Thyroid function tests in dogs using radioimmunoassay kits

Thyroid function has been assessed using radioimmunoassay kits for total and free thyroxine (T4). A radioimmunoassay kit for total T4, designed for human samples, was unable to detect total T4 in 35 per cent of normal canine serum tested, due to the kit being designed to measure total T4 over the normal human range which is four times the canine normal range. The canine normal range for free T4 (7.5–50 pmol/1) was found to be of the same order as the human range and therefore a free T4 kit was suitable for measuring the free hormone in dogs. In response to thyroid stimulating hormone in normal dogs, total T4 rose 6.2 times whereas free T4 rose only 2.6 times. Hypothyroid animals could be distinguished from normal dogs by free T4 assay whereas they were indistinguishable from many normal dogs by total T4 assay. Response to thyroid stimulating hormone was used to confirm hypothyroidism, but also revealed one animal with normal total and free T4 but which had a negligible response on stimulation.     

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.     

Ultrasonographic visualization of the adrenal glands of healthy ferrets and ferrets with hyperadrenocorticism

A protocol was developed to compare the ultrasonographic characteristics of the adrenal glands of 21 healthy ferrets and 37 ferrets with hyperadrenocorticism. By using specific landmarks, the adrenal glands were imaged in 97% of the cases. The adrenal glands of ferrets with hyperadrenocorticism had a significantly increased thickness, with changes in shape, structure, and echogenicity compared to the adrenal glands of healthy ferrets. Based on the findings of the study, adrenal glands may be classified as abnormal when they have a rounded appearance, increased size of the cranial/caudal pole (thickness >3.9 mm), a heterogeneous structure, increased echogenicity, and/or signs of mineralization.     

Effects of long-term phenobarbital treatment on the thyroid and adrenal axis and adrenal function tests in dogs

Phenobarbital can interfere with the thyroid axis in human beings and rats by accelerating hepatic thyroxine metabolism because of enzyme induction. In human beings, it also can interfere with the low-dose dexamethasone suppression test (LDDST) used to assess adrenal function by accelerating dexamethasone metabolism. This effect can cause a lack of suppression of pituitary ACTH and subsequent adrenal cortisol release after dexamethasone administration. The effects of phenobarbital on the thyroid axis, the adrenal axis, and adrenal function tests were prospectively investigated in 12 normal, adult dogs. Phenobarbital was administered at 5 mg per kilogram of body weight (range, 4.8–6.6 mg/kg) PO q12h for 29 weeks, resulting in therapeutic serum concentrations (20–40 μg/mL). Serum total thyroxine (TT4), free thyroxine (FT4) by equilibrium dialysis, total triiodothyronine (TT3), thyrotropin (TSH), and cholesterol were determined before and during phenobarbital treatment. LDDST, ACTH stimulation tests, and ultra-sonographic evaluation of the adrenal glands were performed before and during treatment. TT4 and FT4 decreased significantly ( P ≤ .05), TT3 had minimal fluctuation, TSH had only a delayed compensatory increase, and cholesterol increased during phenobarbital treatment. The delayed increase in TSH, despite persistent hypothyroxinemia, suggests that accelerated hepatic thyroxine elimination may not be the only effect of phenobarbital on the thyroid axis. There was no significant effect of phenobarbital on either of the adrenal function tests. With the methods employed, we did not find any effects of the drug on the hormonal equilibrium of the adrenal axis.     

Composition of cerebrospinal fluid in clinically normal adult ferrets

OBJECTIVE: To determine the protein and cellular composition of CSF in healthy adult ferrets. ANIMALS: 42 clinically normal adult ferrets. PROCEDURE: CSF samples were collected from the cerebellomedullary cistern of anesthetized ferrets by use of disposable 25-gauge, 1.6-cm-long hypodermic needles. Samples were processed within 20 minutes after collection. The number of WBCs and RBCs per microliter of CSF was counted by use of a hemacytometer. The total protein concentration was determined by use of an automated chemistry analyzer. RESULTS: Total WBC counts (range, 0 to 8 cells/microL; mean, 1.59 cells/microL) in CSF of ferrets were similar to reference range values obtained for CSF from other species. Twenty-seven CSF samples had <100 RBCs/microL (mean, 20.3 RBCs/microL). A small but significant effect of blood contamination on WBC counts was found between the 27 CSF samples with <100 RBCs/microL and the remaining samples. Protein concentrations in CSF of ferrets (range, 28.0 to 68.0 mg/dL; mean, 31.4 mg/dL) were higher than has been reported for the CSF of dogs and cats. A significant effect of blood contamination on the CSF protein concentration was not found. CONCLUSION AND CLINICAL RELEVANCE: We have established reference range values for WBC counts and protein concentrations in CSF from healthy adult ferrets that may be useful in the clinical investigation of CNS disease. Results of our study indicate that the WBC count is significantly affected by blood contamination of the CSF sample.     

Effects of phenylbutazone and anabolic steroids on adrenal and thyroid gland function tests in healthy horses

Adrenal and/or thyroid gland function tests were evaluated in horses at various times during short-term therapy with phenylbutazone, stanozolol, and boldenone undecylenate. There were no significant treatment or time effects on mean basal plasma cortisol concentrations in horses during treatment with the following: phenylbutazone, given twice daily (4 to 5 mg/kg, IV) for 5 days; stanozolol, given twice weekly (0.55 mg/kg, IM) for 12 days; boldenone undecylenate, given twice weekly (1.1 mg/kg, IM) for 12 days; or nothing. There was no significant effect of phenylbutazone treatment on the changes in plasma cortisol concentration during the combined dexamethasone-suppression adrenocorticotropic hormone (ACTH)-stimulation test. Plasma cortisol concentration was significantly decreased from base line at 3 hours after dexamethasone administration and was significantly increased from base line at 2 hours after ACTH in all horses (P less than 0.05). Likewise, the stimulation of basal plasma cortisol concentrations at 2 hours after administration of ACTH (P less than 0.05) was not affected by treatment with stanozolol or boldenone undecylenate. There were no significant treatment effects on mean basal plasma concentrations of thyroxine (T4) or triiodothyronine (T3) among horses during the following treatments: stanozolol, given twice weekly (0.55 mg/kg, IM) for 12 days; boldenone undecylenate, given twice weekly (1.1 mg/kg, IM) for 12 days; or nothing. There was a significant time effect on overall mean basal plasma T4 and T3 concentrations (P less than 0.05): plasma T4 was lower on day 8 than on days 1, 10, and 12; plasma T3 was higher on day 8 than on days 4 and 12.(ABSTRACT TRUNCATED AT 250 WORDS)     

Thyroid hormone periodicity in healthy adult geldings

Serum samples were collected from 10 healthy geldings every 4 h for three consecutive days and the triiodothyronine (T3) and thyroxine (T4) concentrations determined by radioimmunoassay. There were significant differences in the hormone concentrations related to time. The mean (+/- sd) T3 concentration peaked around 08.00 h at a level (54.06 +/- 14.02 ng/dl) significantly (P less than .001) higher than the lowest concentration (38.71 +/- 10.81 ng/dl) around midnight. Although the highest mean T3 level was 08.00 h, this value was not significantly different from the noon and 16.00 h levels. Likewise, the mean T3 level at midnight was not significantly different from the 20.00 h and 04.00 h levels, resulting in a plateau from 08.00 h to 16.00 h and a trough from 20.00 h to 04.00 h. The mean (+/- sd) T4 concentration peaked around 16.00 h at a level (2.43 +/- .81 micrograms/dl) significantly (P less than .01) higher than the lowest concentration (1.79 +/- .63 micrograms/dl) around 04.00 h.     

Thyroid function and pregnancy status in broodmares

OBJECTIVE: To determine whether thyroid function was associated with pregnancy status in broodmares. DESIGN: Prospective study. ANIMALS: 79 Thoroughbred and Standardbred broodmares between 2 and 22 years old. PROCEDURE: Serum triiodothyronine (T3) concentration was measured before and 2 hours after i.v. administration of thyrotropin releasing hormone (TRH), and serum thyroxine (T4) concentration was measured before and 4 hours after TRH administration. Pregnancy status was monitored by means of transrectal ultrasonography beginning 16 days after ovulation. RESULTS: Baseline T3 and T4 concentrations varied widely. In all mares, serumT3 concentration increased in response to TRH administration. Serum T4 concentration increased in response toTRH administration in all but 2 mares. Pregnancy rate was 76%. Baseline and stimulated serum T3 and T4 concentrations were not significantly different between mares that became pregnant and those that did not. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that decreased thyroid function is uncommon in mares and poor thyroid function is not a common cause of infertility. Thus, the practice of indiscriminately treating broodmares with thyroid hormone to enhance fertility appears questionable at this time.     

Determination of thyroxine, triiodothyronine, and cortisol changes during simultaneous adrenal and thyroid function tests in healthy dogs

Changes in thyroxine (T4), triiodothyronine (T3), and cortisol during a combined adrenal (dexamethasone suppression/adrenocorticotrophic hormone response test) and thyroid function tests (thyroid-stimulating hormone [TSH] response test) were determined in 20 healthy hospitalized pet dogs. The effect of dexamethasone on T4 and T3 changes was evaluated during a simultaneous TSH response/dexamethasone suppression adrenocorticotrophic hormone response test. Greater ranges in basal cortisol concentrations and slower changes after dexamethasone was administered were observed in healthy pet dogs kenneled in a hospital setting than those reported for conditioned laboratory dogs. Pet dogs were observed to demonstrate cortisol suppression more reliably at 4 hours than at 2 hours after dexamethasone was administered. Dexamethasone had no effect on the response to TSH as assessed by T4 and T3 assays, thus supporting the validity of combining adrenal and thyroid response tests in a 5-hour period.     

Effect of 131I-induced hypothyroidism on indices of reproductive function in adult male dogs

Hypothyroidism has been cited as a cause of infertility, abnormal semen quality, and poor libido in people and animals. The purpose of this study was to evaluate the effect of hypothyroidism on variables indicative of reproductive function in adult male dogs. Nine normal dogs were randomly assigned to 2 groups. Hypothyroidism was induced with 131I in 6 dogs. Three dogs remained untreated, normal, and euthyroid. Thyroid hormone concentrations, body weight, clinical signs, and reproductive function were determined for each dog every 3 months for 2 years. Reproductive function was assessed by determining daily sperm output, total scrotal width, spermatozoal motility and morphology, libido, and serum testosterone and luteinizing hormone concentration responses to exogenous gonadotropin-releasing hormone. The 131I-treated dogs developed clinical and laboratory signs of hypothyroidism. In the hypothyroid dogs, serum concentrations of thyroid hormones were consistently below the reference range and were significantly lower than that in the euthyroid dogs. There was no difference in reproductive function between the hypothyroid and euthyroid dogs. The results of this study show that 131I-induced hypothyroidism does not affect indices of reproductive function in adult male dogs.     

Thyroid function testing in Greyhounds.

OBJECTIVE: To evaluate thyroid function in healthy Greyhounds, compared with healthy non-Greyhound pet dogs, and to establish appropriate reference range values for Greyhounds. ANIMALS: 98 clinically normal Greyhounds and 19 clinically normal non-Greyhounds. PROCEDURES: Greyhounds were in 2 groups as follows: those receiving testosterone for estrus suppression (T-group Greyhounds) and those not receiving estrus suppressive medication (NT-group Greyhounds). Serum thyroxine (T4) and free thyroxine (fT4) concentrations were determined before and after administration of thyroid-stimulating hormone (TSH) and thyroid-releasing hormone (TRH). Basal serum canine thyroid stimulating hormone (cTSH) concentrations were determined on available stored sera. RESULTS: Basal serum T4 and fT4 concentrations were significantly lower in Greyhounds than in non-Greyhounds. Serum T4 concentrations after TSH and TRH administration were significantly lower in Greyhounds than in non-Greyhounds. Serum fT4 concentrations after TSH and TRH administration were significantly lower in NT-group than T-group Greyhounds and non-Greyhounds. Mean cTSH concentrations were not different between Greyhounds and non-Greyhounds. CONCLUSIONS AND CLINICAL RELEVANCE: Previously established canine reference range values for basal serum T4 and fT4 may not be appropriate for use in Greyhounds. Greyhound-specific reference range values for basal serum T4 and fT4 concentrations should be applied when evaluating thyroid function in Greyhounds. Basal cTSH concentrations in Greyhounds are similar to non-Greyhound pet dogs.     

Surgical treatment and long-term outcome of ferrets with bilateral adrenal tumors or adrenal hyperplasia: 56 cases (1994-1997).

OBJECTIVE: To determine signalment, clinical signs, concurrent diseases, response to surgical treatment, and long-term outcome of ferrets with bilateral adrenal tumors or adrenal hyperplasia. DESIGN: Retrospective study. ANIMALS: 56 ferrets with bilateral adrenal tumors or adrenal hyperplasia confirmed histologically following subtotal bilateral adrenalectomy. PROCEDURE: Medical records of all ferrets with bilateral adrenal tumors or hyperplasia examined between 1994 and 1997 were reviewed. Ferrets underwent a subtotal bilateral adrenalectomy or a unilateral adrenalectomy initially, followed by a unilateral subtotal adrenalectomy when tumors or hyperplasia later developed on the contralateral adrenal gland. A long-term follow-up of a minimum of 18 months after final adrenal gland surgery was obtained by examination of medical records and follow-up telephone conversations. RESULTS: Clinical signs of hyperadrenocorticism included bilaterally symmetric alopecia, return to male sexual behavior in castrated male ferrets, or swollen vulva in spayed female ferrets. Surgical treatment of bilateral adrenal disease by subtotal bilateral adrenalectomy (or unilateral adrenalectomy followed by contralateral unilateral subtotal adrenalectomy) was effective with a mortality rate of < 2%. Only 3 (5%) ferrets required glucocorticoid or mineralocorticoid replacement following subtotal bilateral adrenalectomy. Recurrence after bilateral adrenalectomy was 15% with a mean long-term follow-up period of 30 months. CONCLUSIONS AND CLINICAL RELEVANCE: Bilaterally symmetric alopecia, return to male sexual behavior in castrated male ferrets, or swollen vulva in spayed female ferrets are indicative of adrenal tumors or adrenal hyperplasia in ferrets. Surgical treatment of bilateral adrenal disease by subtotal bilateral adrenalectomy is effective, with a low rate of complications and postoperative recurrence rate.