Thyroparathyroidectomy procedures and thyroxine levels in the chinchilla.

Lab Animal Facilities,1 and Center for Hearing and Deafness,2 University at Buffalo, Buffalo, New York; Psychology Department, Western Illinois University, Macomb, Illinois3. *Corresponding author. !e thyroid gland regulates growth, development, and energy metabolism and is especially important in the development of the central nervous system in the fetus (15). Removal of the thyroid gland creates a hypothyroid model that can be used to delineate the role of thyroid hormones in various physiological functions such as memory, reproduction, immunity, endocrinology, metabolism, and cardiology (14). !e parathyroid glands, embedded in the dorsal surface of the thyroid gland, play a crucial role in calcium and phosphorus metabolism (1). Because the parathyroid glands are not easily separated from the thyroid gland in some species, both glands typically are removed together in a procedure referred to as thyroparathyroidectomy. Although thyroparathyroidectomies have been performed in rats, guinea pigs, rabbits, dogs, and pigs (1), descriptions of the procedure have not been documented for the chinchilla (Chinchilla laniger). Researchers from our university required a hypothyroid chinchilla model to determine the effects of thyroid hormone deficiency on hearing sensitivity and susceptibility to hearing loss caused by noise and ototoxic drugs. Chinchillas are commonly used in hearing research because they have a large tympanic bulla that is easily accessed for histological analyses of inner ear tissue, very low incidence of middle ear infections, and a range of hearing closer to the human range than any other rodent (16). !yroxine (3,5,3’,5’-tetraiodothyronine, or T4) is the principal hormone secreted by the thyroid gland. We measured T4 levels prior to surgery and at various times after surgery to ensure that a hypothyroid model was achieved and to determine the stability of the hypothyroid state over time. To our knowledge, the T4 levels of the chinchilla have not been documented; therefore we report the T4 levels in chinchillas prior to surgery along with basal levels in several other species for reference. Because there have been no previous descriptions of thyroparathyroidectomy in chinchillas, this paper will provide useful technical information on the surgical procedure in the chinchilla, avoidance of complications, and postoperative management in this species. !yroid and embedded parathyroid glands were surgically removed (thyroparathyroidectomized) from adult chinchillas (Chinchilla laniger) to create an animal model of hypothyroidism. !yroxine (T4) levels were measured at the time of surgery and one or two times after surgery from 10 thyroparathyroidectomized chinchillas and five sham controls to establish baseline serum T4 levels and to assess the degree and duration of hypothyroidism in this animal model. Baseline T4 levels ranged from 3.4 to 6.4 g/dl (mean 1 standard deviation, 5.25 0.84 g/dl), with no differences between male and female chinchillas (5.4 0.6 g/dl versus 5.2 1.0 g/dl, respectively). T4 levels were significantly reduced in 80% of thyroparathyroidectomized chinchillas when measured 6 to 14 days after surgery, but reductions were variable, ranging from 9 to 89% in individual animals. !ere was rapid regrowth of thyroid tissue and a return of T4 levels to the baseline range in five of the seven animals followed for 1 to 2 months after surgery. T4 levels increased significantly in the sham-operated chinchillas, indicating a nonspecific effect of surgery. !e results establish surgical procedures for creating a model of variable, transient hypothyroidism in the chinchilla. We also summarize published basal T4 values for various laboratory animals, to provide a convenient reference.