Effect of Undernutrition and Amino Acid Deficiency on the Timing of Puberty in Rats

Abstract

Extract: Sexual maturation was examined in underfed or amino acid-deficient rats. We have demonstrated a highly significant negative linear relationship (r = −0.80, P < 0.001) between the age at puberty and the growth rate in rats under conditions of food restriction. The weight at puberty in animals growing at different rates because of undernutrition was not constant but behaved as a quadratic function of growth rate, as predicted from the assumption that growth rate was an independent variable. Growth rate is therefore more important than arrival at a particular fixed weight in determining the timing of puberty. Feeding of low valine diets resulted in delayed sexual maturation. Both the weight at vaginal opening (182 ± 5.9 g) and the weight at first estrus (187 ± 6.1 g) were significantly greater in the valine-deficient group when compared with growth-matched control (139 ± 10.7 g and 161 ± 9.3 g, respectively, P < 0.05). The valine-deficient group also had significantly later vaginal opening (98.8 ± 4.7 days) than growth-matched controls ( 76.6 ± 6.6 days, P < 0.02). Valine deficiency seemed to have a specific effect on the hypothalamic-pituitary-gonadal axis since puberty in valine-deficient animals was delayed more than could be accounted for by impairment of growth. Speculation: In contrast with previous suggestions in animals and man, we have shown that in rats the weight at puberty is not constant under conditions of underfeeding or valine deficiency. Growth rate seems to be more important than arrival at a particular fixed weight in determining the onset of puberty, possibly through a linkage between growth rate and hormone production rates. Valine deficiency may cause delayed puberty by altering central nervous system neurotransmitters.