Metabolic changes during maturation of male monkeys: possible signals for onset of puberty

There is a close relationship between the metabolic status of a maturing animal and the timing of puberty onset. However, the signals linking metabolic status to the maturation of the reproductive axis remain unknown. We looked for metabolic differences before and after puberty by comparing plasma profiles of insulin, glucose, amino acids, beta-hydroxybutyrate, and glycerol between juvenile and adult monkeys in fed and fasted states. Thirteen juvenile and 13 adult male crab-eating macaques (Macaca fascicularis) were fed a mixed meal, and blood samples were collected at intervals between 1.5 and 52 h after the meal. Plasma insulin concentrations decreased in a similar manner in both groups during the first 16 h of fasting. By 20 h after a meal, basal insulin levels were significantly lower (P less than 0.025) in juveniles compared with adults and remained so until the end of the fast. Circulating levels of glucose were similar in juveniles and adults immediately after a meal and then decreased significantly (P less than 0.025) in juveniles by 28 h of fasting and in adults by 52 h of fasting. Plasma concentrations of all large neutral amino acids (i.e., tyrosine, tryptophan, phenylalanine, valine, leucine, and isoleucine, LNAA) except tryptophan decreased more precipitously in juveniles than in adults during the first 20 h of fasting. However, the ratios of tyrosine to other LNAA and tryptophan to other LNAA were similar in juveniles and adults at all times. beta-Hydroxybutyrate concentrations were low in both groups until 24 h after a meal, at which time plasma levels increased more rapidly and attained higher values in juveniles compared with adults.(ABSTRACT TRUNCATED AT 250 WORDS)