Abstract
Studies were performed to examine the effect of two anesthetic agents, ether and pentobarbital,
on the hypothalamic-pituitary-thyroid function in vivo. In non-anesthetized animals,
plasma thyrotropin (TSH) increased rapidly from basal values of 0.1, a peak of 0.49
µg/ml, 25 min after exposure to the cold. Anesthesia with ether during exposure to
the cold completely prevented the rise in TSH. During pentobarbital anesthesia, the
rise in TSH after exposure to cold was reduced by more than 90%. Even a three minute
period of ether anesthesia prior to cold exposure reduced the peak response to cold
as well as delayed this response when compared to the untreated group. During two
hours of anesthesia with ether, the TSH concentration declined in animals which were
fed a low iodine diet at essentially the same rate as in animals on the same diet
given an injection of 3 µg of triiodothyronine. Pentobarbital did not suppress TSH
at room temperature. The release of thyrotropin after injection of synthetic thyrotropin-releasing
hormone (TRH) was greater in animals anesthetized with pentobarbital than in controls
and was slightly reduced in ether-anesthetized animals. This difference was observed
when thyrotropin was given intraperitoneally or intravenously and the slope of the
dose-response curves to TRH showed a flattening of the curve of rats treated with
ether and a steeper slope of response in animals anesthetized with pentobarbital.
We conclude that pentobarbital inhibited TSH response to cold but did not reduce the
resting levels. Ether inhibited the rise of TSH in the cold and lowered the basal
levels of TSH in animals at room temperature. Pentobarbital increased the response
to TRH and ether may have reduced the response to TRH.
Key words
TSH - TRH - Thyroid Function - Anesthesia - Rat
1 Supported in part by Grant Nos. AM 19132 and M 15165.
