This study addresses the question of variability of immunoreactive human growth hormone (IRHGH) response to the following types of muscular exercise. 1) One hour of submaximal exercise with restarting for 30 min after 20 min of recovery. Three types of responses were observed: a rise of [IRHGH] occurred in response to muscular activity; [IRHGH] was maintained at rest level during the first bout and then rose in the second bout; or [IRHGH] rose during the first bout and was no longer modified by the restarting. 2) Thirty minutes of heavy exercise. In some subjects [IRHGH] change was almost linear with time, reaching very high values and dropping as soon as exercise had stopped, whereas in others peak values were similar to those of submaximal exercise but, in contrast, plateaued during recovery. 3) One hour of exercise performed either continuously or with alternate sequences of 30-s exercise and 30-s pause. In intermittent exercise, some subjects displayed a similar time course of [IRHGH] as in continuous exercise and others displayed markedly high values. 4) One hour of submaximal exercise at three different intensities carried out at ambient temperatures of 24 and 33 degrees C. At 33 degrees C, in some subjects, [IRHGH] time course at the three intensities was unchanged at 33 degrees C compared with that at 24 degrees C, whereas the maximal value increased in another subject up to 150 ng X ml-1. A significant intrasubject consistency to a given type of exercise was evident over several months. The study emphasizes that caution should be used in drawing definite conclusions from averaged results with high variability.

Males of many species can adjust their behaviors to environmental conditions by changing reproductive tactics. Testosterone surges in adult breeding males typically inhibit the expression of paternal care while facilitating the expression of aggression during environmental changes. Similarly, in non-breeding philopatric males of cooperatively breeding species, up-regulation of testosterone may inhibit alloparental care while facilitating dispersal, i.e. males might become bolder and more explorative. We tested this hypothesis in philopatric male African striped mice, Rhabdomys pumilio. Striped mouse males can either remain in their natal group providing alloparental care or they can disperse seeking mating opportunities. Compared to philopatric males, dispersed males typically show higher testosterone levels and lower corticosterone levels, and more aggression towards pups and same sex conspecifics. We experimentally increased the testosterone levels of philopatric males kept in their family group when pups were present. Testosterone-treated males did not differ significantly from control males in alloparental care and in aggression toward same-sex conspecifics. Compared to control males, testosterone treated males were bolder, more active, less anxious; they also showed lower corticosterone levels. Philopatric males were sensitive to our testosterone treatment for dispersal-and anxiety-like behavior but insensitive for social behaviors. Our results suggest a role of testosterone in dispersal. We tested this hypothesis in philopatric male African striped mice, Rhabdomys pumilio. 28Striped mouse males can either remain in their natal group providing alloparental care or 29 they can disperse seeking mating opportunities. Compared to philopatric males, dispersed 30 males typically show higher testosterone levels and lower corticosterone levels, and more 31 aggression towards pups and same sex conspecifics. We experimentally increased the 32 testosterone levels of philopatric males kept in their family group when pups were present. 33Testosterone-treated males did not differ significantly from control males in alloparental 34 care and in aggression toward same-sex conspecifics. Compared to control males, 35 testosterone treated males were bolder, more active, less anxious; they also showed lower 36 corticosterone levels. Philopatric males were sensitive to our testosterone treatment for 37 dispersal-and anxiety-like behavior but insensitive for social behaviors. Our results 38 suggest a role of testosterone in dispersal. 39

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