Objective   To inquire into the effects of heat stress on the body weight, thymus indexes, spleen indexes, respiration, rectal temperature and the protection function of supplementary L-Arginine(L-Arg)on heat-stressed rats.

  Methods   According to the factorial experiment design for three factors, hebetic male Sprague Dawley rats were randomly divided into A, B, C groups.The relevant indexes change such as the thymus index were observed in SD rats which were exposed under normal temperature and different hyperthermia with supplied different concentration L-Arginine by gavage.

  Results   In normal temperature, the body weight, thymus and spleen indexes increase of the groups supplemented with L-Arginine were higher than those of the control groups gavaged with water(P < 0.05), but the changes of respiration and rectal temperature had no significant difference(P > 0.05).In the differenthigh temperature heat-stressed condition, the body weight, thymus weight and spleen weight of the heat-stressed rats all decreased in both supplementation of L-Arginine and no supplementation of L-Arginine groups, but these decresses were less in rats with supplementation of L-Arginine groups than those with no supplementation of L-Arginine groups.And the thymus weight and spleen weight of heat stress groups were temperature and time of heat stress dependent.The respiration and rectal temperature followed the increase of temperatare were accelerated and elevated within limits, but there was no significant difference between the groups supplemented with L-Arginine and group without supplemented with L-Arginine(P > 0.05).

  Conclusion   Supplied suitable dose of L-Arginine can induce the increase of the body weight, thymus index and spleen index in normal temperature and relieve the atrophy of the thymus and spleen in heat stress.