Bio-assay of prolactin. Analysis of the pigeon crop-sac response to local prolactin injection by an objective and quantitative method.

Abstract

A method is described for objectively quantifying pigeon crop-sac responses to local (intradermal) prolactin injections. The procedure was used to evaluate several aspects of the crop-sac response. An apparatus was designed and constructed for holding pigeon hemicrops while applying a uniform degree of stretch on them. The device permits removal of a standardized 4 cm diameter disc of the crop-sac mucosal epithelium (ME) from the site of local injection. Responses were objectively quantified by determining the dry weight of this disc. Completeness of removal of the ME was verified by histologic inspection of intact and treated hemicrops. The dry weight of the ME was highly correlated with the thickness of the ME. The method permitted measurement of responses which were not visually detectable. Mucosal dry weight responses were highly correlated with response diameter and response area measurements. The responsiveness of the crop-sac ME to local prolactin injection was unrelated to either the initial thickness of the ME, the thickness of the submucosal tissues, or the thickness of the skin overlying the crop at the injection sites. Response variation within groups was not found to be a function of frequency of injection. A variety of injection schedules were tested to determine the optimal injection regimen for local prolactin responses. Administering 4 injections of prolactin in 2 days and killing the pigeons 20 hr after the last injection was found to yield greater responses than any other injection regimen tested. This procedure of quantifying crop-sac responses yielded a satisfactory log-dose response relationship with good precision (λ = 0.21) at low doses of prolactin. The distribution of responses about the dose means did not deviate appreciably from the normal. (Endocrinology80: 641, 1967)