Taurine (2-aminoethane sulfonic acid) is one of the most abundant free amino acids found in mammalian brain, heart and muscle. Taurine levels have also been shown to be altered in certain disease states. A physiological role for taurine in the maintainance of excitatory activity in muscle and nervous tissues has been suggested; however its possible mechanism of action is still uncertain. Early work on the pharmacological actions of taurine involved its possible conversion to isethionic acid (2-hydroxyethane sulfonic acid), a strong anion. This conversion was said to lead to the conductance of cations into the cardiac cell. An analytical technique to measure isethionic acid in mammalian tissues was developed. The method involved extraction, partial purification and methylation with diazomethane, followed by gas-liquid chromatography. With this technique only trace amounts of isethionic acid were detected in rat heart (0.1 mg/lOOg wet weight tissue) and rat brain (0.2 mg per 100 mg wet weight tissue) and none was detected in dog hearts. Recovery of added isethionic acid was between 95 and 100%. The assay was validated using a sample of squid axoplasm. We were also unable to show ¹⁴C-taurine conversion to ¹⁴C-isethionic acid in rat heart slices. Theories on the mode of action of taurine involving bioconversion to isethionic acid were therefore questioned. Some recent work suggested that taurine affects calcium kinetics in perfused guinea-pig hearts and calcium transport in rat skeletal muscle sarcoplasmic reticulum. We have investigated the effect of taurine on ATP-dependent calcium binding and oxalate-dependent calcium uptake in crude preparations of guinea-pig sarcolemma and in microsomal preparations enriched in sarcoplasmic reticulum. Taurine (5-50 mM) was found to have no significant effect on either ATP-dependent Ca²⁺ binding or uptake in both preparations. This result was observed at all calcium concentrations tested (0.5-100 uM) and at all incubation times used (30 seconds to 20 minutes). Taurine (20 mM) neither altered the effect of cyclic AMP-dependent protein kinase on oxalate-dependent calcium uptake nor exerted a stabilization action on calcium transport in these systems. In a further attempt to determine the possible physiological role of taurine in mammalian tissues, we have investigated the effect of taurine on passive transport of sodium, potassium and calcium in synaptosomal preparations of rat brain. Taurine, in a dose dependent manner, was found to have an inhibitory effect on both calcium- uptake and release in these preparations. Amino acids structurally similar to taurine ( β- alanine, homotaurine, hypotaurine and ɣ- aminobutyric acid) were also shown to inhibit calcium uptake in these preparations while a - alanine, proline and valine had no significant effect. Taurine (20 mM), though, did not alter the permeability of these preparations to either sodium or potassium. It thus appeared that taurine, and chemically related amino acids, can specifically alter calcium movements in these preparations. It is suggested that this effect is due to the binding of these agents to taurine receptor sites postulated to be present in these membranes. These observations may help to provide an insight into the physiological and pharmacological effects of taurine reported in cardiac and nervous tissues. / Medicine, Faculty of / Pathology and Laboratory Medicine, Department of / Graduate

In this thesis I investigated the possibility that the kinin system could be involved in the process of ovulation. This study was divided into four parts, these are outlined be 1ow. (1) To determine whether and when the kinin system is activated in relation to ovulation, plasma kininogen levels were estimated in female rats, guinea pigs, and humans at different stages of their estrus or menstrual cycles. Non-ovulating females (women using oral contraceptives,, or post-menopausal women) and male guinea pigs served as controls. The ovulating females of all three species showed a marked decline in kininogen levels shortly before ovulation, suggesting that the kinin system was activated at this time. The fall was absent in the non-ovulating controls, with the exception of women using oral contraceptives. In the latter subjects the fall occurred at a similar time in the 'cycle', and was of a similar magnitude as the fall in normal women. These results showed that the fall is a preovulatory change and raised the possibility that a mechanism more fundamental than the events obstructed by the oral contraceptives could be at least partially responsible for the decline. (2) After establishing the timing of the fall in plasma kininogen levels, an attempt was made to locate the enzymes responsible for the change. The kinin-forming enzymes of the two locations most likely to be involved in kinin release during ovulation, that is, the plasma and the ovary were examined. The evidence indicated that kinin-forming enzymes were present in both locations and suggested that their concentrations increased as ovulation neared. (3) In order to examine the possibility that an ovulatory stimulus can activate the kinin system, female rats were treated with an ovulatory dose of luteinizing hormone (LH) or estradiol -17β one day before the anticipated time of ovulation and kininogen level declines. Estimation of plasma kininogen levels revealed marked declines in the LH-treated animals, estradiol-17β had no observable effect. This evidence suggested that LH, but not estradiol-17β could be responsible, at least in part, for the decreased kininogen values just before ovulation. (4) Lastly, to establish the ability of a kinin to initiate some of the more important events of the ovulatory process, the effects of bradykinin on ovarian smooth muscle contractility and ovarian follicular blood vessel permeability in the rat were examined. Bradykinin stimulated ovarian contractility in in vitro preparations to a significantly greater degree in ovaries isolated during the ovulatory period than at any other stage of the cycle. Also, the degree of movement of the dye Trypan Blue from the general circulation throughout ovarian follicular tissue over a ten minute exposure period was significantly greater in tissue from animals treated with bradykinin than those that were not. This suggests that bradykinin can increase ovarian follicular blood vessel permeability in the rat. Both of these bradykinin-induced effects were reduced, but not eliminated by indomethacin, suggesting that prostaglandins may be involved. Results from this study indicate that the kinin system is activated during the preovulatory period, possibly at the level of the ovary, that LH may be partially responsible for this activation, and that kinins may play a role in triggering increases in ovarian contractility and blood vessel permeability both directly and possibly via the release of prostaglandins. More definite proof awaits the development of a satisfactory kinin antagonist. / Science, Faculty of / Zoology, Department of / Graduate

published_or_final_version / Physiology / Doctoral / Doctor of Philosophy

No description available.

published_or_final_version / Physiology / Doctoral / Doctor of Philosophy

Graduation date: 1986

No description available.

published_or_final_version / Physiology / Doctoral / Doctor of Philosophy

Typescript / Copies of two published papers by the author, in back / Bibliography: leaves 111-133 / 133 leaves : ill ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, 1986

The enzymatic organization of muscle tissue usually is examined in only a select few muscles of any one animal species. However, because the functional demands placed on individual muscles can vary so widely from muscle to muscle, it is inappropriate to generalize findings from one or two muscles to muscle tissue in general. The differences or similarities in metabolic machinery between skeletal muscles of a wide functional range provides crucial information with respect to a particular animals' whole body metabolism. Nowhere is this understanding more important than in the diving marine mammal which must operate as a closed system (with respect to oxygen supply) while submerged. The goals of this thesis are: 1) to provide a broad body of information on the metabolic organization of a large cross-section of marine mammal muscles, both functionally and with regard to location, 2) to assess the implications of the enzyme differences between muscles to the diving habit, and 3) to compare the metabolic organization of skeletal muscle among several species of marine mammal with different diving abilities and habits. A series of 13 enzymes were measured in 21 skeletal muscles of the harbor seal, Phoca vitulina. In addition, 23 enzyme activity ratios were calculated and analyzed for these muscles. A similar analysis of 22 muscles from fin whales, Balaenoptera physalis. was conducted --including 7 key enzymes and 15 activity ratios. Overall, both the maximum activities and the enzyme activity ratios are consistent with the idea that marine mammal muscle is typical mammalian muscle, exhibiting few significant differences from terrestrial species with respect to catabolic enzymes. The only obvious exception to this in the species examined is observed with fin whale locomotory muscle which has extremely high activities of lactate dehydrogenase (over 2000 units/gm wet wt at 25°C) due to an apparent scaling phenomenon. Tight control of this high potential glycolytic flux is indicated by pyruvate kinase activities that scale downward. Comparisons of enzyme relationships between muscles of harbor seals seem to indicate a very aerobically poised metabolic make-up. This is especially true with respiratory and locomotory muscles, which also show a high tendency to utilize fat. This pattern of enzyme activities and activity ratios in the locomotory muscles of harbor seal is evidence that muscle contractile activity while diving is powered primarily through oxidative pathways and largely based on fat as fuel. The majority of non-locomotory muscles appear to be more able to function anaerobically utilizing carbohydrate. This pattern may correlate with circulatory redistributions while diving that preferentially fuel the locomotory muscles with oxygen, leaving the inactive muscles significantly more hypoperfused and, therefore, candidates for energy saving O₂ sparing (metabolic depression). Fin whales exhibit an opposite pattern, with enzyme profiles more typical of "white" muscle. Unlike harbor seals, the locomotory muscles of fin whales are consistently the least oxidatively poised of the muscles examined. This apparently more anaerobic nature of fin whale muscle is possibly complicated by scaling adaptations, but appears to be a real phenomenon. The examination of three to four skeletal muscles from each of three additional phocid seal species from Antarctica, leopard seals (Hydrurga leptonyx). crab-eater seals (Lobodon carcinophagus). and Weddell seals (Leptonychotes weddelli) confirm that the harbor seal pattern of enzyme profiles is fairly consistent among phocid seals. By these criteria skeletal muscles of phocid seals (particularly the locomotory and respiratory muscles) appear to be designed for sustained aerobic metabolism during diving regardless of the habits or diving capabilities of the seal. / Science, Faculty of / Zoology, Department of / Graduate