ANNUAL VARIATION IN THE RESPONSE OF CROP-SACS AND VISCERA OF PIGEONS TO PROLACTIN

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Abstract
In 24 groups of 10 young White Carneau pigeons injected at intervals over a period of 2 yrs. the crop-sacs showed a semi-annual cyclic variation in their wt. response to a total dose of 2.0 mg. (28 I.U.) of the same prep. of prolactin. Two complete cycles of responsiveness were observed in tests made in each of the 2 yrs. High values were obtained during winter (highest) and summer. Low values were obtained for much shorter periods during Apr.-May and again during Oct.-Nov. When crop-sac wts. are converted into equivalent units of prolactin the values found during winter and summer are 3 times as large as those obtained during the short periods of spring and autumn. Season is therefore an important factor in the bioassay of prolactin and it should be controlled by a concurrent test with a standardized prolactin. The low dosage used in these tests increased body wt. over that of the controls by about 4%. Wt. of pancreas was increased by 26%; liver by 29%; intestine by 36%. These data strongly reinforce our earlier evidence that in pigeons prolactin has a specific trophic action on these organs. Wts. of testes, thyroids, adrenals and heart were not significantly affected by the treatment with prolactin. Wts. of heart and adrenals showed no obvious cyclical or seasonal change. In these young pigeons the body wts. attained at 7 wks. showed an annual variation with a maximum in winter and a minimum in late summer. Gut length and wt. at this age were essentially constant throughout the yr. and independent of different body wts. Corrected to constant body wt. these values show annual cycles reciprocally related to body wt. When wts. of pancreas and liver are calculated to constant body wt. they tend to show a semi-annual cyclic variation similar to that found, with or without that calculation, in the crop-sacs.