Loss of body weight as a predictor of reserpine-induced amine depletion.

Loss of body weight was proved to be a convenient and reliable way to predict the degree of reserpine-induced amine depletion after i.p. injections of reserpine (2.5, 5 and 10 mg/kg) and it thus helps reduce variability. Two populations of animals were sharply distinguished lying on either side of the 5% cutoff point within the first 24 hr. One group (approximately 20% of all animals) lost less than 5% of their body weight, showed absence of physiological and behavioural effects, a moderate 5-HT depletion and a moderate 5-HIAA increase. These animals were called 'partially reserpinized'. Another group always lost 5% or more of body weight, exhibited the reserpine syndrome as well as a larger extent of 5-HT depletion and 5-HIAA increase. This group comprised 'reserpinized' rats. There were significant correlations between the percent weight loss and the degree of 5-HT depletion and 5-HIAA increase in the group of 'partially reserpinized' animals. The two groups differed also in the time course of amine changes. Dose had no effect in the differentiation of the two groups but did affect the extent of amine depletion. When reserpine was given i.v. or s.c., all animals were 'reserpinized'. The phenomenon of partial reserpinization is discussed.