Abstract
Several groups of investigators (1-3) have shown that the growth rates of young rapidly growing rats cannot be increased by infection with plerocercoids of the tapeworm Spirometra mansonoides. However, Steelman et al. (4) showed that adult female rats respond to plerocercoid infection with a body weight gain similar to that produced by growth hormone (GH). Glitzer and Steelman (2) also observed a marked decrease in pituitary weight (37%) and in plasma GH levels from control values of 27 ng/ml to nondetectable levels at 10 days following worm infection. These observations have been confirmed by Garland and Daughaday (5).
Steelman and Morgan (6) infected 22 day old castrated male rats with plerocercoids and observed a body weight increase similar to that obtained with GH. No effect was observed on the seminal vesicle and prostate weights but when worm-infected animals were supplemented with methyl testosterone a striking potentiation of the seminal vesicle and prostate weights resulted. These studies point to yet another similarity between pituitary GH and the plerocercoid growth factor (PGF).
In view of these observations, the experiments described in this paper were performed to determine the age at which rats show a growth response to plerocercoid infection. Food efficiency measurements were also made and the skeletal muscles of the host rats were analyzed for moisture and lipid content. If plerocercoid infection should produce appreciable increases in the body weight and food efficiency of older rats without undesirable effects on skeletal muscle, similar studies would be indicated for selected commercial animals.
Methods. Thirty-five day-old Holtzman male rats weighing approximately 100 g were castrated at the Hormone Assay Laboratories (Chicago) and held for 1 wk prior to shipment. Intact male rats of the same age, strain, and approximate weight were included in the same shipment.
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