Acromegaly due to a somatroph adenoma in a dog

Transsphenoidal hypophysectomy for the treatment of hypersomatotropism secondary to a pituitary somatotroph adenoma in a dog

Pituitary-dependent hypersomatotropism is rarely diagnosed in dogs and surgical treatment is not reported. A 6-year-10-month male neutered Patterdale Terrier presented with polyuria, polydipsia, progressive pharyngeal stertor, excessive hair growth and widened facial features and paws. Serum insulin-like growth factor-1 concentration via radioimmunoassay was consistent with hypersomatotropism (1783 ng/mL). A pituitary mass was identified on magnetic resonance and computed tomography imaging. Six weeks later, glucosuria, starved hyperglycemia and serum fructosamine above the reference range (467.6 μmol/L, RI 177-314) were documented, consistent with diabetes mellitus. Transsphenoidal hypophysectomy was performed under general anesthesia without complications. Pituitary histopathology identified an acidophil neoplasm, with positive immunostaining for growth hormone. Postoperatively, there was rapid resolution of clinical, biochemical and morphologic changes of hypersomatotropism with persistence of diabetes mellitus. This case demonstrates successful resolution of hypersomatotropism with ongoing diabetes mellitus in a dog after surgical treatment by transsphenoidal hypophysectomy.

Acromegaly in dogs and cats

Acromegaly is an endocrine disease that leads to elevated production and secretion of growth hormone (GH). It can occur in adult and aged cats and is usually associated with neoplasms, such as functional pituitary macroadenoma of somatotropic cells. In dogs it is usually related to an increase in serum progesterone that induces production of GH by the mammary glands. The main clinical signs are related to insulin resistance and the anabolic effect induced by GH: polyuria, polydipsia, polyphagia, increased tissue growth, weight gain, prognathism, and other changes. The condition can be diagnosed from clinical signals and imaging associated to measurement of serum concentrations of GH and insulin-like growth factor 1 (IGF-1, also known as somatomedin C). The main therapeutic modalities are radiotherapy, hypophysectomy, and several drugs such as somatostatin analogs, dopaminergic agonists and GH receptor antagonists. The present review aims to provide a relevant animal model of acromegaly with an update on the therapeutic approach that may help clinicians to consider the GH axis-IGF-1 system, its pathogenesis and the clinical signs induced by this hormonal disorder.

Pituitary tumour types in dogs and cats

Pituitary tumours are common in dogs and are being increasingly recognized in cats. Pituitary tumours are usually classified as adenomas and should only be classified as carcinomas when there is evidence of metastatic spread of the tumour, which is rare. Despite the benign nature of most pituitary tumours, they can still compress or invade neighbouring tissues. Pituitary tumours can be functional (hormonally active) or non-functional (hormonally silent). The aim of this review was to provide an overview of the different pituitary tumour types in dogs and cats that have been reported in the literature. In dogs, the most common pituitary tumour type is the corticotroph adenoma, which can cause pituitary-dependent hypercortisolism. In cats, the most common pituitary tumour is the somatotroph adenoma, which can cause hypersomatotropism, and the second-most common is the corticotroph adenoma. A lactotroph adenoma has been described in one dog, while gonadotroph, thyrotroph and null cell adenomas have not been described in dogs or cats. Hormonally silent adenomas are likely underdiagnosed because they do not result in an endocrine syndrome. Tools used to classify pituitary tumours in humans, particularly immunohistochemistry for lineage-specific transcription factors, are likely to be useful to classify canine and feline pituitary tumours of unknown origin. Future studies are required to better understand the full range of pituitary adenoma pathology in dogs and cats and to determine whether certain adenoma subtypes behave more aggressively than others. Currently, the mechanisms that underlie pituitary tumorigenesis in dogs and cats are still largely unknown. A better understanding of the molecular background of these tumours could help to identify improved pituitary-targeted therapeutics.

Comparative occurrence of diabetes in canine, feline, and few wild animals and their association with pancreatic diseases and ketoacidosis with therapeutic approach

Diabetes mellitus (DM) is a chronic metabolic disorder in which blood glucose level raises that can result in severe complications. However, the incidence increased mostly by obesity, pregnancy, persistent corpus luteum, and diestrus phase in humans and animals. This review has focused on addressing the possible understanding and pathogenesis of spontaneous DM in canine, feline, and few wild animals. Furthermore, pancreatic associated disorders, diabetic ketoacidosis, hormonal and drug interaction with diabetes, and herbal remedies associated with DM are elucidated. Bibliographic search for the present review was done using PubMed, Scopus, and Google Scholar for articles on concurrent DM in small and wild animals. Persistent corpus luteal and pseudopregnancy in female dogs generate gestational DM (GDM). GDM can also be caused by extensive use of drugs/hormones such as glucocorticosteroids. Although many similarities are present between diabetic cats and diabetic humans which present islet amyloidosis, there was a progressive loss of β- and α-cells and the normal number of δ-cells. The most prominent similarity is the occurrence of islet amyloidosis in all cases of diabetic cat and over 90% of human non-insulin dependent DM Type-2. Acute pancreatic necrosis (APN) occurs due to predisposing factors such as insulin antagonism, insulin resistance, alteration in glucose tolerance, obesity, hyperadrenocorticism, and persistent usage of glucocorticoids, as these play a vital role in the progression of APN. To manage such conditions, it is important to deal with the etiological agent, risk factors, diagnosis of diabetes, and hormonal and drug interaction along with its termination with suitable therapy (herbal) protocols. It should be noted that the protocols used for the diagnosis and treatment of human DM are not appropriate for animals. Further investigations regarding diabetic conditions of pets and wild animals are required, which will benefit the health status of all animals health worldwide.

Prolactinoma in a Dog

A 12-year-old male Yorkshire Terrier was presented because of decreased appetite. Physical examination revealed mammary gland swelling and galactorrhea. Contrast-enhanced computed tomographic scanning of the skull indicated an enlarged pituitary gland, compatible with a pituitary tumor. The serum prolactin concentration was markedly elevated. One week after the start of treatment with the dopamine agonist cabergoline, the serum prolactin concentration normalized and the galactorrhea resolved. Cabergoline was administered for approximately 4 months and then discontinued. Subsequently, serum prolactin concentration increased again, and mammary gland swelling and galactorrhea reappeared. The dog was euthanized 10 months after the first detection of the galactorrhea because of problems not directly related to pituitary disease. Postmortem examination revealed an infiltrative adenoma of the pituitary gland with immunolabeling for prolactin. The clinical and histopathologic findings indicated the diagnosis of a functional prolactinoma in a male dog.

Carbenoxolone Disodium Treatment for Canine Pituitary-Dependent Hyperadrenocorticism

Pituitary-dependent hyperadrenocorticism (PDH) is mainly caused by pituitary corticotroph tumors in dogs. A characteristic feature of corticotroph tumors is their resistance to negative feedback by glucocorticoids. In some animal species, including dogs, the aberrant expression of 11β-hydroxysteroid dehydrogenase (11HSD), a cortisol metabolic enzyme, is observed in corticotroph tumors. We previously reported that carbenoxolone (CBX), an inhibitor of 11HSD, suppressed ACTH secretion from the pituitary gland, and decreased cortisol concentrations in healthy dogs. Therefore, the aim of this study was to investigate the therapeutic effects of CBX on dogs with PDH. Six dogs with PDH were treated with 60 to 80 mg/kg/day of CBX for 6 weeks, followed by trilostane, which is a commonly used agent for canine PDH. CBX treatment led to a gradual decrease in both basal and in corticotropic releasing hormone (CRH)-stimulated plasma ACTH concentrations and CRH-stimulated serum cortisol concentrations, without side effects. However, basal and stimulated ACTH and cortisol concentrations remained higher than those of healthy dogs, and clinical symptoms such as polydipsia and polyuria were not ameliorated. After a 2-week wash-out interval, trilostane was administered for 2 weeks. Although basal plasma ACTH concentrations were higher after trilostane treatment than CBX treatment, polydipsia and polyuria resolved in all six dogs. The reason for the lack of improvement in polydipsia and polyuria with CBX treatment is unclear. Other mechanisms, in addition to a partial decrease in ACTH secretion, are likely to be involved. In conclusion, this is the first study to report the in vivo effects of CBX in dogs with PDH. The findings suggest that CBX inhibits ACTH secretion from canine pituitary tumors, resulting in lower cortisol concentrations.

Effects of Carbenoxolone on the Canine Pituitary-Adrenal Axis

Cushing’s disease caused by pituitary corticotroph adenoma is a common endocrine disease in dogs. A characteristic biochemical feature of corticotroph adenomas is their relative resistance to suppressive negative feedback by glucocorticoids. The abnormal expression of 11beta-hydroxysteroid dehydrogenase (11HSD), which is a cortisol metabolic enzyme, is found in human and murine corticotroph adenomas. Our recent studies demonstrated that canine corticotroph adenomas also have abnormal expression of 11HSD. 11HSD has two isoforms in dogs, 11HSD type1 (HSD11B1), which converts cortisone into active cortisol, and 11HSD type2 (HSD11B2), which converts cortisol into inactive cortisone. It has been suggested that glucocorticoid resistance in corticotroph tumors is related to the overexpression of HSD11B2. Therefore it was our aim to investigate the effects of carbenoxolone (CBX), an 11HSD inhibitor, on the healthy dog’s pituitary-adrenal axis. Dogs were administered 50 mg/kg of CBX twice each day for 15 days. During CBX administration, no adverse effects were observed in any dogs. The plasma adrenocorticotropic hormone (ACTH), and serum cortisol and cortisone concentrations were significantly lower at day 7 and 15 following corticotropin releasing hormone stimulation. After completion of CBX administration, the HSD11B1 mRNA expression was higher, and HSD11B2 mRNA expression was significantly lower in the pituitaries. Moreover, proopiomelanocortin mRNA expression was lower, and the ratio of ACTH-positive cells in the anterior pituitary was also significantly lower after CBX treatment. In adrenal glands treated with CBX, HSD11B1 and HSD11B2 mRNA expression were both lower compared to normal canine adrenal glands. The results of this study suggested that CBX inhibits ACTH secretion from pituitary due to altered 11HSD expressions, and is potentially useful for the treatment of canine Cushing’s disease.

Hypothyroidism associated with acromegaly and insulin-resistant diabetes mellitus in a Samoyed

BACKGROUND

The aetiology of insulin resistance (IR) in naturally occurring canine hypothyroidism is poorly understood and likely multifactorial. Excess secretion of growth hormone (GH) by transdifferentiated pituitary cells may contribute to IR in some hypothyroid dogs, but although this has been demonstrated in experimental studies, it has not yet been documented in clinical cases.

CASE REPORT

A 4-year-old male entire Samoyed presented with an 8-month history of pedal hyperkeratosis and shifting lameness, which had been unresponsive to zinc supplementation, antibiotics and glucocorticoid therapy. The dog also exhibited exercise intolerance and polydipsia of 12 and 2 months duration, respectively. On physical examination, obesity, poor coat condition, widened interdental spaces and mild respiratory stridor were noted. Initial laboratory test results revealed concurrent hypothyroidism and diabetes mellitus (DM). Further investigations showed IR, GH excess and a paradoxical increase of GH following stimulation with thyrotropin-releasing hormone.

CONCLUSIONS

To the authors' knowledge, this is the first reported case that suggests that GH alterations may have clinical significance in naturally occurring hypothyroidism. Among other factors, hypothyroidism-induced GH excess should be considered as a possible cause of IR in patients suffering from hypothyroidism and concurrent DM. In such cases, DM may reverse with treatment of hypothyroidism, as was documented in this case.

Central diabetes insipidus after transsphenoidal surgery in dogs with Cushing's disease

Transsphenoidal surgery (TSS) is an effective treatment for canine Cushing's disease, as well as human Cushing's disease. In humans, only the pituitary adenoma tissue is resected by TSS. However, in dogs, the whole pituitary including normal tissue is resected. Hence, central diabetes insipidus (CDI) may complicate the postoperative course in almost all dogs with Cushing's disease treated by TSS. However, it is difficult to assess the duration of the postoperative CDI, and whether it may be transient or permanent. In this study, postoperative CDI in 21 dogs with Cushing's disease and its predicted prognosis by preoperative parameters was investigated. In this study, CDI after TSS was classified as either transient or permanent based on the requirement for desmopressin. Preoperative circulating serum cortisol concentrations and pre- and post-operative plasma AVP concentrations were not significantly different between the transient CDI dogs and permanent CDI dogs. The duration of postoperative CDI was not correlated to the signal intensity ratio (posterior lobe of the pituitary/cerebral cortex), which is obtained from preoperative magnetic resonance imaging (MRI). However, the pituitary height/brain area (P/B) ratio of the permanent CDI dogs was significantly greater than that of the transient CDI dogs. In addition, there was a significant difference between the enlarged-pituitary (P/B ratio > 0.31) transient CDI dogs and the permanent CDI dogs. These results suggest that the incidence of postoperative permanent CDI is strongly influenced by the pituitary size.

Efficacy of transsphenoidal surgery on endocrinological status and serum chemistry parameters in dogs with Cushing's disease

Postoperative changes in endocrinological status and serum chemistry during the 4 years after transsphenoidal surgery (TSS) in 25 dogs with Cushing's disease were investigated in a prospective study. In all 25 dogs, Cushing's disease was diagnosed from resected pituitary tissues as a corticotroph adenoma in the anterior lobe of the pituitary. Prior to TSS, all 25 dogs showed hypercortisolemia. After TSS, the ACTH stimulation test showed continued low serum cortisol concentrations in 21 dogs (84%). In addition, the serum thyroid stimulating hormone concentrations decreased sequentially, while the serum T4 concentrations tended to increase due to the postoperative hormone substitution therapy utilized to avoid secondary hypothyroidism. In regard to serum chemistry, alkaline phosphatase (ALP), alanine aminotransferase (ALT) and total cholesterol are commonly increased in canine Cushing's disease. In this study, ALP, ALT and total cholesterol were increased in 23 cases (92%), 19 cases (76%) and 20 cases (80%), respectively. However, postoperatively, these concentrations gradually decreased. The postoperative serum concentrations of ALP at 1 year, that of ALT at six months to 2 years and that of total cholesterol over the course of the 4 years decreased significantly compared with the concentrations before TSS. These results show that TSS is an effective treatment for canine Cushing's disease and for long-term improvement of hypercortisolemia. Moreover, TSS is effective in improvement of hypercortisolism, such as increased concentrations of serum ALP, ALT and total cholesterol.

Hypophysectomy for a dog with coexisting Cushing's disease and diabetes mellitus

An 11-year-old male mixed breed dog diagnosed with Cushing's disease and diabetes mellitus was treated by hypophysectomy. After surgery, the hypercortisolemia disappeared and the diabetes status improved. The insulin requirement to control hyperglycemia gradually decreased. At 12 weeks after surgery, there was no requirement for insulin and we suspected the diabetes was completely resolved. In the present case, diabetes mellitus seems to be secondary to Cushing's disease. In conclusion, this mixed breed dog with coexisting Cushing's disease and diabetes mellitus is the first case showing the effectiveness of hypophysectomy to treat diabetes mellitus secondary to Cushing's disease in dogs.

Corticotroph adenoma in the dog: pathogenesis and new therapeutic possibilities

The corticotrophinoma, causing pituitary dependent hypercortisolism, represents the highest percentage of pituitary tumours in the dog. The mechanism by which it develops is currently unknown and two theories are postulated: the hypothalamic and the monoclonal. It is not clear either what factors are involved in the tumour genesis; nevertheless, firm candidates are the Rb1 gene, proteins p27, p21 and p16, as are also defects in the glucocorticoid receptor and Nur77/Nurr1. The role of BMPs remains to be evaluated in greater depth. Although at present the chosen treatment in human is surgical, there are various pharmacological treatments already in use that have favourable results and others, still under research, also showing promising results.

Unusually rapid growth and adult stature in an American hairless terrier puppy

A puppy was evaluated for rapid growth and large stature. Extensive diagnostic evaluation suggested a growth hormone independent disorder. As the sole detected abnormality was elevated leptin concentration, an obesity syndrome causing leptin resistance was speculated to explain the puppy's condition but was not confirmed. Except for large body size, the puppy remained clinically normal.

Trilostane-induced inhibition of cortisol secretion results in reduced negative feedback at the hypothalamic-pituitary axis

Cushing's disease caused by pituitary corticotroph adenoma in dogs is usually treated by medical treatment, and the efficacy of this treatment has been reported. However, controversy remains as to whether reduced negative feedback through the inhibition of cortisol secretion, similar to Nelson's syndrome, may appear as an adverse effect. The purpose of this study was to investigate the effect of reduced negative feedback through the inhibition of cortisol secretion by daily trilostane administration on the pituitary-adrenal axis in clinically normal dogs. Dogs were administered 5mg/kg trilostane twice a day every day for 8 weeks (n=8) or 16 weeks (n=3). After the initiation of trilostane administration, plasma adrenocorticotropic hormone (ACTH) concentrations were increased remarkably. As assessed by magnetic resonance imaging (MRI) during administration, the pituitary became enlarged. After trilostane administration, the cytoplasmic areas of the pituitary corticotrophs were increased and the ratio of pituitary corticotrophs to all cells in the anterior lobe was greater in the trilostane-treated dogs than that in untreated animals. In addition, histological examinations revealed bilateral adrenal cortical hyperplasia. Using real-time PCR quantification, the expression of proopiomelanocortin (POMC) mRNA in the pituitary and ACTH receptor (ACTH-R) mRNA in the adrenal gland was greater in the dogs treated with trilostane than in untreated dogs. These results indicate that reduced negative feedback induced hyperfunction of the pituitary corticotrophs and pituitary enlargement in healthy dogs. These changes suggest that the inhibition of cortisol secretion by trilostane may increase the risk for accelerating the growth of corticotroph adenomas in dogs with Cushing's disease.

Expression of genes related to corticotropin production and glucocorticoid feedback in corticotroph adenomas of dogs with Cushing's disease

Cushing's disease caused by pituitary corticotroph adenoma is a common endocrine disease in dogs. A characteristic biochemical feature of corticotroph adenomas is their relative resistance to negative feedback by glucocorticoids. In this study, we examined gene expression related to adrenocorticotropic hormone (ACTH) production and secretion, and the negative feedback by glucocorticoids in canine corticotroph adenoma. We used resected corticotroph adenomas from 10 dogs with Cushing's disease. In order to investigate the alteration of gene expression between corticotroph adenoma and normal corticotrophic cells, ACTH-positive cells in the anterior lobe were microdissected using a laser-capture microdissection system, and mRNA levels of proopiomelanocortin (POMC), corticotropin releasing hormone receptor 1 (CRHR1), glucocorticoid receptor (GR), mineralocorticoid receptor (MR), and 11 beta hydroxysteroid dehydrogenase (11HSD) type 1 and type 2 were determined using real-time RT-PCR. POMC, CRHR1, and 11HSD2 mRNA levels in corticotroph adenoma were greater than those in normal corticotrophic cells (POMC, 5.5-fold; CRHR1, 4.9-fold; 11HSD2, 4.2-fold, P<0.01, respectively). MR and 11HSD1 mRNA levels in corticotroph adenoma were lower than those in normal corticotrophic cells (MR, 2.2-fold; 11HSD1, 2.9-fold, P<0.01, respectively). GR mRNA levels did not differ between corticotroph adenoma and normal corticotrophic cells. Our results may help to understand the increased ACTH production and the resistance to negative feedback suppression by glucocorticoids in canine corticotroph adenomas. These changes in gene expression may have a role in the growth of canine corticotroph adenoma, and help elucidate the pathophysiology of dogs with Cushing's disease.