Objective—To evaluate the effect of trilostane on
serum concentrations of aldosterone, cortisol, and
potassium in dogs with pituitary-dependent hyperadrenocorticism
(PDH), compare the degree of reduction
of aldosterone with that of cortisol, and compare
aldosterone concentrations of healthy dogs with
those of dogs with PDH.
Animals—17 dogs with PDH and 12 healthy dogs.
Procedure—For dogs with PDH, the initial dose of
trilostane was selected in accordance with body
weight. A CBC count, serum biochemical analyses,
and ACTH stimulation tests were performed in each
dog. Dogs were evaluated 1, 3 to 4, 6 to 8, and 10 to
12 weeks after initiation of treatment. Healthy dogs
were evaluated only once.
Results—Serum aldosterone concentrations before
ACTH stimulation did not change significantly after initiation
of treatment with trilostane. At each evaluation
after initiation of treatment, serum aldosterone concentrations
after ACTH stimulation were significantly
lower than corresponding concentrations before initiation
of treatment. The overall effect of trilostane on
serum aldosterone concentration was less pronounced
than the effect on serum cortisol concentration.
Median potassium concentrations increased
slightly after initiation of treatment with trilostane.
Dogs with PDH had significantly higher serum aldo
sterone concentrations before and after ACTH stimulation
than healthy dogs.
Conclusions and Clinical Relevance—Treatment
with trilostane resulted in a reduction in serum cortisol
and aldosterone concentrations in dogs with PDH,
although the decrease for serum aldosterone concentration
was smaller than that for serum cortisol concentration.
There was no correlation between serum
concentrations of aldosterone and potassium during
treatment. (Am J Vet Res 2004;65:1245–1250)
Objective—To evaluate the use of recombinant human (rh) thyroid-stimulating hormone (TSH) in dogs with suspected hypothyroidism.
Animals—64 dogs with clinical signs of hypothyroidism.
Procedures—Dogs received rhTSH (75 μg/dog, IV) at a dose independent of their body weight. Blood samples were taken before and 6 hours after rhTSH administration for determination of total serum thyroxine (T4) concentration. Dogs were placed into 1 of 3 groups as follows: those with normal (ie, poststimulation values indicative of euthyroidism), unchanged (ie, poststimulation values indicative of hypothyroidism; no thyroid gland stimulation), or intermediate (ie, poststimulation values between unchanged and normal values) post-TSH T4 concentrations. Serum canine TSH (cTSH) concentration was determined in prestimulation serum (ie, before TSH administration).
Results—14, 35, and 15 dogs had unchanged, normal, and intermediate post-TSH T4 concentrations, respectively. Basal T4 and post-TSH T4 concentrations were significantly different among groups. On the basis of basal serum T4 and cTSH concentrations alone, 1 euthyroid (normal post-TSH T4, low basal T4, and high cTSH concentrations) and 1 hypothyroid dog (unchanged post-TSH T4 concentration and low to with-in reference range T4 and cTSH concentrations) would have been misinterpreted as hypothyroid and euthyroid, respectively. Nine of the 15 dogs with intermediate post-TSHT4 concentrations had received medication known to affect thyroid function prior to the test, and 2 of them had severe nonthyroidal disease.
Conclusions and Clinical Relevance—The TSH-stimulation test with rhTSH is a valuable diagnostic tool to assess thyroid function in selected dogs in which a diagnosis of hypothyroidism cannot be based on basal T4 and cTSH concentrations alone.
Objective—To evaluate whether use of recombinant human (rh) thyroid-stimulating hormone (TSH) induces equivalent stimulation, compared with bovine TSH (bTSH), and to evaluate activity of rhTSH in dogs of various large breeds.
Animals—18 healthy research Beagles and 20 healthy client-owned dogs of various breeds with body weight > 20 kg.
Procedures—The 18 Beagles were randomly assigned to 3 groups, and each dog received either 75 μg of rhTSH, IM or IV, or 1 unit of bTSH, IM, respectively, in a crossover design. The 20 client-owned dogs received 75 μg of rhTSH, IV. Blood samples were taken before and 6 hours after TSH administration for determination of total serum thyroxine (T4) concentration. Additional blood samples were taken after 2 and 4 hours in Beagles that received rhTSH, IM.
Results—There was a significant increase in T4 concentration in all dogs, but there were no differences between values obtained after administration of bTSH versus rhTSH or IV versus IM administration of rhTSH. Although there was a significant difference in age and body weight between Beagles and non-Beagles, there was no difference in post-TSH simulation T4 concentration between the 2 groups.
Conclusions and Clinical Relevance—Results indicated an equivalent biological activity of rhTSH, compared with bTSH. Use of 75 μg of rhTSH, IV, did not induce a different magnitude of stimulation in large-breed dogs, compared with Beagles. Euthyroidism was confirmed if post-TSH simulation T4 concentration was ≥ 2.5 μg/dL and at least 1.5 times basal T4 concentration.
PROCEDURES Each dog underwent 3 iohexol-injection protocols (700 mg of iodine/kg administered at a constant rate over 20 seconds, 700 mg of iodine/kg administered following an exponentially decelerated injection over 20 seconds, and 350 mg of iodine/kg at a constant rate over 10 seconds) during dynamic, whole renal-volume CT in randomized order with an interval of ≥ 7 days between experiments. Values of GFR determined from Patlak plots derived by use of 4 measurement techniques (standard transverse section, optimized transverse section, dorsal reconstruction, and volume calculation techniques) were compared.
RESULTS The measurement technique influenced the mean ± SD GFR results (standard transverse section technique, 2.49 ± 0.54 mL/kg/min; optimized transverse section technique, 2.72 ± 0.52 mL/kg/min; dorsal reconstruction technique, 3.00 ± 0.60 mL/kg/min, and volume calculation technique, 2.48 ± 0.51 mL/kg/min). The lower iodine dose resulted in a significantly higher GFR value (3.00 ± 0.65 mL/kg/min), compared with that achieved with either higher dose administration (constant rate injection, 2.54 ± 0.45 mL/kg/min and exponentially decelerated injection, 2.47 ± 0.48 mL/kg/min).
CONCLUSIONS AND CLINICAL RELEVANCE In healthy Beagles, the CT-derived GFR measurements obtained after injection of a full dose of contrast medium were reduced, compared with measurements obtained after injection of a half dose. This finding is important with regard to potential nephrotoxicosis in dogs with impaired renal function and for GFR measurement with CT-contrast medium protocols.
OBJECTIVE To assess the effects of 3 contrast medium injection techniques on attenuation values for canine adrenal glands during contrast-enhanced CT.
ANIMALS 9 healthy Beagles.
PROCEDURES 3 protocols were evaluated in a randomized cross-over design study: 700 mg of iodine/kg at a constant injection rate over 20 seconds (full-dose constant rate), the same dose at a rate following an exponential decay curve over 20 seconds (full-dose decelerated rate), and 350 mg of iodine/kg at a constant injection rate over 10 seconds (half-dose constant rate). Multislice CT images were obtained before and at predetermined time points after the start of contrast medium injection.
RESULTS Median peak attenuation values were 129, 133, and 87 Hounsfield units with the full-dose constant rate, full-dose decelerated rate, and half-dose constant rate injection protocols, respectively. Peak attenuation differed significantly between the full-dose constant rate and half-dose constant rate injection protocols and between the full-dose decelerated rate and half-dose constant rate injection protocols. Median time to peak attenuation did not differ significantly among injection methods and was 30, 23, and 15 seconds for the full-dose constant rate, full-dose decelerated rate, and half-dose constant rate injections, respectively.
CONCLUSIONS AND CLINICAL RELEVANCE The dose of contrast medium and the timing of postinjection CT scanning were main determinants of peak attenuation for adrenal glands in healthy dogs; effects of the 3 injection protocols on attenuation were minor. The exponentially decelerated injection method was subjectively complex. A constant injection protocol delivering 700 mg of iodine/kg over 20 seconds, with scans obtained approximately 30 seconds after starting contrast medium injection, provided images with maximum adrenal gland attenuation values. (Am J Vet Res 2016;77:144–150)