d24-hour changes in circulating prolactin, follicle-stimulating hormone, luteinizing hormone and testosterone in male rats subjected to social isolation

Abstract

BACKGROUND: This work analyzes the effect of social isolation (a mild stressor) on the 24-h variation of pituitary-testicular function in young Wistar rats, assessed by measuring circulating levels of prolactin, FSH, LH and testosterone. METHODS: Animals were either individually caged or kept in groups (4-5 animals per cage) under a 12:12 h light-dark cycle (lights on at 0800 h) for 30 days starting on day 35 of life. Rats were killed at 4-h intervals during a 24-h cycle, beginning at 0900 h. RESULTS: Isolation brought about a decrease in prolactin, LH and testosterone secretion and an increase of FSH secretion. In isolated rats the 24-h secretory pattern of prolactin and testosterone became modified, i.e., the maximum in prolactin seen in control animals at the beginning of the activity span was no longer detected, whereas the maximum in circulating testosterone taking place at 1700 h in controls was phase-delayed to 2100 h in isolated rats. CONCLUSION: Social isolation affects the 24-h variation of pituitary-testicular function in young rats. Secretion of prolactin, LH and testosterone decreases, and secretion of FSH increases, in isolated rats. The maximum in prolactin seen in group-caged rats at the beginning of the activity span is not observed in isolated rats. The maximum in circulating testosterone taking place at the second part of the rest span in controls is phase-delayed to the light-dark transition in isolated rats.

Figure 1

Effect of isolation on 24-h changes of plasma prolactin 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. 0900, 1300, 0100 and 0500 h. For further statistical analysis, see text.

Figure 2

Effect of isolation on 24-h changes of plasma FSH 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. For further statistical analysis, see text.

Figure 3

Effect of isolation on 24-h changes of plasma LH 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. For further statistical analysis, see text.

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.