Pubertal Food Intake, Body Length, Weight, and Composition in the Well Fed Female Rat

Abstract

Summary: Pubertal age, food intake, body length, weight, and composition were determined by direct measurements in 29 well fed female rats studied from birth to first estrus. The average birth and weaning weights of the 12 early maturing rats were 6.99 ± 0.13 g and 50.13 ± 1.16 g, respectively, and did not differ significantly from those of the 11 late maturers (6.97 ± 0.16 g and 49.72 ± 1.42 g, respectively). Mean values for all pubertal measurements arc included in Table 1. At puberty, the late maturing animals were heavier, longer, and had attained a greater quantity of total body water than the early maturers. Although both groups ate the same total amounts of food, late maturing rats at vaginal opening and at first estrus consumed relatively less food per 100 g body weight than did early maturers. Estrus was simultaneous with vaginal opening in 10 (83%) of early and 4 (36%) of the late maturing rats. Despite the similarity in the proportions of total body water, fat, and protein in early and late maturers, a regression analysis, shown in Figure 1, indicates a significant decrease in the proportion of body water (P < 0.001), and a significant increase in the proportion of body fat (P < 0.05) with increasing age at first estrus. The percentage of body protein does not change with increasing age at first estrus (regression coefficient = 0.13). Speculation: Our findings in female rats are consistent with those in monkeys and domestic animals which show pubertal age to be positively correlated with body weight. These observations are at variance with results reported for girls who show an unchanging average body weight at all ages of puberty. The differences in metabolic and somatic development observed in pubertal rats suggest that the attainment of a “critical” body weight, level of fat, and food intake may not be the principal factors initiating puberty.