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Biomedical subjects

T L Owen

Publications and source records attributed to T L Owen.

11 recordsLinked to original sources
PubMed1992

Behavioral thermoregulation by hypoxic rats.

To address whether a shift in hypothalamic thermal setpoint might be a significant factor in induction of hypoxic hypothermia, behavioral thermoregulation was examined in 7 female Sprague-Dawley rats implanted with radiotelethermometers for deep body temperature (Tb) measurement in a thermocline during normoxia (PO2 = 125 torr) and hypoxia (PO2 = 60 torr). Normoxic rats (TNox) selected a mean ambient temperature of 19.7 +/- 1.4 (SE) degrees C and maintained Tb at 37.0 +/- 0.2 degrees C. Hypoxic rats selected a significantly higher ambient temperature (THox = 28.6 +/- 2.2 degrees C) but maintained Tb significantly lower at 35.5 +/- 0.3 degrees C. Without a thermal gradient (ambient temperature = 25 degrees C), Tb during hypoxia was 35.4 +/- 0.4 degrees C. The maintenance of a lower body temperature during hypoxia through behavioral thermoregulation despite having warmer temperatures available supports the hypothesis that the thermoregulatory setpoint of hypoxic rats is shifted to promote thermoregulation at a lower Tb, effectively reducing oxygen demand when oxygen supply is limited.

Animals↗
PubMed1991

Effect of age on cold acclimation in rats: metabolic and behavioral responses.

To determine whether senescence affects the metabolic and behavioral responses of rats to chronic cold exposure, 8- and 22-mo-old male Fischer 344 rats were studied before and after 6 wk of cold (6-10 degrees C) exposure. Measurements of body weight, food consumption, oxygen consumption, body temperature, and ambient temperature selection in a thermocline (7-37 degrees C linear gradient) were made at regular intervals throughout the acclimation period. Before acclimation, age groups differed significantly only by weight. During acclimation, older rats had increased mortality and morbidity below 10 degrees C. After acclimation at 10 degrees C, younger and older rats both selected cooler ambient temperatures (7 and 5 degrees C cooler than preacclimation, respectively), and older rats had a significantly greater decrease in body temperature in the thermocline. Both age groups increased resting metabolic rate at 25 degrees C with cold acclimation (16.5 and 10% increase for younger and older rats, respectively). This study indicates distinct differences in metabolic and behavioral responses of younger and older rats to cold acclimation. Chronic cold exposure is detrimental to thermoregulatory function in older rats, since it is not as effective in stimulating sustained increases in metabolic rate in older rats as in young adults and it leads to a preference for cooler ambient temperatures, resulting in increased heat loss and reduced body temperature.

Acclimatization↗
PubMed1986

Effect of age on blood pressure and small vessel reactivity in male rabbits.

Direct blood pressure measurements were made on male rabbits from 3 to 55 months old to determine if blood pressure increases with age in this animal model as it does in humans. To assess the effects of age on vascular reactivity, strips of small ear artery and skeletal muscle artery were taken from these animals and tested with norepinephrine, potassium, histamine, and isoproterenol in vitro. Heart rate did not differ between age groups, but blood pressure was significantly higher in older age groups compared to 3-month-old-rabbits. Vessels from older animals were thicker and less sensitive to norepinephrine. Responses to potassium, histamine, and isoproterenol were not different between age groups. The results suggest that male rabbits offer a good model of age-related increases in blood pressure, and that changes in vascular adrenergic reactivity may occur with age in male rabbits.

Aging↗
PubMed1985

Reactivity of small vessels from mature to senescent female rabbits.

In order to determine if there are differences in reactivity of small arteries of cutaneous and skeletal muscle vascular beds taken from rabbits of different ages, vascular smooth muscle strips were tested in vitro with a variety of drugs. Arteries from the ear and hind limb skeletal muscle were removed from adult female rabbits, aged 6-48 months. Developed force of the vessel strips was measured during exposure to cumulative concentrations of norepinephrine, norepinephrine following propranolol, angiotensin II (skeletal muscle artery only) and histamine (ear artery only). Comparable segments of arteries from rabbits of different ages showed no significant differences in size or in maximum developed force attributable to age. A lack of beta-adrenoceptor activity was indicated in the ear arteries of all adult age groups studied, while propranolol enhanced contractile responses to norepinephrine in skeletal muscle arteries independent of age. Likewise, there were no consistent, age-related changes in the reactivity of either vessel type to norepinephrine, histamine, or angiotensin. This study indicates that small cutaneous and skeletal muscle arteries from mature female rabbits do not undergo any appreciable change in adrenergic and nonadrenergic sensitivity with age.

Aging↗
PubMed1975

Interaction of O2 and CO2 in sustained exercise hyperemia of canine skeletal muscle.

The relative contribution of O2 and CO2 to the metabolic control of blood flow in long-term exercise was examined in the denervated gracilis muscle of the anesthetized dog. The data show that 1) on initiation of heavy exercise, the effluent blood PO2 and pH fall markedly and then rise slowly but remain depressed relative to control during 60 min of exercise hyperemia, while the initial increases in [K+] and osmolality rapidly approach and eventually reach preexercise levels. 2) The enhanced vasodilator activity of venous blood from exercising muscle is attenuated when effluent blood PO2 or pH is corrected to preexercise levels; it is completely abolished when both are corrected. 3) Induced reduction PO2 or pH in the arterial inflow, and thus venous outflow, of resting muscle produces a fall in resistance; simultaneous reductions of both to levels seen in heavy exercise produce a fall in resistance to near that observed during exercise. Since the enhanced vasodilator activity of venous blood from the contracting muscle was abolished by simultaneous correction of the PO2 and pH, it seems likely that these factors, acting directly or indirectly, are the principal chemicals responsible for the maintenance of the vasodilation seen in canine skeletal muscle during heavy exercise.

Animals↗
PubMed1975

Effects of indomethacin on local blood flow regulation in canine heart and kidney.

In two series of experiments we studied the effects of indomethacin on (a) coronary reactive hyperemia and, (b) renal blood flow, autoregulation, and reactive dilation. Coronary blood flow was measured in closed-chest dogs. Reactive hyperemia was induced by coronary occlusion for 5 and 15 sec. Indomethacin, an inhibitor of prostaglandin synthesis, was infused intra-arterially in doses of 90-200 mg over periods ranging from 30-120 min. Coronary reactive hyperemia was not affected by indomethacin. The canine renal vascular bed was studied under conditions of natural flow, controlled flow, and controlled pressure. Intra-arterial infusion of 90 mg of indomethacin over a 30- to 60- min period caused increased renal vascular resistance and an attenuation of reactive dilation (induced by stopping renal blood flow for 90 sec). Indomethacin slightly attenuated the autoregulatory response to decreasing perfusion pressures, but did not affect the respone to increasing pressures. Thus the study fails to provide evidence for participation of the prostaglandins in regulation of coronary blood flow and suggests only minimal participation of prostaglandings in renal blood flow regulation.

Animals↗