Biomedical subjects

A Lanni

Publications and source records attributed to A Lanni.

At least 37 records · Page 2Linked to original sources

PubMed1996

Calorigenic effect of diiodothyronines in the rat.

1. In hypothyroid rats, we determined the effects of administration of different doses of 3,3',5-triiodo-L-thyronine (T3), 3,3'-diiodo-L-thyronine (3,3'-T2) and 3,5-diiodo-L-thyronine (3,5-T2) ("T2 isomers' refers specifically to these latter two isomers throughout this paper) on resting metabolism (RM) and on the oxidative capacity (measured as cytochrome oxidase activity) of tissues that are metabolically very active. 2. The T2 isomers induced a dose-dependent calorigenic effect when injected I.P. into hypothyroid rats. The increase in RM was already evident at a dose of 2.5 micrograms (100 g body wt)(-1), and the greatest effect was observed at the highest dose, 10 micrograms (100 g body wt)(-1), when RM reached a value not significantly different from that of the euthyroid controls (1.92 +/- 0.08 and 1.93 +/- 0.13 (1 O2) kg(-1) h(-1) for 3,5'-T2, respectively, vs. 2.1 +/- 0.12 (1 O2) kg(-1) h(-1) for euthyroid controls). T3 administration restored RM to normal euthyroid values, even at a dose of 2.5 micrograms (100 g body wt)(-1). 3. The effect of T2 isomers on RM was paralleled by an increase in the oxidative capacity of tissues that are metabolically very active (liver, skeletal muscle, brown adipose tissue (BAT) and heart). The increases were between 33% (liver + 3,3'-T2) and 63% (muscle + 3,3'-T2). By contrast, T3 induced its greatest effect on the liver, with a smaller effect on skeletal muscle, but no significant stimulation in heart and BAT, whatever the dose. 4. These results suggest that T8 isomers might be mediators of the direct thyroid hormone regulation of energy metabolism.

Animals↗

PubMed1996

Biochemical and functional differences in rat liver mitochondrial subpopulations obtained at different gravitational forces.

Previous studies have reported that liver mitochondria may be fractionated into different subpopulations. However, no careful studies have been performed to exclude mitochondrial damage and to investigate more thoroughly the possible biochemical differences existing between the subpopulations. In this study, we analysed the integrity and the biochemical properties of rat liver mitochondria. Mitochondrial fractions were obtained by differential centrifugation at different gravitational forces: 1000 g (M1 fraction), 3000 g (M3 fraction) and 10,000 g (M10 fraction). The integrity of these organelles was checked by measuring citrate synthase activity both in the presence and absence of Triton X-100 detergent. Biochemical analyses included polarographic determination of cytochrome oxidase activity and respiratory parameters and spectrophotometric determination of cytochrome content. (1) The integrity of mitochondria was almost homogeneous between fractions (88.5, 80 and 78.3% in M1, M3 and M10 fractions, respectively). (2) The heaviest M1 fraction contains mitochondria which are on average twice as large as M3 and about three times as large as M10. (3) The M1 fraction exhibited the highest specific cytochrome oxidase activity (1040 +/- 20 n Atoms O/min x mg protein) and the highest respiratory rates (72 +/- 3 n Atoms O/min x mg protein and 526 +/- 45 n Atoms O/min x mg protein for States 4 and 3, respectively). Oxidative capacity and respiratory rates decreased as the size of the organelles decreased, reaching values of 1/5 and 1/14 in the M3 and M10 fractions as compared to the M1. (4) These changes are accompanied by a change in the respiratory control ratio (RCR), which varies from 7.3 in M1 to about 2.0 in M10. A similar trend was observed in cytochrome contents but the differences were not as great as cytochrome oxidase activity and State 3 respiration. These results, as a whole, show that a mitochondrial heterogeneity exists in rat liver cell. We suggest that the above-mentioned differences might represent steps of mitochondrial maturation. The maturation would be fundamentally based on the increase of efficiency of the mechanism for ATP synthesis.

Acid Phosphatase↗

PubMed1995

Relationship between dose, mode of administration and effects of triiodothyronine on two hepatic responsive enzymes.

We have examined serum 3,3',5-triiodo-L-thyronine (T3) levels and the activity of two hepatic responsive enzymes [malic enzyme (ME) and alpha-glycerophosphate dehydrogenase (alpha-GPD)] in the livers of hypothyroid rats, under conditions where different doses of T3 (1 and 2.5 micrograms/100 g b.w.) were administered daily for one week either by intraperitoneal injection or by continuous infusions. In infused animals, serum T3 concentrations were constant for the whole period of treatment while in injected groups, widely oscillating diurnal levels were observed. The injection of 2.5 micrograms/100 g b.w. resulted, at the end of the treatment, in serum T3 levels which were higher than in animals receiving the same dose by infusion. No significant differences were observed when the administered dose was 1 microgram/100 g b.w. The basal levels of alpha-GPD and ME, which were markedly reduced in the livers of hypothyroid rats, were returned to normal both in infused rats (both with the dose of 1 microgram and 2.5 micrograms/100 g b.w. of T3) and in rats injected with a dose of 1 microgram/100 g b.w.). On the other hand, the dose of 2.5 micrograms/100 g b.w. when administered by injection, resulted in alpha-GPD and ME activities which were significantly higher even than those found in normal ones. The results indicate that both the diurnal T3 profile and the activity of the two hepatic T3 responsive enzymes are dependent not only on the dose but also on the administration mode.

Animals↗

PubMed1994

Specific binding sites for 3,3'-diiodo-L-thyronine (3,3'-T2) in rat liver mitochondria.

Specific binding sites for 3,3'-T2 can be detected in swollen and osmotically treated mitochondria (OTM) from normal and hypothyroid rat liver. In hypothyroid animals, maximal values of binding were obtained at 0 degrees C while values were lower at 37 degrees C and no specific binding could be observed at 60 degrees C. Binding was maximal at pH 6.4 and the mean values for the apparent association constant (Ka) and the binding capacity were on average 0.5 x 10(8) M-1 and 2.4 pmol/mg mitochondrial protein, respectively. No differences were observed between normal and hypothyroid rats with the exception of the capacity that was higher in normal animals (5.5 pmol/mg mitochondrial protein). The specificity of 3,3'-T2 binding, examined in competition studies, followed this order: 3,3'-T2 > 3,5-T2 > rT3. The other iodothyronines (3',5'-T2, T3, T4, 3-T1, 3'-T1, 3,5-Diac and 3,3'-Diac) showed only a small competition or none at all.

Animals↗

PubMed1994

Interaction of diiodothyronines with isolated cytochrome c oxidase.

Diiodothyronines (3,3'-T2 and 3,5-T2) stimulate the activity of isolated cytochrome c oxidase (COX) from bovine heart mitochondria. Maximal stimulation of activity (about 50%) is obtained with 3,3'-T2 at pH 6.4 and with 3,5-T2 at pH 7.4. In contrast, 3,5,3'-triiodothyronine (T3) exhibited no or little stimulation of COX activity. Binding of the hormones to COX leads to conformational changes as shown by modified visible spectra of the oxidized enzyme. It is suggested that 'short-term' effects of thyroid hormones on mitochondrial respiration are at least partly due to the allosteric interaction of diiodothyronines with the COX complex.

Animals↗

PubMed1994

Cold exposure induces different uncoupling-protein thermogenin masking/unmasking processes in brown adipose tissue depending on mitochondrial subtypes.

The effect of cold exposure on thermogenic parameters such as mitochondrial protein content, GDP-binding and uncoupling protein (UCP) levels in different mitochondrial fractions from rat brown adipose tissue has been investigated. Rats were exposed from 12 h to 5 days at 4 degrees C, and three mitochondrial fractions were isolated by differential centrifugation: the M1 fraction (1000 g), the M3 fraction (3000 g) and the M15 fraction (15,000 g). Cytochrome c oxidase activity as an index of mitochondrial mass showed an increase during cold exposure. During the first 24 h of cold exposure UCP was incorporated specifically into the M3 and M15 mitochondrial fractions, and thereafter UCP appeared in the heaviest M1 fraction. However, specific GDP binding was increased during the first 24 h in the same way in all subpopulations, and this increase continued up to 72 h of cold exposure. Results suggest that different molecular events are involved during acute and chronic adaptation to cold: during the first 24 h of cold acclimatization, thermogenic activity is increased by an unmasking process of the UCP binding sites in the M1 mitochondrial fraction as UCP levels were constant and GDP binding increased, but in the M3 and M15 fraction the increase in thermogenic activity was completely due to an increase in GDP binding induced by a specific incorporation of UCP targeted to these mitochondria. Thus thermogenic parameters change in a different way in the brown-fat mitochondrial subpopulations during cold acclimatization.

Acclimatization↗

PubMed1994

Rapid stimulation in vitro of rat liver cytochrome oxidase activity by 3,5-diiodo-L-thyronine and by 3,3'-diiodo-L-thyronine.

The effect of the iodothyronines (thyroxine (T4), 3,5,3'-triiodo-L-thyronine (L-T3), 3,5-diiodo-L-thyronine (3,5-T2), 3,3'-diiodo-L-thyronine (3,3'-T2), 3',5'-diiodo-L-thyronine (3',5'-T2), 3'-monoiodo-L-thyronine (3'-T1), 3-monoiodo-L-thyronine (3-T1) and thyronine (T0)) on rat liver cytochrome oxidase (COX) activity after their addition to rat liver homogenate and isolated mitochondria from normal and hypothyroid rats has been investigated. The addition of 3,3'-T2 and 3,5-T2 (T2s) to the liver homogenate from hypothyroid rats, but not from normal rats, significantly enhanced COX activity. The addition of T3 had a remarkably lower effect that was almost completely abolished when the propylthiouracil (PTU), an inhibitor of the type I deiodinase activity, was also added to the incubation mixture. After the addition of T2s the maximum effect was obtained at a concentration of about 10(-6) M for both 3,3'-T2 and 3,5-T2, while a 50% increase was obtained at a concentration of about 10(-9) M in both cases. The effects of T2s were rapid and already evident after 5 min of incubation (+40-50%). The maximal effect was reached after only 30 min of incubation. The above effects were not observed after the addition of T2s to the isolated mitochondria. The results clearly demonstrate that both 3,3'-T2 and 3,5-T2 directly stimulate mitochondrial COX activity which is possibly achieved through a cytoplasmic factor. The addition of the other iodothyronines (T4, 3',5'-T2, 3'-T1, 3-T1 and T0).

Animals↗

PubMed1994

Effect of thyroid status on the oxidative capacity of Sertoli cells isolated from immature rat testis.

Our previous studies indicate the Sertoli cell as a target for thyroid hormone action at testis level. In the present study we evaluated the effect of thyroid hormone on Sertoli cell oxidative capacity measured by specific cytochrome oxidase (COX) activity and intracellular adenosine triphosphate (ATP) content. Sertoli cells were isolated from 21-day-old rats. Hypothyroidism, induced from the day of birth by administration of 0.025% methimazole, was characterized by a severe delay of body and testis growth and resulted in a lower COX activity (-40%, p < or = 0.01) and a lower ATP content (-35%, p < or = 0.01) by isolated Sertoli cells. Administration of triiodothyronine (10 micrograms/100 g body wt on alternate days) to hypothyroid rats improved body and testis growth and restored both COX activity and ATP content. The presence of high-affinity, low-capacity binding sites for triiodothyronine in Sertoli cell mitochondria also was demonstrated. This study, unlike that carried out on the whole testis from adult rats, demonstrates that thyroid hormone affects the energy metabolism of Sertoli cells from midpubertal rat testes.

Adenosine Triphosphate↗

PubMed1994

In vitro binding of 3,5-di-iodo-L-thyronine to rat liver mitochondria.

In this study we have demonstrated that specific binding sites for 3,5-di-iodo-L-thyronine (3,5-T2) can be detected in rat liver mitochondria. After incubation with the homogenate, liver mitochondria bound only a small portion of [3,5-125I]T2. The addition of a 100-fold excess of unlabelled 3,5-T2 caused the displacement of on average 50-60% of the [3,5-125I]T2 bound. Specific binding of 3,5-T2 to rat liver mitochondria occurred rapidly; a maximum was achieved after 5 min. Maximal binding was obtained at 37 degrees C, while at 0 degrees C and 20 degrees C the values were only slightly lower. Binding was maximal at pH 7.0; mean (+/- S.E.M.) values for the apparent association constant and the binding capacity (calculated at pH 7.0, 0 degrees C and after 30 min of incubation) were 0.5 +/- 0.04 x 10(8) M-1 and 0.4 +/- 0.04 pmol/mg mitochondrial protein respectively. The specificity of binding, examined in competition studies, followed the order: 3,5-T2 > 3,3'-di-iodo-L-thyronine > 3',3,5-tri-iodo-L-thyronine > thyroxine. Other iodothyronines (3',5'-di-iodo-L-thyronine, 3,5-di-iodo-D-thyronine, 3,3',5'-tri-iodo-L-thyronine, 3-iodo-L-thyronine and 3,5-di-iodothyroacetic acid) showed little or no competition. This suggests that the specific 3,5-T2 binding sites could be of biological relevance with respect to the understanding of the mechanism of physiological action of thyroid hormones at the cellular level.

Adenosine Triphosphate↗

PubMed1993

Effect of cold acclimation on oxidative capacity and respiratory properties of liver and muscle mitochondria in ducklings, Cairina moschata.

1. The effect of cold acclimation on the oxidative capacity of the skeletal muscle (gastrocnemius and pectoralis) and the liver of ducklings was investigated. 2. In cold-acclimated (CA) ducklings, the oxidative capacity of the liver was higher (+40%) than in ducklings reared at thermoneutraility (TN). In these animals an increase in state 4 respiration and a decrease in the respiratory control index (RCI) was also found. 3. The oxidative capacity of both pectoralis and gastrocnemius muscles also increased in CA animals. 4. In these muscles the oxidatibe capacity of the subsarcolemmal mitochrondrial fraction of CA ducklings was higher (+96% in the gastrocnemius and +58% in the pectoralis) than the intermyofibrillar one (+51% in the gastrocnemius and +33% in the pectoralis). No variations were observed in either the RCI or the ADP/O ratios. 5. These findings indicate that the energy expenditure needed for non-shivering thermogenesis (NST) in cold-acclimated ducklings can be met by the increase in the oxidative capacity of the skeletal muscle and the liver, each by different mechanisms; the gastrocnemius muscle would seem to play a prominent role.

Acclimatization↗

PubMed1993

Effect of 3,3'-di-iodothyronine and 3,5-di-iodothyronine on rat liver mitochondria.

In the present study we report that 3,3',5-tri-iodothyronine (T3) as well as two iodothyronines (3,5-di-iodothyronine (3,5-T2) and 3,3'-di-iodothyronine (3,3'-T2)) significantly influence rat liver mitochondrial activity. Liver oxidative capacity (measured as cytochrome oxidase activity/g wet tissue) in hypothyroid compared with normal rats was significantly reduced (21%, P > 0.01) and the administration of T3 and both iodothyronines restored normal values. At the mitochondrial level, treatment with T3 stimulated respiratory activity (state 4 and state 3) and did not influence cytochrome oxidase activity. On the other hand, both the mitochondrial respiratory rate and specific cytochrome oxidase activity significantly increased in hypothyroid animals after treatment with 3,3'-T2 or 3,5-T2 (about 50 and 40% respectively). The actions of both iodothyronines were rapid and evident by 1 h after the injection. The hepatic mitochondrial protein content which decreased in hypothyroid rats (9.6 mg/g liver compared with 14.1 in normal controls, P < 0.05) was restored by T3 injection, while neither T2 was able to restore it. Our results suggest that T3 and both iodothyronines have different mechanisms of action. T3 acts on both mitochondrial mass and activity; the action on mitochondrial activity was not exerted at the cytochrome oxidase complex level. The action of the iodothyronines, on the other hand, is exerted directly on the cytochrome oxidase complex without any noticeable action on the mitochondrial mass.

Animals↗

PubMed1992

Effect of 3,3'-diiodothyronine and 3,5-diiodothyronine on rat liver oxidative capacity.

We report that 3,5,3'-triiodothyronine (T3) as well as two other iodothyronines (3,3'-diiodothyronine and 3,5-diiodothyronine (T2s)) stimulate rat liver oxidative capacity (measured as cytochrome oxidase activity (COX)). In hypothyroid rats COX activity and mitochondrial protein content are significantly lower than in normal control animals. The administration of both T3 and T2s to hypothyroid rats significantly enhances hepatic COX activity with T3 having the greatest effect (+60%); moreover, T3 restores the mitochondrial protein content whereas the T2s are ineffective. Administration of T2s results in a faster stimulation (already significant 1 h after the injection) of hepatic COX activity than T3 injection. Our results suggest that T3 acts on the protein synthesis mechanism involved in the regulation of the mitochondrial mass while T2s would act directly at the mitochondrial level.

Animals↗

PubMed1992

Morphometric-stereologic analysis of brown adipocyte differentiation in adult mice.

Brown adipocyte differentiation from interstitial stem cells was analyzed by morphometric-stereologic methods in adult mice. Confirming previous studies, four different stages of development were identified: 1) interstitial cells----2) protoadipocytes (interstitial cells with tiny lipid droplets)----3) preadipocytes----4) mature brown adipocytes. Brown adipocyte precursor cells (interstitial cells and protoadipocytes) occupied only a small fraction of total brown adipose tissue (BAT) volume (1.7 and 1.8%, respectively). Most of the BAT volume was occupied by fully differentiated multilocular cells (65% vol/vol), preadipocytes (12%), and blood capillaries (10%). The differentiation of protoadipocytes into preadipocytes was characterized by a doubling in the cellular volume (from 800 to 1,500 microns 3) that was associated with a fivefold increase in the number of mitochondria (221 to 1,464), an eightfold augmentation in mitochondrial size (from 0.042 to 0.37 microns 3), a fourfold increase in the surface density of the inner mitochondrial membrane (from 8 to 35 microns 2/microns 3), resulting in a 14-fold enlargement in the relative volume of the mitochondrial compartment (from 2 to 29%). This remarkable mitochondrial proliferation was accompanied by an increase in the number and volume of cytosolic lipid droplets. In contrast, the differentiation of preadipocytes into brown adipocytes was mainly characterized by a doubling in the size of the lipid compartment; the mean volume of single droplets increased 35 times but their number decreased 6-7 times. The mitochondrial modifications were minor; there was only a slight increase in the surface density of the inner membrane. In conclusion, the major step of brown adipocyte differentiation consists in the transformation of protoadipocytes into preadipocytes.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue, Brown↗

PubMed1991

Nonshivering thermogenesis in king penguin chicks. I. Role of skeletal muscle.

In cold-acclimatized (CA) king penguin chicks exhibiting nonshivering thermogenesis (NST), protein content and cytochrome oxidase (CO) activity of tissue homogenates were measured together with protein content, CO, and respiration rates of isolated mitochondria from skeletal muscle (gastrocnemius and pectoralis) and liver. The comparison was made with chicks reared at thermoneutrality (TN) for at least 3 wk. In CA chicks showing a NST despite the lack of brown adipose tissue, an increase in thermogenic capacity was observed in skeletal muscle in which the oxidative capacity rose (+28% and +50% in gastrocnemius and pectoralis muscles, respectively), whereas no change occurred in the liver. Oxidative capacity of skeletal muscle increased together with the development of mitochondrial inner membrane plus cristae in muscles of CA chicks contrary to their TN littermates (+30 to +50%). Subsarcolemmal mitochondria of CA chicks had a higher protein content (+65% in gastrocnemius muscle) and higher oxidative capacities than in controls. The lower respiratory control ratio of these mitochondria might result from a low ADP phosphorylation rate. No change occurred in the intermyofibrillar fraction nor in liver mitochondria. These findings together with earlier results obtained in cold-acclimated ducklings indicate the marked and suited adaptation of skeletal muscle and in particular of subsarcolemmal mitochondria allowing them to play a role in NST.

Acclimatization↗

PubMed1991

Nonshivering thermogenesis in king penguin chicks. II. Effect of fasting.

The effect of fasting on the energy metabolism of skeletal muscle and liver was investigated in cold-acclimatized short-term fasting (STF) (3 wk) and naturally long-term fasting (LTF) (4-5 mo) king penguin chicks, both groups exhibiting nonshivering thermogenesis (NST). A comparison was made with nourished cold-acclimatized controls. In these chicks, no brown adipose tissue deposits could be found on electron-microscopic observations of fat deposits. Protein content and cytochrome oxidase (CO) activity of tissue homogenates were measured in liver and pectoralis and gastrocnemius muscles, as were protein content, CO activity, and respiration rates of mitochondria isolated from these organs. Fasting-induced protein loss affected the pectoralis more than the gastrocnemius muscle, thus preserving locomotor function. In STF chicks, specific mitochondrial protein content and specific tissue CO activity were preserved but total organ CO capacity was reduced by half in pectoralis and liver following the fall in organ mass. In LTF chicks, both specific and total CO activity were drastically reduced in muscles, whereas specific CO activity was preserved in liver. In these LTF chicks, muscle mitochondria showed an energized configuration associated with an increased area of inner membrane in gastrocnemius. A reduction of respiratory control ratio (RCR) was observed in subsarcolemmal muscle mitochondria of STF chicks, whereas intermyofibrillar and liver mitochondria kept high RCR values.(ABSTRACT TRUNCATED AT 250 WORDS)

Acclimatization↗

PubMed1990

Liver and brown fat mitochondrial response to cold in the garden dormouse (Eliomys quercinus).

The involvement of two organs, i.e. the liver and the brown adipose tissue (BAT) in response to cold in a hibernating species such as the garden dormouse has been studied. 2. In animals living in the cold, mitochondrial respiratory rates significantly increased (with respect to those living at 28 degrees C) in both organs with a larger increase in the BAT (+152% in the BAT and 67% in the liver). 3. The increase in BAT activity was obtained by a concomitant increase in: (a) the BAT mass (+30%), (b) the total mitochondrial mass (+20%), and (c) the mitochondrial respiratory rate (+64%). In the liver the increase was due only to an augmentation in mitochondrial mass and activity. 4. These results indicate that: (a) the BAT exerts a pre-eminent role in the physiological response to cold of garden dormouse, (b) a certain non-shivering thermogenesis (NST) is present in the liver of such species. In addition we suggest that a local thermoregulatory response would take place in a metabolically important organ such as the liver.

Acclimatization↗

PubMed1990

Elevated hepatic mitochondrial oxidative capacities in cold exposed rats.

1. Hepatic mitochondrial oxidative capacities were studied in rats exposed to cold for periods ranging from 5 to 15 days. The mitochondria obtained in this study were well coupled as shown by RCR and ADP/O ratios. 2. The liver mitochondria of cold exposed rats showed significantly increased respiratory rates (ng atoms of oxygen consumed min-1 mg prot-1), starting from day 10 of cold exposure, using lipid and non-lipid substrates. 3. For non-lipid substrates, the elevated respiratory rates found in the mitochondria could indicate an increased capacity to oxidize these substrates. For the lipid substrate, on the other hand, an enhanced oxidation through Krebs-cycle of a part of acetyl-CoA otherwise utilized to form ketone bodies, could also occur. 4. Taken together the results suggest that, during cold exposure, liver mitochondria could participate in cold adaptation mechanisms, by improving ATP production.

Acclimatization↗

PubMed1989

The effect of thyroid state on respiratory activities of three rat liver mitochondrial fractions.

In this paper we report that three different rat liver mitochondrial fractions, differing in density, exhibit differential effects when the animals are made hypo- or hyperthyroid. The investigations have been performed by correlating the protein content, the succinic dehydrogenase behaviour and the respiratory features of the three fractions in different thyroid states with morphometric-stereologic analysis the electron micrographic level. The results indicate that the thyroid hormone influences both the mass and the functionality of the heavy (H) and light (L) fraction. In hypothyroid rats the H fraction increases (+43%) while the L fraction decreases (-32%) and their respiratory activity is drastically reduced. Adenosine triphosphate (ATP) synthesis in the H fraction is also inhibited. Triiodothyronine (T3) administration to the above animals restores the values observed in control rats. At morphometric level we note in hypothyroid rats an increase in the number of mitochondria together with a concomitant increase in the average volume of a single mitochondrion. We are inclined to explain the above results through an action exerted by T3 on a hypothetical mitochondrial cycle starting with the formation of light organelles from heavy ones.

Animals↗