Abstract
Recently, we reported that the clearance of 131I-labeled IAP from subcutaneous tissue of male rats is more rapid than that of females especially at the age of maximal sexual development (1). This led us to postulate that male sex hormones are stimulators of the subcutaneous blood flow, while female hormones have an inhibitory effect. Since this postulate could be tested by castration of male rats and administration of diethylstilbestrol (DES), we decided to pursue this line of experimentation.
Methods. Twenty-eight sexually mature Sprague-Dawley rats (strain CD-1, Charles River) were divided into four groups of seven as follows: Group I, females with no treatment; Group II, males treated with nine daily subcutaneous injections1 of 0.2 ml placebo (vegetable oil vehicle) over a 2-week period before the clearances; Group III, castrated males treated with placebo as in Group II; and, Group IV, castrated males treated with nine daily subcutaneous injections of 25 mg/kg DES2 over a 2-week period before the clearances.
The methods of isotope clearance determination were described previously in earlier publications of this series (1-3). Briefly, in the present experiment, two subcutaneous injections were given at the dorsal lumbosacral area of each anesthetized rat. Each injection contained 0.1 ml of 131IAP in saline-phosphate buffer (pH 7.4) at physiologic osmolarity. The disappearance rate of IAP from the injection site was monitored and was used as an indicator of the capillary blood flow status as described by Kety (4). The mean initial clearance rate (as determined from the straight line portion of the clearance curves) of the two injections for each rat was used in the data analysis. The rectal temperature was maintained between 98.0 and 101.2°F.3 Three experimental hypotheses were tested, using separate one-way analysis of variance tests: (a) Clearance rates in male rats (Group II) would be more rapid than in female rats (Group I).
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