Effect of hypothermia on insulin-receptor interaction in different rat tissues

Experimental hypothermia caused extensive changes in the number of both classes of insulin receptors in different rat tissues. In the liver, the number of high affinity insulin receptors (HAIRs) decreased by 50% (from 25.3 to 12.6 fmol/mg membrane protein), whereas number of low affinity insulin receptors (LAIRs) was almost unchanged in comparison to normothermic animals (5.63 and 4.39 pmol/mg, respectively). In the adipose tissue, number of both classes was reduced--HAIRs by 81% (from 24.0 to 4.50 fmol/mg) and LAIRs by 92% (from 16.0 to 1.29 pmol/mg). In the skeletal muscle, capacity of HAIRs was not changed (16.2 and 19.3 fmol/mg in normo- and hypothermic animals, respectively), whereas number of LAIRs increased by 150% (from 6.65 to 16.6 pmol/mg). Hypothermic rats also showed lower amount (by 85%) of LAIRs in the heart muscle (9.37 and 1.43 pmol/mg in control and experimental animals, respectively). Simultaneously, no significant changes were found in HAIRs (16.3 and 11.9 fmol/mg, respectively) and LAIRs (4.43 and 3.88 pmol/mg, respectively) in the brain. These differences in insulin receptors responses to hypothermia may reflect different physiological role of insulin in the regulation of target cell metabolism and/or the differences in tissue distribution of the insulin receptor isoforms.     

31P-NMR determination of phosphomonoesters in relation to phospholipid biosynthesis in testis of the rat at different ages

Changes in the phosphomonoester (PM) peak, as observed in in vivo 31P-NMR spectra, are often attributed to changes in phospholipid synthesis and therefore to changes in cell proliferation. However, this technique provides information about the absolute size of the phosphomonoester pool rather than its turnover rate. To investigate whether there is a good correlation between changes in PM concentration and its turnover rate, we studied the turnover rate of the two major PM compounds, phosphocholine and phosphoethanolamine, in rat testes at different stages of testis development. [3H]Choline and [3H]ethanolamine were injected intraperitoneally into rats at the age of 3, 6 and 13 weeks, respectively. Phosphorylation of these compounds and their incorporation into phospholipids, were followed up to 6 h after injection of the phospholipid precursors. When these data were compared with the changes observed in the in vivo 31P-NMR PM peak, the concentration of the PM compounds appeared to correlate linearly, both with the conversion of choline into phosphocholine, as well with the rate of phospholipid synthesis, and therefore with the rate of cell proliferation. Hence, it is suggested that cell proliferation can be monitored by determining the changes in the PM peak that is observed in in vivo 31P-NMR spectra.     

Effect of perfusate potassium concentration on the contraction rate of the isolated rat heart during profound hypothermia

Effect of different concentration of K+ in perfusion fluid ([K+]) (5.9 mM, 3.6 mM, 2.38 mM) and the heart temperatures of 20 degrees C and below on the rat heart rate in the Langendorf preparations, were examined in conditions of retrograde perfusion with a modified Krebs-Henseleit buffer at constant perfusion volume. The lowering of [K+] diminished the temperature/heart rate ratio and depressed the heart standstill temperature from 12.3 +/- 0.6 degrees C at [K+] 5.9 mM (n = 12) to 6.7 +/- 0.6 degrees C at [K+] 3.6 mM (n = 5) and to 2.24 +/- 0.40 degrees C at [K+] 2.38 mM (n = 5). Temperature of the cold heart standstill had the liner relationship to Ig[K+]. Change the perfusion fluid with 5.9 mM K+ after heart cold standstill by the perfusion fluid with 3.6 mM K+ restored the heart beats to the rate of 40-50 min-1 in some experiments. The second heart standstill was at the mean temperature 3.6 degrees C lower than the first one.     

Effect of a ubiquinone-like molecule on oxidative energy metabolism in rat cortical synaptosomes at different ages

Persistent stimulation of energy consumption, induced by depolarization with veratridine, mimics a condition of abnormally enhanced energy demand and causes an increase in the oxygen consumption rate (QO₂) and in the interconversion of pyruvate dehydrogenase complex (PDHc) into its active form. Wistar rats at the age of 26 months do not show alterations of QO₂ and of the ability of veratridine to increase QO₂ in comparison with 6 month-old animals whereas the active form of PDHc is slightly but significantly reduced. Idebenone, a ubiquinone-like molecule (1 M), does not affect the QO₂ or PDHc activation state in resting conditions but attenuates the veratridine-challenged increase in QO₂ at all the ages tested and attenuates the increase in the percentage of PDHa reaching statistical significance in 26-month-old rats. At higher concentration (10 M) idebenone totally abolishes the veratridine-induced increase in PDHa also in the 6 month-old rats. At the lower concentration, the drug does not affect the increase in QO₂ induced by an uncoupler of oxidative phosphorylation. The results obtained suggest a protective effect of idebenone on the cerebral tissue against stressful conditions; this action may be exerted at the level of some mitochondrial component and/or on the Na⁺ homeostasis.     

Volumetric studies on the red nucleus of the rat at different ages.

The postnatal development of the red nucleus in albino rat was quantitatively studied. Planimetric studies on stained paraffin sections of the midbrain showed that the red nucleus has a rounded contour with tapering ends and a broad centre. The volume of the red nucleus revealed an increase from birth, to reach its maximum at the age of 3 months, then declines until the age of 2 years. However, the size does not regain its newly born value. On the other hand, the number of cells remains constant during the entire life span of the animal.     

Rosette-forming T cells in human peripheral blood at different ages

Rosette-forming T cells (RFC) were studied in 51 human volunteers, ranging in age from 16 to 69 yr. Subjects were divided in six groups, according to age (Table 1). The percentage of RFC was constant in Groups 2, 3, and 4 (20–49 yr) and slightly but significantly higher in Group 1. On the contrary, it dropped significantly in Groups 5 and 6. This drop in per cent of RFC is coincident with a drop of thymic function; it should be taken in account whenever RFC are studied as a clinical test.     

Embryos of different ages transferred to the rat oviduct enter the uterus at different times

Indirect evidence of embryo signalling to the oviduct was sought in rats by examining the transport of embryos of different ages. One-cell or four-cell embryos were transferred to the oviducts of recipient rats on Day 1 of pregnancy, and the number, condition, and location of native and transferred embryos was assessed on Day 4. To control for the effect of the presence of foreign embryos and excess number of eggs and the transfer procedure upon the fate of native embryos, other groups of rats were sham-operated or left undisturbed. Recipients had a mean number of ova significantly higher than controls. In controls and recipients of 1-cell embryos, the majority of eggs reached the morula stage and all of them were located in the oviducts. In those animals receiving 4-cell embryos, half of the eggs had reached the blastocyst stage and 28% were in the uteri (p less than 0.005). These results support the idea that advanced embryos can influence the timing of their entrance to the uterus in rats.     

Calcitonin- and somatostatin-positive cells in thyroid gland of pigs at different ages

Immunohistochemical studies were carried out on calcitonin-, somatostatin- and serotonin-reactive cells in newborn pigs and pigs at 3 weeks and 7 months old. The aim of these studies was to examine if the expression of various bioactive substances by parafollicular cells in the pig thyroid varied during development. The volume density of the follicular epithelium was nearly the same in newborn and 3-week-old piglets and significantly lower in 7-month-old animals. The volume density of calciton-in-positive cells, expressed as a percentage of the follicular epithelium density, was similar in young animals, being 12.10% and 13.03% in newborn and 3-week-old piglets, respectively. A small but significant increase to 14.40% was seen in 7-month-old pigs. Somatostatin-positive cells formed a much smaller population at all time points, but these also showed a significant increase with age (0.13%, 0.17% and 0.52% of follicular epithelium density in newborn, 3-week- and 7-month-old pigs, respectively). However the changes in the volume density of somatostatin-positive cells correlated inversely with thyroid activity, the density being highest when the activation index was lowest, suggesting that thyroid activity may be regulated by an increase in the synthesis of this inhibitory peptide. Serotonin-positive cells were extremely rare at all time points and their volume density was not calculated.     

Effects of chronic exercise on the kidneys at different ages

In order to determine the effects of chronic exercise on the kidneys at different ages, young, adult, and old rats swam 1 hour either daily or twice a week for 10 weeks and then were killed along with unexercised controls. The kidneys were removed and sections were prepared for histometric analysis including planimetric measurements on camera lucida drawings of renal components and line sampling. With both degrees of exercise young rats showed lower kidney weight, fewer glomeruli and less medullary tissue than unexercised controls. In the adult group no significant differences were noted between exercised and unexercised rats. In old rats both degrees of exercise resulted in a loss of kidney weight and medullary and cortical mass, and a decrease in size of glomeruli while total number of glomeruli remained unchanged. Thus the effects of chronic exercise on the kidneys varied with age. Retarded kidney development occurred in young animals; a loss of renal tissue in old animals; and no change in adult animals.     

The relation of protein synthesis to the concentrations of free and membrane-bound ribosomes in brain at different ages

Free and membrane-bound ribosomes were prepared from the brains of young (3- and 8-day-old) and adult (30 day) rats by the method of Ramsey and Steele (1977). Though the concentration of RNA in young brain is higher than that in adult brain, the fraction of the RNA which is ribosomal is virtually the same (64%) as is the ratio of free ribosomes total ribosomes (61%) at all ages studied. The rate of protein synthesis measured in vivo, expressed in the usual terms of “% per h”, is much higher in young compared to adult brain, but when expressed as the ribosomal specific activity, i.e. “mg protein synthesized per hour per mg ribosomal RNA”, is the same in the three age groups (0.61, 0.58 and 0.60, respectively). Thus, even during early development, when protein is increasing rapidly, ribosomes are no more active than in adult brain, suggesting that synthesis rates in brain are limited by ribosomal content.