Cerebrospinal fluid concentrations of large neutral and basic amino acids in Macaca mulatta: diurnal variations and responses to chronic changes in dietary protein intake.

In rats, dietary protein intake influences brain concentrations of tryptophan, tyrosine, and other large neutral amino acids (LNAAs) and the neurotransmitters to which they are linked. Few experiments have examined these dietary protein-amino acid relationships in nonhuman primates, in relation to time of day or dietary protein content. We therefore examined the effect in monkeys of changes in chronic protein intake on 24-hour plasma and cerebrospinal fluid (CSF) concentrations of LNAAs (tyrosine, phenylalanine, branched-chain amino acids) and basic amino acids. Juvenile male monkeys (Macaca mulatta) consumed for sequential 4-week periods diets differing in protein content (approximately 23% --> approximately 16% --> approximately 10% --> approximately 6% protein [percentage of energy]). The daily ration was presented as a morning meal of fruit and an afternoon meal of fruit and a commercial diet to mimic feeding patterns in the wild. During week 4 on each diet, blood and CSF were sampled repeatedly over a 48-hour period via indwelling catheters. Plasma and CSF LNAA concentrations varied markedly with time of day and dietary protein content, showing up to 4-fold variations. Diurnal variations in plasma and CSF basic amino acids were smaller in magnitude and generally not strongly linked to dietary protein content. A measure of the competitive transport of LNAAs across the blood-brain barrier, calculated using plasma concentrations of the LNAAs and their blood-brain barrier kinetic constants, predicted the observed CSF concentration of each LNAA examined remarkably well, except for phenylalanine. Based on observations in rats, the variations in the CSF concentrations of the LNAAs in monkeys may be large enough to influence metabolic and signaling pathways in brain to which they have been linked.

Distribution of postpartum amenorrhea in rural Bangladeshi women.

Previous studies of postpartum amenorrhea (PPA) demonstrated distinct subgroups of women with short and long durations of amenorrhea. This phenomenon was attributed to cases where breastfeeding is absent because of pregnancy loss or infant death, or confusion of postpartum bleeding with resumption of menses. We explored these ideas using data from an 11-month prospective study in Bangladesh in which 858 women provided twice-weekly interviews and urine specimens for up to 9 months; 300 women were observed while experiencing PPA. The resulting exact, interval-censored, or right-censored durations were used to estimate parameters of two-component mixture models. A mixture of two Weibull distributions provided the best fit to the observations. The long-duration subgroup made up 84% (+/- 4% SE) of the population, with a mean duration of 457 (+/- 31) days. The short-duration subgroup had a mean duration of 94 (+/- 17) days. Three covariates were associated with the duration of PPA: women whose husbands had high-wage employment had a greater probability of falling in the short-duration subgroup; women in the long-duration subgroup whose husbands seasonally migrated had shorter periods of PPA within the subgroup; and mothers in the short-duration subgroup who gave birth during the monsoon season experienced a shortened duration of PPA within the subgroup. We conclude that the bimodal distribution of PPA reflects biological or behavioral heterogeneity rather than shortcomings of data collection.

Hormonal correlates for the initiation of breast-feeding in Bangladeshi women.

Hormonal changes that occur before or during parturition are known to trigger early postpartum maternal behaviors in many mammals. In humans, little evidence has been found for hormonal mediation of early postpartum maternal behavior. In this paper, we investigate associations between fetoplacental hormone concentrations in late pregnancy on the time from parturition to initiation of breast-feeding. A sample of 91 pregnant rural Bangladeshi women, enrolled in a 9-month prospective study, provided twice-weekly urine specimens and structured interviews. The subjects provided self-reports of time from parturition to initiation of breast-feeding. Specimens were assayed for urinary concentrations of human chorionic gonadotropin (hCG), pregnanediol-3alpha-glucuronide (PdG, a metabolite of progesterone), and urinary estrone conjugates (E1C). Parametric hazards analysis was used to investigate the effects of hCG, PdG, and E1C concentrations and other covariates (mother's age, parity, and child's sex) on the duration from parturition to breast-feeding. Mother's age, parity, the child's sex, hCG, and PdG showed no association with the onset of breast-feeding. Urinary E1C was significantly associated with time to initiation of breast-feeding, explaining about 4% of the variation in the behavior. The relationship was positive so that higher prepartum concentrations of EIC were associated with later times to initiation of breast-feeding. The direction of this relationship is opposite that found for many other species of mammals but is consistent with some recent findings in primates.

Patterns for the initiation of breastfeeding in humans.

Establishment of lactation has important biological and emotional health consequences for the newborn. Even so, substantial variation within a culture and among different cultures is seen in the onset of breastfeeding. Parametric mixture models are used to explore this variation and to uncover general human patterns for the initiation of breastfeeding. The model components reflect two hypothesized patterns of behavior. The first component is a "natural" pattern of breastfeeding that reflects, to some extent, a general mammalian behavior. The second component arises through culturally mediated behaviors that affect the initiation of breastfeeding. The model was fit by maximum likelihood to interval- and right-censored observations on 26220 mother-infant pairs collected from 25 previously published studies of breastfeeding behavior. Both model components were clearly statistically identified. Effects of cultural and geographic covariates were found to have significant effects on all components of the model. Although there is clear evidence for two distinct patterns of behavior in the initiation of breastfeeding, the results suggest that learned behaviors play an important role in mediating even "natural" breastfeeding behavior.