Thyroid function after injury

The influence of various anesthetics on the release and metabolism of thyroid hormones: results of two clinical studies

Normal functioning of the thyroid gland during surgery is important, but few data are available on the possible interactions between anesthesia and thyroid hormones. In two independent studies we examined the influence of different types of general anesthesia on the plasma levels of the thyroid hormones. They revealed an intraoperative increase of free thyroxine (fT4) and total thyroxine (tT4) in plasma to approximately 150% of preanesthesia levels when enflurane was used. No increase in thyroid-stimulating hormone (TSH) secretion was noted prior to this. The increase was not due to a quantitative change in the binding proteins. The plasma levels of fT4 and tT4 returned to normal postoperatively; however, no accompanying increase in plasma triiodothyronine levels was observed. Hence we assume the increase to be due to hormone release from thyroid and/or extrathyroidal stores--an intercompartmental shifting.

The effect of acute spinal cord compression injury on thyroid function in the rat

The effect of acute spinal cord injury on thyroid function was studied in rats subjected to severe spinal cord compression at T1. Serum thyroxine (T4), effective thyroxine index (ETI), and thyroid stimulating hormone (TSH) were measured at 1 and 100 minutes at one, three, and seven days after laminectomy and spinal cord injury. Control animals were subjected to laminectomy only. T4 was decreased at 1 minute after laminectomy with or without spinal cord injury, though the animals with cord injury had a much more profound reduction. The effects on TSH at 1 minute were dramatically different: laminectomy alone caused an elevation of TSH, while spinal cord injury produced a marked decline. At the later time intervals both groups showed gradual normalization of T4 and TSH levels, and at seven days there were no significant differences between the groups. Thus, acute spinal cord compression injury produced a major alteration in thyroid function during the acute phase.