i></b> Gonadotropin-releasing hormone (GnRH), follicle-stimulating hormone (FSH), and luteinizing hormone (LH) are involved in the reproductive cycle and regulate the secretion of sex steroids from the gonads. In mammals, GnRH1 is secreted as a hormone from the hypothalamus, whereas both GnRH1 and GnRH2 are present as neuropeptides in a variety of tissues. This review describes the role of GnRH in the gastrointestinal tract. <b><i>Summary:</i></b> GnRH1, GnRH2, and LH receptors in humans and rats, and GnRH receptors in rats, have been described in the gastrointestinal tract, where they affect motility, gastric and hormone secretion, and cell proliferation. GnRH analogs are clinically used in the treatment of sex hormone-dependent diseases, i.e., endometriosis and malignancies, and as pretreatments for in vitro fertilization. Severe gastrointestinal dysmotility has been shown to develop in some women after such treatment, along with a reduction in the number of enteric neurons and autoantibodies against GnRH. Consequently, a rat model of enteric neurodegeneration has been developed based on the administration of the GnRH analog buserelin. Serum IgM antibodies against GnRH1, the GnRH2 precursor progonadoliberin-2, and the GnRH receptor have also been described in patients with irritable bowel syndrome and dysmotility, as well as in patients with gastrointestinal disorders associated with diabetes mellitus, posterior laryngitis, and primary Sjögren's syndrome, although no treatments using GnRH analogs have been administered. <b><i>Conclusion:</i></b> GnRH and receptors for GnRH and LH are present in the human and rat gastrointestinal tract. Treatment with GnRH analogs may induce severe dysmotility, and a rat model of enteric neurodegeneration has been developed based on stimulation by the GnRH analog buserelin. Autoantibodies against GnRH and its receptor are found in a subgroup of patients with functional bowel disorders and dysmotility, independent of treatment with GnRH analogs.

Buserelin treatment to rats causes enteric neurodegeneration with moderate effects on CRF-immunoreactive neurons and Enterobacteriaceae in colon, and in acetylcholine-mediated permeability in ileum

Background

The gonadotropin-releasing hormone (GnRH) analog buserelin causes enteric neuronal loss. Acute stress or injection of corticotropin-releasing factor (CRF) affects motility, secretion, and barrier function of the gastrointestinal tract. The aim of the study was to characterize the CRF immunoreactivity in enteric neurons after buserelin treatment, and to evaluate possible effects of enteric neuropathy on gut microbiota, intestinal permeability, and stress response behavior.

Results

Sixty rats were given buserelin (20 μg) or saline subcutaneously for 5 days, repeated four times with 3 weeks in-between. At the study end, enteric neuronal density, enteric expression of CRF, gut microbial composition, and plasma levels of adrenocorticotropic hormone (ACTH) and CRF were analyzed. Intestinal permeability was examined in Ussing chambers and the reaction to stressful events was measured by behavior tests. Buserelin treatment reduced the number of neurons along the entire gastrointestinal tract, with increased relative numbers of CRF-immunoreactive submucosal and myenteric neurons in colon (p < 0.05 and p < 0.01, respectively). The overall microbial diversity and relative abundance did not differ between groups, but Enterobacteriaceae was decreased in colon in buserelin-treated rats (p = 0.020). Basal intestinal permeability did not differ between groups, whereas carbachol stimulation increased ileum permeability in controls (p < 0.05), but not in buserelin-treated rats. Buserelin did not affect stress behavior.

Conclusions

Although buserelin treatment leads to enteric neuronal loss along the gastrointestinal tract with an increased percentage of CRF-immunoreactive neurons in colon, the physiology is well preserved, with modest effects on colon microbiota and absence of carbachol-induced permeability in ileum as the only observed changes.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-015-1800-x) contains supplementary material, which is available to authorized users.

Luteinizing hormone receptors are expressed in rat myenteric neurons and mediate neuronal loss

BACKGROUND

Clinical observations have suggested repeated gonadotropin-releasing hormone (GnRH) exposure to cause intestinal dysfunction and loss of enteric neurons. This has been further studied and confirmed in a rat in vivo model involving iterated GnRH treatments. Mechanisms behind are enigmatic since no GnRH receptors are found to be expressed in enteric neurons neither in man nor rat. Both species, however, harbor substantial subpopulations of luteinizing hormone (LH) receptor-immunoreactive myenteric neurons which suggests that intestinal GnRH-induced neuropathy may be mediated by LH release.

AIMS

To reveal if exposures of GnRH or LH to rat myenteric neurons in vitro cause neuronal loss.

METHODS

Primary cultured adult rat myenteric neurons were exposed to single or repeated treatments of the GnRH analog buserelin or the LH analog lutrotropin alpha, and neuronal survival was determined by cell counting. Possible presence of GnRH- or LH receptor -immunoreactive neurons was determined by immunocytochemistry.

RESULTS

Exposure to the LH, but not the GnRH, analog caused significantly reduced neuronal survival. LH, but not GnRH, receptors were found to be expressed on cultured myenteric neurons.

CONCLUSION

Myenteric neurons express LH receptors in vitro and LH exposure causes reduced neuronal survival. This suggests that GnRH-induced enteric neuropathy in vivo is mediated by way of LH release and activation of enteric neuronal LH receptors.

Severe gastrointestinal dysmotility developed after treatment with gonadotropin-releasing hormone analogs

BACKGROUND

Sporadic cases of abdominal pain and dysmotility has been described after treatment with gonadotropin-releasing hormone (GnRH) analogs. The aim of the present study was to scrutinize for patients with severe gastrointestinal complaints after treatment with GnRH analogs, to describe the expression of antibodies against progonadoliberin-2, GnRH1, GnRH receptor (GnRHR), luteinizing hormone (LH), and LH receptor in serum in these patients, and to search for possible triggers and genetic factors behind the development of this dysmotility.

METHODS

Patients suffering from prolonged gastrointestinal complaints after treatment with GnRH analogs at the Department of Gastroenterology, Skåne University Hospital, were included. GnRHR and LH receptor (LHCGR) genes were exome-sequenced. Serum was analyzed by enzyme-linked immune sorbent assays for the presence of antibodies. Healthy blood donors and women treated with GnRH analogs because of in vitro fertilization (IVF) were used as controls.

RESULTS

Seven patients with severe gastrointestinal complaints after GnRH treatment were identified, of whom six suffered from endometriosis. Several variants were found within the 11 exons of LHCGR. The minor allele G, at the single nucleotide polymorphism rs6755901, was detected in homozygosity in two patients (28.5%) who had developed chronic intestinal pseudo-obstruction and in 5.5% of the IVF controls. Three patients expressed IgM antibodies against progonadoliberin-2 and three against GnRH1 (42.9%) when cut off was set to a titer >97.5th percentile in blood donors.

CONCLUSION

A high prevalence of endometriosis, polymorphism in the LHCGR and GnRH1 and progonadoliberin-2 antibodies in serum was found among the patients with severe dysmotility after treatment with GnRH analogs.

Structural and functional consequences of buserelin-induced enteric neuropathy in rat

BACKGROUND

Women treated with gonadotropin-releasing hormone (GnRH) analogs may develop enteric neuropathy and dysmotility. Administration of a GnRH analog to rats leads to similar degenerative neuropathy and ganglioneuritis. The aim of this study on rat was to evaluate the early GnRH-induced enteric neuropathy in terms of distribution of neuronal subpopulations and gastrointestinal (GI) function.

METHODS

Forty rats were given the GnRH analog buserelin (20 μg, 1 mg/ml) or saline subcutaneously, once daily for 5 days, followed by 3 weeks of recovery, representing one treatment session. Two weeks after the fourth treatment session, the animals were tested for GI transit time and galactose absorption, and fecal weight and fat content was analyzed. After sacrifice, enteric neuronal subpopulations were analyzed. Blood samples were analyzed for zonulin and antibodies against GnRH and luteinizing hormone, and their receptors.

RESULTS

Buserelin treatment transiently increased the body weight after 5 and 9 weeks (p < 0.001). Increased estradiol in plasma and thickened uterine muscle layers indicate high estrogen activity. The numbers of both submucous and myenteric neurons were reduced by 27%-61% in ileum and colon. The relative numbers of neurons containing calcitonin gene-related peptide (CGRP), cocaine- and amphetamine-related transcript (CART), galanin, gastrin-releasing peptide (GRP), neuropeptide Y (NPY), nitric oxide synthase (NOS), serotonin, substance P (SP), vasoactive intestinal peptide (VIP) or vesicular acetylcholine transporter (VAchT), and their nerve fiber density, were unchanged after buserelin treatment, but the relative number of submucous neurons containing somatostatin tended to be increased (p = 0.062). The feces weight decreased in buserelin-treated rats (p < 0.01), whereas feces fat content increased (p < 0.05), compared to control rats. Total GI transit time, galactose absorption, zonulin levels in plasma, and antibody titers in serum were unaffected by buserelin treatment.

CONCLUSIONS

A marked enteric neuronal loss with modest effects on GI function is found after buserelin treatment. Increased feces fat content is suggested an early sign of dysfunction.