| Abstrakt: |
Undernutrition has proven to be a useful model for exploring the relationship between growth and pubertal development in female rats, such as the “critical body weight” hypothesis of pubertal timing, but corresponding studies in the male have been hampered by lack of specific discrete markers of puberty similar to vaginal opening or first estrus in females. In the current study, we explored the effect of five different levels of food intake (as low as one-thrid of normal) beginning at weaning on pubertal development and timing in male rats, using the date of the initial successful conception with normal females as a discrete marker for puberty in males. In underfed males, there was a weak inverse correlation (r–0.31, P<0.05) between the age at puberty and the growth rate, the latter being used as an index of the degree of underfeeding. In contrast, there was a strong direct correlation (r0.78, P<0.001) between body weight at puberty and growth rate. In the most severely underfed groups, the Lee index of body fat remained subnormal before and after puberty. Initial litter size also tended to be reduced when the males were underfed. At age 51 days (prior to puberty), graded underfeeding led to progressive reductions in serum luteinizing hormone and follicle-stimulating hormone levels as well as in parameters of androgen status (serum and testicular testosterone, prostate, and seminal vesicle weights). Testicular size was also reduced, but daily sperm production rate was not greatly affected by underfeeding. Testicular histology at age 51 days revealed mature step 19 spermatids in all groups, with some reduction in seminiferous tubular diameter in the most severely underfed group. The effect of underfeeding on testicular testosterone and spermatogenesis appeared to decrease as underfeeding was continued for an additional 70 days. We conclude that graded underfeeding beginning at weaning leads to major reductions in gonadotropins and androgens but has less effect on spermatogenesis or the timing of puberty. Therefore, in normal rats, the timing of puberty is closely related to spermatogenic development, which can proceed once initiated despite low gonadotropin and androgen levels. Underfed male rats have low body weights and low body fats at puberty, refuting the “critical body weight” and “critical body fat” hypotheses of pubertal timing. |
