ABSTRACT
NEW FINDINGS: What is the central question of this study? What are the mechanisms by which equine sweat glands transport sodium, potassium and water into sweat? What is the main finding and its importance? The flux of sodium into sweat does not have an active transport component, the flux of potassium into sweat is partially dependent on an active transport mechanism, and there is no evidence for paracellular transport. ABSTRACT: In two series of experiments, this study used radioactive sodium (Na+ ) and potassium (K+ ) to trace the net flux, and calculate the unidirectional fluxes, of these ions from extracellular fluid into sweat of horses during exercise and recovery. The effect of an oral electrolyte supplement (PNW) on the sweating responses and ion fluxes was also examined. Compared to 8 litres of water (controls), provision of 8 litres of PNW resulted in significantly increased sweating duration (P < 0.001). Two hours before exercise, 99 Tc-labelled diethylene-triamine-pentaacetate (DTPA) was administered i.v. to determine if there was paracellular flux of this molecule in sweat glands during the period of sweating. One hour before beginning moderate-intensity exercise, horses were nasogastrically administered either 24 Na (1-3 litres) or 42 K (8 litres) with water (control) or an electrolyte supplement. Both radiotracers appeared in sweat within 10 min of exercise onset, and the sweat specific activity of both ions increased during exercise (P < 0.001), approaching plasma specific activities. There was no appearance of 99 Tc-DTPA in sweat. The activities of 24 Na and 42 K, together with the concentrations Na+ , K+ and Cl- , argued against significant paracellular flux of these ions into the lumen of sweat glands. The flux analysis for 24 Na indicated a small intracellular pool within sweat gland cells, and no evidence for an active transport component. The flux analysis for 42 K indicated a relatively large intracellular equilibration pool within sweat gland cells, with evidence for an active transport component. The results are discussed with respect to the current understanding of sweat gland epithelial cell ion transport mechanisms at both the basal and the apical membranes. It appears likely that the majority of ions appearing in sweat pass through sweat gland epithelial cells by transcellular mechanisms that include ion transporting pathways as well as apical vesicular exocytosis.
Subject(s)
Physical Conditioning, Animal , Sweat , Animals , Chlorides/metabolism , Horses , Physical Conditioning, Animal/physiology , Potassium/metabolism , Sodium/metabolism , Sweat/metabolism , Sweating , WaterABSTRACT
RESUMO: The effects of anesthesia with the essential oil of Ocimum gratissimum (EOO) in parameters of stress after handling were investigated in silver catfish (Rhamdia quelen). EOO was obtained from the aerial parts by hydrodistillation. Juveniles were anesthetized with 70 or 300 mg L-1 EOO and submitted to air exposure for 1 minute. The fishes were sampled immediately or transferred to anesthetic-free aquaria until sampling. In the first experiment, juveniles had their blood collected at 0, 1, 4, and 8 h after handling to assay plasma cortisol and blood glucose levels. The unanesthetized animals were restrained manually for blood collection. In the second experiment, water samples of the recovery aquaria were collected to evaluate net ion fluxes at 0 - 4 h and 4 - 8 h. Water and ethanol controls were also performed under the same conditions. The results showed that the cortisol levels did not differ among the treatments. Hyperglycemia was verified in fish exposed to 70 and 300 mg L-1 EOO at 1 h and 4 h after handling. After 8 h, cortisol and glucose concentrations were lower or similar than those from immediately after handling for all treatments. EOO anesthesia prevented Na+ efflux observed in the control groups in both flux periods. There were net Cl- and K+ effluxes at 0 - 4 h and influxes at 4 - 8 h after handling in most treatments, and these fluxes did not differ among the treatments. The results suggest that EOO did not impair stress recovery and did not act as an additional handling stressor in silver catfish.
RESUMO: Os efeitos da anestesia com o óleo essencial de Ocimum gratissimum (EOO) em parâmetros de estresse após manuseio foram investigados em jundiás (Rhamdia quelen). EOO foi obtido a partir das partes aéreas por hidrodestilação. Os juvenis foram anestesiados com 70 ou 300 mg L-1 de EOO e expostos ao ar por 1 minuto. Os peixes foram amostrados imediatamente ou transferidos para aquários sem anestésico até amostragem. No primeiro experimento, os juvenis tiveram seu sangue coletado em 0, 1, 4, e 8 h após manuseio para avaliar os níveis de cortisol e glicemia. Os animais não anestesiados foram contidos manualmente para coleta sanguínea. No segundo experimento, amostras de água foram coletadas do aquário de recuperação dos animais para avaliação do fluxo iônico entre 0 - 4 h e 4 - 8 h. Grupos controles em água e etanol também foram realizados sobre as mesmas condições. Os resultados demonstraram que os níveis de cortisol não diferiram entre os tratamentos. Hiperglicemia foi detectada em peixes expostos a 70 e 300 mg L-1 de EOO em 1 h e 4 h após o manuseio. Após 8 h, os teores de cortisol e glicose foram menores ou similares aqueles imediatamente após o manuseio para todos os tratamentos. A anestesia com EOO preveniu o efluxo de Na+ observado para os grupos controle em ambos os períodos avaliados. Ocorreram efluxos de Cl- and K+ entre 0 - 4 h e influxos entre 4 - 8 h após o manuseio para a maioria dos tratamentos, e estes eventos não diferiram entre os tratamentos. Os resultados sugerem que o EOO não prejudica a recuperação do animal frente ao evento estressor ou atua como estressor adicional ao manuseio em jundiás.
