FITNESS TO DIVE

Stephen Glen
Stirling Royal Infirmary, Livilands, Stirling, Scotland

ABSTRACT
Diving is a recreational sport, which is increasing in popularity world-wide. The risks of diving are significant and medical supervision is required to identify divers with certain medical conditions liable to affect their performance underwater. The UK recently changed the system of medical supervision to a self-administered questionnaire, with support from a national network of doctors with diving medicine experience.
Certain conditions substantially increase the risk of diving, such as epilepsy or recurrent pneumothorax. Divers with conditions such as diabetes and asthma may still be certified fit to dive by if they meet specific criteria. Although most diving incidents are related to technical failure or human error, it is still important to minimise the risk of medical complications in the sequence of events. Divers with patent foramen ovale are at more risk of neurological and cutaneous decompression sickness, although the development of percutaneous closure techniques has allowed such individuals to return to diving.

Key words: diving, decompression sickness, patent foramen ovale, scuba

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INTERRELATIONSHIP BETWEEN CARBOHYDRATE AND LIPID METABOLISM (GLUCOSE - FATTY ACID CYCLE)

Grażyna Lutosławska
Department of Biochemistry, Faculty of Physiology and Biochemistry, Academy of Physical Education, Warsaw, Poland

ABSTRACT
It is well-documented that elevated free fatty acid availability inhibits glucose oxidative metabolism both in vitro and in vivo. This reciprocal relationship between lipid and carbohydrate was described over thirty years ago by Randle in isolated rat heart and diaphragm and named glucose-free fatty acid cycle. The importance of this cycle for physiology and pathophysiology of fuel homeostasis depends on details of its operation in skeletal muscles since this tissue accounts for the largest part of glucose disposal by an insulin-sensitive mechanism in vivo. It is noteworthy that glucose-fatty acid operates in complicated milieu of extramuscular and intramuscular lipids and carbohydrate stores, mutual reciprocal relationship within intramuscular and extramuscular lipid and carbohydrate stores, FFA inhibition of glucose transport into the muscle, FFA stimulation of gluconeogenesis in the liver and FFA stimulation of -cell responsiveness to insulin. This interaction would not have been predicted by the original Randle concept. Nowadays the mechanism of the cycle is well-documented in the myocardium, and in rat liver with a key role of glucose-originated malonyl-CoA, a product of acetyl-CoA carboxylase (ACC) reaction, and a potent inhibitor of carnitine palmitoyltransferase I (CPT I), FFA transport into mitochondria and its oxidation. However, data concerning malonyl-CoA effects on CPT I activity and FFA oxidation in human muscle are still fragmentary. Recently, it has been found that CPT I activity in humans is sensitive to training and it is markedly higher in trained than in untrained muscles. In addition, malonyl-CoA concentration in human muscle is altered in response to fasting and feeding, denervation and glucose. However, more studies are needed to establish malonyl-CoA action on CPT I activity in contracting muscles. On the other hand, an excessive FFA supply may inhibit carbohydrate metabolism affecting glucose transport - insulin signalling pathway, glucose transporter expression and/or hexokinase II activity. Many aspects of reciprocal glucose-fatty acid relationship are fundamental in the studies concerning insulin resistance, obesity as well as training effects on the muscle metabolism.

Key words: free fatty acid, glucose, muscle, fuel selection


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Leptin – an adipose tissue hormone and its role in metabolism

Grażyna Lutosławska
Department of Biochemistry, Faculty of Physiology and Biochemistry, Józef Piłsudski Academy of Physical Education, Warsaw
ABSTRACT
Leptin is a protein produced mainly by peripheral adipose tissue. The leptin gene was identified in 1994, leptin receptors were found in the hypothalamus, liver, skeletal muscles, ovary, testes, kidney and adipose tissue. The role of leptin in metabolism is far from being elucidated. However, it was postulated that leptin contributed to appetite regulation, puberty and fat metabolism. Blood leptin concentration is significantly correlated with body fat content, but also related to body response to insulin. In obese insulin-resistant subjects the blood leptin level was markedly higher than in their lean, insulin-sensitive counterparts. Furthermore, blood leptin was found to be positively correlated with estradiol concentration, but negatively with testosterone levels. In consequence, in females the blood leptin level, irrespective of the age and body fat, was higher than in males. A significant positive correlation was demonstrated between blood leptin concentration and fat consumption. On the contrary, blood leptin was negatively correlated with physical activity. Regular, moderate physical activity was shown to decrease blood leptin concentration, regardless of the decrease in body fat. In sportsmen blood leptin concentration was much lower than in sedentary individuals. Moreover, low blood leptin level in female athletes was recognized as a reason for delayed menarche and menstrual disturbances.

Key words: leptin, body fat, puberty, metabolism, physical activity

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ALTERATIONS OF BRAIN CATECHOLAMINES AND EXERCISE PERFORMANCE IN (+/-) NT3-KNOCK-OUT MICE

Michael I. Kalinski¹,
Dean E. Dluzen², Robert Stadulis¹

1 School of Exercise, Leisure and Sport, Kent State University, Kent, OH, USA, 2Department of Anatomy, Northeastern Ohio Universities of College of Medicine, Rootstown, OH, USA

ABSTRACT
The influence of neurotrophin-3 (NT3) upon brain catecholamine concentrations and exercise performance were evaluated in mice carrying a targeted single copy inactivation of the NT3 gene (+/-). Concentrations of dopamine and norepinephrine were sampled from the hypothalamus, corpus striatum and olfactory bulb, and were found to be lower in +/- NT3 than +/+ wild type mice. Following exercise to exhaustion, the dopamine concentrations of +/- NT3 mice remained lower than their +/+ wild type littermate controls, however, the direction of the changes in dopamine (increases within hypothalamus and decreases within corpus striatum and olfactory bulb) were very similar between the +/+ and +/- NT3 mice. In contrast to dopamine, the profiles of changes in norepinephrine concentrations following exercise diverged with analyses of these data showing a significant genotype x exercise interaction. The times required for +/- NT3 mice to achieve exhaustion during exercise were significantly lower compared with +/+ NT3 mice. These data provide evidence supporting the theory suggesting central nervous system catecholaminergic involvement in exercise fatigue that can be studied within the +/- NT3 mouse model.

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