Orexin‐B‐like immunoreactivity in pituitary αMSH‐producing cells and median eminence GnRH‐containing fibres of the flat‐tailed house gecko

We examined the distribution of the orexin‐like peptides in the pituitary and median eminence of the flat‐tailed house gecko (Hemidactylus platyurus) using immunohistochemistry. Orexin‐B‐like, but not orexin‐A‐like, immunoreactivity was detected in the pituitary, specifically in the pars intermedia, and these cells corresponded to alpha‐melanocyte‐stimulating hormone (αMSH)‐producing cells. Orexin‐B and αMSH secreted from pars intermedia may modulate secretion of adenohypophyseal cells in the pars distalis. In the median eminence, orexin‐B‐immunoreactive puncta and fibres were observed, and these structures corresponded to gonadotropin‐releasing hormone (GnRH)‐immunoreactive puncta and fibres. Orexin‐B secreted from GnRH‐containing neurons in the hypothalamus may affect thyrotropin‐releasing hormone‐containing neurons resulting in modulation of αMSH secretion of melanotrophs in the pars intermedia.     

The Effect of Season on the Histologic and Histomorphometric Appearance of the Equine Pituitary Gland

The objective of this study was to determine the effect of season on the histologic and histomorphometric appearance of the normal equine pituitary gland. Pituitary glands were collected at necropsy from 121 horses throughout the year. Plasma was also collected from 59 of these horses before euthanasia. Hematoxylin and eosin stained median sagittal sections of each pituitary were evaluated and histologically graded by three pathologists. Histomorphometric analysis was performed on the same slides. Plasma α-melanocyte stimulating hormone was measured by radioimmunoassay in a subset of horses (n = 59). A total of 118 pituitary glands were included in the study after exclusions were made on the basis of the presence of pars intermedia (PI) adenomas (>5 mm). There was a positive correlation between PI hormone concentration (α-melanocyte stimulating hormone) and PI area. Pituitary gland measurements and grades from samples collected in the fall were compared with those collected in the nonfall months using t-test. The PI area, total pituitary area, and PI/total pituitary ratio were significantly greater in the fall compared with nonfall months (P < .0001, P < .01, P < .0001, respectively). Pituitary grades were also higher in the fall compared with nonfall months (P < .001). There was no seasonal difference in pars distalis or pars nervosa area. The results of this study show that the normal equine pituitary shows seasonal changes in appearance and size. These changes must be considered when using postmortem histologic evaluations in the diagnosis of pituitary pars intermedia dysfunction or for validation of antemortem diagnostic tests.     

The Influence of the Size,Age and Sex on the Computed Tomographic Measured Size of the Pituitary Gland in Normal Horses

The objective of this study was to examine the influence of the size, age and sex of the horse on the size of the pituitary gland and determine the possibility of using the pituitary gland height‐to‐brain area ratio (P:B ratio) to allow comparison of different sized and aged horses. Thirty‐two horses without pituitary pars inter‐media dysfunction that underwent a contrast‐enhanced computed tomographic (CT) examination were included in a cross‐sectional study. On the CT images, the pituitary gland height was measured and the P:B ratio was calculated. These measurements were correlated to the size, age and sex of the horses. The pituitary gland height was significantly associated with the size (P < 0.001) and the age (P < 0.001), but not with the sex (P = 0.40), of the horses. No significant association was found between the P:B ratio and the size (P = 0.25), the age (P = 0.06) or the sex (P = 0.25) of the horses. In conclusion, the pituitary gland size varies between different sized and aged horses. The use of the P:B ratio is a valuable metric for making comparisons between the pituitary glands of these horses.     

Successful treatment of Sarcoptes scabiei in a 33‐year‐old pony with underlying pituitary pars intermedia dysfunction

A pony presented with a severe, chronic dermatitis around the ears, neck and trunk of the body, hind quarters and ventral abdomen. The pony was intensely pruritic as was an in‐contact pony and both owners. A superficial skin scraping demonstrated multiple living mites, identified as Sarcoptes scabiei. Equine pituitary pars intermedia dysfunction (PPID) was diagnosed as an underlying, potentially immunosuppressive disorder. The pony was treated for Sacroptes scabiei as well as PPID and is doing well 2 months after initial presentation.     

Endocrine disorders and laminitis

Two common endocrine disorders, pituitary pars intermedia dysfunction and equine metabolic syndrome, predispose horses and ponies to laminitis and may even induce the condition. The exact mechanisms involved in endocrinopathic laminitis have not been elucidated but hyperinsulinaemia and insulin resistance are currently being investigated. Obesity and regional adiposity may also contribute to laminitis susceptibility through the release of inflammatory cytokines and adipokines. In the case of pituitary pars intermedia dysfunction, glucocorticoid excess is likely to weaken hoof structures, alter vascular dynamics within the foot and induce or exacerbate insulin resistance. This review will summarise current theories regarding the pathophysiology of endocrinopathic laminitis and provide recommendations for the diagnosis and management of these common equine endocrine disorders.     

Antidiuretic response of a horse affected with pituitary pars intermedia dysfunction to desmopressin acetate

Central diabetes insipidus (DI) was diagnosed in a 20‐year‐old American Quarter Horse gelding that was concomitantly affected with pituitary pars intermedia dysfunction (PPID). The diagnosis of DI was supported by a positive response to administered desmopressin acetate. Diagnosis of PPID was supported by physical appearance and elevated plasma adrenocorticotropic hormone concentration following domperidone administration. The horse's physical condition improved following treatment with pergolide but long‐term treatment with desmopressin was not undertaken and severe polyuria and polydipsia persisted. Desmopressin acetate appears to be useful for the diagnosis of DI in mature horses concomitantly affected with PPID.     

Insulin dysregulation

Abnormalities of insulin metabolism include hyperinsulinaemia and insulin resistance, and these problems are collectively referred to as insulin dysregulation in this review. Insulin dysregulation is a key component of equine metabolic syndrome: a collection of endocrine and metabolic abnormalities associated with the development of laminitis in horses, ponies and donkeys. Insulin dysregulation can also accompany prematurity and systemic illness in foals. Causes of insulin resistance are discussed, including pathological conditions of obesity, systemic inflammation and pituitary pars intermedia dysfunction, as well as the physiological responses to stress and pregnancy. Most of the discussion of insulin dysregulation to date has focused on insulin resistance, but there is increasing interest in hyperinsulinaemia itself and insulin responses to feeding. An oral sugar test or in‐feed oral glucose tolerance test can be performed to assess insulin responses to dietary carbohydrates, and these tests are now recommended for use in clinical practice. Incretin hormones are likely to play an important role in postprandial hyperinsulinaemia and are the subject of current research. Insulin resistance exacerbates hyperinsulinaemia, and insulin sensitivity can be measured by performing a combined glucose‐insulin test or i.v. insulin tolerance test. In both of these tests, exogenous insulin is administered and the rate of glucose uptake into tissues measured. Diagnosis and management of hyperinsulinaemia is recommended to reduce the risk of laminitis. The term insulin dysregulation is introduced here to refer collectively to excessive insulin responses to sugars, fasting hyperinsulinaemia and insulin resistance, which are all components of equine metabolic syndrome.     

Correlation of pituitary histomorphometry with adrenocorticotrophic hormone response to domperidone administration in the diagnosis of equine pituitary pars intermedia dysfunction

Functional evaluation of the pars intermedia (PI) is required for the early diagnosis of equine pituitary PI dysfunction (PPID), yet most assays target the hypothalamic-pituitary-adrenal axis, which regulates the pars anterior. In contrast, the PI is regulated by dopaminergic tone from hypothalamic neurons. Loss of dopaminergic inhibition is hypothesized to cause the PI hypertrophy and hyperplasia that result in the clinical manifestations of PPID. Domperidone, a dopamine receptor antagonist, should exacerbate the loss of dopaminergic inhibition in horses with PPID and increase the release of endogenous adrenocorticotrophic hormone (eACTH) by PI melanotrophs. To test this, plasma eACTH concentration was determined in horses with or without clinical signs of PPID at 0, 4, and 8 hours after oral administration of 3.3 mg domperidone/kg. Pituitary glands were evaluated postmortem by histologic grading and morphometry. In the 33 horses, median age, plasma ACTH concentration 8 hours after domperidone, and PI area in median sagittal sections were associated with histologic grade as follows: pituitary grade 1 (normal), n = 3, 7.5 years, 20.0 pg/ml, 0.16 cm(2); grade 2 (focal hypertrophy or hyperplasia), n = 9, 14.5 years, 27.1 pg/ml, 0.27 cm(2); grade 3 (diffuse adenomatous hyperplasia), n = 5, 21.0 years, 64.4 pg/ml, 0.48 cm(2); grade 4 (microadenomas), n = 12, 23.3 years, 128.0 pg/ml, 0.87 cm(2); grade 5 (adenoma), n = 4, 24.9 years, 720.5 pg/ml, 2.1 cm(2). Results suggest that horses with pituitary histologic grade > or =3 respond to domperidone with increased plasma ACTH concentration.     

Circadian and circannual rhythms of cortisol,ACTH, and α-melanocyte-stimulating hormone in healthy horses

Cosinor analysis was used to evaluate whether pituitary and adrenal hormones exhibit circadian rhythmicity in horses. The effect of season and animal age on their respective rhythms was also determined. In addition, the usefulness of evaluating cortisol rhythmicity for the diagnosis of pituitary pars intermedia dysfunction (PPID) was assessed. Serum cortisol concentrations (P < 0.01), but not plasma ACTH or α-melanocyte-stimulating hormone (α-MSH), showed a significant circadian periodicity in horses. An effect of season on hormone concentration was observed with plasma ACTH and α-MSH concentration greater in the fall and cortisol concentration greater in the spring (P < 0.001). Age did not affect cortisol rhythm, but it did blunt the variation in cortisol concentration in horses, similar to what has been previously reported to occur in aged people and dogs. In addition, our results suggest that clinically and diagnostically normal, non–PPID-affected horses commonly have a loss of cortisol diurnal rhythm. Therefore, measurement of circadian rhythm is not an appropriate diagnostic test for PPID.     

The effect of geographic location, breed, and pituitary dysfunction on seasonal adrenocorticotropin and α-melanocyte-stimulating hormone plasma concentrations in horses

Background: Plasma α‐melanocyte‐stimulating hormone (α‐MSH) and adrenocorticotropin (ACTH) concentrations in horses vary with season, confounding diagnostic testing for pituitary pars intermedia dysfunction (PPID). Hypothesis: The goals of this study were to determine whether seasonal variation in plasma α‐MSH and ACTH concentrations in horses is influenced by geographic location, breed, or PPID. Animals: Healthy light breed horses residing in Florida, Massachusetts, and Finland (n = 12 per group); healthy Morgan horses (n = 13); healthy ponies (n = 9) and horses with PPID (n = 8). Methods: Monthly plasma α‐MSH and ACTH concentrations were measured by radioimmunoassay. Nonlinear regression analysis was used to estimate the time of peak hormone concentrations. Mean hormone concentrations in fall and nonfall months were compared. Results: The fall peak plasma α‐MSH concentration occurred earlier in horses residing at more northern locations. Mean seasonal α‐MSH concentrations were similar in all healthy groups at all locations, but in the fall, plasma ACTH concentrations were higher in horses living in more southern locations. Plasma ACTH but not α‐MSH concentrations were higher in Morgan horses compared with light breed horses from the same location. Hormone concentrations of ponies did not differ from those of horses during either season. Concentrations of both hormones were high in the fall compared with the spring in horses with PPID. Conclusions and Clinical Importance: These findings suggest geographic location of residence and breed may affect the onset, amplitude, or both of the seasonal peak of pars intermedia (PI) hormones and should be considered when performing diagnostic testing for PPID. Horses with PPID maintain seasonal regulation of PI hormone output.     

Cytokine dysregulation in aged horses and horses with pituitary pars intermedia dysfunction

BACKGROUND: Equine pituitary pars intermedia dysfunction (PPID) is the result of a loss of dopaminergic inhibition of the pars intermedia secondary to neurodegeneration of periventricular hypothalamic neurons. The pathologic events contributing to development of neurodegeneration or clinical signs in equids with PPID are unknown. Chronic inflammation may contribute to initiation or progression of PPID. HYPOTHESIS: Horses with PPID have a distinct systemic cytokine profile compared with that of normal adult or aged horses. The cytokine profile of healthy aged horses differs from that of adult horses. ANIMALS: Aged horses with PPID, healthy aged-matched controls, and adult controls (n = 14 per group). METHODS: Total leukocyte cytokine expression was determined by quantitative polymerase chain reaction (PCR), and tumor necrosis factor (TNF)-alpha plasma concentration was determined by enzyme-linked immunosorbent assay (ELISA). Peripheral blood mononuclear cell (PBMC) TNF-alpha response after endotoxin (lipopolysaccharide [LPS]) treatment was assessed by ELISA. RESULTS: Aged healthy horses had increased expression of interleukin (IL)-6, IL-8, and interferon-gamma as well as PBMC TNF-alpha release after LPS stimulation compared with healthy adult horses. In contrast, aged horses with PPID had increased IL-8 expression, but expression of other cytokines was similar to that of healthy adult horses, not age-matched controls. CONCLUSIONS AND CLINICAL IMPORTANCE: Aged horses show evidence of a proinflammatory state that may contribute to development of age-associated diseases. Horses with PPID have increased expression of IL-8, which may influence the ability of horses with PPID to respond to bacterial pathogens. The general decrease in proinflammatory cytokine expression observed in horses with PPID may be the outcome of high plasma concentrations of anti-inflammatory hormones.     

Severe eosinophilic cholangiohepatitis due to fluke infestation in a pony in Scotland

Fasciola hepatica infestation is reported as a cause of severe eosinophilic cholangiohepatitis in a 28‐year‐old Warmblood cross pony gelding. The gelding presented initially for investigation of acute laminitis found to be secondary to pars pituitary intermedia dysfunction (PPID). Six weeks of treatment including administration of pergolide achieved good control of the laminitis but there was a marked general clinical deterioration over this period with notable weight loss, tachycardia, anorexia and ventral oedema. Hepatobiliary enzymes were increased significantly and there was mild elevation of plasma bile acid concentration. An eosinophilia in both blood and peritoneal fluid specimens and histopathological confirmation of an eosinophilic cholangiohepatitis on examination of liver biopsies supported a primary parasitic aetiology. The pony was treated for Fasciola hepatica with triclabendazole 12 mg/kg bwt but clinical signs continued to progress. Due to poor clinical response the pony was subjected to euthanasia and post mortem examination revealed an overwhelming infestation of the biliary tracts with Fasciola hepatica and a secondary chronic and severe cholangiohepatitis with marked fibrosis. To the authors' knowledge this is the first equine report demonstrating the relationship between the clinical disease syndrome, eosinophilic cholangiohepatitis and hepatic fluke infestation. Depending on geographical location, fasciolosis should be considered as a differential diagnosis for equine hepatopathies and can result in severe disease.     

Facial cutaneous phaeohyphomycosis associated with Alternaria infectoriae infection

Cutaneous nodular disease in the horse is relatively rare and usually associated with arthropod bites, dermal hyperplasia and inflammatory or neoplastic infiltrates. Equine phaeohyphomycosis, particularly alternariosis, has been previously described in the literature and is usually associated with Alternaria alternata. In this article we report a case of phaeohyphomycosis caused by a member of Alternaria section Infectoriae in a horse. To our knowledge this is the first time that this organism has been identified in equids. Despite A. Infectoriae being commonly isolated in individuals receiving immunosuppressive therapy and/or suffering from Cushing's syndrome, we could not determine a link between pituitary pars intermedia dysfunction and fungal infection in this case. The mare responded well to surgical excision of the cutaneous lesions and made a full recovery.     

Seasonal changes in plasma adrenocorticotropic hormone and α-melanocyte-stimulating hormone in response to thyrotropin-releasing hormone in normal, aged horses

Background: Results of diagnostic tests for equine pituitary pars intermedia dysfunction (PPID), including endogenous ACTH concentration and the overnight dexamethasone suppression test (DST), are affected by season. New and potentially more sensitive diagnostic tests for equine PPID, such as thyrotropin‐releasing hormone (TRH)‐stimulated ACTH response, have been developed, but have had limited evaluation of seasonality. Objective: Our purpose was to evaluate seasonal changes in plasma ACTH and alpha‐melanocyte‐stimulating hormone (α‐MSH) responses to TRH administration. Animals: Nine, healthy, aged horses with normal DST results. Methods: Synthetic TRH (1 mg) was administered IV. Plasma ACTH and α‐MSH concentrations were measured at 0, 5, 10, 15, 20, 25, 30, 45, 60, and 180 minutes. Testing was performed in February, July, August, September, October, and November. Mean TRH‐stimulated ACTH and α‐MSH concentrations were compared across months and time by repeated measures analysis of variance. Significance was set at the P < .05 level. Results: Concentrations of ACTH and α‐MSH significantly increased after TRH administration. Endogenous and TRH‐stimulated ACTH and α‐MSH concentrations were significantly different across months with higher concentrations in the summer and fall compared with February. Conclusions and Clinical Importance: Plasma ACTH and α‐MSH responses to TRH administration experience seasonal variation, with TRH‐stimulated ACTH and α‐MSH concentrations increasing from summer through fall. These results support previous evidence of a seasonal influence on the equine pituitary‐adrenal axis. More research is warranted with a larger number of horses to determine if seasonal reference ranges for TRH stimulation testing need to be defined.     

Effect of supplements during the cold season on the reproductive system in prepubertal Tibetan sheep ewes

We examined the development of the reproductive system in prepubertal Tibetan sheep ewes when fed only oat hay (CON) or supplemented with either lick blocks (BS) or concentrate feed (CS) during the cold season. The average daily gain of the CS ewes was greater than that of the BS ewes (P  < 0.05), which was greater than that of the CON ewes. The same pattern was observed in the number of ovarian follicles (P  < 0.001), that is, CS > BS > CON. Serum concentrations of gonadotropin‐releasing hormone, follicle‐stimulating hormone, luteotrophic hormone, estradiol and progesterone in the CS and BS groups were higher than in the CON group (P  < 0.05). The messenger RNA (mRNA) expression of KiSS‐1, GPR54 (G protein‐coupled receptor 54), ERα (estradiol receptor α) in the hypothalamic anteroventral periventricular area of the CS group were higher than in both the BS and CON groups (P  < 0.05), while the BS group was higher than in the CON group (P  < 0.05). Similar differences among groups were observed for gonadotropin‐releasing hormone receptor mRNA expression in the pituitary, follicle‐stimulating hormone receptor and luteinizing hormone receptor mRNA expression in the ovary. These results indicated that the KiSS1/GPR54 system was more active with nutrition or trace mineral supplementation during the cold season. The system stimulated the hypothalamic–pituitary?gonadal axis and enhanced folliclar development in prepubertal Tibetan sheep ewes. We concluded that energy, protein and trace minerals supplements could improve the reproductive performance of Tibetan sheep on the Qinghai‐Tibetan plateau.     

Autologous Platelet Concentrates as an Adjunctive Treatment for Chronic Laminitis in a Mare with Pituitary Pars Intermedia Dysfunction

The aim of this article was to describe a case of a 7-year-old mare with chronic laminitis secondary to pituitary pars intermedia dysfunction that was successfully treated with autologous platelet concentrates (APC) obtained by the tube method, 4 months before being treated with oral pergolide. After the diagnosis of pituitary pars intermedia dysfunction, the patient was treated with three intralesional injections of APC at 10-day intervals. APC presented a mean concentration of 430 ± 22 × 10⁶ platelets and 8.6 ± 1.3 leukocytes/mL. The treatment with APC produced growth of the hooves at a rate of 5 mm/wk and substantially reduced the foot pain (lameness) after two APC applications. The mare could be ridden 2 weeks after the third APC treatment. The treatment with oral pergolide 4 months later improved the clinical picture of the patient, albeit hirsutism remained. APC could be useful as adjunctive treatment of chronic laminitis in horses. However, additional clinical studies are necessary to determine the safety and effectiveness of APC in chronic laminitis.     

Protein and mRNA expression of follicle‐stimulating hormone receptor and luteinizing hormone receptor during the oestrus in the yak (Bos grunniens)

Follicle‐stimulating hormone (FSH) and luteinizing hormone (LH) have a central role in follicle growth, maturation and oestrus, but no clear pathway in the seasonal oestrus of yak (Bos grunniens) has been found. To better understand the role of FSH and LH in seasonal oestrus in the yak, six yaks were slaughtered while in oestrus, and the pineal gland, hypothalamus, pituitary gland, and gonads were collected. Using real‐time PCR and immunohistochemical assays, we determined the mRNA and protein expression of the FSH and LH receptors (FSHR and LHR) in these organs. The analysis showed that the FSHR mRNA expression level was higher in the pituitary gland tissue compared with LHR (p < .01) during oestrus. By contrast, there was low expression of FSHR and LHR mRNA in the pineal gland and hypothalamus. FSHR mRNA expression was higher than that of LHR (p < .05) in the ovary, whereas LHR mRNA expression was higher than that of FSHR (p < .01) in the uterus. FSHR and LHR proteins were located in the pinealocyte, synaptic ribbon and synaptic spherules of the pineal gland and that FSH and LH interact via nerve fibres. In the hypothalamus, FSHR and LHR proteins were located in the magnocellular neurons and parvocellular neurons. FSHR and LHR proteins were localized in acidophilic cells and basophilic cells in the pituitary gland, and in surface epithelium, stromal cell and gland epithelium in the uterus. In the ovary, FSHR and LHR protein were present in the ovarian follicle. Thus, we concluded that FSHR and LHR are located in the pineal gland, hypothalamus, pituitary and gonad during oestrus in the yak. However, FSHR was mainly expressed in the pituitary gland and ovaries, whereas LHR was mainly expressed in the pituitary gland and uterus.     

Sex steroid hormones do not enhance the direct stimulatory effect of kisspetin‐10 on the secretion of growth hormone from bovine anterior pituitary cells

The aims of the present study were to clarify the effect of kisspeptin10 (Kp10) on the secretion of growth hormone (GH) from bovine anterior pituitary (AP) cells, and evaluate the ability of sex steroid hormones to enhance the sensitivity of somatotrophic cells to Kp10. AP cells prepared from 8–11‐month‐old castrated calves were incubated for 12 h with estradiol (E₂, 10^?8 mol/L),progesterone (P₄, 10^?8 mol/L), testosterone (T, 10^?8 mol/L), or vehicle only (control), and then for 2 h with Kp10. The amount of GH released in the medium was measured by a time‐resolved fluoroimmunoassay. Kp10 (10^?6 or 10^?5 mol/L) significantly stimulated the secretion of GH from the AP cells regardless of steroid treatments (P < 0.05), and E₂, P₄, and T had no effect on this response. The GH‐releasing response to growth hormone‐releasing hormone (GHRH, 10^?8 mol/L) was significantly greater than that to Kp10 (P < 0.05). The present results suggest that Kp10 directly stimulates the release of GH from somatotrophic cells and sex steroid hormones do not enhance the sensitivity of these cells to Kp10. Furthermore, they suggest that the GH‐releasing effect of Kp10 is less potent than that of GHRH.