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Article

Plasma Amino Acids in Horses Suffering from Pituitary Pars Intermedia Dysfunction

by
Sabita Diana Stoeckle
1,*,
Detlef Timmermann
2,†,
Roswitha Merle
3 and
Heidrun Gehlen
1
1
Equine Clinic: Surgery and Radiology, Freie Universitaet Berlin, 14163 Berlin, Germany
2
MembraPure GmbH, 16761 Hennigsdorf, Germany
3
Institute for Veterinary Epidemiology and Biostatistics, Freie Universitaet Berlin, 14163 Berlin, Germany
*
Author to whom correspondence should be addressed.
†
Current address: Laborservice Onken GmbH, 63584 Gruendau, Germany.
Animals 2022, 12(23), 3315; https://doi.org/10.3390/ani12233315
Submission received: 2 October 2022 / Revised: 24 November 2022 / Accepted: 25 November 2022 / Published: 27 November 2022
(This article belongs to the Section Equids)
Versions Notes

Abstract

:

Simple Summary

Pituitary pars intermedia dysfunction (PPID), also known as equine’s cushing syndrome, is one of the most common diseases of aged horses and ponies. The pathogenesis of PPID includes oxidative damage to dopaminergic pathways, similar to Parkinson’s disease in humans. Here, alterations in the concentrations of the serum amino acids were reported previously. To examine changes in the plasma amino acid profile in horses with PPID, EDTA plasma of horses that were presented for various reasons that required laboratory examinations of blood anticoagulated with EDTA was collected. With this plasma, the basal ACTH concentration, as well as the amino acid profile, was determined. The basal ACTH concentration is commonly used to diagnose PPID. Horses were considered PPID patients if the ACTH concentration was ≥ 100 pg/mL, i.e., they would be considered affected at any time. Horses were defined as non-PPID (nPPID) patients if the ACTH concentration was below 30 pg/mL. PPID is commonly treated with pergolide. Horses receiving pergolide with ACTH ≤ 30 pg/mL were allocated to the group PPIDrr (PPID, ACTH in reference range) and horses receiving pergolide with ACTH ≥ 100 pg/mL to the group PPIDarr (PPID, ACTH above reference range). In total, 93 horses were examined, including 88 horses at the clinic and 5 horses at a private practice. Of these, 53 horses fulfilled the inclusion criteria (ACTH ≤ 30 pg/mL or ACTH ≥ 100 pg/mL). A total of 25 horses were diagnosed as nPPID, 20 as PPID, 5 as PPIDrr, and 3 as PPIDarr. Arginine was significantly higher in PPIDrr than in PPID and nPPID, asparagine was significantly higher in PPID, PPIDrr, and PPIDarr than in nPPID, citrulline was significantly higher in PPIDrr than in nPPID and PPID, cysteine was significantly lower in PPIDrr than in PPID, nPPID, and PPIDarr, and glutamine was significantly higher in PPID and PPIDarr than in nPPID. Especially, asparagine, citrulline, and glutamine may be potential diagnostic markers and may offer interesting approaches for research regarding amino supplementation in PPID.

Abstract

Pituitary pars intermedia dysfunction is one of the most common diseases of aged horses and ponies. In Parkinson’s disease, which is, similar to PPID, a disease that involves oxidative damage to dopaminergic pathways but with different clinical signs, alterations to the serum amino acid profile have been reported. To examine changes in the plasma amino acid profile in horses with PPID, EDTA plasma of horses that were presented for various reasons that required laboratory examinations of blood anticoagulated with EDTA was collected. With this plasma, the basal ACTH concentration as well as the amino acid profile was determined. Horses were considered PPID patients if the ACTH concentration was ≥ 100 pg/mL, i.e., they would be considered affected at any time. Horses were defined as non-PPID (nPPID) patients if the ACTH concentration was below 30 pg/mL. Horses receiving pergolide with ACTH ≤ 30 pg/mL were allocated to the group PPIDrr (PPID, ACTH in reference range) and horses receiving pergolide with ACTH ≥ 100 pg/mL to the group PPIDarr (PPID, ACTH above reference range). In total, 93 horses were examined, including 88 horses at the clinic and 5 horses at a private practice. Of these, 53 horses fulfilled the inclusion criteria (ACTH ≤ 30 pg/mL or ACTH ≥ 100 pg/mL). A total of 25 horses were diagnosed as nPPID, 20 as PPID, 5 as PPIDrr, and 3 as PPIDarr. Arginine was significantly higher in PPIDrr than in PPID and nPPID, asparagine was significantly higher in PPID, PPIDrr, and PPIDarr than in nPPID, citrulline was significantly higher in PPIDrr than in nPPID and PPID, cysteine was significantly lower in PPIDrr than in PPID, nPPID, and PPIDarr, and glutamine was significantly higher in PPID and PPIDarr than in nPPID. Especially, asparagine, citrulline, and glutamine may be potential diagnostic markers and may offer interesting approaches for research regarding amino supplementation in PPID.

1. Introduction

Pituitary pars intermedia dysfunction is one of the most common diseases of aged horses and ponies (≥15 years) [1,2,3]. Laminitis occurs in 30–40% of PPID patients and may necessitate euthanasia [4,5,6]. In PPID, hypertrophy, hyperplasia, and microadenoma or macroadenoma formation of the pars intermedia of the pituitary occurs [7]. This leads to an increased secretion of the pars intermedia-derived POMC (Pro-Opiomelanocortins) into the circulation [7]. From the healthy equine pars intermedia, only a small amount of the adrenocorticotropic hormone (ACTH) is released and it is further cleaved into α-melanocyte stimulating hormone (α-MSH), β-endorphine (β-END), and corticotropine-like intermediate lobe peptide (CLIP) [7]. In the diseased equid, the pars intermedia secretes an increased amount of POMC-derivates into the systemic circulation. An increase up to 40-fold was reported previously [8]. Nowadays, the basal ACTH concentration is a commonly used test to diagnose PPID with a sensitivity of approximately 70–80% and a spe-cificity of approximately 80–90% [5,9,10]. ACTH stimulates the adrenal gland to synthesize and release cortisol into circulation [11]. Previous research has suggested that the increased endogenous glucocorticoid concentrations may be responsible for laminitis, since these are known to be associated with systemic insulin resistance [12,13,14,15,16,17]. The suspected mechanism is that binding of insulin to the insulin-like growth factor 1 receptor (IGF-1R) has an effect in the lamellar tissue of the hoof [18,19,20] and also that insulin can directly trigger laminitis even through mechanisms that have not yet been identified [21]. In addition to its effects on the glucose metabolism, insulin is an important regulator of protein metabolism. Due to an increased utilization of amino acids, hyperinsulinemia can contribute to an increased amino acid and protein turnover, for example, in the skin or skeletal muscles [22,23,24,25,26].
Furthermore, in human Parkinson’s disease, which is, similarly to PPID, a disease that involves oxidative damage to dopaminergic pathways but has a different clinical presentation [27], the arginine, alanine, and phenylalanine concentrations were significantly lower in patients with advanced disease and dyskinesia than in patients suffering from early disease and could therefore serve as a biochemical marker of disease progression [28]. As possible reasons for the significant differences in the serum amino acid profile malabsorption and changes in amino acid metabolism, the effects of mitochondrial dysfunction and oxidative stress, reflection of progressive neurodegenerative processes in the brain, and the effect of dopaminergic medications and aromatic L-amino decarboxylase inhibitors were suggested [28].
Beside Parkinson’s disease, a change in the amino acid level in plasma or serum has been demonstrated in other human diseases, including autism and cancer. A study by Naushad et al. reported increased concentrations of glutamic acid and asparagine, and lower concentrations of phenylalanine, tryptophan, methionine, and histidine in autistic children [29]. Another study reported significantly higher concentrations of histidine, 1-methyl-histidine and 3-methyl-histidine, and significantly lower concentrations of homocysteine, carnosine, methionine, cystathionine, cystine, tyrosine, and threonine in autistic children compared to healthy children [30]. Therefore, it appears that increased concentrations of excitatory amino acids (glutamate and asparagine) and decreased concentrations of essential amino acids (phenylalanine, tryptophan, and methionine), as well as decreased concentrations of neurotransmitter precursors (tyrosine and tryptophan), may be distinctive features of the plasma amino acid profile of autistic children and that this could offer an opportunity for early diagnosis [29].
Even in disease caused by the novel coronavirus (SARS-CoV-2), significant differences in the amino acid profile in the plasma in hospitalized adults and children with multisystem inflammatory syndrome, in particular a reduced arginine concentration and arginine bioavailability, are considered important. It was suggested that arginine deficiency may contribute to endothelial dysfunction, T cell dysregulation, and coagulopathy [31]. Changes in plasma amino acid profile were also found in cancer patients. This could be due to changes due to cancer-induced protein metabolism in tumors, skeletal muscle, and liver in cancer patients. Cancer-related plasma amino acid profiles are particularly present in cancers which affect the digestive organs. These are not only influenced by the type of cancer, but also by the cancer stage [32,33,34,35,36,37]. The plasma amino acid profile seems to undergo specific changes during different diseases, not only in humans, but also in animals, which was previously shown in horses suffering from equine metabolic syndrome [38,39] or in experimentally-induced hyperinsulinemia [21].
Therefore, we hypothesized that there may be differences in the amino acid profile of healthy horses and horses affected with PPID. Furthermore, we assumed that treatment with pergolide may affect the amino acid profile as well and that these may be used as a potential diagnostic biochemical marker.

2. Material and Methods

2.1. Study Population

Included in the study were horses that were presented for various reasons at the Equine Clinic of Freie Universität Berlin (FU Berlin) that required laboratory examinations of blood anticoagulated with EDTA. The horses had to be clinically healthy except for possible orthopaedic or ophtalmological reasons for examination and/or surgery. After a physical examination, the horses were stabled. The time between transport and sample collection varied; however, all horses were given time to accommodate to their surroundings before sample collection (at least 30 min after transport). At the moment of sample collection, all horses showed no signs of pain. Their vital parameters were within normal limits and the horses were relaxed and comfortable in their surroundings. Besides the ACTH concentration, age, weight, breed, gender, and feeding regimen were recorded. Further, 5 horses that presented to a private practice to evaluate the response to therapy by determining the ACTH concentration were included in the study. Individuals with suspected or diagnosed endocrinopathies (previous dynamic testing for equine metabolic syndrome, suspicious fat accumulations) other than PPID were excluded from the statistical analysis. Since the samples were collected at different times of the year, horses were classified as healthy if the measured ACTH concentration was normal (ACTH ≤ 30 pg/mL) at any time of the year. The reference value of LABOklin (Holding—GmbH, Bad Kissingen/Germany) were used. Horses were considered PPID patients if an ACTH concentration ≥ 100 pg/mL was present, i.e., they would be considered affected at any time. Horses were defined as non-PPID (nPPID) patients if the ACTH concentration was below 30 pg/mL and as PPID patients (PPID) if the ACTH concentration above 100 pg/mL. Horses receiving pergolide with ACTH ≤ 30 pg/mL were allocated to the group PPIDrr (PPID, ACTH in reference range) and horses receiving pergolide with ACTH ≥ 100 pg/mL to the group PPIDarr (PPID, ACTH above reference range).

2.2. Laboratory Diagnostics

After required laboratory diagnostics were performed (within 10 min of collection), the blood samples, uncoagulated with EDTA, were centrifuged and the plasma was separated from the solid blood components.

2.2.1. ACTH

The plasma for the ACTH determination was sent cooled to the laboratory within a maximum of 12 h after collection. ACTH was determined with a chemoluminiscence-assay by Laboklin (LABOklin Holding—GmbH Bad Kissingen/Germany).

2.2.2. Amino Acid Concentrations

The amino acid profiles were determined by MembraPure GmbH (Hennigsdorf/Germany). In order to determine the total cysteine concentration, bound cysteine had to be reduced to free cysteine. For this, 500 μL plasma and 100 μL dithiothreitol solution (4%) were mixed in an Eppendorf tube and incubated at 40 °C for 30 min. Then, 150 µL sulfosalicylic acid solution (10%) was added and the sample was stored for 30 min at 5–8 °C. Afterwards, 500 μL sample dilution buffer (with internal standard norleucine 100 nmol/mL) was added. The sample was centrifuged at 13,150× g for 5 min. After these steps, the amino acid analyses were performed with the Aracus amino acid analyzer, using the amino acid analysis method based on ion exchange chromatography with post column derivatization with Ninhydrin. The amino acid concentrations were determined by comparing the sample with a standard solution with predefined concentrations using the Clarity Chromatography Software (DataApex Company, Prague, Czech Republic).

2.3. Statistical Analysis

Data were analyzed using IBM SPSS Statistics version 27 (IBM Corp., Armonk, New York, USA). Data were tested for normal distribution with the Shapiro Wilk Test. The Chi-Squared-test was used to compare gender distribution between groups. Further statistical tests used were the ANOVA for normally distributed data and the Kruskal–Wallis test for non-normally distributed data. For post hoc testing, the Tukey test and the Games–Howell test or Bonferroni test were used. Laboratory data that could not be measured as they exceeded the maximum which is validated for the test or fell below the detection limit, were regarded as either the maximum (ACTH > 1250 pg/mL, n = 1) or the minimum (Asp < 5 nmol/mL, n = 20, nPPID = 7, PPID = 12, PPIDarr = 1). As per usual, the significance level was set at 0.05.

2.4. Ethical Statement

The study was not declared according to the German Animal Welfare law §8.1, since all samples were taken as a part of a routine clinical examination. Written owner’s consent to involve their horses in the study was obtained during the admission process at the clinic as well as at the private practice.

3. Results

3.1. Study Population

In total, 93 horses were examined, including 88 horses at the clinic and 5 horses at the private practice. Of these, 53 horses fulfilled the inclusion criteria (ACTH ≤ 30 pg/mL or ACTH ≥ 100 pg/mL):
A total of 25 horses were diagnosed as nPPID, 20 as PPID, 5 as PPIDrr, and 3 as PPIDarr.
There was no significant difference regarding gender between these groups (p = 0.428, Welch Test). Information on breed was unavailable for two horses. Ten of the twenty individuals in the PPID group were ponies, compared to 7/25 horses in the nPPID, 1/5 in the PPIDrr, and 2/3 in the PPIDarr group. Six horses had a history of laminitis (3 nPPID, 2 PPID, and 1 PPIDarr), and there was no significant difference between the groups (p = 0.553, Kruskal–Wallis Test). However, significant differences between the groups were detected for feeding, age, and ACTH concentration. All horses identified as PPIDrr were exclusively maintained on a hay diet, whereas the nPPID and PPID patients also received concentrates (1 nPPID), Mash (10 nPPID, and 3 PPID) or grass (1nPPID and 12 PPID) in addition to hay (p = 0.005, Kruskal–Wallis Test). One horse (nPPID) received grass only. Information on age was unavailable for one horse (PPIDrr). Horses suffering from PPID were significantly older than nPPID horses (p < 0.001, ANOVA with Games-Howell test). Between the other groups, there were no significant differences regarding age. There were no significant differences in the ACTH concentration between nPPID and PPIDrr (p = 0.972, ANOVA with Games-Howell test). The ACTH concentration of PPID patients was significantly higher than in nPPID (p < 0.001, ANOVA with Games-Howell test), PPIDrr (p < 0.001, ANOVA with Games-Howell test), and PPIDarr (p = 0.014, ANOVA with Games-Howell test). Furthermore, PPIDarr horses had significantly higher ACTH concentrations than PPIDrr horses (p = 0.017, ANOVA with Games-Howell test). Mean and standard deviations of age and ACTH are displayed in Table 1.

3.2. Amino Acid Analysis

The mean ± standard deviation and the median, minimum and maximum of the measured amino acid concentrations are displayed in Table 2 and Table 3. The p-values of ANOVA or Kruskal–Wallis tests are included in these tables as well.
Significant group differences were detected for arginine, asparagine, citrulline, cysteine, glutamine, and threonine.
Arginine in PPIDarr was significantly higher than in nPPID (p = 0.016, Tukey test). Asparagine was significantly higher in PPID when compared to nPPID (p < 0.001, Games-Howell test) and PPIDrr (p = 0.043, Games-Howell Test). Furthermore, the asparagine concentration was significantly higher in PPIDarr when compared to nPPID (both: p = 0.039, Games-Howell test). Citrulline was significantly higher in PPIDrr when compared to nPPID (p = 0.024, Tukey test) and PPID (p = 0.012, Tukey test). The cysteine concentration in PPIDrr was significantly lower than in all other groups (nPPID vs PPIDrr p = 0.003, Games-Howell test, PPID vs PPIDrr p = 0.043, Games-Howell test, PPIDrr vs PPIDarr p = 0.044, Games-Howell test). When compared to nPPID, the glutamine concentration in PPID (p < 0.001, Tukey test) and PPIDarr (p = 0.014, Tukey test) was significantly higher. For threonine, no significant group differences were identified by post hoc testing.

4. Discussion

The main limitation of this study is the insufficient number of PPIDrr and PPIDarr that were included in the analysis. However, since an adequate number of horses was included PPID and nPPID, the comparisons between these groups should provide valid results. Furthermore, even if only a few horses medicated with pergolide were available for the study, the detected differences clearly show that the amino acid profile is potentially affected by this medication. For PPID, epidemiological differences regarding gender or breed were not reported previously; however, increasing age was identified as a risk factor for PPID [1,40,41], which may explain that horses in the PPID group were significantly older than in the nPPID group. A frequently reported sign of ageing horses, loss of muscle tone, was reported by owners of geriatric horses [42,43], which was previously reported as a sign of ageing in horses [44]. Among hypertrichosis and/or other haircoat abnormalities, laminitis, lethargy, depression and weight loss, and epaxial muscle wastage or muscle atrophy are counted to be the most common clinical signs reported in horses suffering from PPID [45,46]. These changes may also be responsible for some of the changes in the amino acid profile.
In human ACTH—secreting pituitary adenoma, changes in the amino acid metabolism have been reported; particularly, these concern the alanine, aspartate, and glutamate metabolism [47]. Significant differences in the plasma concentration of asparagine, the neutral derivative of aspartic acid, were also detected in horses suffering from PPID. Healthy horses and PPIDrr patients had significantly lower asparagine concentrations when compared to PPID patients. Furthermore, PPIDarr had significantly higher asparagine concentrations than healthy horses. Additionally, higher asparagine concentrations in horses suffering from PPID compared to healthy horses have already been reported previously [48]. However, the results for asparagine must be interpreted with care since 20 horses fell below the detection limit. Also, glutamine, which was significantly lower in plasma in healthy horses than in untreated PPID patients and PPID patients who received pergolide but whose ACTH concentration was above the reference range, is synthesized from glutamic acid and ammonia [49]. An altered activity of this metabolic pathway also seems conceivable in horses suffering from PPID, especially since epaxial muscle wasting is a typical sign of PPID [45,46] and glutamine is assumed to potentially be a direct regulator of muscle synthesis and degradation [50,51]. Therefore, it could be suggested that a higher glutamine concentration in PPID patients may be assumed, since stress leads to a release of high concentrations of glutamine [52,53]. However, the storages eventually become depleted [52,53], which may explain the lower glutamine concentrations in the PPID and PPIDarr groups.
Furthermore, decreased glutamic acid, arginine, cysteine, and glutamine levels were shown to be associated with oxidative stress and neurodegeneration in Parkinson’s disease [28]. Since PPID is a neurodegenerative disease as well, decreased concentrations of these amino acids may also reflect the progression of the disease and might be used as potential markers of disease severity in the future.
The non-proteogenic amino acid citrulline was significantly higher in PPIDrr horses than in nPPID and PPID horses. This amino acid is mostly metabolized by the small intestine; therefore, it is considered to be a biomarker for the functional small intestinal bowel mass [54,55]. Furthermore, since citrulline is an intermediate metabolite in ureagenesis [56,57], during which citrulline is metabolized to arginine, a major regulator of vascular tone [58,59,60] in the kidney [61], it also is a functional biomarker for kidney function. In some cells, citrulline can act as a precursor for arginine [62] and, therefore, may be of importance for the metabolism and regulation of nitric oxide (NO) [63]. Regarding decreased citrulline concentrations and increased arginine concentrations, an upregulation of this pathway in the PPIDrr group seems conceivable; however, it should be clearly underlined again that only a few of these animals were included in the study. However, a previous study on gastrointestinally-diseased horses developing laminitis found significantly lower citrulline concentrations in horses developing laminitis than in those that did not [64]. Horses suffering from PPID are at risk for developing (endocrinopathic) laminitis [65]; however, endocrinopathic laminitis has a different pathogenesis than laminitis caused by gastrointestinal disease. Whether or not a decreased citrulline concentration is also a characteristic in equine endocrinopathic laminitis remains to be elucidated.
Cysteine is one of the least abundant, but functionally important, amino acids in proteins [66]. Mutations including cysteine residues include genetic diseases [67]. Cysteine molecules can react with other cysteine molecules by forming the typical disulfide bond, which can functionally interchange with another amino acid, selenocysteine, which is assumed to occur exclusively at functional sites [68]. A study performed on anterior pituitary cells in primary culture showed that cysteine proteases, in addition to aspartyl proteases, may be involved in the cellular metabolism of ACTH [69]. An association of these findings with lower cysteine concentrations due to altered ACTH production and pergolide treatment in PPIDrr patients remains to be elucidated, especially since these experiments were not conducted in horses but in cellular culture. Studies on human subjects with ACTH-secreting pituitary tumors also revealed metabolic changes: one study reported on 12 initially significantly changed metabolites in pituitary adenoma samples when compared to the control samples; after performing a Bonferroni correction, there were only three metabolites significantly changed: pyridoxate, deoxycholic acid, and 3-methyladipate [47]. Several changes were also detected in the metabolic pathway analysis, including changes in amino acid metabolism. Alanine, aspartate and glutamate metabolism, and starch and sucrose metabolism, as well as amino sugar and nucleotide sugar metabolism, lysine biosynthesis, vitamin B6 metabolism, aminoacyl-tRNA biosynthesis, glycolysis or gluconeogenesis, and purine metabolism, were significantly affected. The metabolism of alanine, aspartate, and glutamate was particularly affected [47]. Similarly, significant differences in the asparagine concentration, which is the neutral derivate of aspartate, were observed between the PPIDarr and the nPPID group. Different observations between the mentioned study and our study are probably caused by the different pathogenesis of the diseases.

5. Conclusions

Altered amino acid concentrations are found in horses suffering from PPID when compared to healthy horses. Especially asparagine, citrulline, and glutamine may be potential diagnostic markers and may offer interesting approaches for research regarding amino acid supplementation in PPID patients.

Author Contributions

Conceptualization: S.D.S., D.T. and H.G.; Methodology: S.D.S. and D.T.; Formal analysis: S.D.S. and R.M.; Investigation: S.D.S. and D.T.; Data curation: S.D.S. and D.T.; Writing—original draft preparation, S.D.S.; Writing—review and editing: S.D.S., D.T., R.M. and H.G.; Supervision: H.G.; Project administration: S.D.S. and H.G. All authors have read and agreed to the published version of the manuscript.

Funding

The amino acid analysis was sponsored by MembraPure GmbH, Hennigsdorf, Germany. We acknowledge support by the Open Access Publication Fund of the Freie Universität Berlin.

Institutional Review Board Statement

The study was not declared according to the German Animal Welfare law §8.1 since all samples were taken as a part of a routine clinical examination.

Informed Consent Statement

Written owner’s consent to involve their horses in the study was obtained during the admission process at the clinic.

Data Availability Statement

Additional data are available from the corresponding author.

Acknowledgments

The publication of this article was funded by Freie Universität Berlin.

Conflicts of Interest

The authors declare no conflict of interest.

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Table
Table 1. Age and ACTH concentrations of the tested horses (mean ± standard deviation).
Table 1. Age and ACTH concentrations of the tested horses (mean ± standard deviation).
ParameternPPIDPPIDPPIDrrPPIDarr
ACTH (pg/mL)19.76 ± 6.96382.85 ± 352.6918.1 ± 7.88154.0 ± 23.07
Age (years)15.91 ± 6.9627.79 ± 6.721.25 ± 3.7727.33 ± 4.16
nPPID: non-PPID horse, PPID: horse suffering from PPID, PPIDrr: horse treated for PPID and ACTH ≤ 30 pg/mL, and PPIDarr: horse treated for PPID and ACTH ≥ 100 pg/mL.
Table
Table 2. Mean and standard deviations of the normally distributed amino acid concentrations (nmol/mL); p-values (ANOVA).
Table 2. Mean and standard deviations of the normally distributed amino acid concentrations (nmol/mL); p-values (ANOVA).
nPPIDPPIDPPIDrrPPIDarrp
MeanSDMeanSDMeanSDMeanSD
1mHis17.16.015.86.018.59.223.76.20.231
Ala205.869.0215.085.1164.241.721370.30.595
Arg67.329.786.720.095.727.1116.016.00.004
Asn35.620.368.029.133.012.278.953.10.018
Cit56.420.253.319.183.912.068.117.40.016
Cys135.681.9169.832.918.77.4146.4115.0<0.001
GABA20.48.019.38.012.91.121.911.10.258
Gln239.856.1334.843.9286.446.0337.442.363<0.001
Glu40.924.435.720.318.35.341.423.20.21
Gly410.2161.6431.9119.5400.8146.7384.490.20.92
His71.213.481.317.277.58.086.45.10.89
Ile60.616.070.219.453.215.472.911.50.113
Leu100.930.6112.636.897.824.7123.520.70.458
Orn59.518.157.414.364.05.555.75.20.83
Phe54.911.453.511.260.17.259.03.60.603
Ser212.464.6244.268.1220.934.0227.120.50.419
Tau41.312.647.314.640.113.142.913.30.473
Trp50.912.852.216.356.011.572.612.50.102
Val157.452.0162.749.2172.726.5174.842.90.88
nPPID: non-PPID horse, PPID: horse suffering from PPID, PPIDrr: horse treated for PPID and ACTH ≤ 30 p g/mL, PPIDarr: horse treated for PPID and ACTH ≥ 100 pg/mL, SD: Standard deviation, 1mHis: 1-methyl histidine, Ala: Alanine, Arg: Arginine, Asn: Aspargine; Citr: Citrulline, Cys: Cysteine, GABA: Gamma-aminobutyric acid, Gln: Glutamine, Glu: Glutamic acid, Gly: Glycine, His: Histidine, Ile: Isoleucine, Leu: Leucine, Met: Methionine, Orn: Ornithine, Phe: Phenylalanine, Ser: Serine, Tau: Taurine, Trp: Tryptophan, Val: Valine.
Table
Table 3. Median, minimum, and maximum of the non—normally distributed amino acid concentrations (nmol/mL); Kruskal—Wallis Test.
Table 3. Median, minimum, and maximum of the non—normally distributed amino acid concentrations (nmol/mL); Kruskal—Wallis Test.
nPPIDPPIDPPIDrrPPIDarrp
MedMinMaxMedMinMaxMedMinMaxMedMinMax
Asp8.1516.55520.78.15.79.98.35.016.50.304
Lys76.145.5153.892.629.3143.587.846.7122.9114.680.0126.20.498
Pro76.342.8308.774.035.8147.168.246.6104.1102.278.2112.70.315
Thr94.741.1203.9129.665.9208.4113.239.6138.6151.5125.7156.60.047
Tyr52.136.597.658.036.493.563.846.596.763.250.864.40.528
nPPID: non-PPID horse, PPID: horse suffering from PPID, PPIDrr: horse treated for PPID and ACTH ≤ 30 p g/mL, PPIDarr: horse treated for PPID and ACTH ≥ 100 pg/mL, Med: median, Min: minimum, Max: maximum, Asp: aspartic Acid, Lys: lysine, Pro: proline, Thr: threonine, Tyr: tyrosine.
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Stoeckle, S.D.; Timmermann, D.; Merle, R.; Gehlen, H. Plasma Amino Acids in Horses Suffering from Pituitary Pars Intermedia Dysfunction. Animals 2022, 12, 3315. https://doi.org/10.3390/ani12233315

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Stoeckle SD, Timmermann D, Merle R, Gehlen H. Plasma Amino Acids in Horses Suffering from Pituitary Pars Intermedia Dysfunction. Animals. 2022; 12(23):3315. https://doi.org/10.3390/ani12233315

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Stoeckle, Sabita Diana, Detlef Timmermann, Roswitha Merle, and Heidrun Gehlen. 2022. "Plasma Amino Acids in Horses Suffering from Pituitary Pars Intermedia Dysfunction" Animals 12, no. 23: 3315. https://doi.org/10.3390/ani12233315

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Stoeckle, S. D., Timmermann, D., Merle, R., & Gehlen, H. (2022). Plasma Amino Acids in Horses Suffering from Pituitary Pars Intermedia Dysfunction. Animals, 12(23), 3315. https://doi.org/10.3390/ani12233315

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