Biomedical subjects
Publications and source records attributed to A Joasoo.
The circulating thyroid hormones were found to respond to general anaesthesia and surgery of the thyroid gland in a similar manner to that reported with general surgery. When compared with the preoperative plasma concentration, the post-operative thyroxine levels showed a significant rise, whereas the triiodothyronine level fell.
The in vitro response of sensitized splenic lymphocytes to antigen (thyroglobulin) was increased by crowding and decreased by isolation in female rats. Both isolated and crowded male rats responded by a decrease in the in vitro reactivity of lymphocytes to antigen. The response of the lymphocytes to PHA was not altered in any consistent manner. Similar animals, both control and those immunized with thyroglobulin, were tested for an effect of in vivo injections of epinephrine on the in vitro reactivity of lymphocytes; epinephrine was given intraperitoneally 30 min before the rats were killed for removal of spleens. Incorporation of 3H-thymidine by lymphocytes was greater in control cultures (neither PHA nor antigen present) but there was a decreased response to either PHA or antigen when epinephrine had been injected.
A homologous receptor assay system using human thyroid membranes and 125I-labelled human TSH (hTSH) was used to study the effect of serum and serum fractions on the binding of [125I]hTSH to the membranes. Scatchard analysis showed a single population of binding sites for TSH. Gamma globulin fractions prepared from sera of patients with Graves' disease were able to displace [125I]hTSH from the membrane to a greater extent than normal gamma globulin in 21 out of 45 cases. Increased displacement activity was seen in patients with thyroiditis, hot nodules and euthyroid eye disease but not in patients with toxic multinodular goitres. Further fractionation of the gamma globulin fraction showed that the stimulatory activity was not confined to the IgG fraction. Scatchard plots showed gamma globulin fractions decreased the number of receptor sites available for TSH binding but did not alter the affinity of the receptor for TSH. IgG fractions showed different slopes and intercepts and appeared to decrease the affinity of the receptor for TSH. LATS activity in human serum may be explained on the basis of these observations on the properties of the TSH receptor.
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Eight patients are described with elevated plasma thyroxine (T4) concentrations, but normal or low plasma triiodothyronine (T3) concentrations by radioimmunoassay. All were suffering also from non-thyroidal illness, which in six cases was severe, and in two fatal. The two patients in reasonable general health were acromegalic. It is possible that in sick thyrotoxic patients there is an impairment of peripheral conversion of T4 to T3, similar to that occurring in sick euthyroid patients. However, further proof of thyrotoxicosis must be obtained in patients with high T4 and normal or low T3 levels by studying the response of the pituitary to TRH. Meanwhile, in the sick or elderly, estimation of serum or plasma T3 concentration may not be a good screening test for thyrotoxicosis.
The adrenergic receptors mediating the inhibitory effect of epinephrine on the rat thyroid in vivo have been studied by the use of more specific alpha- and beta-adrenergic stimulators, and blocking agents. The effect of methoxamine was similar to that of epinephrine, while isoproterenol stimulated 131-I uptake slightly, and did not alter the ratio of monoiodotyrosine (MIT) to diiodotyrosine (DIT). However, like methoxamine, isoproterenol resulted in a decrease in thyroxine (T4) formation. Phentolamine could partially prevent epinephrine-induced decrease in 131-I uptake and T4 synthesis. The changes in the MIT/DIT ratio could be completely prevented by high doses of phentolamine. Propranolol enhanced the effects of epinephrine. It is concluded that the effect of epinephrine on the rat thyroid in vivo is predominantly alpha-adrenergic, but T4 synthesis may be decreased by stimulation of either receptor.
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