Abstract
The activities of a factor produced by plerocercoid (spargana) larvae of the tapeworm, Spirometra mansonoides have been compared to several mammalian hormones. Harlow et al. (1) found that plerocercoids as well as an acetone extract prepared from the plerocercoids exhibited activity similar to that of insulin. Mueller and Reed (2) found that implantation of plerocercoids into propylthiouracil-treated, growth-arrested rats produced a growth response comparable to that of administered thyroxin. Steelman et al. (3) compared the plerocercoid growth factor to growth hormone and Garland et al. (4) found that spirometrid plerocercoids induced sulfation factor (somatomedin) in hypophysectomized (hypox) rats. However, there is no mention in the literature of possible similarities between the plerocercoid factor and prolactin.
Bern and Nicoll (5) compiled a list of the actions attributed to prolactin in the vertebrates. These actions include: stimulation of larval growth and reduction of lipid deposition in reptiles, and stimulation of growth and lipogenesis in birds and mammals. Later work (6) has shown that prolactin hypersecretion can produce nearly normal growth in human subjects whose level of growth hormone is below normal. It is obvious that prolactin enhances growth in several groups of vertebrates.
One of the most striking effects of prolactin is seen in the Order Columbiformes. Prolactin preparations from many vertebrate species have the ability to stimulate the crop sac of pigeons and doves to produce crop “milk” (5). Crop sac stimulation has subsequently been used as a definitive bioassay for prolactin. In addition, somatotropin has lactogenic activity (7, 8) and exhibits other actions similar to those attributed to prolactin (5).
The objectives of the experiments described in this paper were to determine: (a) if plerocercoid growth factor (PGF) will stimulate the production of pigeon crop “milk” and (b) if the projected “prolactinlike” activity of PGF on the pigeon crop sac might be used as an assay system for PGF activity.
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