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Biomedical subjects

M E Peterson

Publications and source records attributed to M E Peterson.

At least 19 recordsLinked to original sources
PubMed1995

Radioiodine treatment of 524 cats with hyperthyroidism.

OBJECTIVE: To evaluate a protocol for subcutaneous radioiodine treatment of cats with hyperthyroidism in which the dose was determined on the basis of severity of the cat's clinical signs, thyroid tumor size, and magnitude of the serum thyroxine (T4) concentration. DESIGN: Prospective case series. ANIMALS: 524 cats with hyperthyroidism. PROCEDURE: A scoring system based on 3 factors (severity of clinical signs, size of the thyroid gland, and magnitude of the serum T4 concentration) was used to select the dose of radioiodine to be administered subcutaneously. RESULTS: On the basis of the scoring system, 310 (59%) cats were treated with a low dose of radioiodine (< 3.5 mCi; median, 3.0 mCi), 158 (30%) were treated with a moderate dose (3.5 to 4.4 mCi; median, 4.0 mCi), and 56 (11%) were treated with a high dose (> or = 4.5 mCi; median, 5.0 mCi). At time of discharge from the hospital, serum T4 concentration was still high in 80 (15.3%) cats, but by 6 months after administration of radioiodine, the serum T4 concentration had decreased to within or below reference range in all but 8 (1.5%) cats with persistent hyperthyroidism. Many cats had low serum T4 concentrations at some time after radioiodine treatment, but only 11 (2.1%) cats developed clinical and clinicopathologic features of hypothyroidism and required supplementation with L-thyroxine. Thirteen (2.5%) cats had a relapse of hyperthyroidism 1.1 to 6.5 years after initial radioiodine treatment. Overall, the response to treatment was considered good in 94.2% of the cats. Median survival time in the cats was 2.0 years; the percentage of cats alive after 1, 2, and 3 years of treatment was 89, 72, and 52%, respectively. CLINICAL IMPLICATIONS: Results of the study suggest that this method of dose estimation works well and that subcutaneous administration of radioiodine provides a safe and effective means of treating hyperthyroidism in cats.

Animals↗
PubMed1995

Effects of disease on the results of diagnostic tests for use in detecting hyperadrenocorticism in dogs.

The purpose of the study reported here was to assess 3 commonly used screening tests for hyperadrenocorticism (low-dose dexamethasone suppression test, ACTH stimulation test, and urinary cortisol:creatinine ratio) in dogs with various diseases other than those of the adrenal glands (nonadrenal diseases). A group of 100 dogs was studied: 59 dogs with nonadrenal disease, 21 clinically normal dogs, and 20 dogs with pituitary-dependent hyperadrenocorticism. Of 59 dogs with nonadrenal disease, 20 (34%) had high baseline cortisol concentration (greater than reference range limits), and 22 (38%) and 33 (56%) had inadequate serum cortisol suppression at 4 and 8 hours, respectively, after administration of a low dose of dexamethasone. Compared with clinically normal dogs, dogs with nonadrenal disease had significantly (P < 0.05) higher mean serum cortisol concentration at 4 and 8 hours after administration of a low dose of dexamethasone; however, significant differences were not detected between the mean cortisol concentration at 8 hours after administration for dogs with nonadrenal disease and for dogs with hyperadrenocorticism. After ACTH stimulation, only 8 of 59 (14%) dogs with nonadrenal disease had high serum cortisol concentrations. Significant differences did not exist after ACTH stimulation between mean cortisol concentration of clinically normal dogs and that of dogs with nonadrenal disease. Of 59 dogs with nonadrenal disease, 45 (76%) had a high urinary cortisol:creatinine ratio. When compared with clinically normal dogs, dogs with nonadrenal disease had a significantly higher mean urinary cortisol:creatinine ratio, but significant differences did not exist between the mean urinary cortisol:creatinine ratio of dogs with nonadrenal disease and that of dogs with hyperadrenocorticism.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocortical Hyperfunction↗
PubMed1995

Effects of desoxycorticosterone pivalate administration on blood pressure in dogs with primary hypoadrenocorticism.

A study was designed to evaluate the effects of desoxycorticosterone pivalate (DOCP) on blood pressure in 8 dogs with primary hypoadrenocorticism, and to attempt to identify other factors that might suggest overdosage of the drug. In 4 dogs, primary hypoadrenocorticism had been diagnosed immediately before entry of the dog into the study, and the dogs had not received any mineralocorticoid supplementation. In the other 4 dogs, primary hypoadrenocorticism had been diagnosed 1 to 6 years previously, and dogs were being treated with DOCP at the time of entry into the study. In all 8 dogs, DOCP (2.2 mg/kg of body weight, IM) was administered on days 0, 30, 60, and 90 of the study; each dog was examined on days 0, 30, 60, 75, 90, and 105. At the time of each visit, a medical history was obtained, a complete physical examination and serum biochemical analyses were performed, and body weight and blood pressure were measured. Doppler-shift ultrasonic sphygmomanometry was used to indirectly record systemic systolic and diastolic pressures. None of the dogs developed hypernatremia or hypokalemia or any clinical signs suggestive of hypoadrenocorticism during the study. However, in 6 dogs (3 that had not been previously treated with mineralocorticoids and 3 that had been), there was a significant increase in body weight over the course of the study. Compared with baseline (day 0) arterial blood pressure, neither systolic nor diastolic blood pressure was significantly increased during the study, and all systolic and diastolic blood pressure measurements were within reference ranges at all evaluation times.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Insufficiency↗
PubMed1995

Potent effects of low levels of MHC class II-associated invariant chain on CD4+ T cell development.

Invariant chain (Ii)-negative mice exhibit defects in MHC class II assembly and transport that results in reduced levels of surface class II, altered antigen presentation, and inefficient positive selection of CD4+ T cells. Many CD4+ T cells that do mature in Ii-negative mice express a cell surface phenotype consistent with aberrant positive selection or peripheral activation. Reconstitution of these mice with low levels of either the p31 or p41 form of Ii does not restore transport of the bulk of class II or class II surface expression, but surprisingly does restore positive selection as measured by numbers and surface phenotype of CD4+ T cells. Thus, an Ii-dependent process, independent of effects on class II surface density, appears to be required for normal positive selection of CD4+ T cells.

Animals↗
PubMed1995

Insulin therapy.

Insulin therapy is the most important treatment aspect of diabetes mellitus. Since the discovery of insulin in 1921, a variety of insulin formulations have been developed. The purpose of this article is to describe the current sources, formulations, and types of insulins available for therapy of diabetes mellitus in small animals and to provide the veterinarian with guidelines for insulin therapy in dogs and cats.

Animals↗
PubMed1995

Diagnosis and management of insulin resistance in dogs and cats with diabetes mellitus.

Both dogs and cats with diabetes occasionally develop resistance to the action of insulin during treatment. Clinical insulin resistance should be suspected in any animal in which marked hyperglycemia persists throughout the day despite insulin doses of greater than 1.5 U/kg per injection. In a clinical setting it may be difficult to determine the underlying cause for insulin resistance, which makes management difficult. This article reviews the known causes for insulin resistance and outlines recommendations for diagnosis and management of diabetic dogs and cats.

Animals↗
PubMed1994

Preservative effect of aprotinin on canine plasma immunoreactive adrenocorticotropin concentrations.

The susceptibility of adrenocorticotropin (ACTH) in canine blood and plasma to enzymatic degradation has limited the availability of endogenous ACTH assay for veterinary use. This study examined if a proteinase (enzyme) inhibitor, aprotinin, mixed with blood at the time of collection, would limit the loss of immunoreactive (IR) ACTH from canine plasma stored at various temperatures. Blood was collected from laboratory-maintained dogs or dogs with hyperadrenocorticism and placed into EDTA-containing tubes in the presence or absence of aprotinin. Plasma obtained was stored for 4 d at temperatures ranging from -86 degrees C to room temperature (22 degrees C). Results showed that addition of aprotinin preserved IR-ACTH concentrations in plasma stored for 4 d at temperatures < or = 4 degrees C, or in unfrozen plasma stored inside insulated shipping containers containing frozen refrigerant packs. Plasma collected with aprotinin and stored at 22 degrees C showed a slight (17-23%) but significant (P < 0.05) decline in IR-ACTH. Unfrozen plasma collected without aprotinin showed significant (P < 0.05) loss of IR-ACTH during storage under identical conditions. These data indicate that aprotinin has a profound preservative effect upon canine plasma IR-ACTH and that it may be possible to submit unfrozen samples collected with this inhibitor to appropriate reference laboratories for analysis of IR-ACTH.

Adrenocorticotropic Hormone↗
PubMed1992

Glucose tolerance and insulin secretion in spontaneously hyperthyroid cats.

Glucose tolerance and insulin secretion after administration of a glucose load were determined in 11 clinically normal cats and 15 cats with spontaneous hyperthyroidism. In six hyperthyroid cats, a glucose tolerance test was repeated after treatment with radioactive iodine (131I). All cats had similar baseline glucose concentrations. However, the cats with hyperthyroidism had a significantly decreased glucose clearance, which was worse after treatment. Hyperthyroidism also caused a marked increase in basal and glucose-stimulated insulin secretion, which was not improved with treatment. It is concluded that hyperthyroidism in cats may lead to long-lasting alterations of glucose tolerance and insulin secretion which may not be reversed by treatment.

Animals↗
PubMed1992

Effects of synthetic ovine corticotropin-releasing hormone on plasma concentrations of immunoreactive adrenocorticotropin, alpha-melanocyte-stimulating hormone, and cortisol in dogs with naturally acquired adrenocortical insufficiency.

We evaluated the effect of ovine corticotropin-releasing hormone (CRH) on plasma immunoreactive (IR) concentrations of ACTH, alpha-melanocyte-stimulating hormone, and cortisol in 8 dogs with naturally acquired adrenocortical insufficiency. Of the 7 dogs with primary adrenal insufficiency, 6 had markedly high basal plasma IR-ACTH concentrations and exaggerated ACTH responses to CRH administration, whereas 1 dog that was receiving replacement doses of prednisone at the time of testing had normal basal IR-ACTH concentrations and a nearly normal response to CRH. In contrast, the 1 dog with secondary adrenocortical insufficiency had undetectable basal plasma IR-ACTH concentrations, which failed to increase after administration of CRH. Basal plasma alpha-melanocyte-stimulating hormone concentrations in the dogs with adrenal insufficiency were within normal range and were unaffected by CRH administration. In all 8 dogs with adrenal insufficiency, plasma cortisol concentrations were low and did not increase after administration of CRH. Therefore, stimulation with CRH produced 2 patterns of plasma IR-ACTH response when administered to dogs with naturally acquired adrenal insufficiency. Dogs with primary adrenal insufficiency had high basal plasma IR-ACTH concentrations and exaggerated responses to CRH, whereas the dog with secondary adrenal insufficiency had undetectable basal plasma concentrations of IR-ACTH that did not increase after stimulation with CRH.

Adrenal Cortex Hormones↗
PubMed1992

Comparison of the immunoreactive plasma corticotropin and cortisol responses to two synthetic corticotropin preparations (tetracosactrin and cosyntropin) in healthy cats.

Plasma cortisol and immunoreactive (IR)-ACTH responses to 125 micrograms of tetracosactrin and cosyntropin--the formulation of synthetic ACTH available in Europe and the United States, respectively--were compared in 10 clinically normal cats. After administration of tetracosactrin or cosyntropin, mean plasma cortisol concentration reached a peak and plateaued between 60 and 120 minutes, then gradually decreased to values not significantly different from baseline concentration by 5 hours. Mean plasma IR-ACTH concentration reached a maximal value at 15 minutes after administration of tetracosactrin or cosyntropin and was still higher than baseline concentration at 6 hours. Difference between mean plasma cortisol and IR-ACTH concentrations for the tetracosactrin or cosyntropin trials was not significant at any of the sample collection times. Individual cats had some variation in the time of peak cortisol response after administration of either ACTH preparation. About half the cats had peak cortisol concentration at 60 to 90 minutes, whereas the remainder had the peak response at 2 to 4 hours. In general, however, peak cortisol concentration in the cats with delayed response was not much higher than the cortisol concentration at 60 to 90 minutes. Overall, these results indicate that tetracosactrin or cosyntropin induce a comparable, if not identical, pattern of adrenocortical responses when administered to healthy cats.

Adrenocorticotropic Hormone↗
PubMed1992

Serum free and total iodothyronine concentrations in dogs with hyperadrenocorticism.

Serum concentrations of total and free thyroxine (T4 and FT4, respectively), 3,5,3'-triiodothyronine (T3), 3,3',5'-triiodothyronine (reverse T3) were measured in 42 dogs with hyperadrenocorticism, and were compared with values determined in clinically normal dogs. Mean total T4 concentration in dogs with hyperadrenocorticism (14.3 nmol/L) was significantly (P less than 0.001) lower than the normal value (25.7 nmol/L), with 38% of the dogs having low serum T4 concentration. Although 16 (38%) of the 42 dogs with hyperadrenocorticism had a high FT4 fraction, indicative of diminished serum T4 binding, normal FT4 concentration was found in only 6 of the 16 dogs (38%) with low total T4 values. Mean serum T3 concentration in dogs with hyperadrenocorticism (0.79 nmol/L) was also significantly (P less than 0.001) lower than the normal value (1.16 nmol/L), with 39% of the dogs having T3 values below the normal range. Individual T3-to-T4 and T3-to-FT4 ratios, indices of T3 production and/or clearance, were above the normal range in 29 and 24% of dogs with hyperadrenocorticism, respectively. Mean reverse T3 concentration in dogs with hyperadrenocorticism (0.17 nmol/L) was also significantly (P less than 0.001) lower than the normal mean value (0.39 nmol/L), with 48% of the dogs having reverse T3 values below the normal range. Of the 21 dogs in which all iodothyronines were measured, 6 (29%) had undetectable values for all hormones.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocortical Hyperfunction↗
PubMed1992

Comparison of intravenous and intramuscular routes of administering cosyntropin for corticotropin stimulation testing in cats.

Plasma cortisol and immunoreactive (IR)-ACTH responses to 125 micrograms of synthetic ACTH (cosyntropin) administered IV or IM were compared in 10 clinically normal cats. After IM administration of cosyntropin, mean plasma cortisol concentration increased significantly (P less than 0.05) within 15 minutes, reached maximal concentration at 45 minutes, and decreased to values not significantly different from baseline concentration by 2 hours. After IV administration of cosyntropin, mean plasma cortisol concentration also increased significantly (P less than 0.05) at 15 minutes, but in contrast to IM administration, the maximal cortisol response took longer (75 minutes) and cortisol concentration remained significantly (P less than 0.05) higher than baseline cortisol concentration for 4 hours. Mean peak cortisol concentration (298 nmol/L) after IV administration of cosyntropin was significantly (P less than 0.05) higher than the peak value (248 nmol/L) after IM administration. All individual peak plasma cortisol concentrations and areas under the plasma cortisol response curve were significantly (P less than 0.05) higher after IV administration of cosyntropin than after IM administration. Mean plasma IR-ACTH concentration returned to values not statistically different from baseline by 60 minutes after IM administration of cosyntropin, whereas IR-ACTH concentration still was higher than baseline concentration 6 hours after IV administration. Peak plasma IR-ACTH concentration and area under the plasma IR-ACTH response curve also were significantly (P less than 0.05) higher after IV administration of cosyntropin. Results of the study confirmed that IV administration of cosyntropin induces significantly (P less than 0.05) greater and more prolonged adrenocortical stimulation than does IM administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenal Cortex↗
PubMed1991

Pharmacokinetics of methimazole in normal cats and cats with hyperthyroidism.

The intravenous and oral disposition of the antithyroid drug methimazole was determined in 10 clinically normal cats and nine cats with naturally occurring hyperthyroidism. After intravenous administration of 5 mg methimazole, the mean residence time was significantly (P less than 0.05) shorter in the cats with hyperthyroidism than in the normal cats, but there was no significant difference between the mean values for total body clearance (CL), steady state volume of distribution (Vdss), terminal elimination rate constant (ke), or serum terminal half-life (t1/2) in the two groups of cats. After oral administration, the mean bioavailability of methimazole was high in both the normal cats (77.6 per cent) and cats with hyperthyroidism (79.5 per cent). The values for mean residence time, ke and serum terminal t1/2 after oral dosing were significantly shorter in the cats with hyperthyroidism than in the normal cats. However, after oral administration of methimazole there were no significant differences between the mean values for CL, Vdss, bioavailability and maximum serum concentrations or the time for maximal concentrations to be reached in the two groups of cats. Overall, most pharmacokinetic parameters for methimazole were not altered by the hyperthyroid state. However, the cats with hyperthyroidism did show a trend toward faster elimination of the drug compared with the normal cats, similar to what has been previously described for the antithyroid drug propylthiouracil in cats. These results also indicate that methimazole is well absorbed when administered orally and has a higher bioavailability than that of propylthiouracil in cats with hyperthyroidism.(ABSTRACT TRUNCATED AT 250 WORDS)

Absorption↗
PubMed1991

Autonomous growth and function of cultured thyroid follicles from cats with spontaneous hyperthyroidism.

Spontaneous feline hyperthyroidism is a unique experimental model of toxic nodular goiter. To determine whether feline toxic goiter is caused by extrathyroidal stimulating factors or by the intrinsic autonomy of follicular cells, primary cultures of enzymatically dissociated follicles from 15 hyperthyroid cat goiters and from 3 normal cat thyroid glands were embedded in collagen gels. Growth and function in chemically defined media were assessed by autoradiography after double labeling with 3H-thymidine and 131I-Na. Iodine organification in follicles from normal glands was TSH dependent, but intense radioiodine organification occurred in follicles from hyperfunctioning goiters even in the absence of TSH. Similarly, twice as many follicular cells of hyperfunctioning thyroid tissue, maintained without TSH in the medium, were labeled after exposure to 3H-thymidine than in follicles from normal glands. The results strongly suggest that intrinsic alterations of cell function lead to autonomy of follicular growth and function and subsequently to the development of hyperplastic nodules, causing thyrotoxicosis. The reason for the focal nature of the disease remains an unresolved challenge. Further investigation using this model may further understanding of the growth of autonomous endocrine tumors.

Animals↗
PubMed1991

Pharmacokinetics of intravenous and oral methimazole following single- and multiple-dose administration in normal cats.

The pharmacokinetics of methimazole (MMI) administered intravenously and orally were determined in six adult domestic shorthaired cats. There was no significant difference between mean serum MMI concentrations after oral and i.v. administration by 30 min post-MMI administration, indicating relatively rapid and complete absorption of the drug. The bioavailability of MMI ranged from 27% to 100% (mean = 81.1 +/- 11.4%). The mean serum elimination half-life was 6.6 +/- 2.0 h, with a wide range of values (1.9 h to 15.1 h). After repeat i.v. administration of MMI following 2 weeks of oral administration of the drug, no significant difference was found between mean serum concentrations after single-dose and multiple-dose administration. No significant change in serum elimination half-life or total body clearance was found after multiple-dose administration of MMI. Two cats with the longest half-lives (9.9 h and 15.1 h), however, did exhibit markedly shorter t1/2 values (3.5 h and 3.3 h, respectively) after multiple-dose administration. Values for central and steady state volumes of distribution also decreased after multiple-dose administration, possibly indicating saturation of thyroid uptake of MMI with chronic administration. These results indicate that MMI has good oral bioavailability and has a longer mean serum elimination half-life than propylthiouracil, the other anti-thyroid drug that has been evaluated in cats. Although no significant change in mean values occurred after multiple-dose administration of MMI, drug-induced acceleration of metabolism may occur in some cats after long-term MMI administration.

Absorption↗
PubMed1991

Plasma free cortisol concentrations in dogs with hyperadrenocorticism.

Unbound or free cortisol constitutes a small fraction of total plasma cortisol, but is believed to represent the biologically active portion of this circulating glucocorticoid. We tested the hypothesis that the percentage free cortisol was altered in plasma from dogs with hyperadrenocorticism, which could account for a greater target tissue response to this circulating hormone. The percentage free cortisol in plasma samples from human beings, healthy dogs, and dogs with hyperadrenocorticism was estimated, using centrifugal ultrafiltration-dialysis. Total cortisol concentrations were determined by use of radioimmunoassay. Total cortisol concentrations appeared greater in plasma from human beings than in plasma from either group of dogs. However, the percentage free cortisol was lower in plasma from human beings, resulting in a calculated concentration of free cortisol that was quite similar between plasma from human beings and healthy dogs. Total plasma cortisol concentrations were greater (P less than 0.01) in samples from dogs with hyperadrenocorticism (190 +/- 113 nmol/L; mean +/- SD) than in healthy dogs (102 +/- 85 nmol/L), but the percentage free cortisol was not different between these 2 groups (dogs with hyperadrenocorticism, 16 +/- 9%; healthy dogs, 13 +/- 6%). However, plasma free cortisol concentrations (product of total and the percentage of free cortisol) were greater (P less than 0.01) in samples from dogs with hyperadrenocorticism (36 +/- 41 nmol/L) than in those from healthy dogs (16 +/- 9 nmol/L). Significant (P less than 0.001) positive linear relationships were found between total cortisol concentrations and percentage free cortisol in plasma samples from healthy dogs and dogs with hyperadrenocorticism.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗