Abstract
Summary
The experiment investigated the effect of a high ambient temperature (35.6°) of varying duration on the hypothalamic content of growth hormone releasing activity (GHRA). These experiments consisted of five treatment groups: one group of normals at 24°, one sham-treated group receiving only diluent in which hypothalami were extracted, and three groups, each heatexposed for 1, 24, or 168 hr, respectively. The GHRA was measured by in vivo depletion of pituitary growth hormone (GH) content in 30-day-old rats. Pituitaries of the recipient rats were assayed by the “tibia test” method for GH content. The standard assay was based on three doses of bovine growth hormone (NIH-GH-B12) with a threefold difference between consecutive levels. Growth hormone was evaluated by two parameters: (a) epiphyseal cartilage width, and (b) GH content of the unknown estimated from the response in terms of the reference standard. An exposure to heat for 1 or 24 hr resulted in an enhanced hypothalamic GHRA with a concomitant marked (significant at 1% level) depletion of pituitary GH content and a return to near normal values by 168 hr post-exposure.
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