Accommodating high levels of variable generation
Pinealectomy induces a moderate increase in thyroid weight, The diurnal variation in hypothalamic TRH content, reflecting both rhythmic synthesis and secretion, is, however, blunted in the absence of cyclical light changes.Since thyroid hormone plays a central role in the regulation of total body metabolism, it is not surprising that nutritional factors may profoundly alter the regulation, supply, and disposal of this thermogenic hormone.Although many dietary changes can affect the thyroid economy, the most striking and important effects are related to alterations in total caloric intake and the supply of iodine.As indicated above, thyroid hormone levels in serum tend to be lower during the summer months.
A decrease in the serum T3 concentration, with reciprocal changes in the levels of r T3, have been observed in normal subjects acutely exposed to heat and during febrile illnesses.
Additionally, studies of individuals with prolonged residence in Arctic and Antarctic regions may be confounded by other alterations in daylight, activity levels, living conditions and sleep deprivation. More prolonged exposure to cold generally results in maintenance of the total T4 (TT4) and free T4 (f T4) levels with maintenance of a normal or decreased total T3 (TT3) and free T3 (f T3) levels.
Accommodating high levels of variable generation comments