These estimates of protein requirements for older women are higher than the current EAR and RDA based on nitrogen balance data, which are 0.66 and 0.80 g · kg(-1) · d(-1), respectively. This trial was registered at clinicaltrials.gov as NCT01604980.

In previous studies, nonlethal CdCl2 concentrations apparently inhibited basal Y-1 mouse adrenal tumor cell endogenous mitochondrial cholesterol conversion to pregnenolone. In addition, CdCl2 inhibited all agents stimulating both plasma membrane-dependent cAMP synthesis and 20 alpha-hydroxy-4-pregnen-3-one (20DHP) secretion. Bypassing the plasma membrane using dibutyryl-cAMP (dbcAMP) stimulated cytoplasmic cholesterol metabolism and 20DHP secretion in the presence of CdCl2. Since CdCl2 competed at metabolic steps requiring Ca2+ in other tissues, experiments were designed to examine Cd2+ competition with Ca2+ during steroidogenesis. Sets of cells incubated with either medium or adrenocorticotropin (ACTH) with or without CdCl2 were also treated with 0, 1.0, 5.0 or 10.0 mmol/L CaCl2 in the presence or absence of EGTA, a relatively specific Ca2+, but not Cd2+, chelating agent. Another experimental cell set incubated with either medium or ACTH, with or without CdCl2, was treated with or without 1 mmol/L A23187, an ionophore specifically facilitating extracellular Ca2+ transfer across plasma membranes. Besides determining Ca2+ involvement in steroidogenesis using steroid secretion as an endpoint, we directly measured Ca2+ concentrations using intracellular fura-2 fluorescence. Following loading with 2 mumol/L fura-2, cells remained untreated or medium was infused with CdCl2, ACTH, ACTH/CdCl2 or ACTH followed after 50 s by CdCl2. Using Ca(2+)-supplemented media, we observed that Cd2+ inhibition of ACTH-stimulated 20DHP secretion was completely reversed. Standard Ca(2+)-containing medium supplemented with Ca2+ also enhanced maximally stimulated 20DHP secretion by ACTH. 20DHP secretion by ACTH-treated and ACTH/Cd(2+)-treated cells was only reduced by EGTA, when Ca2+ was not supplemented. The ionophore A23187 increased basal and ACTH-stimulated 20DHP secretion by Cd(2+)-treated cells, suggesting that extracellular Ca2+ resources may compete against Cd2+ effects on plasma membrane cAMP synthesis and on basal cholesterol metabolism by mitochondria. No time-dependent change in Ca2+ concentrations occurred within untreated cell suspensions. ACTH stimulation caused a 25 s burst in Ca2+ concentrations before returning to basal, steady-state levels. Cd2+ also stimulated intracellular fura-2 fluorescence. Untreated cell suspensions infused with Cd2+ exhibited a continuous rise in intracellular fluorescence. ACTH/CdCl2-treated cells exhibited a hyperbolic rise in intracellular fluorescence over the 300 s study period. Cells treated with Cd2+ 50 s after ACTH treatment initially exhibited the 25 s fluorescence burst followed by a Cd(2+)-induced hyperbolic rise in intracellular Cd2+. These fluorescence measurements suggested that cytoplasmic Ca2+ changes do not appear to be necessary for basal 20DHP synthesis and secretion; only a 25 s burst in intracellular Ca2+ is necessary to a slightly higher plateau level for stimulated 20DHP synthesis and secretion. Cd2+ freely enters the cell under basal conditions and Cd2+ entry is accelerated...

Current dietary protein requirement for adult males aged 65–75 are based on nitrogen balance data and suggest no difference in requirement between the elderly and young adults. Recent studies in young adult males using IAAO technique suggest that nitrogen balance estimates are too low. The objective of this study was to determine the protein requirement of elderly men using the IAAO technique with L‐[1‐13C]‐phenylalanine as the indicator. Preliminary studies have been conducted in 3/7 (65–75 year old) men. Each received a minimum of 7 protein intakes (0.2 – 1.8 g.kg−1.d−1) in random order after a 2 day adaptation providing energy at 1.7 times measured resting energy expenditure and protein at 1.0 g.kg−1.d−1. Oxidation study day diets were amino acid based liquid diets patterned after egg protein. The mean protein requirement was determined by visual inspection of the preliminary F13CO2 obtained from the oxidation of L‐[1‐13C]‐phenylalanine in response to graded protein intakes. Preliminary estimates suggest a mean protein requirement of 0.8 g.kg−1.d−1. This preliminary data suggest that the mean protein requirement of elderly men aged 65–75 years is 20% higher than current recommendations.This study was supported by a grant from the Canadian Institute for Health Research (CIHR).

Studies of dietary protein requirement in vulnerable groups, including elderly adults, are needed using methods other than nitrogen balance. The objective of this study was to determine the protein requirement in 8 healthy free‐living elderly females (65 – 75y old) by measuring the oxidation of L‐[1‐13C]‐phenylalanine to 13CO2 in response to graded intakes of protein. Subjects received a maximum of 7 protein intakes (0.2 to 2.0g.kg−1.d−1) for a total of 43 studies (preliminary data). The diets provided energy at 1.7 times measured resting energy expenditure and were isocaloric. Protein was given as an amino acid mixture patterned after egg protein. All subjects consumed controlled diets containing 1 g protein.kg−1.d−1 for 2 days prior to the study day. The mean protein requirement was determined by applying a 2‐phase linear regression crossover analysis on F13CO2 (label tracer oxidation in 13CO2), which identified a breakpoint in the F13CO2 in response to graded intakes of protein. Mean protein requirement was determined to be 1.1 g.kg−1.d−1. These preliminary results suggest the mean protein requirement of elderly women is higher than current recommendation derived from nitrogen balance studies. This study was supported by a CIHR grant.