Abstract
While conducting experiments to determine drug effects upon subcutaneous isotope clearance using the method of Kety (1), it was observed that control clearances varied appreciably in successive groups of rats. Some of these groups were known to differ in sex and age. Also, animals anesthesized with a barbiturate (which was used in these experiments) tend to have depressed core temperatures which may vary with the ambient temperature. It was hypothesized, therefore, that differences in age, sex and core temperature might account for the observed variability in subcutaneous isotope clearance. Two studies (2, 3) have shown that isotope clearance rates from injection sites can vary with core temperature. However, no specific studies demonstrating the effects of age and sex and their interaction with core temperature on isotope clearance rates have been found.
The purpose of the present study was to test the effects (both independent and interactive) of age, sex md core temperature upon isotope clearances following injection of the isotope in saline solution.
In addition, two local anesthetics, prilocaine and tetracaine which were reported to have opposite effects upon clearance rate (4) were added to the isotope solutions as positive controls under all the conditions of the experimental design.
Methods. All rats used were of the Strain CD- 1 (Sprague-Dawley derived) and were obtained from Charles River. Nine rats of each sex in each of four designated age categories were selected and randomly assigned to three core temperature ranges, 93.5°-95.5°, 100°-102°, and 105.0°-107°F.
The age categories were: (a) immature (about 45 days old), (b) pubescent (about 84 days old), (c) mature (about 5 mo old) and (d) aged (about 12 mo old). Each rat was anesthetized with a mixture of pentobarbital (35 mg/kg) and barbital (90 mg/kg) and was equilibrated to one of the three core temperature ranges by adding or removing radiant heat sources.
Get full access to this article
View all access options for this article.