The effect of exercise training intensity on thyroid activity at rest.

The influence of exercise training intensity on thyroid activity at rest was studied in male Wistar rats, weighting 114 g +/- 24 (mean +/- SD) at the beginning of the experiment. Animals were assigned to the following groups: untrained controls and rats trained on a treadmill at the speed of 20 m/min over a 5-week period with different intensities: 2 x 60 min weekly, 4 x 60 min, 6 x 20 min, 6 x 40 min and 6 x 60 min weekly. Thyroid peroxidase (TPO) and hepatic iodothyronine 5'-monodeiodinase (5'DI) activities as well as plasma thyroxine (T4), 3,3'5-triiodothyronine (T3) and 3,3'.5'-triiodothyronine (rT3) concentrations were determined. Training intensity was found to influence parameters under investigation. TPO activity was decreased in groups trained 240 min (4 x 60 min and 6 x 40 min) and 360 min (6 x 60 min) weekly in comparison to control, untrained group. Furthermore, a drop in T4 plasma concentration in all trained groups and a decrease in T3 plasma concentration in groups exercising for 120 min (2 x 60 min and 6 x 20 min) weekly, as compared to control, untrained rats, was found. Hepatic 5'DI activity and rT3 plasma concentration were not affected by training. Thus, exercise training in rats seems to elicit the fall in TPO activity and T4 plasma concentration at rest but without changing hepatic 5'DI activity and rT3 plasma concentrations. A decline in T3 plasma concentration, observed in rats trained with the lowest exercise intensities, cold be regarded as transitional effect in adaptation to chronic exercise.

In vivo longitudinal variations in protein synthesis in developing ovine intestines.

Changes in fractional rates of protein synthesis (Ks) were investigated at different small and large intestinal sites in 1-, 5-, and 8-wk-old milk-fed and 8-wk-old weaned lambs, a species with early intestinal maturation similar to most domestic animals and humans, with the use of a flooding dose of L-[3H]valine. Between 1 and 8 wk of age, Ks did not change significantly in the duodenum, the cecum, or the colon of milk-fed lambs, but was depressed by 30% in the jejunum and by 39% in the ileum. This was because of reduced ribosomal capacity, i.e., total RNA-to-protein ratio (Cs) in the jejunum, and also alterations in both Cs and protein synthetic efficiency, i.e., rate of synthesis relative to RNA (KRNA) in the ileum. Ks values throughout the small intestine were significantly higher (45-55%) in weaned lambs than in 8-wk-old milk-fed animals. This enhancement of protein synthesis was mainly related to an increase in KRNA (27-40%). Ks decreased by 43% from the duodenum to the ileum in both milk-fed and weaned 8-wk-old animals, but not in 1- and 5-wk-old milk-fed lambs, because of a marked reduction in KRNA. It was concluded that changes in nutrients at weaning, weaning itself, or both, enhanced protein synthesis without any specific effect on small intestinal site. By contrast, intrinsic developmental factors were responsible only for the regional differences in small intestinal Ks that occurred at 8 wk of age. Longitudinal variations in protein synthesis may contribute to the establishment of the well-recognized jejunoileal gradients of brush-border enzymes and villus height that characterize the mature mammalian small intestine.

Whole-body and tissue protein synthesis during brief and prolonged fasting in the rat.

1. Little information is currently available on protein turnover during chronic protein loss situations. We have thus measured the whole-body and tissue protein fractional synthesis rates (ks), the whole-body fractional protein degradation rate (kd), the capacity for protein synthesis (Cs) and the efficiency of protein synthesis (kRNA) in vivo in fed and fasted (1, 5 and about 9 days) 400 g rats. 2. One day of starvation resulted in a reduced ks and an increased kd in the whole body. ks was selectively depressed in skeletal muscles, mainly owing to a reduced kRNA, and was not modified in heart, liver and skin. The contribution of skin to whole-body protein synthesis increased by 39%. 3. During the phase of protein sparing (5 days of fasting), kd in the whole body decreased below the control fed level. ks in skeletal muscles was sustained because kRNA was restored to 82-98% of the control value. 4. Rats were in a protein-wasting phase after 9 days of starvation. kd in the whole body did not increase and was actually 78% of the value observed in fed animals. By contrast, ks in the whole body and tissues decreased to 14-34% of the control values, owing to reductions in both Cs and kRNA. Whatever the duration of the fast, the contribution of the skin to whole-body protein synthesis largely exceeded that of skeletal muscle. 5. The present findings suggest that the main goal in the treatment of chronic protein loss should be to sustain protein synthesis.(ABSTRACT TRUNCATED AT 250 WORDS)

Brief fasting decreases protein synthesis in the brain of adult rats.

The influence of starvation on protein synthesis in the adult rat brain was studied in vivo by an intravenous injection of a flooding dose of unlabeled valine including a tracer dose of L-[3,4(n)-3H]valine. Brief starvation (24 hours) induced a 20% decline in fractional and absolute rates of brain protein synthesis. This decline resulted from a 20% decrease in the efficiency of protein synthesis (microgram protein synthesized per day per microgram RNA) whereas the capacity for protein synthesis (microgram RNA per mg protein) was maintained. Prolonged starvation (5 days) was marked by no further significant changes in the fractional rate, absolute rate and efficiency of protein synthesis, whereas the capacity for protein synthesis decreased slightly. The relative contribution of brain to whole-body protein synthesis increased during fasting, and neither the protein nor the RNA brain content did change during the experiment. These results clearly indicate that brain proteins are spared in response to brief and prolonged food deprivation, and that brain protein synthesis is very sensitive to short-term fasting.

Pineal influence on the diurnal rhythm of nonspecific immunity indices in chickens.

The effect of pinealectomy and melatonin injections on the diurnal rhythms of serum lysozyme and blood granulocytes was examined in White Leghorn cockerels kept from time of hatching for 5 weeks in L:D 12:12 conditions and immunized twice with sheep red blood cells (SRBC). Pinealectomy or sham-operation was made during first week of life. Pinealectomized chickens were injected daily with a melatonin dosage increased over 4 consecutive weeks (the dosage was 10, 13, 16, and 20 ng per bird daily during the 4 weeks, respectively; MEL I) at the beginning of darkness. The same treatment was performed on chickens with an intact pineal gland using additional melatonin doses increased 10 times (MEL II) and 500 times (MEL III). Intact chickens were also injected with MEL II and MEL III 4 hr before the end of light. Control birds received equivalent injections of vehicle. Five-week-old chickens were sacrificed during a 24-hr period every 4 hr. The existence of diurnal rhythm was evaluated by cosinor analysis. Pinealectomy shifted the acrophase of the diurnal rhythm of granulocytes and abolished that of serum lysozyme. Both rhythms were restored in pinealectomized chickens by MEL I but not by vehicle injections. The same melatonin dose was unable to change the granulocyte rhythm but delayed the acrophase of that of serum lysozyme in chickens with an intact pineal gland. Two higher melatonin doses influenced the diurnal rhythm of granulocytes as a function of dose and time of administration. The rhythm of serum lysozyme was dependent only on the time of injection. The pineal gland seems to control, via its hormone melatonin, the diurnal rhythm of nonspecific immunity in chickens.

Influences of age and weaning on in vivo pancreatic protein synthesis in the lamb.

In vivo pancreatic protein synthesis rates were obtained from the uptake of L-[3,4(n)-3H]valine co-injected with a flooding dose of unlabeled valine into 1-, 5-, and 8-wk-old suckling lambs, and 8-wk-old weaned animals. Protein fractional synthesis rate was 184%/d at 1 wk of age and 153%/d in 5-wk-old animals (P greater than 0.05). This lack of developmental change resulted from constant (P greater than 0.05) ribosomal capacities (total RNA/protein ratios) and efficiencies of protein synthesis (synthetic rates relative to RNA). No further alteration for protein fractional synthesis rate (144%/d) occurred in 8-wk-old suckling animals (P greater than 0.05). In contrast, 8-wk-old ruminants exhibited higher protein fractional synthesis rate (244%/d) than 8-wk-old suckling animals, although ribosomal capacity was markedly higher in both 8-wk-old groups than in youngest animals (P less than 0.05). The present findings clearly indicate that in vivo protein synthesis in the developing ovine pancreas depends primarily on age. Potentialities for increased rates of pancreatic protein synthesis, i.e., increases in total RNA content and ribosomal capacity appear between 5 and 8 wk of age in this species. At 8 wk of age, however, when lambs are generally weaned, solid food ingestion resulted in a rise for both fractional and absolute rates of protein synthesis, essentially because ruminants maintained a higher efficiency of protein synthesis than milk-fed animals (P less than 0.005). Finally, there was a relationship between pancreatic protein synthesis and protein intake in only ruminant lambs.

Respective influences of age and weaning on skeletal and visceral muscle protein synthesis in the lamb.

1. The influences of age and weaning on muscle protein synthesis were studied in vivo, by injecting a large dose of [3H]valine into 1-, 5- and 8-week-old suckling or 8-week-old weaned lambs. 2. The fractional rates of protein synthesis, in red- and white-fibre-type skeletal muscles or striated and smooth visceral muscles, were in 8-week-old suckling animals 24-37% of their values at 1 week of age. This developmental decline was related to decreased capacities for protein synthesis, i.e. RNA/protein ratios. 3. At 8 weeks of age, suckling and weaned lambs had similar fractional synthesis rates, capacities for protein synthesis and efficiencies of protein synthesis (i.e. rates of protein synthesis relative to RNA) in skeletal muscles. 4. In contrast, visceral-muscle fractional synthesis rates were lower in 8-week-old suckling lambs than in weaned animals, owing to decreased efficiencies of protein synthesis. It was concluded that developmental factors and the change to a solid diet, or weaning in itself, or both, affect differently skeletal and visceral muscle protein synthesis in the immature lamb.

Effect of prolactin on the diurnal changes in immune parameters and plasma corticosterone in white leghorn chickens.

The effect of PRL on the diurnal changes in peripheral lymphocyte and granulocyte number, anti-sheep red blood cells, and natural anti-rabbit red blood cells serum agglutinins titre as well as plasma corticosterone concentration was examined in White Leghorn cockerels, immunized twice with sheep red blood cells. PRL was administered for six consecutive days at 4 or 8 h after light onset. Control birds were treated at the same times with hormone solvent alone. Immunized non-treated birds served as an additional control group. PRL injections influenced markedly the diurnal changes in all parameters examined. The effect of PRL administration on the diurnal changes in lymphocyte and granulocyte number and natural anti-rabbit red blood cells serum agglutinins consisted in elimination of the influence of solvent injections. In those cases where the solvent injections did not alter the pattern of the diurnal changes, i.e. in anti-sheep red blood cells serum agglutinins and in plasma corticosterone concentration, the pattern was modified by PRL injections. PRL administration affected also the correlations between the diurnal changes in plasma corticosterone concentration and those in lymphocyte number and anti-sheep red blood cells agglutinin titre. This suggests that the role of PRL in the regulation of the diurnal variations of immunity in chickens may be realized either directly, via its receptors in immune system or by its influence on plasma corticosterone concentration.

Daily variations in response of certain immunity indices to prolactin in White Leghorn chickens.

The purpose of this experiment was to elucidate whether the effect of exogenous prolactin (PRL) on immunity parameters of White Leghorn chickens varies during the day. The experiment was carried out on cockerels kept after hatching during 6 weeks under L:D = 12:12 conditions. During 5 consecutive days cockerels were injected with bovine PRL (150 micrograms per bird daily) or its solvent at different time points, i.e., at 0, 4, 8 or 12 HALO (Hours After Light Onset). The birds were sacrificed 24 hours after the last injection at the same time point when the injections were given. It was found that given at 4 HALO prolactin raised, whereas at 8 HALO it decreased the peripheral lymphocyte number. PRL had no effect on granulocyte number, natural anti-rabbit red blood cells (anti-RRBC) agglutinin titre and serum lysozyme activity. Administered at 0 and 12 HALO PRL tended to decrease the thymus and bursa of Fabricius weight. This different PRL effect on peripheral lymphocytes in chickens during the circadian period may be one of the causes of varying effect of this hormone on immunity (stimulatory or suppressive) described in literature. The role of PRL in regulation of immunity is discussed in relation to the possibility of PRL receptors occurrence on chickens lymphocytes.

Effect of exogenous prolactin on immunity in chickens.

The effect of exogenous prolactin on the number of peripheral white blood cells (WBC), anti-sheep red blood cell (anti-sheep RBC) and anti-rabbit red blood cell (anti-rabbit RBC) agglutinins was investigated in White Leghorn cockerels immunised twice with sheep RBC. It was found that prolactin, when administered for five days after second immunisation, raised production of anti-sheep RBC antibodies and lymphocyte number in comparison with the control group given injections of the solvent. Repeated injections of the solvent resulted in statistically significant differences in the number of granulocytes and lymphocytes.

Diurnal changes in certain immunity indices and plasma corticosterone concentration in white Leghorn chickens.

The experiment was performed on 3 groups of White Leghorn chickens kept under L : D = 6 : 18, 12 : 12 and 18 : 6 photoperiods, respectively. One half of each group was immunized twice with SRBC. Non-immunized birds served as controls. It was found that diurnal variations in lymphocyte and granulocyte number, serum lysozyme activity, agglutinins anti-sheep red blood cells (SRBC) and anti-rabbit red blood cells (RRBC) titer and plasma corticosterone concentration depended on light conditions. Immunization affected diurnal changes in different degree, depending also on the photoperiod applied. Various interrelationships between the diurnal changes in plasma corticosterone level and those in immune parameters were found. A distinct negative correlation between plasma corticosterone concentration and lymphocyte number was seen in L : D = 12 : 12 in the non-immunized group only.