Double antibody radioimmunoassays for thyroxine (T4) and triiodothyronine
(T3) were optimised and validated for use in cats. Serum total T4 concentrations
of 318 and total T3 concentrations of 299 healthy cats were measured. In both
sexes, T4 concentrations tended to decrease until five years of age and then rise
again. For any given age, females and neutered females tended to have
significantly higher T4 values than males and neutered males. Pedigree animals
tended to have higher concentrations of T3 at any given age than cross-bred cats.
Animals living in the same environment had significantly similar T4 and T3
concentrations respectively which, for T3 only, appeared to be due to a definite
There was no obvious difference in the results of the T4 uptake test
between euthyroid, hyperthyroid and hypothyroid cats. In normal feline serum,
after agarose gel electrophoresis with tris-maleate buffer at pH 7.4, T4 was
bound only to albumin and alpha-globulin, and feline T3 mainly to alpha-2-
globulin and beta-globulin. In thyrotoxicosis, the percentages of T4 bound to
albumin and alpha-globulin were decreased and increased respectively. These
changes were not the result of hyperthyroxinaemia per se, nor to interference
of T4 binding to albumin by non-esterified fatty acids. Changes in iodothyronine
binding were seen in two euthyroid cats with elevated serum T3 and/or T4
concentrations, in two cats with euthyroid diseases, but not in two experimental
The historical, clinical and diagnostic features of 74 hyperthyroid cats are
presented. Approximately 70 per cent of cases had unilateral goitre. Surgical
treatment for both unilateral and bilateral lobe involvement was effective but
post-operative hypocalcaemia was common in the latter group.
Hypothyroidism was induced in two cats using and the resultant state
monitored for 91 weeks. Both cats developed sub-normal rectal temperatures,
reduced heart rates and bilaterally symmetrical alopecia and hyperpigmentation of
the distal pinnae. Hyperkeratosis, myxoedema and apocrine gland changes were
found in skin biopsies. Serum gamma-globulin concentrations increased
progressively after thyroid ablation.
The historical and clinical features of 26 cases of feline endocrine alopecia
(FEA) are described. A raised blood eosinophil count was highly reliable in
distinguishing between FEA and physically similar conditions. Seventy-three per
cent of cases responded totally to treatment with T3.
The thyroid stimulating hormone (TSH) stimulation test was optimised for
cats. Six hours after TSH administration, cats with FEA had significantly lower,
and absolute increases in, T4 concentrations than healthy cats. The serum T4
and T3 concentrations of the experimental hypothyroid cats failed to increase
after TSH but a single hyperthyroid cat responded normally.
Thyroid and antinuclear antibodies were demonstrated in serum from ten and
four of 29 hyperthyroid cats respectively, using the indirect immunofluorescence
test with normal cat thyroid as substrate. Fifteen healthy control cats were
negative for autoantibodies. Animals with strong positive results for thyroid
antibodies were significantly more likely to have bilateral goitre with
lymphocytic infiltrations than other thyrotoxic cats.