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-threatening thyrotoxicosis. 2 Among the various treatment modalities for FHT, methimazole administration, 2 – 4 radioactive iodine, 2 – 4 iodine-restricted diets, 5 and thyroidectomy 6 – 9 have been commonly applied. In general, radioactive iodine is selected as part of
have evaluated the perioperative complications and outcomes associated with unilateral thyroidectomy in dogs, and those studies generally did not involve large numbers of dogs. Often, research has been limited in focus to specific procedures (eg
T hyroidectomy is the recommended treatment for dogs with nonmetastatic thyroid carcinoma in which the thyroid mass is mobile. 1–3 However, thyroidectomy can be a challenging surgical procedure because of the vascularity of thyroid carcinomas and
Abstract
Objective
To investigate hemodynamic effects of thyroidectomy in horses at rest.
Animals
6 healthy aged Quarter Horse mares.
Procedure
Horses were monitored for 5 months before and 4 weeks after thyroidectomy and for an additional 4 weeks after administration of thyroid hormone supplement (2.5 µg of thyroxine/kg of body weight, PO, q 12 h, and 0.6 µg of triiodothyronine/kg, PO, q 12 h). Responses to thyroid-stimulating hormone (TSH) were measured before and 4 weeks after thyroidectomy. Other variables monitored daily were resting rectal temperature (T), heart rate (HR), respiratory rate (RR), and body weight (BW), Monthly cardiac output (Q), blood volume (BV), plasma volume (PV), standard electrocardiographic measures, systolic and right ventricular blood pressure, and HR responses were determined after IV administration of isoproterenol and phenylephrine. Variables were analyzed by use of repeated-measures ANOVA.
Results
Complete thyroidectomy was confirmed by minimal response to TSH 4 weeks after surgery. Resting HR, RR, T, Q, and β-adrenergic responsiveness to isoproterenol decreased significantly after thyroidectomy. Resting T, Q, and β-adrenergic responsiveness increased after administration of supplement and was not significantly different from euthyroid values. Blood volume and PV increased significantly after thyroidectomy but did not return to euthyroid values despite administration of supplement. Response to phenylephrine was minimally different between treatments.
Conclusions and Clinical Relevance
Thyroidectomy in horses caused decreased resting HR, RR, T, Q, and isoproterenol responsiveness and increased BV, PV, PQ interval, and QT interval corrected for HR. Some of these surgically induced changes appeared to be partially reversed by administration of thyroid hormone supplement. (Am J Vet Res 1999;60:14–21)
the salivary glands (dotted arrow). Thyroidectomy of both lobes was performed 1 week later. A routine approach (ventral midline caudal to the larynx) was used. Cefazolin i (22 mg/kg [10 mg/lb], IV, once) was administered perioperatively as
differences in behavior based on the cell of origin are well established in human thyroid cancer, 7 , 8 the impact of tissue type is unclear in canine thyroid carcinoma. Clinically, many dogs fare well following thyroidectomy, with median survival times of 17
heart base mass excisions, are also associated with a risk for life-threatening hemorrhage. 10–13 Additionally, extra-abdominal or extrathoracic surgeries known for increased risk of hemorrhage include neoplastic thyroidectomy, rhinotomy, and perineal
radiographs, and no evidence of local invasion of vascular or other surrounding tissues was seen during abdominal ultrasonography. Therefore, surgery was scheduled for LA on the left side concurrent with a right thyroidectomy and parathyroidectomy. To increase
Abstract
Objective
To measure and compare concentrations of selected blood lipids before and after thyroidectomy in horses.
Animals
5 healthy adult mares.
Procedure
Mares were confirmed to be euthyroid. Thyroidectomy was performed, and hypothyroidism was confirmed. Selected blood lipid variables were measured before hypothyroidism was induced and weekly for 4 weeks after induction. Plasma concentrations of very low-density lipoprotein (VLDL), low-density lipoprotein (LDL), serum triglyceride (TG), total cholesterol (TC), and nonesterified fatty acid (NEFA) were measured. The composition of VLDL and LDL also was examined.
Results
Mean plasma concentrations of VLDL and LDL increased significantly after thyroidectomy. By 4 weeks after thyroidectomy, a ninefold increase in mean plasma concentration of VLDL and a threefold increase in LDL, compared with baseline values, were detected. After thyroidectomy, mean percentage of TG in VLDL increased significantly, whereas free cholesterol and cholesterol ester content decreased. Mean percentage of TG in LDL also increased by 3 to 4 weeks after thyroidectomy. Serum concentrations of TG and TC increased, whereas serum NEFA concentration decreased.
Conclusions
Hypothyroidism significantly alters blood lipid concentrations of horses. After thyroidectomy, markedly high VLDL concentration, appearance of TG-rich VLDL, increased serum concentrations of TG and TC, and decreased blood concentration of NEFA were evident.
Clinical Relevance
Examination of blood lipid concentrations of horses may be useful for detecting naturally acquired hypothyroidism. (Am J Vet Res 1999; 60:730-733)
Abstract
Objective—To compare kinetics of the metabolism of very-low-density lipoprotein (VLDL) apolipoprotein B (apoB) before and after thyroidectomy in mares.
Animals—5 healthy adult mares.
Procedure—Thyroidectomy was performed in euthyroid mares. Kinetics of VLDL apoB metabolism were measured before and after thyroidectomy by use of a bolus IV injection of 5,5,5-2H3 (98%) leucine (5 mg/kg) and subsequent isolation of labeled amino acid from plasma and VLDL. Labeled leucine was quantified by use of gas chromatography-mass spectrometry. Production rate (PR), delay time, and fractional catabolic rate (FCR) were calculated for the 2 forms of equine VLDL, apoB-48 VLDL, and apoB-100 VLDL. Plasma lipid concentrations were measured, and VLDL composition was determined.
Results—Physical appearance of horses was not altered by thyroidectomy. Significantly lower mean blood concentrations of thyroid hormones and nonesterified fatty acids were detected following thyroidectomy. Mean percentage of free cholesterol in VLDL was significantly higher after thyroidectomy. Mean plasma VLDL concentration or kinetics of apoB-48 or apoB-100 were not significantly altered by thyroidectomy. Mean ± SEM PR was significantly lower (8.70 ± 1.61 mg/kg/d) and mean delay time significantly longer (1.58 ± 0.12 hours) for apoB-48 VLDL in euthyroid mares, compared with values for thyroidectomized mares (16.15 ± 2.24 mg/kg/d and 0.93 ± 0.10 hours, respectively).
Conclusions and Clinical Relevance—Hypothyroidism did not significantly alter plasma VLDL concentrations or kinetics of VLDL apoB metabolism. Metabolism of apoB-48 VLDL differed significantly from that of apoB-100 VLDL in euthyroid mares. (Am J Vet Res 2003;64:1052–1058)
