Problems of in vitro SPF measurements brought about by viscous fingering generated during sunscreen applications.

Up to date, no worldwide standard in vitro method has been established for the determination of the sun protection factor (SPF), since there are many problems in terms of its repeatability and reliability. Here, we have studied the problems on the in vitro SPF measurements brought about by the phenomenon called viscous fingering. A spatially periodic stripe pattern is usually formed spontaneously when a viscous fluid is applied onto a solid substrate. For the in vitro SPF measurements, the recommended amount of sunscreen is applied onto a substrate, and the intensity of the transmitted UV light through the sunscreen layer is evaluated. Our theoretical analysis indicated that the nonuniformity of the thickness of the sunscreen layer varied the net UV absorbance. Pseudo-sunscreen composites having no phase separation structures were prepared and applied on a quartz plate for the measurements of the UV absorbance. Two types of applicators, a block applicator and a 4-sided applicator were used. The flat surface was always obtained when the 4-sided applicator was used, while the spatially periodic stripe pattern was always generated spontaneously when the block applicator was used. The net UV absorbance of the layer on which the stripe pattern was formed was found to be lower than that of the flat layer having the same average thickness. Theoretical simulations quantitatively reproduced the variation of the net UV absorbance led by the change of the geometry of the layer. The results of this study propose the definite necessity of strict regulations on the coating method of sunscreens for the establishment of the in vitro SPF test method.

Changes in hypothalamic temperature of rats after daily exposure to heat at a fixed time.

Rats were subjected to an ambient temperature (Ta) of 33 degrees C for ca. 5 h during the last half of the dark phase for 5, 14 or 28 consecutive days (heat-exposed rats, HE), while control rats were kept at a constant Ta of 24 degrees C. After the heat exposure schedule, the levels of hypothalamic temperature (T(hy)) as an index of body core temperature in the HE were significantly lower than those of the controls for 2-4 h in the last half of the dark phase. The low levels of T(hy) persisted during the specific period for 1, 3 and 6 days after the end of the 5-, 14- and 28-day heat exposure schedules, respectively. These results confirm that, in rats subjected to daily heat exposure for ca. 5 h at a fixed time per day, their T(hy) falls during the period when the rats were previously exposed to heat, and suggest that the duration of the specific T(hy) change observed after completing the heat exposure schedule depends on the length of the heat exposure schedule.

Increase in plasma thyroid hormone levels during the previous heat exposure time in heat-acclimated rats.

The present study was conducted to investigate day-night variations of plasma thyroid hormone and energy substrate levels in rats after acclimation to heat loaded for several hours at a fixed time per day. The heat-acclimated rats were exposed to an ambient temperature of 33 degrees C for 5 h in the last half of the dark phase for 16 consecutive days, while the control rats were kept at 24 degrees C for the same period. After completing the schedule, plasma levels of triiodothyronine (T3), free T3 (FT3), thyroxine (T4), free T4 (FT4), cortisol, triglyceride, nonesterified fatty acid, total protein, and glucose were measured at 3-h intervals between 00:00 and 18:00 (dark phase, 03:00-15:00). The plasma levels of T3 and FT3 of the heat-acclimated rats were higher than those of the controls in the last half of the dark phase. Similar differences were observed for T4 and FT4 levels. The plasma cortisol level was consistently higher in the heat-acclimated rats than in the control rats. There were no particular differences in energy-substrate levels between the two groups at any time of the day. These results indicate that heat exposure at a fixed time per day alters the pattern of day-night variations of plasma thyroid hormone levels in rats. It is noteworthy that the plasma levels of thyroid hormones, especially T3 and FT3, increased during the period when the rats had been previously exposed to heat.

Relationship between body core and peripheral temperatures at the onset of thermoregulatory responses in rats.

The relationships between body core temperature and environmental temperature (T(a)) at the onset of tail skin vasodilation, thermally-induced salivary secretion and cold-induced thermogenesis were examined in rats. Hypothalamic temperature (Thy) was measured as an index of body core temperature. Internal body heating and cooling were made using an intravenous thermode chronically implanted in the inferior vena cava at various T(a)s. External heating and cooling were made by changing T(a) at a constant rate, while Thy was controlled at constant levels with the thermode. Internal heating induced tail skin vasodilation but not thermally-induced salivary secretion, and internal cooling induced cold-induced thermogenesis. External warming caused tail skin vasodilation and thermally-induced salivary secretion, but external cooling failed to induce cold-induced thermogenesis. There were significant correlations between Thy and T(a) at the onset of tail skin vasodilation, thermally-induced salivary secretion and cold-induced thermogenesis. When T(a) was taken as an indicator of thermal input from the skin, the ratios of the potency of inputs from the body core and skin were estimated to be between 8:1 and 6:1 at the onset of tail skin vasodilation, 8:1 at the onset of thermally-induced salivary secretion, and 5:1 for the control of cold-induced thermogenesis. These results suggest that, in rats, the contribution of thermal input from the skin to the onset of thermoregulatory responses is relatively small.

Alteration of nyctohemeral changes in body core temperature by repeated cold exposure given at a fixed time daily in rats [corrected].

The effects of cold exposure for several hours at a fixed time once a day on nyctohemeral variations of hypothalamic temperature (Thy), heat balance, and feeding and locomotor activities were examined in rats. The cold-exposed group was subjected to an ambient temperature of 3 degrees C for about 5 h in the last half of the dark phase daily for 10 or more than 21 consecutive days, while the control rats were kept constant at 24 degrees C. The 10-d cold exposure had little effect on nyctohemeral changes in Thy and locomotor activity. However, after completing a 3- to 4-week cold exposure schedule, the levels of Thy, heat loss, heat production, and feeding and locomotor activities of the cold-exposed rats significantly decreased for 1-2 h during the period of the previous cold exposure time. These decreases lasted for at least 2 d after the end of the cold exposure schedule. These results suggest that the patterns of nyctohemeral changes in body core temperature and feeding and locomotor activities were altered after repeated cold exposure at a fixed time once a day in rats.

Influence of atrial fibrillation on coagulo-fibrinolytic markers in patients with cerebral infarction.

To examine the influence of atrial fibrillation (Af) on stroke onset, we measured the plasma D-dimer level, thrombin antithrombin III complex and plasmin alpha 2 antiplasmin complex (PAP) in 46 stroke patients with Af and 87 stroke patients without Af. These marker levels were significantly higher in Af patients with stroke than in those without stroke (n = 16), and thus do not seem to be affected by Af alone. Abnormal values were also more frequent in acute Af stroke patients with visible occlusion of the major cerebral artery than in those without Af. The D-dimer and PAP levels in all Af stroke patients in the younger-aged patients (< or = 64 years) were significantly higher than those without Af, but not noted in the older-aged group (> or = 75 years). These results suggest that the D-dimer and PAP levels in younger-aged patients with Af indicate the existence of cerebral emboli due to Af.

Clinical significance of new coagulation and fibrinolytic markers in ischemic stroke patients.

BACKGROUND AND PURPOSE: We investigated plasma levels of D-dimer products of crosslinked fibrin degradation products, thrombin-antithrombin III complex, and plasmin-alpha 2-antiplasmin complex for detecting coagulation system activation in ischemic stroke patients to determine the possible effect of age on these marker levels. METHODS: We measured plasma levels of these three markers in 54 acute ischemic stroke patients within 5 days of stroke onset, in 44 chronic ischemic stroke patients over 3 months from onset, and in 50 age-matched healthy subjects. We divided the stroke patients into two subgroups, those with visible occlusion and those with nonvisible occlusion having obstruction of the major cerebral artery. RESULTS: The plasma levels of these three markers were significantly (p less than 0.01) higher in the stroke patients than in controls. Significant differences did not exist at any level between the patients and controls in the younger-aged subjects (less than or equal to 64 years of age), but did exist in the older-aged subjects (greater than or equal to 75 years of age). An age-related increase of the marker levels was noted between stroke patients and controls. No significant difference in the three markers was found among any of the stroke patients. CONCLUSIONS: Increased levels of these markers in stroke patients seem to be related mostly to age.