M. Judith Radin

Adipokines: a review of biological and analytical principles and an update in dogs, cats, and horses

In addition to its role as an energy storage depot, adipose tissue is now recognized as a complex endocrine organ. Adipose tissue releases a variety of factors, termed adipokines, that regulate energy metabolism, cardiovascular function, reproductive status, and immune function. Some of the better-studied adipokines include leptin, adiponectin, and components of the renin-angiotensin system such as angiotensinogen. The function of more recently discovered adipokines such as resistin are under intense scrutiny. Abnormal production or regulation of adipokines occurs in obese individuals and is implicated in the development of a variety of associated co-morbidities including metabolic syndrome, type 2 diabetes, atherosclerosis, heart disease, and cancer in people, although evaluation in domestic species is just beginning. Adipokines are now being examined as potential biomarkers for risk assessment for development of complications related to obesity. This article summarizes the function and regulation of some better-characterized adipokines. It also reviews the current information on the characterization of adipokines in some domestic species in which rates of obesity and obesity-related disorders are increasing, such as the dog, cat, and horse.

SHHF/Mcc-/fa cp Rat Model: A Genetic Model of Congestive Heart Failure

The SHHF/Mcc-fa cp rat is a relatively new model of reproducible spontaneous congestive heart failure (CHF) that has been maintained for 25 generations. The genetics of the CHF is multifactorial. All of the rats are hypertensive and eventually develop CHF. The males die before the females, and the obese rats develop CHF earlier than their lean littermates. The classic signs of CHF—dyspnea, orthopnea, cyanosis, subcutaneous edema, and ascites—are present in these animals. The hearts are enlarged (up to 4.5 g), all chambers are dilated, and ventricular walls are thickened. A progressive functional decompensation has been noted in electrocardiographic patterns (prolonged P waves and PQ and QRS intervals), hemodynamic studies (depression of +dP/dT and increased EDP in both ventricles), and by echocardiographic analysis. With increasing severity of CHF, atrial natriuretic peptide levels increase in the heart tissue as well as in plasma, and myocardial myosin isozymes shift to almost entirely V3. The drugs captopril, enalapril, nifedipine, felodipine, and a fatty acid oxidation inhibitor all delay the heart enlargement and myosin shift; however, verapamil triggers overt CHF. This rat model mimics many of the findings in human CHF patients.

Increased salt sensitivity secondary to leptin resistance in SHHF rats is mediated by endothelin

A link between leptin resistance, obesity, and salt sensitivity has been suggested. SHHF/Mcc-facp rats (SHHF) were used to study the effect of gene dosage of a null mutation of the leptin receptor (cp) on salt sensitivity and response to a combined endothelin A and B receptor antagonist (bosentan). Obese (cp/cp), heterozygous (+/cp), and homozygous lean (+/+) male SHHF were fed a low salt diet (0.3% NaCl) for 7 days, followed by a high salt diet (8.0% NaCl) for 7 days. There were no significant differences in systolic blood pressure between genotypes on low salt. In response to high salt, cp/cp had significantly greater systolic pressure than +/cp and +/+. On high salt diet, cp/cp showed a significant increase in 24 h urinary endothelin excretion and increased renal expression of preproendothelin mRNA. There was no effect of high salt diet on renal excretion of nitric oxide (NOx) or on gene expression of endothelial, neuronal, or cytokine-induced nitric oxide synthase isoforms (eNOS, nNOS, iNOS, respectively). Treatment with bosentan prevented the high salt-induced increment in systolic blood pressure in cp/cp. This was associated with a doubling of renal NOx excretion, but without changes in eNOS, nNOS, or iNOS expression. Endothelin receptor antagonism did not normalize systolic pressure in any of the genotypes. Our studies indicate that obesity secondary to leptin resistance (cp/cp) results in increased salt sensitivity that is mediated by endothelin in the SHHF rat.

Effect of ovariectomy in heart failure-prone SHHF/Mcc-facp rats

The importance of the loss of ovarian function to the progression of hypertension and heart disease in women is controversial. We investigated whether ovariectomy would accelerate development of hypertension, congestive heart failure, and neurohumoral activation in adult spontaneous hypertension heart failure (SHHF) rats, a genetic model of heart failure. Six months after ovariectomy, no significant differences between control and ovariectomized rats were seen in systolic or diastolic blood pressure, left ventricular fractional shortening by echocardiography, or heart weight. Percent V1 myosin isozyme was significantly lower in ovariectomized rats. Northern blot analysis failed to show significant differences between groups in expression of hepatic angiotensinogen, renal renin, or left ventricular atrial or brain natriuretic peptide mRNA. In a second experiment, serial measures of systolic pressure and left ventricular shortening fractions failed to document a significant difference between control and ovariectomized rats as they developed heart failure, although there was a significant decline in shortening fraction in both groups at the age when regular estrous cycling naturally ceases. Survival time was similar between groups. In summary, ovariectomy of adult SHHF rats does not appear to affect the progression of genetically programmed hypertension and heart failure in this model.The importance of the loss of ovarian function to the progression of hypertension and heart disease in women is controversial. We investigated whether ovariectomy would accelerate development of hypertension, congestive heart failure, and neurohumoral activation in adult spontaneous hypertension heart failure (SHHF) rats, a genetic model of heart failure. Six months after ovariectomy, no significant differences between control and ovariectomized rats were seen in systolic or diastolic blood pressure, left ventricular fractional shortening by echocardiography, or heart weight. Percent V1 myosin isozyme was significantly lower in ovariectomized rats. Northern blot analysis failed to show significant differences between groups in expression of hepatic angiotensinogen, renal renin, or left ventricular atrial or brain natriuretic peptide mRNA. In a second experiment, serial measures of systolic pressure and left ventricular shortening fractions failed to document a significant difference between control and ovariectomized rats as they developed heart failure, although there was a significant decline in shortening fraction in both groups at the age when regular estrous cycling naturally ceases. Survival time was similar between groups. In summary, ovariectomy of adult SHHF rats does not appear to affect the progression of genetically programmed hypertension and heart failure in this model.

Animal models of bacterial gastritis : the role of host, bacterial species and duration of infection on severity of gastritis

Gastric bacteria from cheetahs with gastritis were used to inoculate specific-pathogen free kittens and conventional mice. Helicobacter sp. and Gastrospirillum sp. colonized kittens, while only Gastrospirillum sp. colonized mice. In kittens, both bacterial species induced mild lymphofolliclar gastritis which did not change over the course of the 11 months observation period. In mice, Gastrospirillum sp. induced lymphoplasmacytic and follicular gastritis which increased in severity over 6 months and persisted for the 12 month observation period. Gastric ulcers and gastric mucosal hypertrophy were present in chronically infected mice. These results indicate that host but not bacterial factors influence the severity of gastritis, and that in mice, bacterial gastritis increases in severity with time and may lead to gastric ulceration in some individuals.

Salt-Induced Cardiac Hypertrophy Is Independent of Blood Pressure and Endothelin in Obese, Heart Failure-Prone SHHF Rats

The interaction of salt sensitivity and obesity in development of cardiac hypertrophy is incompletely understood. The SHHF/Mcc-facp (SHHF) rat model was used to examine the effect of high salt on cardiac hypertrophy and expression of endothelin (ET) and nitric oxide synthase (NOS) isoforms. Homozygous lean (+/+) and obese (facp/facp) SHHF were fed a low-salt diet (0.3% NaCl) for seven days followed by a high-salt diet (8.0% NaCl) for seven days. To assess the role of ET in mediating cardiac hypertrophy and gene expression with high salt, additional groups were treated with an ETA/ETB receptor antagonist (bosentan) while on high salt. Obese SHHF showed an increase in systolic blood pressure and cardiac hypertrophy in response to the high-salt diet. High salt resulted in decreased expression of preproET as well as all three NOS isoforms in the Obese, while cytokine induced NOS (iNOS) and neuronal NOS (nNOS) increased in Leans. Though the salt-sensitive component of the hypertension observed in the Obese was prevented by bosentan, cardiac hypertrophy still occurred and expression of all NOS isoforms remained lower in Obese compared to Lean. Endothelial NOS (eNOS) expression increased in the Lean with bosentan. These studies suggest that cardiac hypertrophy is independent of the level of hypertension and may be mediated by altered production of NOS isoforms in salt-sensitive, obese SHHF.

Differential cardiotoxicity in response to chronic doxorubicin treatment in male spontaneous hypertension-heart failure (SHHF), spontaneously hypertensive (SHR), and Wistar Kyoto (WKY) rats.

Life threatening complications from chemotherapy occur frequently in cancer survivors, however little is known about genetic risk factors. We treated male normotensive rats (WKY) and strains with hypertension (SHR) and hypertension with cardiomyopathy (SHHF) with 8 weekly doses of doxorubicin (DOX) followed by 12weeks of observation to test the hypothesis that genetic cardiovascular disease would worsen delayed cardiotoxicity. Compared with WKY, SHR demonstrated weight loss, decreased systolic blood pressure, increased kidney weights, greater cardiac and renal histopathologic lesions and greater mortality. SHHF showed growth restriction, increased kidney weights and renal histopathology but no effect on systolic blood pressure or mortality. SHHF had less severe cardiac lesions than SHR. We evaluated cardiac soluble epoxide hydrolase (sEH) content and arachidonic acid metabolites after acute DOX exposure as potential mediators of genetic risk. Before DOX, SHHF and SHR had significantly greater cardiac sEH and decreased epoxyeicosatrienoic acid (EET) (4 of 4 isomers in SHHF and 2 of 4 isomers in SHR) than WKY. After DOX, sEH was unchanged in all strains, but SHHF and SHR rats increased EETs to a level similar to WKY. Leukotriene D4 increased after treatment in SHR. Genetic predisposition to heart failure superimposed on genetic hypertension failed to generate greater toxicity compared with hypertension alone. The relative resistance of DOX-treated SHHF males to the cardiotoxic effects of DOX in the delayed phase despite progression of genetic disease was unexpected and a key finding. Strain differences in arachidonic acid metabolism may contribute to variation in response to DOX toxicity.

OBESE FEMALE SHHF/Mcc-facp RATS RESIST ANTIHYPERTENSIVE EFFECTS OF RENIN-ANGIOTENSIN SYSTEM INHIBITION

Gender and obesity may influence response to pharmacological modulation of the renin-angiotensin system. We used SHHF/Mcc-facp rats to study effect of obesity and gender on the ability of an AT1 receptor antagonist to decrease blood pressure. After 2 weeks treatment with irbesartan (50 mg/kg), only lean and obese males showed significant decreases in blood pressure, while obese females were completely resistant. Lean females showed a trend toward lowering of pressure (p = 0.06). However, irbesartan similarly shifted angiotensin II dose response curves to the right in all groups. Twelve weeks of irbesartan also failed to decrease blood pressure, but did significantly reduce heart weight in obese females. In untreated rats, obese females had lower plasma renin activity and serum angiotensin converting enzyme activity compared to lean males, while lean and obese females had increased urinary endothelin excretion. Despite an otherwise similar genetic background contributing to hypertension and heart failure, obese females have different patterns of humoral activation compared to lean males, which may contribute to their resistance to the depressor effects of irbesartan.

THE EFFECT OF ATRIAL NATRIURETIC PEPTIDE INFUSION ON RENAL HAEMODYNAMICS AND PLASMA LIPOPROTEINS IN PUROMYCIN AMINONUCLEOSIDE NEPHROSIS IN RATS

1. The effect of continuous intravenous administration of 1 UmUg/h atrial natriuretic peptide (ANP) for 4 days was studied in normal male Sprague‐Dawley rats and rats made nephrotic with puromycin aminonucleoside (PA).

Multicentric mast cell tumors in a horse

A 6-year-old female Rocky Mountain horse was presented for evaluation of draining tracts and distal limb subcutaneous edema on the left front and left hind limbs that had been present for 2 weeks. Direct smears of fluid collected by fine-needle aspiration of subcutaneous fluid from both limbs were highly cellular with a predominance of eosinophils accompanied by numerous, moderately atypical, variably granulated mast cells. The cytologic diagnosis was mast cell tumor (MCT) with prominent eosinophilic infiltration with a differential diagnosis of eosinophilic granuloma. Histologic evaluation of surgical biopsies of lesions from both limbs was performed on sections stained with H&E, toluidine blue, and Luna stains. The histologic diagnosis was MCT, and staining with toluidine blue and Luna stains confirmed the presence of mast cells and eosinophils, respectively. In addition, the mast cells strongly expressed CD117. This is the first reported case of cutaneous mast cell neoplasia in a horse in which primary presenting complaints were draining tracts and distal limb subcutaneous edema involving multiple limbs. This case illustrates the utility of staining for CD117 expression in combination with traditional stains, such as toluidine blue and Luna, in differentiating MCTs from other eosinophilic lesions in horses.