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SUMMARY

The objectives of this experiment were to determine serum concentrations of triiodothyronine (T3), thyroxine (T4), and free thyroxine (fT4) at rest, following thyroid-stimulating hormone (tsh) administration, and following phenylbutazone administration in healthy horses. This was done to determine which available laboratory test can best be used for diagnosis of hypothyroid conditions in horses. Serum T3, T4, and fT4 concentrations in serum samples obtained before and after tsh stimulation and following phenylbutazone administration for 7 days were determined.

Baseline values ranged from 0.21 to 0.80 ng of T3/ml, 6.2 to 25.1 ng of T4/ml, and 0.07 to 0.47 ng of fT3/dl. After 5 IU of tsh was administered IV, serum T3 values increased to 6 times baseline values in 2 hours. Thyroxine values increased to 3 times baseline values at 4 hours and remained high at 6 hours. Free T4 values increased to 4 times baseline values at 4 hours and remained high at 6 hours. Administration of 4.4 mg of phenylbutazone/kg, every 12 hours for 7 days significantly decreased T4 and fT4 values, but did not significantly affect serum T3 concentrations. It was concluded that a tsh stimulation test should be performed when hypothyroidism is suspected. Measurement of serum fT4 concentrations, by the single-stage radioimmunoassay, does not provide any additional information about thyroid gland function over that gained by measuring T4 concentrations. Phenylbutazone given at a dosage of 4.4 mg/kg every 24 hours, for 7 days did significantly decrease resting T4 and fT4 concentrations, but did not significantly affect T3 concentrations in horses.

Free access
in American Journal of Veterinary Research

SUMMARY

Direct effects of endotoxin (lipopolysaccharide [lps]) on equine wbc are known to stimulate the release of a variety of mediators including thromboxane, prostacyclin, and leukotrienes. In this study, 0.1 μg of lps/ml stimulated an early increase in tumor necrosis factor, succeeded by an increase in interleukin-1, but concentrations of lps up to 5.0 μg/ml caused no significant increase in superoxide anion release. The concentration of lps (0.1 μg/ml) used in this experiment was in the range of concentrations measured in plasma of some horses with gastrointestinal problems.

These results indicate that mediators released in response to low concentrations of lps may be responsible for many of the lps-induced pathophysiologic effects. This is indicated because concentrations of lps detected in plasma of some horses with severe gastrointestinal problems are approximately 0.1 μg/ml, a concentration that will stimulate cells to produce tumor necrosis factor, but will not stimulate any other measurable cytotoxic effect.

Free access
in American Journal of Veterinary Research

Summary

Serum free thyroxine (fT4), thyroxine (T4), and 3,5,3'-triiodothyronine (T3) concentrations were determined in 62 healthy dogs, 51 dogs with hypothyroidism, and 59 euthyroid dogs with concurrent dermatopathy or concurrent illness for which hypothyroidism was a diagnostic consideration. Status of thyroid function was based on history, physical findings, results of thyrotropin response testing, requirement for thyroid hormone replacement therapy, and in 31 dogs, on results of histologic examination of a thyroid gland biopsy specimen. Serum fT4 concentration was determined, using a single-stage radioimmunoassay. Mean (±sd)serumfT4 concentration was significantly (P < 0.05) greater in healthy dogs vs dogs with hypothyroidism (0.51 ± 0.27 ng/dl vs 0.10 ± 0.07 ng/dl). Significant difference in mean serum fT4 concentration was not evident between dogs with hypothyroidism and euthyroid dogs with hyperadrenocorticism (0.16 ± 0.13 ng/dl) or peripheral neuropathy (0.19 ± 0.10 ng/dl). Mean serum fT4 concentration in all other groups of euthyroid dogs with concurrent illness was similar to values in healthy dogs and was significantly (P < 0.05) greater, compared with values in dogs with hypothyroidism.

Similar results were found for mean serum T4 concentration. Comparison of serum fT4 vs T4 concentration revealed: sensitivity, 0.97 vs 0.98; specificity, 0.78 vs 0.73; predictive value for a positive test result, 0.79 vs 0.80; predictive value for a negative test result, 0.97 vs 0.97; and accuracy, 0.78 vs 0.86, respectively. Ten (17%) and 12 (20%) of 59 serum fT4 and T4 concentrations, respectively, were inappropriately low in euthyroid dogs with concurrent illness. Of euthyroid dogs with concurrent illness, those with hyperadrenocorticism, peripheral neuropathy, or idiopathic generalized megaesophagus had the lowest serum fT4 and T4 concentrations. Significant difference in mean serum T3 concentration was not detected among healthy dogs, dogs with hypothyroidism, or euthyroid dogs with concurrent illness. Measurement of serum fT4 concentration using the single-stage radioimmunoassay, did not provide additional information about thyroid gland function other than that gained by measurement of serum T4 concentration.

Free access
in Journal of the American Veterinary Medical Association

SUMMARY

Glucose tolerance and insulin response were evaluated in 9 normal-weight and 6 obese cats after iv administration of 0.5 g of glucose/kg of body weight. Blood samples for glucose and insulin determinations were collected immediately prior to and 2.5, 5, 7.5, 10, 15, 30, 45, 60, 90, and 120 minutes after glucose infusion.

Baseline glucose concentrations were not significantly different between normal-weight and obese cats; however, mean ± sem glucose tolerance was significantly impaired in obese vs normal-weight cats after glucose infusion (half time for glucose disappearance in serum—77 ± 7 vs 51 ± 4 minutes, P < 0.01; glucose disappearance coefficient—0.95 ± 0.10 vs 1.44 ± 0.10%/min, P < 0.01; insulinogenic index—0.20 ± 0.02 vs 0.12 ± 0.01, P < 0.005, respectively). Baseline serum insulin concentrations were not significantly different between obese and normal-weight cats. Insulin peak response after glucose infusion was significantly (P < 0.005) greater in obese than in normal-weight cats. Insulin secretion during the first 60 minutes (P < 0.02), second 60 minutes (P < 0.001), and total 120 minutes (P < 0.0003) after glucose infusion was also significantly greater in obese than in normal-weight cats. Most insulin was secreted during the first hour after glucose infusion in normal-weight cats and during the second hour in obese cats. The impaired glucose tolerance and altered insulin response to glucose infusion in the obese cats was believed to be attributable to deleterious effects of obesity on insulin action and β-cell responsiveness to stimuli (ie, glucose).

Free access
in American Journal of Veterinary Research

Abstract

Objective

To determine whether continuous venovenous hemofiltration, proposed to remove inflammatory mediators from circulation, would resolve cardiopulmonary derangements in a model of established endotoxic shock.

Animals

16 clinically normal pigs.

Procedure

Endotoxin was infused, IV, into anesthetized pigs for a total of 50 minutes. Thirty minutes after termination of the infusion period, extracorporeal circulation was initiated through a 50-kd diafilter, or past the filter without ultrafiltrate formation. Cardiac and respiratory variables were monitored for a period of 4 hours.

Results

Infusion of lipopolysaccharide resulted in a severe hypodynamic circulatory state, with significant decreases in mean arterial pressure and cardiac output concurrent with a significant increase in pulmonary arterial pressure. Hemofiltration was not associated with any correction of lipopolysaccharide-induced cardiopulmonary derangements.

Conclusions

Continuous venovenous hemofiltration, as used in this acute experiment, did not improve cardiopulmonary dysfunction during endotoxic shock.

Clinical Relevance

Continuous venovenous hemofiltration needs further investigation before it can be recommended as a clinically effective treatment. (Am J Vet Res 1997;58:408–413)

Free access
in American Journal of Veterinary Research

SUMMARY

The effect of a high insoluble-fiber (if) diet containing 15% cellulose in dry matter, high soluble-fiber (sf) diet containing 15% pectin in dry matter, and low-fiber (lf) diet on glycemic control in 6 dogs with alloxan-induced insulin-dependent diabetes mellitus was evaluated. Each diet contained > 50% digestible carbohydrate in dry matter. A crossover study was used with each dog randomly assigned to a predetermined diet sequence. Each dog was fed each diet for 56 days. Caloric intake was adjusted weekly as needed to maintain each dog within 1.5 kg of its body weight measured prior to induction of diabetes mellitus. All dogs were given pork lente insulin and half of their daily caloric intake at 12-hour intervals.

Mean (± sem) daily caloric intake was significantly (P < 0.05) less when dogs consumed the if diet vs the sf and lf diets (66 ± 3 kcal/kg, 81 ± 5 kcal/kg, and 79 ± 4 kcal/kg, respectively). Serum alkaline phosphatase activity was significantly (P < 0.05) higher when dogs consumed the lf diet vs the if and sf diets (182 ± 37 IU/L, 131 ± 24 IU/L, and 143 ± 24 IU/L, respectively). Mean postprandial plasma glucose concentration measured every 2 hours for 24 hours, beginning at the time of the morning insulin injection, was significantly (P < 0.05) lower at most blood sampling times in dogs fed if and sf diets, compared with dogs fed the lf diet. As a result, 24-hour mean plasma concentration of glucose (if, 165 ± 17 mg/dl; sf, 169 ± 19 mg/dl; lf, 218 ± 29 mg/dl), 24-hour mean plasma-glucose fluctuation (if, 49 ± 2 mg/dl; sf, 47 ± 4 mg/dl; lf, 63 ± 7 mg/dl), and 24-hour urine-glucose excretion (if, 31 ± 10 g/d; sf, 42 ± 16 g/d; lf, 67 ± 13 g/d) were significantly (P < 0.05) lower in dogs fed if and sf diets, compared with dogs fed the lf diet. These variables were not significantly different between dogs fed if and sf diets. Mean glycosylated hemoglobin concentration also was significantly (P < 0.05) lower when dogs consumed the if diet, compared with the lf diet (4.3 ± 0.4% vs 5.2 ± 0.4%, respectively).

In dogs with alloxan-induced insulin-dependent diabetes mellitus, consumption of diets containing 15% cellulose or 15% pectin and > 50% digestible carbohydrate on a dry-matter basis resulted in improvement in glycemic control, compared with consumption of a diet containing > 50% digestible complex carbohydrate without added fiber.

Free access
in American Journal of Veterinary Research

SUMMARY

Serum glucose and immunoreactive insulin concentrations were monitored after topical administration of an insulin-containing ophthalmic solution in 20 clinically normal cats. Three ophthalmic surface-acting agents, benzalkonium chloride, dimethyl sulfoxide, and proparacaine hydrochloride, were evaluated individually for their effectiveness in enhancing absorption of topically applied insulin. The ophthalmic effects of insulin-containing ophthalmic preparations were assessed by complete ophthalmic examination before and at the conclusion of each test period. Withholding of food overnight (12 hours) preceded each topical application of insulin-containing ophthalmic solution (12.25 to 26.4 U/cat), either alone or in combination with surface-acting agents, after which blood samples were drawn serially from an indwelling iv catheter over a period of 8 hours. Baseline serum insulin concentration, after food was withheld for 12 hours, in nonstressed cats was 6.0 μU/ml (geometric mean), and an exponentiation of the logarithmic quantity (mean ± sd) yielded values of 1.5 to 23.0 μU/ml. All ophthalmic solutions tested failed to significantly lower serum glucose concentration or increase serum insulin concentration. Solutions used did not induce deleterious effect on ocular structures. Results indicate that topical administration of insulin-containing ophthalmic solution, either alone at the concentrations used or in combination with surfaceacting agents, did not result in effective absorption of insulin across the conjunctival and lacrimal nasal mucosa in biologically relevent quantities. Thus, this route of insulin administration, under these specific conditions, is not an effective alternative or adjunct to SC administration of insulin for treatment of cats with insulin-dependent diabetes mellitus or severe noninsulin-dependent diabetes mellitus.

Free access
in American Journal of Veterinary Research

SUMMARY

The absorption kinetics of porcine regular insulin following iv, im, and sc administration were evaluated in 10 dogs with alloxan-induced diabetes mellitus. Plasma immunoreactive insulin (iri) concentrations were evaluated immediately prior to and at 10, 20, 30, 45, 60, 90, 120, 180, and 240 minutes following iv administration; and immediately prior to and every 30 minutes for 2 hours and then every hour for 6 hours following im and sc administration of 0.55 U of porcine regular insulin/kg of body weight. Model-independent pharmacokinetic analysis was performed on each data set.

Plasma iri concentration declined rapidly after iv administration of regular insulin and then returned to baseline iri concentration by 3.2 ± 0.8 hours. The absorption kinetics following iv administration of regular insulin were similar to those found in earlier studies in healthy dogs and human beings.

The im and sc routes of regular insulin administration resulted in a pharmacologic concentration of iri at 30 minutes. The peak mean (± SD) plasma iri concentration was significantly (P < 0.05) greater following sc administratin than it was following im administration of regular insulin (263 ± 185 and 151 ± 71 IμU/ml, respectively). The time of the peak plasma iri concentration (68 ± 31 minutes and 60 ± 30 minutes) and the time to return to baseline plasma iri concentration (5.8 ± 1.2 hours and 5.8 ± 1.3 hours) were not significantly different following sc and im administration of regular insulin, respectively. The absorption kinetics following sc administration of regular insulin were similar to those found in earlier studies in healthy dogs and human beings. The absorption kinetics following im administration of regular insulin differed from those found in earlier studies and was similar to the absorption kinetics of regular insulin administered sc in this study. The reasons for this similarity were not readily apparent.

Free access
in American Journal of Veterinary Research

Summary

Progesterone was administered im to 6 adult anestrous bitches at a dosage of 2 mg/kg of body weight. Serum progesterone concentrations were measured prior to progesterone administration and for 72 hours thereafter. The serum progesterone concentration time data were analyzed by use of a pharmacokinetics modeling computer program. The mean (± sd) peak serum progesterone concentration (34.3 ± 7.8 ng/ml) was reached at 1.8 ± 0.2 hours after progesterone administration. The mean serum progesterone concentration was 6.9 ± 1.4 ng/ml at 24 hours and 2.0 ± 0.4 ng/ml at 48 hours after progesterone administration. By 72 hours after administration, mean serum progesterone concentration was 0.9 ± 0.2 ng/ml, which was comparable to serum progesterone concentrations prior to injection. The mean half-life of the absorption phase was 0.5 hours (range, 0.3 to 0.7 hours). The mean half-life of elimination was 12.1 hours (range, 9.5 to 13.8 hours). By analysis of the data, it was established that a dosage of 3 mg/kg, when the hormone was given im to dogs once a day, would maintain serum progesterone concentration > 10 ng/ml.

Free access
in American Journal of Veterinary Research