APPLICATION OF A RADIORECEPTOR ASSAY FOR LACTOGENIC ACTIVITY TO THE DETECTION OF FISH PROLACTIN-LIKE HORMONE

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Abstract
A new approach to fish prolactin bioassay using rabbit mammary gland prolactin receptors is reported. Pituitary and hypothalamic extracts were prepared by homogenizing lyophilized salmon (Oncorhynchus tshawytscha) tissues in 25 mM-Tris-HCl, pH 7.6, 10 mM-MgCl2 buffer. Extracts were centrifuged (5000 g, 20 min, 4.degree. C) before use. Extracts of male and female salmon pituitary glands competed with ovine prolactin on the rabbit mammary gland receptors. There was no difference between male and female preparations. The sensitivity of the technique allowed determination of prolactin activity in the range equivalent to 1-10 ng ovine prolactin; under these conditions 1 mg protein extracted from salmon pituitary glands contained the equivalentof 46 .mu.g of ovine prolactin. A specific binding of prolactin-like material in the salmon pituitary extracts is suggested. These preliminary results do not demonstrate exact parallelism between displacement curves of ovine prolactin and fish pituitary extracts; the values obtained do not represent an exact quantification of prolactin-like hormone present in the salmon hypophysis. But the apparent absence of effects due to protein concentration alone demonstrates a specific binding between rabbit mammary gland receptors and fish prolactin. The use of the system is proposed for detection of fish prolactin-like hormone.

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