RESUMO
Hovering flight has been described as the most energetically expensive form of locomotion. Among the vertebrates, hummingbirds weighing only 1.5-20 g are the elite practitioners of this aerial art. Their flight muscles are, therefore, the most oxygen demanding locomotor muscles per unit tissue mass of all vertebrates. Tissue level functional and structural adaptations for oxygen transport are compared between hummingbirds and mammals in this paper. Hummingbirds present extreme structural adaptations in their flight muscles. Mitochondrial densities greater than 30 per cent are observed in their pectoral muscles, and the surface area of the inner membrane of their mitochondria is tvace that of mammals. This doubling of their mitochondrial oxidative capacity is accompanied by a proportional increase in the specific activity (per g tissue) of the mitochondrial manganese superoxide dismutase (SOD-Mn) in their flight muscles, thus indicating that oxygen toxicity is not a constraint in the aerobic performance of hummingbirds during hovering flight. Finally, the liver appears to play a major role in providing the necessary substrates for their high aerobic performance, and also in eliminating the oxygen free radicals formed during oxidative phosphorylation.
Assuntos
Animais , Citrato (si)-Sintase/metabolismo , Consumo de Oxigênio/fisiologia , Voo Animal/fisiologia , Mitocôndrias Musculares/fisiologia , Aves/fisiologia , Fosforilação OxidativaRESUMO
Hovering flight has been described as the most energetically expensive form of locomotion. Among the vertebrates, hummingbirds weighing only 1.5-20 g are the elite practitioners of this aerial art. Their flight muscles are, therefore, the most oxygen demanding locomotor muscles per unit tissue mass of all vertebrates. Tissue level functional and structural adaptations for oxygen transport are compared between hummingbirds and mammals in this paper. Hummingbirds present extreme structural adaptations in their flight muscles. Mitochondrial densities greater than 30% are observed in their pectoral muscles, and the surface area of the inner membrane of their mitochondria is twice that of mammals. This doubling of their mitochondrial oxidative capacity is accompanied by a proportional increase in the specific activity (per g tissue) of the mitochondrial manganese superoxide dismutase (SOD-Mn) in their flight muscles, thus indicating that oxygen toxicity is not a constraint in the aerobic performance of hummingbirds during hovering flight. Finally, the liver appears to play a major role in providing the necessary substrates for their high aerobic performance, and also in eliminating the oxygen free radicals formed during oxidative phosphorylation.
Assuntos
Aves/fisiologia , Citrato (si)-Sintase/metabolismo , Voo Animal/fisiologia , Mitocôndrias Musculares/fisiologia , Consumo de Oxigênio/fisiologia , Animais , Fosforilação OxidativaRESUMO
The processes of chylomicron lipolysis and removal from plasma were investigated by the intra-arterial infusion of doubly labeled artificial chylomicrons in rats. The rate of lipolysis was measured as a delipidation index (DI), which is the glyceryl-tri-9,10(N)-3H oleate (3H-TO) fraction removed from the particle as fatty acids, whereas the cholesteryl(1-14C) oleate (14C-CO) plasma disappearance rate measures the splanchnic organ particle uptake. In the alloxan-diabetic rats, despite a normal DI, the 14C-CO plasma residence time (RT) was longer than in control animals and remained longer after stimulation of the lipoprotein lipase by heparin. DI and 14C-CO removal rate were not significantly altered by insulin administration to glucose-supplemented control rats. Lipolysis was remarkable in propylthiouracil (PTU)-induced hypothyroidism, and yet the 14C-CO removal rate was retarded. In hypothyroidism, heparin enhanced the 14C-CO removal more than in the control group; however, after heparin, the 14C-CO RT still remained higher in the hypothyroid animals as compared with the control group. Hyperthyroidism lowered the DI; nevertheless, the 14C-CO disappearance rate was faster than in controls. In summary, lack or excess of thyroid hormone influences both the chylomicron lipolysis and removal systems, whereas lack of insulin impairs mostly the particle removal from plasma, and excess of insulin has no effect on the chylomicron metabolism.
Assuntos
Quilomícrons/sangue , Insulina/farmacologia , Hormônios Tireóideos/farmacologia , Animais , Ésteres do Colesterol/sangue , Quilomícrons/síntese química , Diabetes Mellitus Experimental/sangue , Heparina/farmacologia , Hipertireoidismo/sangue , Hipotireoidismo/sangue , Lipólise , Masculino , Ratos , Ratos Endogâmicos , Trioleína/análiseRESUMO
Lovastatin, a potent inhibitor of the enzyme 3-hydroxy-3-methylglutaryl-coenzyme-A-reductase, was investigated in a placebo-controlled trial of 26 primary hypercholesterolemic subjects. Drug dosage varied from 20 to 40 mg/d in a single dose on a 12 weeks treatment period. Average plasma cholesterol reduction levels were 17 and 31%, and LDL-cholesterol 24 and 41% on 20 and 40 mg/d respectively. High-density lipoprotein and triglycerides levels did not change significantly. Similar mean decreases in total plasma cholesterol and LDL-cholesterol levels were observed in hypercholesterolemics irrespectively of being of familial origin or not. No serious clinical and laboratory abnormalities were observed. In this study, lovastatin was a well tolerated and effective agent for the treatment of non familial and heterozygous familial hypercholesterolemia.