Qualitative and semiquantitative assessment of thyroid hormone binding proteins in greyhounds and other dog breeds

Total thyroxine (T4) concentrations are lower in healthy greyhounds compared to most other non-sighthound breeds. In humans, variations in the structure or concentration of the major thyroid hormone binding proteins are responsible for most reported differences between total T4 concentrations in healthy individuals from different ethnic groups or other subpopulations. The aim of this study was to determine if such variations are also responsible for the lower total T4 concentrations in greyhounds. The predicted protein sequences of thyroxine-binding globulin (TBG), transthyretin and albumin were determined in liver tissue from a euthyroid greyhound with decreased T4 concentration and a Jack Russell terrier using reverse-transcriptase PCR. Sequences were compared to each other and online reference sequences. Serum proteins from 21 greyhounds and 21 non-sighthound dogs were separated by denaturing electrophoresis and immunoblots probed with polyclonal antibodies to human TBG and transthyretin. Reactive bands were quantified by densitrometry, expressed relative to the mean of reference samples included in each gel. Serum albumin concentrations were measured using a commercially-available assay. Several SNPs were identified but none was thought likely to explain the lower total T4 concentrations in greyhounds. There was no significant difference between the quantity of any of the binding proteins in serum from greyhounds and non-sighthound dogs. However, total T4 and transthyretin concentrations were highly correlated in the greyhound group (r = 0.73, P = 0.0002). Variation in the sequence of thyroid hormone binding proteins is not responsible for low greyhound total T4 concentrations. Further evaluation of the role of transthyretin is warranted.

Association between hyperinsulinaemia and laminitis severity at the time of pituitary pars intermedia dysfunction diagnosis

BACKGROUND

Hyperinsulinaemia is the suspected component of insulin dysregulation having the strongest association with laminitis and occurs variably in equids with pituitary pars intermedia dysfunction (PPID).

OBJECTIVES

We hypothesised that magnitude of hyperinsulinaemia correlates with laminitis severity in PPID-affected equids. Furthermore, we hypothesised that owners can be unaware of chronic endocrinopathic laminitis.

STUDY DESIGN

Cross-sectional study.

METHODS

Serum insulin concentrations, owner-reported laminitis history and radiographic evidence of laminitis were determined in 38 client-owned horses and ponies with confirmed PPID. Laminitis severity was classified into four categories (normal [nonlaminitic], mild, moderate or severe laminitis) based on degree of distal phalangeal rotation. Animals were also categorised as normoinsulinaemic (<20 μU/ml), mildly hyperinsulinaemic (20-50 μU/ml) and severely hyperinsulinaemic (>50 μU/ml). One-way ANOVA, t tests and Fisher's exact tests were performed.

RESULTS

While owners reported laminitis in 37% of animals, 76% were laminitic based on study criteria (P = 0.01). Owners reported laminitis more frequently in hyperinsulinaemic vs. normoinsulinaemic animals; recognition increased with severity of hyperinsulinaemia (P = 0.03). Mean insulin concentrations were higher in equids with moderate to severe radiographic laminitis (geometric mean 74.1, 95% confidence interval (CI) 38.4-143.1 uU/ml) vs. those classified radiographically as normal to mild (31.9, 95% CI 21.1-48.1 uU/ml P = 0.03).

MAIN LIMITATIONS

Dynamic insulin testing was not performed; some normoinsulinaemic animals might have had subtle insulin dysregulation.

CONCLUSIONS

Although radiographic abnormalities were present in most animals at the time of PPID diagnosis, chronic laminitis remained unrecognised by many owners. Owner awareness of laminitis increased with severity of hyperinsulinaemia and higher insulin concentrations were detected in association with more severe radiographic changes. The Summary is available in Chinese - See Supporting Information.

Effects of Levothyroxine Administration and Withdrawal on the Hypothalamic-Pituitary-Thyroid Axis in Euthyroid Dogs

Background

Chronic supplementation can suppress the hypothalamic‐pituitary‐thyroid axis (HPTA) and make it difficult to assess thyroid function after withdrawal of levothyroxine.

Objectives

To determine whether the HPTA is suppressed after levothyroxine administration in euthyroid dogs and the time required for resolution of any suppression.

Animals

Twenty‐eight healthy euthyroid dogs.

Methods

A prospective, randomized study administering levothyroxine to euthyroid dogs for 8 weeks (group 1) or 16 weeks (group 2). Serum concentrations of total thyroxine (T₄), free thyroxine (fT₄) by equilibrium dialysis, thyroid stimulating hormone; thyrotropin (TSH), and 3,5,3′‐triiodothyronine (T₃) were measured every 4 weeks during supplementation and for 16 weeks after levothyroxine was discontinued.

Results

Mean serum concentrations of T₄ and fT₄ were significantly higher (P < .0001) and TSH was lower (P < .0001) in all dogs during levothyroxine administration compared to baseline. Mean serum concentrations of T₄, fT_4, and TSH in both groups, beginning 1 week after levothyroxine was discontinued, were significantly different (P < .01) compared to values during levothyroxine administration but not compared to baseline values (P > .3).

Conclusions and Clinical Importance

Assessing thyroid function tests 1 week after cessation of levothyroxine at 26 μg/kg once a day for up to 16 weeks will provide an accurate assessment of thyroid function in healthy euthyroid dogs.

Evaluation of Basal Serum or Plasma Cortisol Concentrations for the Diagnosis of Hypoadrenocorticism in Dogs

Background

Previous studies that included limited numbers of affected dogs have suggested basal cortisol concentrations ≤55 nmol/L (2 μg/dL) are sensitive, but nonspecific, for a diagnosis of hypoadrenocorticism. A detailed assessment of the diagnostic utility of basal cortisol concentrations is warranted.

Hypothesis/Objectives

To evaluate the utility of basal cortisol concentrations for the diagnosis of hypoadrenocorticism in a large number of dogs, including those with and without serum electrolyte abnormalities.

Animals

Five hundred and twenty‐two dogs, including 163 dogs with hypoadrenocorticism, 351 dogs with nonadrenal gland illness, and 8 dogs with equivocal results.

Methods

Retrospective study. Basal and post‐ACTH cortisol concentrations and sodium and potassium concentrations were collected from medical records. A receiver operating characteristic (ROC) curve was constructed for basal cortisol concentrations by standard methodologies. Sensitivity, specificity, and predictive values were determined for various cut‐points.

Results

The area under the ROC curve was 0.988 and was similarly excellent regardless of serum electrolyte concentrations. At the most discriminatory cut‐point of 22 nmol/L (0.8 μg/dL), sensitivity and specificity were 96.9 and 95.7%, respectively. A basal cortisol concentration of ≤55 nmol/L (2 μg/dL) resulted in a sensitivity of 99.4%. Conversely, a basal cortisol concentration of ≤5.5 nmol/L (0.19 μg/dL) resulted in a specificity of 99.1%.

Conclusions and Clinical Importance

Similar to findings in previous studies, basal cortisol concentrations >55 nmol/L (2 μg/dL) are useful in excluding a diagnosis of hypoadrenocorticism. Interestingly, excellent specificities and positive predictive values were observed at lower cut‐point cortisol concentrations.

Hypervitaminosis D and Metastatic Calcification in a Colony of Inbred Strain 13 Guinea Pigs, Cavia porcellus

A commercial diet fed to a colony of inbred strain 13 guinea pigs for approximately 6 weeks was subsequently recalled for excessive levels of vitamin D. Twenty-one of 62 animals exhibited clinical signs, including anorexia, lethargy, and poor body condition. Nine affected and 4 clinically normal animals were euthanized for further evaluation, including serum chemistry, urinalysis, and gross and/or histopathology. Macroscopic findings included white discoloration in multiple organs in 8 animals, and microscopic evaluation confirmed multiorgan mineralization in tissues from 7 animals. Serum 25-hydroxyvitamin D levels were elevated in 10 animals. Serum inorganic phosphorus and alkaline phosphatase levels were increased in all exposed animals; however, total calcium and ionized calcium levels were not significantly higher in exposed animals than in control strain 13 guinea pigs from a different institution. The data support a diagnosis of hypervitaminosis D with metastatic calcification. Following the diet recall, the remaining guinea pigs increased their food intake and regained body condition. Diagnostic testing of 8 animals euthanized approximately 3 months after returning to a normal diet demonstrated that serum parathyroid hormone remained significantly lower, and ionized calcium and ionized magnesium were significantly higher, in recovered animals compared to controls and exposed animals. These results indicate that diagnostic tests other than serum calcium are necessary for a diagnosis of hypervitaminosis D in guinea pigs.

Serum concentrations of gastrin after famotidine and omeprazole administration to dogs

Background

The duration of antacid‐induced hypergastrinemia after cessation of administration of omeprazole and famotidine apparently has not been determined in dogs.

Hypothesis

That serum gastrin will return to basal concentrations by 7 days after cessation of famotidine or omeprazole administration.

Animals

Nine healthy, adult, male, research colony dogs.

Methods

Randomized, cross‐over design. Serum gastrin was determined daily for 7 days to establish baseline concentrations. Famotidine (1.0 mg/kg q24h) or omeprazole (1.0 mg/kg q24h) was administered PO for 7 days followed by a 14‐day washout. Serum concentrations of gastrin were determined daily during 7 days of administration and daily for 7 days after cessation of administration. Each drug was evaluated in 8 of the 9 dogs.

Results

Omeprazole caused a significant increase in serum gastrin concentration (37.2 ± 7.3 to 71.3 ± 19.0 ng/L; P = .006). Famotidine induced a transient increase in serum gastrin (37.2 ± 7.3 to 65.5 ± 38.5 ng/L; P = .02) that peaked at administration day 3 and declined thereafter. By day 7 after cessation of both drugs, there was no difference in serum gastrin concentrations compared to those before administration (famotidine P = .99; omeprazole P = .99). During or after administration, gastrin concentrations above 3 times the upper reference range were rare (12 of 224 samples).

Conclusions and Clinical Importance

A 7‐day withdrawal from short‐term administration of famotidine or omeprazole is sufficient for serum gastrin to return to baseline concentrations. Withholding famotidine or omeprazole for longer before investigating pathologic causes of hypergastrinemia is unnecessary.

Relationship among serum creatinine, serum gastrin, calcium-phosphorus product, and uremic gastropathy in cats with chronic kidney disease

BACKGROUND

Chronic kidney disease (CKD) in cats is associated with gastrointestinal signs commonly attributed to uremic gastropathy. Consequently, patients often are treated with antacids and gastrointestinal protectants. This therapeutic regimen is based on documented gastric lesions in uremic humans and dogs, but the nature and incidence of uremic gastropathy in cats are unknown.

HYPOTHESIS/OBJECTIVES

Evaluate uremic gastropathy in CKD cats to facilitate refinement of medical management for gastrointestinal signs.

ANIMALS

Thirty-seven CKD cats; 12 nonazotemic cats

METHODS

Stomachs were evaluated for the presence of classic uremic gastropathy lesions. Histopathologic lesions were compared with serum creatinine concentrations, calcium-phosphorus product (CPP), and serum gastrin concentrations.

RESULTS

Gastric ulceration, edema, and vascular fibrinoid change were not observed. The most important gastric lesions in CKD cats were fibrosis and mineralization. Sixteen CKD cats (43%) had evidence of gastric fibrosis of varying severity and 14 CKD cats (38%) had gastric mineralization. CKD cats were more likely to have gastric fibrosis and mineralization than nonazotemic controls (P = .005 and P = .021, respectively). Only cats with moderate and severe azotemia had gastric mineralization. CPP was correlated with disease severity; severely azotemic CKD cats had significantly higher CPP when compared with nonazotemic controls, and to mildly and moderately azotemic cats (P < .05). Gastrin concentrations were significantly higher in CKD cats when compared with nonazotemic controls (P = .003), but increased concentrations were not associated with gastric ulceration.

CONCLUSIONS AND CLINICAL IMPORTANCE

Uremic gastropathy in CKD cats differs from that described in other species and this difference should be considered when devising medical management.

Thyroid hormone responses to endurance exercise

REASONS FOR PERFORMING STUDY

Limited information exists about changes in circulating thyroid hormone concentrations during prolonged endurance exercise in horses.

OBJECTIVE

To examine the effects of prolonged exercise on serum iodothyronine concentrations in horses performing endurance exercise of varying distances.

METHODS

Serum concentrations of iodothyronines were measured in horses before and after completion of 40, 56, 80 and 160 km endurance rides (Study 1); daily during a 5 day, 424 km endurance ride (Study 2); and before and for 72 h after completion of a treadmill exercise test simulating a 60 km endurance ride (Study 3).

RESULTS

In Study 1, 40 and 56 km of endurance exercise had little effect on serum iodothyronine concentrations with the exception of a 10% decrease (P<0.05) in free thyroxine (FT4) concentration after the 56 km ride. In contrast, total thyroxine (T4), total triiodothyronine (T3), FT4 and free triiodothyronine (FT3) concentrations all decreased (P<0.05) after successful completion of 80 and 160 km rides, with decreases ranging from 13-31% and 47-54% for distances of 80 and 160 km, respectively. Further, pre-ride T4 concentration was lower (P<0.05) and FT3 concentration was higher (P<0.05) in horses competing 160 km as compared to horses competing over shorter distances. In Study 2, serum concentrations of T4, T3 and reverse triiodothyronine (rT3) progressively decreased (P<0.05) over the course of the multi-day ride. In Study 3, the greatest decrease (P<0.05) in all iodothyronines was observed at 12 h of recovery, ranging from 25% for FT4 to 53% for FT3, but all thyroid hormone concentrations had returned to the pre-exercise values by 24 h of recovery.

CONCLUSION

Endurance exercise results in transient decreases in serum iodothyronine concentrations.

POTENTIAL RELEVANCE

These data are important to consider when thyroid gland function is assessed by measurement of serum iodothyronine concentrations in endurance horses.

An investigation of the action of Neutral Protamine Hagedorn human analogue insulin in dogs with naturally occurring diabetes mellitus

BACKGROUND

Neutral Protamine Hagedorn human analogue insulin (Humulin N) is commonly used for treatment of canine diabetes mellitus (DM). However, blood glucose and serum insulin concentrations in Humulin N-treated dogs with naturally occurring DM have not been reported.

OBJECTIVE

To investigate blood glucose and serum insulin concentrations in the clinical setting of client-owned Humulin N-treated dogs with naturally occurring, well-regulated DM.

ANIMALS

Ten client-owned dogs with naturally occurring, well-regulated DM.

METHODS

In this clinical study, blood glucose and serum insulin concentrations were measured when dogs received food and insulin (T(0)), at approximately every half hour for the next 2 hours, and then approximately every 2 hours for an additional 8 hours. Insulin duration of action was defined as the number of hours from T(0) to the lowest blood glucose concentration and until blood glucose concentration returned to an interpolated value of 70% of basal blood glucose concentration (Glucose(b)).

RESULTS

Mean percent of insulin-induced blood glucose suppression was 49.9 +/- 17.1% (median, 46%; range, 29-78%). Insulin duration of action ranged from 4 to 10 hours. Blood glucose concentration increased initially and returned to Glucose(b) within 0.6-2.2 hours after T(0) in 5 dogs. This initial blood glucose surge then was followed by blood glucose suppression in all 5 dogs.

CONCLUSIONS AND CLINICAL IMPORTANCE

These results suggest that Humulin N administered SC twice daily is an effective mode of treatment for dogs with naturally occurring DM. Postprandial hyperglycemia is present in some well-regulated diabetic dogs treated with Humulin N.

Influence of isoflurane general anesthesia or anesthesia and surgery on thyroid function tests in dogs

BACKGROUND

Anesthesia and surgery affect thyroid function tests in humans but have not been studied in dogs.

HYPOTHESIS

Anesthesia and anesthesia with surgery will affect thyroid function tests in dogs.

ANIMALS

Fifteen euthyroid dogs.

METHODS

Prospective, controlled, interventional study. Dogs were assigned to one of 3 groups: control, general anesthesia, and general anesthesia plus abdominal exploratory surgery. Dogs in the anesthesia and surgery groups were premedicated with acepromazine and morphine, induced with propofol, and maintained on isoflurane. Samples for measurement of serum thyroxine (T4), free T4 (fT4) by equilibrium dialysis, triiodothyronine (T3), reverse T3 (rT3), and thyroid-stimulating hormone concentrations were collected from each dog immediately before premedication, at multiple times during anesthesia, surgery, 4, 8, 12, 24, 36, and 48 hours after anesthesia, once daily for an additional 5 days, and once 14 days after anesthesia. Sampling was performed at identical times in the control group.

RESULTS

Serum T4 decreased significantly from baseline in the surgery and anesthesia groups compared with the control group at 0.33 (P= 0.043) and 1 hour (P= 0.018), and 2 (P= 0.031) and 4 hours (P= 0.037), respectively, then increased significantly in the surgery group compared with the control group at 24 hours (P= 0.005). Serum T3 decreased significantly from baseline in the anesthesia group compared with the control group at 1 hour (P= 0.034). Serum rT3 increased significantly from baseline in the surgery group compared with the control and anesthesia groups at 8 (P= 0.026) and 24 hours (P= 0.0001) and anesthesia group at 8, 12, 24, and 36 hours (P= 0.004, P= 0.016, P= 0.004, and P= 0.014, respectively). Serum fT4 increased significantly from baseline in the surgery group compared to the control at 24 hours (P= 0.006) and at day 7 (P= 0.037) and anesthesia group at 48 hours (P= 0.023).

CONCLUSIONS AND CLINICAL IMPORTANCE

Surgery and anesthesia have a significant effect on thyroid function tests in dogs.

Adult-onset hair loss in Chesapeake Bay retrievers: a clinical and histological study

Ten Chesapeake Bay retriever (CBRS) dogs with hair loss were recruited in collaboration with the American Chesapeake Club. All dogs had nonpruritic, noninflammatory, regionalized hair loss affecting the same areas of the body in male and female dogs. Hormonal investigations showed increased adrenal and sex steroid concentration in seven cases. Histopathology revealed follicular hyperkeratosis and plugging, follicular atrophy, and occasional melanin clumping with malformed hair shafts. This study suggests that hair loss in CBRS is a breed syndrome in which young adult dogs have hair loss characterized by unusual histological features and abnormal steroid production. A familial predisposition seems likely and selective breeding might reduce the occurrence of this condition.

Effects of propylthiouracil and bromocryptine on serum concentrations of thyrotrophin and thyroid hormones in normal female horses

REASONS FOR PERFORMING STUDY

There exists a need for better diagnostic tests to characterise thyroid disease in horses. Currently available diagnostic tests fail to differentiate between thyroid gland disorders and thyroid abnormalities resulting from pituitary or hypothalamic problems.

OBJECTIVES

To evaluate the effects of treatment with propylthiouracil (PTU) and bromocryptine (BROM) on serum concentrations of triiodothyronine (T3), thyroxine (T4), reverse T3 (rT3) and equine thyroid-stimulating hormone (e-TSH, thyrotrophin) in mature horses.

METHODS

Healthy mature horses were treated using either PTU or BROM for 28 days. The effect of treatment on the thyroid axis was assessed by measuring T3, T4, rT3 and e-TSH before and at +14 and +28 days. The effect of PTU and BROM on the response of T3, T4, rT3 and e-TSH to thyrotrophin-release hormone (TRH) administration was also assessed before and at +14 and +28 days of treatment.

RESULTS

Treatment with PTU led to a significant reduction in serum concentrations of T3, T4 and rT3 on Day 28 and increase of e-TSH on Day 28 (P < 0.05). Treatment with BROM did not cause any measurable effect on serum concentrations of T3, T4, rT3 or e-TSH. The percentage increment by which serum concentration of T4, T3 and e-TSH increased following stimulation with TRH was decreased by treatment with PTU for 28 days (P < 0.05) but were not affected by treatment with BROM for 28 days.

CONCLUSIONS

These results suggest that 1) treatment with PTU may be used in horses as a model of primary hypothyroidism; 2) the use of BROM as a model of secondary hypothyroidism in horses is not supported; and 3) e-TSH assay deserves further investigation for the clinical diagnosis of thyroid axis dysfunction in horses.

POTENTIAL RELEVANCE

Propylthiouracil effectively causes primary hypothyroidism. There is substantial variability between horses with respect to their sensitivity to this substance when administered orally. Further studies pertaining to the characterisation of equine thyroid disorders are warranted and the use of both PTU for the experimental induction of primary hypothyroidism and e-TSH for the diagnostic characterisation of thyroid disorders in horses should be considered.

Heparinised blood ionised calcium concentrations in horses with colic or diarrhoea compared to normal subjects

Our objectives were to 1) establish ionised calcium (ICa), C-terminal PTH and biologically active PTH (intact molecule) concentrations in blood from normal horses, 2) examine the stability of ionised calcium and acid-base values in stored equine heparinised blood and serum and 3) check the applicability of the formulas based on these parameters in certain disease states. Mean +/- s.d. % ionised calcium in heparinised blood of normal Warmbloods was 51 +/- 2.7 (n = 20) of total calcium, range 1.45-1.75 mmol/l (n = 15) at Michigan State University and 1.43-1.69 mmol/l (n = 20) at Utrecht University. Mean +/- s.d. EDTA plasma concentration for intact +/PTH in normal horses measured 0.6 +/- 0.3 pmol/l (n = 11). Both mean serum and the heparinised blood ionised calcium concentrations changed (not significantly) after 102 h storage at room temperature. Six cycles of freezing and thawing did not affect serum ionised calcium concentration significantly. Ionised calcium concentration and pH in heparinised blood of 20 normal Warmbloods were used to calculate the regression equation for the prediction of the adjusted ionised calcium concentration to a pH of 7.4. The linear regression equation found was: adjusted plasma ICa at pH 7.4 mmol/l = -6.4570 + 0.8739 x (measured pH) + 0.9944 x (measured ICa mmol/l). By means of this formula, mean adjusted ionised calcium concentration in heparinised blood calculated was 100% of the actual value given by the analyser in the normal horses. When using this formula in horses with colic or diarrhoea, mean adjusted ionised calcium concentration was underestimated by 0.2 and 0.3%, respectively. Furthermore, to adjust the measured ionised calcium concentration in heparinised blood to a pH of 7.4 in healthy as well as in 2 groups of diseased horses 2 formulas with a good prediction are now available.

Update on the diagnosis and treatment of disorders of calcium regulation

The availability of PTH, iCa, PTHrP, and 25OHD assays for evaluation of calcium abnormalities in companion animals has been well received [table: see text] by clinicians and diagnosticians. Use of these assays has heightened awareness that some of these disorders are more common than originally thought. Also, there is added insight of alterations of calcium homeostasis as a consequence of other illness or environmental factors such as diet. Animal counterparts of other disorders of calcium metabolism in people are likely to be identified, and use of these assays should play a significant role. As already emphasized, the foundation of using [table: see text] these assays is first assessing whether the calcium abnormality is of a parathyroid-dependent or parathyroid-independent classification.

Lymphocytic thyroiditis

Lymphocytic thyroiditis is a common canine condition that can lead to functional hypothyroidism. It is associated with more than 50% of cases of canine hypothyroidism. Evidence in human beings and experimental situations suggests that it is a disease of defective immunoregulation, but specific investigation of the molecular pathogenesis of the naturally occurring disease in dogs has not yet been carried out. The condition is heritable in those breeds that have been studied, and progression to hypothyroidism, if it occurs, can be slow. Factors that influence the progression from subclinical thyroiditis to hypothyroidism in dogs are still to be identified, but excessive iodine intake is an important factor in other species.

The postmortem diagnosis of cholecalciferol toxicosis: a novel approach and differentiation from ethylene glycol toxicosis

The objectives of this study were to develop a novel approach to postmortem diagnosis of cholecalciferol (CCF) toxicosis in dogs using kidney, bile, and urine samples, and to differentiate CCF from ethylene glycol (EG) toxicosis. To achieve these objectives, specimens collected from 2 previous laboratory studies in which dogs were given a single oral toxic dose of CCF (8.0 mg/kg) were used. For EG toxicosis, historical data from the previous 13 years (1985-1998) were reviewed and confirmed cases of EG toxicosis were selected. The historical data were used to compare trace mineral concentrations, specifically of calcium and phosphorus to differentiate between intoxications caused by CCF from that caused by EG in dogs. Kidneys, bile, and urine from dogs that died of CCF toxicosis were analyzed for 25 monohydroxy vitamin D3 (25(OH)D3) and 1,25 dihydroxy vitamin D3 (1,25(OH)2D3) and compared to known control unexposed dogs. Results of this study show that biliary and renal 25(OH)D3 concentrations and renal calcium to phosphorus ratio are of diagnostic value in dogs exposed to toxic concentrations of CCF. The renal calcium to phosphorus ratio was <0.1 in normal dogs, 0.4-0.9 in dogs that died of CCF toxicosis, and >2.5 in dogs that died of EG toxicosis.

Effects of electrolyte and glycerol supplementation on recovery from endurance exercise

Incomplete recovery from endurance exercise after an overnight rest period is reflected by persisting weight loss and an elevated plasma aldosterone concentration, even in successful competitors. To determine whether supplementation with high doses of electrolytes, with or without glycerol, enhances recovery, the following were measured in 6 Arabian horses before and after completion of a 60 km treadmill exercise test simulating an endurance ride and after 12, 24, 48, and 72 h of recovery: bodyweight; plasma osmolality; plasma concentrations of protein, electrolytes, aldosterone and cortisol; and urine and faecal electrolyte concentrations. Before and during the exercise test, horses were supplemented with a total of 2.4 ml/kg bwt of water (W); 0.2 g/kg bwt KCl and 0.4 g/kg bwt NaCl in 2.4 ml/kg bwt of water (E); or 0.2 g/kg bwt KCl and 0.4 g/kg bwt NaCl in 2.4 ml/kg bwt (3 g/kg bwt) of glycerol (GE). Although weight loss after completion of the simulated ride was greater (P < 0.01) for W (3.2%) than for E and GE (1.0 and 0.9%, respectively), horses supplemented with E or GE experienced further weight loss by 24 h after the simulated ride (2.2 and 2.1% for E and GE, respectively) while bodyweight with W remained unchanged (3.0%) from the finish value. After 48 h of recovery, bodyweight was not different from the starting values with E and GE but remained decreased (P < 0.01) with W throughout the recovery period (2.2% persisting weight loss after 72 h of recovery). Plasma osmolality and plasma Na+ and Cl- concentrations increased (P < 0.01) and plasma protein concentration decreased (P < 0.01) after the exercise test with E and GE but were unchanged with W. Plasma osmolality and protein and electrolyte concentrations returned to pre-exercise values within 12 h of recovery with the exception of a persistent increase in plasma Na+ concentration with GE. The greatest plasma aldosterone concentration was measured after 12 h of recovery with W (1357 pmol/l) and was greater (P < 0.02) than that with E and GE (24 and 304 pmol/l, respectively). Urine production during the simulated ride increased (P < 0.01) with GE and resulted in loss of approximately 20% and essentially 100% of supplemented Na+ and K+, respectively. In contrast, electrolyte losses in faeces were unaffected by electrolyte or glycerol supplementation. In conclusion, supplementation with high doses of electrolytes as hypertonic oral pastes attenuated weight loss during a simulated endurance ride (by enhancing voluntary water intake); however, it did not prevent development of significant weight loss during the initial 24 h of recovery. Glycerol administration resulted in no benefits, and actually increased urine electrolyte losses, in comparison to supplementation with electrolytes alone.

Short-term influence of prednisone and phenobarbital on thyroid function in euthyroid dogs

The short-term effects of prednisone and phenobarbital on serum total thyroxine (tT4), free thyroxine (fT4), and thyroid stimulating hormone (TSH) were evaluated in euthyroid dogs. Twenty-six beagles were randomly divided into 3 groups receiving, respectively, a placebo, prednisone (1.2 to 2 mg/kg body weight, per os, every 12 hours for 3 weeks), or phenobarbital (1.8 to 3 mg/kg body weight for 1 week, then 2.7 to 4.5 mg/kg body weight, per os, every 12 hours for 2 weeks). Blood samples taken over a 6-week period were assayed for serum tT4, fT4, and TSH. Phenobarbital therapy in our study did not affect serum tT4, fT4, or TSH concentrations. Prednisone therapy, however, significantly decreased serum tT4 and fT4, but did not affect serum TSH concentrations.

Prevalence of autoantibodies to thyroglobulin in dogs with nonthyroidal illness

OBJECTIVE

To evaluate a thyroglobulin autoantibody (TgAA) assay and determine a diagnostic threshold.

SAMPLE POPULATION

Serum samples from dogs with various endocrine abnormalities and from 30 obese adult female Beagles.

PROCEDURE

TgAA were determined by use of the ELISA. Six experiments were done: 1, definition of positive results for TgAA using samples from normal and T3 autoantibody (T3AA) positive dogs; 2, establishment of prevalence of positive results in 91 clinically normal dogs; 3, evaluation of positive results for sera from dogs with nonthyroidal illnesses; 4, testing of samples from dogs with primary hypothyroidism but absence of T4AA or T3AA, or both; 5, determination of prevalence of false-negative results in dogs that are T4AA and/or T3AA positive, which were (18 dogs) or were not (22 dogs) receiving L-thyroxine replacement therapy; and 6, examination of thyroid biopsy specimens from 18 dogs (8 TgAA positive and 10 TgAA negative).

RESULTS

Positive results were defined as at least twice (200%) the optical density of the negative-control sample. False-positive results were obtained for only 3.4% of 146 dogs with nonthyroidal illness. Thirty-seven percent of dogs with primary hypothyroidism, but no evidence of T4AA or T3AA, or both, were TgAA positive. False-negative results were found in 1 of 22 and 2 of 18 T3AA-positive dogs with and without thyroid replacement therapy, respectively. Thyroid biopsy specimens from 8 TgAA-positive dogs had evidence of lymphocytic thyroiditis, whereas those from 10 TgAA-negative dogs did not.

CONCLUSION AND CLINICAL RELEVANCE

The assay is sensitive and specific for identification of lymphocytic autoimmune thyroiditis in dogs, and has potential for aiding early diagnosis of thyroiditis in dogs and identifying dogs likely to perpetuate hypothyroidism in breeding programs.

Ovarian steroid cell tumor resembling luteoma associated with hyperadrenocorticism (Cushing's disease) in a dog

An ovarian steroid cell tumor was diagnosed in a 6.5-year-old female Rottweiler. The animal was polydipsic and polyuric, with an enlarged, pot-bellied abdomen. Radiographs and ultrasound examinations revealed an approximately 13-cm-diameter cystic mass below the right kidney. A low-dose dexamethasone suppression test was consistent with hyperadrenocorticism. Surgical exploration revealed an enlarged, lobulated left ovary approximately 10 cm in diameter, weighing 550 gs. Histologically, the ovarian tumor consisted of dense sheets and nests of round to polyhedral cells with abundant, finely vesiculated cytoplasm. The overall features were most consistent with ovarian steroid cells tumor resembling luteoma and associated with hyperadrenocorticism.

Hypercalcemia and renal failure. Etiology, pathophysiology, diagnosis, and treatment

Hypercalcemia is a frequent disorder of calcium metabolism in dogs and cats. Hypercalcemia-induced alterations in renal function and morphology are linked to many of the clinical manifestations observed in hypercalcemic patients. Since many renal effects induced by hypercalcemia are potentially reversible, early recognition and characterization of the problem facilitates rapid therapeutic intervention.

Effects of sample handling temperatures on bovine skim milk progesterone concentrations

The effects of incubation of whole milk at various temperatures and times on the concentration of progesterone in the skim milk fraction was determined. For the study, milk samples were collected from 10 pregnant Holstein cows. The milk from each cow was transferred to culture tubes to provide 32 replicates of 3 ml volume. To begin the incubation study, all samples were placed in a 37 degrees C water bath for 4 h. The end of this incubation was designated as time 0 and a sample from each cow was centrifuged to harvest skim milk. At time 0, samples from each cow were divided among incubation temperatures of 0 degrees, 4 degrees, 20 degrees and 37 degrees C. Samples were removed from each incubation group at 30, 60, 90 and 120 min. After 120 min, all remaining samples were returned to the 37 degrees C incubation and skim milk was collected at 30, 60 and 90 min. Progesterone was measured in skim milk by radioimmunoassay. The mean +/- SE concentration of progesterone in skim milk at time 0 was 10.9 +/- 1.1 nmol/L. The mean concentration of progesterone in skim milk was higher (P < 0.05) in all samples incubated at 0 degrees and 4 degrees C, with incremental increases ranging from 34% to 67% above time 0. Progesterone in skim milk returned to time 0 concentrations in milk samples transferred from 0 degrees or 4 degrees C to 37 degrees C. There was no change in skim milk progesterone in whole milk samples incubated at 20 degrees or 37 degrees C. From this study, it can be concluded that the concentration of progesterone in skim milk is temperature dependent. Inconsistency in handling whole milk samples can have a profound effect in the concentration of progesterone on skim milk. The temperature-dependent effect was reversible and may be related to solubility of progesterone in milk fat.

Effect of food deprivation on baseline iodothyronine and cortisol concentrations in healthy, adult horses

Six healthy, adult horses, with normal (mean +/- SEM) baseline serum concentrations of total triiodothyronine (T3, 1.02 +/- 0.16 nmol/L), free T3 (FT3, 2.05 +/- 0.33 pmol/L), total thyroxine (T4, 19.87 +/- 1.74 nmol/L), free T4 (FT4, 11.55 +/- 0.70 pmol/L), total reverse T3 (rT3, 0.68 +/- 0.06 nmol/L), and cortisol (152.75 +/- 17.50 nmol/L), were judged to be euthyroid on the basis of response to a standardized thyroid-stimulating hormone response test. Serum concentrations of T3, FT3, T4, FT4, rT3, and cortisol were determined immediately before and every 24 hours during a 4-day period of food deprivation, when water was available ad libitum. Similar variables were measured 72 hours after refeeding. Decreases (to percentage of baseline, prefood deprivation value) in circulating T3 (42%), T4 (38%), FT3 (30%), and FT4 (24%) concentrations were maximal after 2, 4, 2, and 4 days of food deprivation, respectively (P < 0.05). Increases (compared with baseline, prefood deprivation value) in rT3 (31%) and cortisol (41%) concentrations were maximal after 1 and 2 days of food deprivation, respectively (P < 0.05). Refeeding resulted in increase in serum T4 and FT4, and decrease in rT3 and cortisol concentrations toward baseline values, after 72 hours (P < 0.05). Refeeding did not effect a return of T3 or FT3 concentration to baseline values after 72 hours (P < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Isolation of thyroid peroxidase and lack of autoantibodies to the enzyme in dogs with autoimmune thyroid disease

Fifty serum samples from dogs with clinical signs of hypothyroidism and autoantibodies (AA) to thyroglobulin (Tg), thyroxine, or triiodothyronine were screened for AA to thyroid peroxidase (TPO). Thyroid peroxidase is the antigen against which microsomal AA are formed in human beings with lymphocytic thyroiditis. The TPO was isolated from canine thyroid tissue, using a modification of the procedure for purifying porcine TPO. The enzyme was solubilized from the membrane, using a deoxycholate-trypsin solution, followed by ammonium sulfate precipitation and diethylaminoethyl Sephadex chromatography. Activity of TPO was determined, using an iodide oxidation assay and a guaiacol assay. A monoclonal antibody to canine Tg, coupled to an immunoaffinity column, was used to eliminate the contaminating Tg from the TPO preparation. Using the TPO preparation as an antigen, an ELISA was performed on 10 serum samples and immunoblot assays were performed on 50 canine sera. Autoantibodies to TPO were not found in any of the sera. Assays also were performed, using purified porcine and human TPO and evidence of cross-reactivity with canine TPO was not identified. The absence of AA to TPO in dogs suggests a different pathogenesis for autoimmune thyroid disease in dogs than that hypothesized for lymphocytic thyroiditis in human beings.

Thyroid function in dogs with spontaneous and induced congestive heart failure

The effects of spontaneous and experimentally induced congestive heart failure on serum thyroxine (T4), 3,5,3'-triiodothyronine (T3), 3,3'5'-triiodothyronine (reverse T3), free T4, free T3 concentrations, and the serum T4 and T3 concentrations in response to administration of thyrotropin were studied. Serum thyroid hormone concentrations were not different between eight dogs with spontaneous congestive heart failure and normal age matched control dogs. Seven dogs with experimental heart failure were tested before and after induction of congestive heart failure by rapid ventricular pacing. Mean serum T4 and free T3 concentrations were decreased and mean serum reverse T3 concentration was increased following induction of heart failure. The serum T4 and T3 responses to thyrotropin were not altered. Thyroid gland morphology appeared normal in dogs with experimental heart failure. Experimental congestive heart failure, similar to some other nonthyroidal illnesses, alters thyroid hormone secretion and metabolism in dogs.

Skim milk progesterone in pregnant cows from insemination throughout lactation

The skim milk progesterone profile was assessed by radioimmunoassay, without extraction, from the day of insemination (day 0) until the cows were dried off on day 225 of gestation. A total of 418 samples were collected from 154 pregnant Holstein cows. The daily variation in skim milk progesterone was recorded from day 1 until day 45 of pregnancy to detect the commencement of progesterone secretion from the corpus luteum after insemination. Subsequent determinations were made every 2 weeks from day 46 until lactation ceased. On the day of artificial insemination and for the first 2 days after insemination, all the cows had a basal progesterone concentration < 0.1 ng/ml. A rise in progesterone (0.2 +/- 0.1 ng/ml) was first detected on the third day after insemination. The progesterone values then increased significantly (p < 0.001) until day 15. The values then remained nearly constant (2.5-3.5 ng/ml) until day 106 of pregnancy, when they began to decline. Between days 120 and 180 of gestation, progesterone was significantly decreased (2.2-2.9 ng/ml) before it rose again to the previous plateau (3.5-3.9 ng/ml) around day 180. The progesterone concentration then remained at the higher level until the animals were dried off.

Pharmacokinetics of L-thyroxine after its oral administration in dogs

Twelve mature (5 sexually intact males, 4 castrated males, and 3 females) mixed-breed dogs were surgically thyroidectomized and used in a Latin-square design pharmacokinetic study of orally administered L-thyroxine. The dogs were treated with 44, 22, and 11 micrograms of L-thyroxine/kg as a single morning dose or in divided doses, morning and evening. Serum concentration of thyroxine (T4) was evaluated to determine a number of pharmacokinetic variables for comparison. Mean steady-state concentrations (Css) were determined from the area under the curve. Variables were analyzed for comparisons between dosages by use of ANOVA. Concentration at steady state was highest for dogs of the 44-micrograms/kg of body weight once-daily group and was lowest for dogs of the group given 11 micrograms/kg in 2 daily doses. Single daily administration resulted in higher Css, except at the 22-micrograms/kg/d dosage. Clearance was faster for the 22- and 44-micrograms/kg/d dosages than for the 11-micrograms/kg/d dosage. The half-life (t1/2) and mean residence time (MRT) also were shorter for the 44-micrograms/kg/d dosage, possibly indicating more rapid elimination of the drug at higher doses and dose-dependent kinetics. Perhaps, as the dogs' metabolism increased with higher iodothyronine concentrations, hormone degradation was accelerated. Interval (divided vs single dose) caused some expected changes: maximal concentration was higher and minimal concentration was lower when single administration was used. These undulations resulted in iodothyronine concentrations above the physiologic range for a number of hours, whereas concentration closer to physiologic ranges was achieved by use of divided doses.(ABSTRACT TRUNCATED AT 250 WORDS)

Radioimmunoassay monitoring of thyroid hormone concentrations in dogs on thyroid replacement therapy: 2,674 cases (1985-1987)

Serum iodothyronine concentrations from 4,064 samples submitted for monitoring of thyroid replacement therapy were evaluated in a retrospective study. After exclusion of samples because of the presence of 3,5,3' triiodothyronine (T3) autoantibodies, insufficient numbers of dogs on some commercial preparations or medication with corticosteroids or synthetic T3 preparations, data from 2,674 dogs remained. Data were analyzed by using information on dose, time after dosing, commercial product, and once-a-day or twice-a-day dosing regimens. Serum total thyroxine (T4) and total T3 and estimates of free T4 and free T3 were significantly high in serum from dogs given higher doses of synthetic L-thyroxine orally. Doubling the oral dosage did not double the serum iodothyronine concentrations, perhaps because of poor absorption or more rapid catabolism of the hormones at higher L-thyroxine doses. Wide variation in the therapeutic hormone concentrations was found. Some dogs given low dosages of L-thyroxine had normal iodothyronine concentrations whereas some others given higher dosages had low normal to low concentrations. Monitoring the serum concentrations is an objective way to ensure adequate concentrations for successful therapy. When a therapeutic trial is used as a diagnostic procedure, one should not rule out hypothyroidism unless a therapeutic monitoring sample has indicated that replacement dose and absorption of the exogenous iodothyronine has been adequate. Thyroid hormone concentrations peaked at 4 to 6 hours after oral administration of L-thyroxine for once-a-day and twice-a-day dosage regimens. Higher concentrations were achieved with once-a-day than with twice-a-day regimens at the same total daily dose.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevalence of autoantibodies to thyroglobulin, thyroxine, or triiodothyronine and relationship of autoantibodies and serum concentrations of iodothyronines in dogs

Assays were developed to detect and measure autoantibodies (AA) to thyroglobulin (Tg) and to the thyroid hormones, thyroxine (T4) and triiodothyronine (T3). An ELISA to detect AA to Tg was developed, using purified canine Tg as the antigen and goat anti-canine IgG conjugated with alkaline phosphatase as the second antibody. A highly charged agarose electrophoresis assay was used for determination of AA to T4 and T3. Sera from dogs (n = 119) with clinical signs consistent with hypothyroidism were tested for AA to Tg, T4, and T3. Autoantibodies to at least 1 of the 3 thyroid antigens were detected in 58 of the 119 (48.7%) sera tested. Autoantibodies to Tg were detected more frequently in samples with low serum concentrations of thyroid hormones than in samples with normal concentrations. The presence of AA to T4, T3, or both was not significantly associated with low thyroid hormone concentrations, but this lack of association may have been attributable to binding of AA in the measurement of thyroid hormones by radioimmunoassay.

Use of the triiodothyronine suppression test for diagnosis of hyperthyroidism in ill cats that have serum concentration of iodothyronines within normal range

Administration of triiodothyronine (liothyronine, 15 micrograms, q 8 h, for 6 treatments) caused marked decrease in serum concentration of thyroxine (T4) and estimates of free T4 (fT4) concentration in clinically normal cats. A prospective clinical study was done to evaluate the use of this suppression test for diagnosis of hyperthyroidism in cats with clinical signs suggestive of the disease, but lacking high serum concentration of iodothyronines. Twenty-three cats were confirmed as hyperthyroid on the basis of histologic changes in the thyroid gland or clinical improvement in response to administration of methimazole. Mean +/- SD serum concentration of T4 (34.3 +/- 12.7 to 31.3 +/- 11.5 nmol/L) and estimate of fT4 concentration (26.6 +/- 6.4 to 25.6 +/- 6.9 pmol/L) did not change after administration of liothyronine to these cats. Twenty-three cats were classified as nonhyperthyroid by histologic confirmation of other disease, abnormal results of other diagnostic tests that strongly supported primary disease other than hyperthyroidism, or spontaneous remission of weight loss without treatment. Mean +/- SD serum concentration of T4 (27.9 +/- 10.3 to 11.7 +/- 6.4 nmol/L) and estimate of fT4 concentration (21.7 +/- 5.4 to 10.4 +/- 4.4 pmol/L) decreased significantly (P less than 0.001) in response to administration of liothyronine. Discriminant analysis was used to identify variables from iodothyronine assays (eg, absolute concentration of T4 or absolute estimate of fT4 concentration, or changes of T4 or fT4 concentration) that provided the best diagnostic sensitivity and specificity.(ABSTRACT TRUNCATED AT 250 WORDS)

Concentrations of estrone sulfate in peripheral serum of pregnant goats: Relationships with gestation length, fetal number and the occurrence of fetal death in utero

Blood sampling was initiated shortly after breeding and continued weekly through 60 to 72 days post breeding in 20 pregnant and 5 nonpregnant dairy goat does. In does not showing a return to estrus by 72 days, collection of blood was continued at 10- to 14-day intervals until 135 days post breeding. At parturition, the numbers of does delivering one, two, three, four or five kids was four, ten, three, two and one, respectively. Immunoreactive estrone sulfate (ES) was measured in serum by radioimmunoassay (RIA). In nonpregnant does, the mean+/-SD concentration of ES was 0.1+/-0.1 nmol/l (n=36 samples). At 40 to 50 days post breeding, ES concentrations increased dramatically in pregnant does. Statistically, does were classified as pregnant when serum ES increased and remained above 1.1 nmol/l (P<0.05). Serum ES in pregnant does peaked at 65 to 75 days of gestation, remained at a relative plateau through 120 days and then gradually increased for the remainder of the sampling schedule. There were positive correlations between serum ES and the number of kids born in sampling periods of 50 to 55 days and after 90 days of gestation (P<0.05). Fetal loss was documented in two does that were not included in the survey data. One doe delivered two normal kids and two mummified fetuses. Time-trend changes in ES were typical of a normal pregnancy. Another doe had a marked decrease in ES (below 0.8 nmol/l) in samples drawn on Days 94 and 108 of gestation while luteal concentrations of progesterone were maintained. This doe delivered one weak, depressed kid, one stillborn kid and a decomposed fetus at the expected time for parturition.

Changes in adrenal cortisol secretion as reflected in the urinary cortisol/creatinine ratio in dogs

In Experiment 1, voided urine samples were collected from 12 adult dogs at 0500, 1400, and 2200 hr for 4 days. Cortisol was measured in unextracted urine by radioimmunoassay, creatinine by spectrophotometry, and the cortisol/creatinine ratio (UCCR) was calculated for each sample. There was considerable variation both within and among dogs in UCCR but there was no consistent time of day fluctuation in UCCR. In Experiment 2, these dogs were randomly assigned to 1 of 4 groups. The groups received each of 4 treatments (saline, dexamethasone, ACTH gel, and aqueous ACTH) at 7 day intervals in Latin square design. All urine was collected from 0 through 8 hr. Blood samples were collected at 20 minute intervals from 0 through 8 hr. Plasma cortisol exposure was determined by quantifying area under the curve (AUC). UCCR measurement was shown to differentiate basal from elevated, but not lowered, cortisol secretion. A positive linear relationship between UCCR and AUC was seen for all treatments except dexamethasone. These results indicate that changes in cortisol secretion are reflected in changes in UCCR, but measurement of UCCR may lack sensitivity to differentiate basal from reduced states of cortisol secretion. In Experiment 3, urine was collected daily before and during induction therapy with o,p'-DDD from dogs with pituitary-dependent hyperadrenocorticism. Successful suppression of the adrenal glands was accompanied by a progressive decrease in UCCR. There was considerable variation in the rate of adrenal suppression.

Caprine beta-mannosidosis. Abnormal thyroid structure and function in a lysosomal storage disease

Deficient activity of the lysosomal enzyme beta-mannosidase leads to widespread tissue accumulation of oligosaccharides in caprine beta-mannosidosis, an autosomal recessive neurovisceral storage disease. Severe thyroid morphologic abnormalities found in a previous light microscopic survey of tissues from neonatal affected goats suggested the possibility of impairment of function. Since considerable evidence indicates that thyroid hormone plays an important role in regulation of myelination, thyroid hormone deficiency, if present during central nervous system development, could be a factor in the hypomyelination seen in affected animals. Thus, this study was designed to characterize thyroid structure and function in beta-mannosidosis. To investigate developmental aspects of structural abnormalities, thyroids from six pairs of affected and control animals ranging in age from 96/150 days gestation to 3 days postnatal were analyzed by light and electron microscopy. Major findings in thyroids from affected animals, as early as 96/150 days gestation, included follicle irregularities and pronounced presence of lysosomal storage vacuoles in all cell types, particularly in follicular cells. The degree of cytoplasmic vacuolation increased with advancing age. To assess thyroid function, thyroid hormone concentrations were determined in six age-matched, neonatal pairs of affected and control goats. Significantly decreased thyroid hormone concentrations were present in affected animals. It is hypothesized that thyroid hormone deficiency plays a role in the pathogenesis of hypomyelination in affected animals. This study comprises, to our knowledge, both the most complete description of developmental abnormalities and the first report of abnormal function in an endocrine organ in a lysosomal storage disease. Further, this report suggests that systemic perturbations induced by a genetically determined deficiency of a lysosomal hydrolase could be a factor in the pathogenesis of central nervous system lesions.

Effects of dietary acidification and potassium depletion on acid-base balance, mineral metabolism and renal function in adult cats

Effects of dietary potassium restriction, with or without dietary acidification, on acid-base balance, mineral metabolism and renal function were evaluated in 12 adult cats. Six cats were fed a potassium-restricted diet (0.2% potassium) for 8 wk, and six cats were fed the same potassium-restricted diet plus a dietary acidifier (0.8% NH4Cl) for 8 wk. Both groups of cats were then fed the same diet supplemented with potassium gluconate (0.7% dietary potassium) for an additional 4 wk. Renal function was evaluated before treatment and again at 8 and 12 wk. Serum potassium concentration declined in all cats by wk 1 and was also lower in NH4Cl-treated cats at 2, 3, 6 and 8 wk than in control cats. Metabolic acidosis developed in both groups of cats. Dietary balance studies indicated negative potassium balance in NH4Cl-treated cats. Glomerular filtration rate declined significantly in NH4Cl-treated cats after 8 wk but was unchanged in control cats. From the results of this study, we conclude that adding a dietary acidifier to a potassium-restricted diet worsens hypokalemia, possibly by affecting gastrointestinal potassium handling, and induces severe metabolic acidosis and renal dysfunction in adult cats.

Thyroid function tests in euthyroid dogs treated with L-thyroxine

The effects of treatment with L-thyroxine (1 mg/m2 of body surface/d, PO, for 8 weeks) on the thyroxine (T4) and triiodothyronine (T3) responses to thyrotropin (TSH) and thyrotropin-releasing hormone (TRH) administration were determined in 10 euthyroid Beagles; 4 other dogs acted as controls. The TSH response test was performed before treatment and at weeks 2, 4, and 8 of treatment in all dogs and at 2 and 4 weeks after cessation of treatment in 6 dogs. The TRH response test was performed before treatment and at week 6 of treatment in all dogs and at 5 weeks after cessation of treatment in 6 dogs. Suppression of the T3 response to TSH was evident at treatment week 2, whereas the T4 response was suppressed at week 4 and remained suppressed for the duration of the study. Four weeks after stopping treatment, T4 and T3 responses to TSH in 2 dogs were within the hypothyroid range. The T4 response to TRH was completely suppressed after 6 weeks of thyroxine treatment, but returned to pretreatment values by 5 weeks after cessation of treatment. Suppression of thyroid and pituitary function is evident after administration of a replacement dose of L-thyroxine to euthyroid dogs.

Pulmonary excretion of H2 in calves with Cryptosporidium-induced malabsorption

Pulmonary hydrogen gas (H2) concentrations were used to assess the malabsorption of dietary nutrients in preruminating calves inoculated with Cryptosporidium sp. Normal values were established in five control calves and seven calves (principals) were inoculated with 1.0 x 10(8) Cryptosporidium sp. oocysts. Hydrogen concentrations and wet fecal weights were measured at three stages: before Cryptosporidium sp. inoculation (stage 1), three days after the onset of diarrhea (stage 2), and after the resolution of diarrhea (stage 3). Mean end-breath and total-breath H2 concentrations in the principal calves were higher (P less than 0.025 and P less than 0.05) for stage 2, when compared to control values. Both end-breath and total-breath H2 concentrations were increased (P less than 0.001 and P less than 0.025, respectively) in the principal calves during stage 2 when compared to values obtained for stages 1 and 3. Concurrently, Cryptosporidium sp. infection was associated with increased (P = 0.06) fecal output during stage 2, only. The increased H2 concentrations and cumulative fecal output show that Cryptosporidium sp. caused malabsorption of fermentable nutrients.

The relationship between composition of gain and circulating hormones in growing beef bulls fed three dietary crude protein levels

Twenty-one Simmental crossbred bulls (311 +/- 11 kg, 9 mo of age) were used to determine the effect of feeding 10, 12 or 14% CP on concentration of hormones in blood and the relationship of these hormones to composition of gain. Six bulls were slaughtered on d 0 to provide an estimate of initial carcass composition (9-11 rib section). Remaining bulls were assigned to dietary treatments. Blood samples were collected every 30 min from 0800 to 2000 on d 0, 66, 136 and 202 of treatment; bulls were slaughtered on d 203. Across all treatments, growth hormone (GH) declined (P less than .05) from d 0 to d 202. Free insulin-like growth factor I (IGF-I) was lowest (P less than .05) on d 0. In four randomly selected bulls, IGF-I fluctuated during the 12-h sampling periods. Within each treatment group, insulin was greatest on d 202 (P less than .05). Testosterone (T) increased from d 0 to d 66, then declined. Cortisol (C) was lowest on d 66. Thyroid hormones increased (P less than .05) after d 0. Growth hormone and IGF-I were correlated negatively with carcass fat percentage, fat accretion rate and fat thickness. IGF-I concentrations were correlated positively with percentage of carcass protein. Testosterone:cortisol ratio was not related to composition, but high T coupled with low C may be related to carcass leanness (mean carcass fat = 24.4%). These data suggest that GH and IGF-I are the hormones most related to composition of gain in growing beef bulls.

Basal and estradiol-induced release of gonadotropins in dairy cows with naturally occurring ovarian cysts

A study was conducted to identify relationships between serum sex steroid concentrations and release of gonadotropins in dairy cows with ovarian cysts. Cows with ovarian cysts were grouped according to sex steroid profiles as being under estrogenic (n = 6) or low steroid (n = 6) influence. All cows were submitted to a sampling and treatment protocol to 1) record basal pulsatile release of gonadotropins and 2) determine whether luteinizing hormone (LH) or follicle stimulating hormone (FSH) was released after sequential administration of exogenous estradiol and gonadotropin releasing hormone (GnRH) treatments were given 30 h apart. Basal LH was higher in the estrogen-influence group (P < 0.05). There were no differences between groups in basal FSH concentrations or frequency and amplitude of pulsatile LH or FSH release. Only one of the twelve cows, an individual from the low steroid group, had a preovulatory-like surge of gonadotropins after exogenous estradiol. All cows released LH and FSH in response to GnRH treatment, with no differences between groups. These results show that 1) there is considerable variation in pulsatile release of gonadotropins in cows with ovarian cysts, even among individuals with similar sex steroid profiles, and 2) suggest that a factor in the persistence, and perhaps initiation, of the cystic condition is refractoriness to the positive feedback effect of estradiol on gonadotropin release.

Adrenal function in 15 dogs with insulin-dependent diabetes mellitus

Pituitary-adrenal function was assessed by a combined dexamethasone suppression-ACTH stimulation test in 15 diabetic and 9 healthy dogs. In both groups, plasma cortisol concentrations decreased (P less than 0.001) after dexamethasone administration and increased (P less than 0.001) after ACTH administration. Differences between groups (P greater than 0.05) and group-by-time interactions were not significant (P greater than 0.05). Seemingly, adrenal function was not altered in well-regulated diabetic dogs.

Effect of nonadrenal illness on adrenal function in the cat

Adrenal function was assessed by a combined dexamethasone suppression-ACTH stimulation test in 18 healthy cats, 17 diabetic cats, and 19 sick nondiabetic cats. In all groups, plasma cortisol concentrations decreased after dexamethasone was administered and increased after ACTH was administered. There were no significant (P greater than 0.05) differences among groups in time trend changes in cortisol concentration. There was considerable variation in adrenal response between cats in each group. Diabetic cats had more variation in base-line and postdexamethasone plasma cortisol concentrations (P less than 0.05) than did other groups. In sick, nondiabetic cats, cortisol concentrations tended to be higher in cats with hyperthyroidism (P = 0.06) than in cats with other diseases.

Breath hydrogen concentration and small intestinal malabsorption in calves

Breath hydrogen concentrations were measured to assess intestinal carbohydrate malabsorption in preruminating calves. Oral administration of 1.25 g of lactulose (a nonabsorbable carbohydrate)/kg to calves produced breath hydrogen concentrations significantly (P less than 0.001) higher than values determined after calves were fed milk and before the treatment was given. This indicates that, in the calf, fermentation of nonabsorbed carbohydrates results in increased breath hydrogen values. To induce small intestinal malabsorption, chloramphenicol was administered orally at 50 mg/kg, 2 times a day, to 5 calves for 3 days. Before therapy was started, each calf was fitted with a duodenal cannula to facilitate collection of intestinal mucosal biopsy samples during treatment. Chloramphenicol therapy significantly (P less than 0.001) increased breath hydrogen concentrations from those values measured after calves were fed milk alone. Concurrently, chloramphenicol administration significantly decreased intestinal villous length (P less than 0.001) and D-xylose absorption (P less than 0.05), compared with those values before treatment was given. These results demonstrate that decreased intestinal absorptive capacity is associated with an increase in breath hydrogen concentrations and that breath hydrogen may be useful in evaluating malabsorption in calves with naturally occurring enteric disease.

Effect of binding and pinealectomy on photoperiod and seasonal variations in secretion of prolactin in cattle

The role of the eyes and pineal gland on photoperiod- and season-induced changes in secretion of prolactin were studied in male cattle. Increasing exposure to light from 8 to 16 hr each day increased basal and thyrotropin-releasing-hormone-induced secretion of prolactin 3.7- and 4.1-fold in three sham-pinealectomized steers. In contrast, basal and thyrotropin-releasing-hormone-induced increases in secretion of prolactin did not change in four blind bulls and were markedly suppressed in three pinealectomized steers when exposure to light was increased from 8 to 16 hr/day. There was no diurnal variation in secretion of prolactin regardless of photoperiod or surgical treatment. However, seasonal changes (averaged 46 ng/ml in June-Aug vs 7 ng/ml in Dec-Feb) in secretion of prolactin persisted in blind and pinealectomized steers previously shown to be nonresponsive to changing photoperiods. Ambient temperature and photoperiod account for most, but not all, of the seasonal variation in secretion of prolactin. We hypothesize there is an endogenous annual rhythm in the secretion of prolactin in cattle.

Testicular degeneration in a male goat. A case report

Semen samples from an 18-month-old infertile Lamancha buck contained less than 10% motile spermatozoa and a high incidence of morphological abnormalities. Degenerate detached heads, tightly coiled tails, and thickened midpieces were the prominent morphological defects, affecting 46%, 30%, and 15% of ejaculated spermatozoa, respectively. At necropsy, the diagnosis of testicular degeneration was made, characterized by focal, noninflammatory seminiferous tubule occlusion and mineralization, with a more generalized sloughing of tubular germinal epithelium. When examining spermatozoa morphology from various sites of the excurrent ducts, detached heads were readily seen in efferent duct fluid (> 30% incidence) and the coiled tails and other midpiece defects became prominent with passage through the caput epididymis.

Estradiol-17 beta cyclopentylpropionate and prostaglandin F for induction of abortion during the first trimester of pregnancy in feedlot heifers

The ability of estradiol-17 beta cyclopentylpropionate (ECP, 20 mg) and prostaglandin F2 alpha (PGF2 alpha; 5, 10, 20, and 40 mg) to induce abortion during early gestation (days 40 to 90, as estimated by palpation per rectum) in pregnant feedlot heifers was compared. All treatments were given by IM injection. All heifers treated with 20 and 40 mg of PGF2 alpha aborted within 7 days after treatment. Six of 10 heifers aborted in the same period after ECP treatment; 1 additional heifer aborted by day 13. Abortions did not occur by day 13 in 10 placebo-treated heifers. Five and 10 mg of PGF2 alpha aborted 2 of 3 and 8 of 10 heifers, respectively, within 7 days of treatment. Quantitation of serum progesterone by specific radioimmunoassay showed that a luteolytic effect was evident in aborting heifers. Complications were not detected in any heifers after treatment or abortion. Ten of the 20 heifers that aborted in response to the 20- and 40-mg doses of PCF2 alpha developed a new corpora lutea by day 20 after treatment. However, none of the heifers that aborted after ECP treatment had a corpus luteum by day 20. It was concluded that PGF2 alpha is a more effective compound than ECP for induction of abortion during the 1st trimester of pregnancy in feedlot heifers, that a wide range of PGF2 alpha doses are capable of inducing abortion in at least some animals treated, and that heifers are likely to resume ovarian activity sooner if aborted with PGF2 alpha than with ECP.

Effect of stage of diestrus and number of cloprostenol (ICI 80, 996) injections on intervals to estrus, LH peak and ovulation in heifers

Intervals to the onset of estrus, luteinizing hormone (LH) peak and ovulation were compared in diestrous heifers after each of two cloprostenol treatments. Diestrous heifers were grouped at the first treatment (T1) according to day of the cycle, with heifers on days 5 through 8 designated as early diestrus and heifers on days 9 through 17 designated as late diestrus. Cloprostenol treatment was repeated (T2) 11 days after T1, at which time heifers in both groups were at similar stages of the estrous cycle. Visual observation, identification of the preovulatory LH peak, and rectal palpation were utilized to estimate data parameters. Split-plot analysis of variance showed a significant treatment x group interaction (P < .05). Time from prostaglandin treatment to the onset of estrus was similar for the early diestrous group after T1 (x = 53.1 hours ) and the early and late diestrous groups after T2 (x = 49.4 hours and 45.4 hours respectively). This interval was longer (P < .05) for the late diestrous group after T1 (x = 60.8 hours ) than for either group after T2, but not different from that for the early diestrous group after T1. Serum progesterone concentrations were higher (P < .05) at the time of T1 in the late diestrous group (x = 5.8 ng/ml ) than in the early diestrous group (x = 3.0 ng/ml ) or in either group at the time of T2 (x = 2.8 and 3.2 ng/ml respectively). Over all heifers, the synchrony of the onset of estrus was more precise (P < .05) after T2 than T1. Intervals from the onset of estrus to ovulation were not affected by group or treatment (overall mean = 24.4 +/- 1.0 hours, n = 42). We conclude that different recommendations for appointment artificial insemination (AI) may be indicated depending on the number of prostaglandin injections which are used in a prostaglandin synchronization program prior to insemination.