No abstract

The lipolytic response of isolated adipocytes from 1 ½-, 6-, 24- and 32-month-old rats to various doses of epinephrine was studied. Both the basal and the maximal stimulated glycerol release were largest in the mature rats (6 months old) which had the largest adipocytes. Expressing glycerol release per unit cell surface area (which was drastically reduced with age) eliminated the difference between mature and senescent rats both in absence of epinephrine and at high doses of the hormone. However, at low epinephrine doses the adipocytes of the very young and the very old rats showed an enhanced response per unit surface area. A simple pharmacodynamic analysis based on the occupancy theory of drug-receptor interaction suggests that the sensitivity of rat adipocyte receptors is increased during senescence; this increase may be related to the decreased surface of old adipocytes. On the other hand, the decreased maximal lipolytic response during senescence may be due in part to a reduced number of receptors and to a reduced sensitivity of the cellular enzymatic system underlying lipolysis.

The B-cells of the endocrine pancreas constitute an adequate model for in vitro study of the aging process in highly differentiated cells. In the present study, collagenase-isolated islets of Langerhans from young and senescent rats were cultured up to 28 days. The response of the B-cells to the stimulatory conditions of the culture medium involved the nucleus, ribosomes, endoplasmic reticulum, Golgi apparatus, and secretory granules. Correlated data from light microscopy, electron microscopy, and insulin radioimmunoassay show that the differentiation and function of senescent B-cells are maintained in culture, as it has been proven for the B-cells of younger animals. On the other hand, signs of cytological deficiency not directly concerned with the specific function of B-cells were observed: abnormal mitochondria and lysosomes are more numerous in the senescent B-cells. The proliferative capacity of the B-cells of aged rats is reduced.

Body weight, epididymal adipose tissue weight, fat cell size, and metabolic activity of fat depot were studied in 30-month-old Wistar rats and compared with rats aged 6 and 24 months old. In very old age a significant reduction of body weight was observed and was paralleled with a decline of adipose mass and a decrease in cell volume. In vitro metabolic studies, with and without insulin, showed a greater oxidation of D-U-14C glucose to 14CO2 and a greater incorporation into triglycerides than in the 24-month-old animals when the data were expressed per cell or per cm2 surface area. The resistance to insulin was elevated in spite of a significant decrease of adipocyte size in very old rats.

Effect of ageing on insulinemia, determined by radio-immunological method, has been studied in male rats aged 3, 12 and During the intravenous hyperglycemia test, the coefficient of glucose assimilation decreases significantly with age, whereas a hype insulinemia is to be seen. This becomes apparent at the moment of the hyperglycemic peak and still persists 20 min after the beginning of the test. Senescence in the rat is, therefore, accompanied by early decrease in glucose tolerance and abnormally high IRI (immunoreactive insulin) level in the blood.