Figure 4.

Effect of isolation on 24-h changes of plasma testosterone concentration in young male rats. Groups of 6–8 rats were killed by decapitation at 6 different time intervals throughout a 24 h cycle. Values at 0900 point are repeated on the "second" day. Bar indicates scotophase duration. Shown are the means ± SEM. Letters indicate the existence of significant differences between time points within each group after a Tukey-Kramer's multiple comparisons test, as follows: ^a p < 0.01 vs. all time points. For further statistical analysis, see text.