Both SD and TP inhibited testicular growth (F = 220.6, p < 0.0001, and F = 122.3, p < 0.0001, respectively; Fig. 2). The effect of both photoperiod and TP were significant at Week 2 and persisted through Week 12 (Fig. 2), but by Week 21, the effects of both TP and photoperiod were no longer apparent, and testis size was similar in all four treatments (Fig. 2). There was a significant interaction between SD and TP treatment (F = 8.3, p < 0.005), showing that TP treatment enhanced the inhibitory effect of SD (Fig. 2). At the time of their greatest differences, at Weeks 4 and 6, the combined effect of SD and TP resulted in testes approximately 10% of the size of LD controls. Before Week 8, the combination of SD and TP almost completely halted testicular growth.
TP treatment did not affect body weight (F = 3.2, p > 0.05; Fig. 3). In contrast, SD significantly inhibited increases in body weight (F = 204.1, p < 0.0001), and SD rats in both treatments weighed approximately 20% less than LD rats in most weeks, confirming previous results. birth control pills
The effect of SD on body weight was significant from Week 2 through Week 16, but at Week 21 the effect of SD was no longer apparent (Fig. 3). There was no interaction between photoperiod and TP treatment (F = 0.1, p > 0.05).
FIG. 1. Average daily food intake (mean ± SE) over 10 wk for male F344 rats placed in LD or SD at weaning (n = 4 per group).
FIG. 2. Mean testis volume (mean ± SE) over 21 wk for male F344 rats given TP or vehicle 3 days after birth and held in SD or LD from weaning (n = 10 per group). For each measurement period, different lowercase letters above bars indicate significant differences (p < 0.05) between treatments.
FIG. 3. Mean body weight (mean ± SE) over 21 wk for male F344 rats given TP or vehicle 3 days after birth and held in SD or LD from weaning (n = 10 per group). For each measurement period, different lowercase letters above bars indicate significant differences (p < 0.05) between treatments.