Male rhesus monkeys (Macaca mulatta) of different age groups representing the species life span were fed ad libitum or a 30% reduced calorie diet over a 7-yr period. During the first 2-3 yr of this longitudinal study, glucose and insulin levels were not altered by diet restriction (DR). However, reductions in fasting blood glucose became apparent in DR animals after 3-4 yr. At the end of the 6th yr of study, glycated hemoglobin was measured, and intravenous glucose tolerance tests (IVGTTs) were conducted. Maximum glucose levels reached during IVGTTs increased with age but were lower in DR animals compared with controls. Several measures of the insulin response (baseline, maximum, and integrated areas under curve) increased with age and were lower in DR monkeys. With the exception of glycated hemoglobin, which was not different in monkeys subjected to DR, these findings confirm previous studies in rodents demonstrating that DR alters glucose metabolism and may be related to the antiaging action of this intervention.

A B S T R A C T Eight normal subjects were administered tracer amounts of a 14C-labeled thyroxine, L-[tyrosyl-14C] T4, by multiple injections. Then serial blood samples were collected for isolation of the thyroxine, triiodothyronine, and tetraiodothyroacetic acid fractions by a combination of column and paper chromatographies. The chromatographic artifacts were corrected by adding to the sera a purified 3H-labeled thyroxine, D,L-[a,,f-3H] T4 immediately after the separation of sera from blood. 1-2% of the serum 14C radioactivity was observed in the triiodothyronine fraction and 2-4% of the serum 14C radioactivity was observed in the tetraiodothyroacetic acid fraction. Complete kinetic studies of thyroxine and triiodothyronine were compared in the same individual in four of the subjects. The extrathyroidal conversion rates of thyroxine to triiodothyronine were calculated from data obtained during both the injection and the postinjection periods as functions of the 14C-labeled thyroxine and triiodothyronine remaining in the body at time t and their fractional turnover rates. The average daily rate of the extrathyroidal conversion of thyroxine to triiodothyronine was 4% of the extrathyroidal thyroxine pool or 33% of the total thyroxine production. The amount of triiodothyronine generated by this pathway (22 ,ug/day) was found to contribute 31% of the extrathyroidal triiodothyronine pool or 41% of the daily triiodothyronine production. This pathway is a major source of triiodothyronine production. The extrathyroidal conversions of thyroxine to triiodothyronine and tetraiodothyroacetic acid are major metabolic pathways of thyroxine in normal man.

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The response of plasma aldosterone concentration to postural variation, adrenocorticotropic hormone (ACTH), and angiotensin II was studied in five kidney allograft recipients and compared with the response observed in the same five subjects during the anephric period. Normal subjects acted as intact controls. After 2 hours of normal ambulation, plasma aldosterone levels increased in normal subjects (6.7 ± 1.6 to 22.9±2.7 ng/100 ml plasma), remained unchanged in anephric patients (4.5±1.0 to 5.2 ± 1 .