Characterization of Somatotropin- and Prolactin-Binding Sites on Bovine Granulosa Cells Using Homologous Hormones

I. Yu. Lebedeva^*, V. A. Lebedev, and T. I. Kuzmina

All-Union Research Institute of Farm Animal Genetics and Breeding, Russian Academy of Agricultural Sciences, Moskovskoe Shosse 55a, Pushkin, St. Petersburg, 189620 Russia; fax: (812) 465-9989

^* To whom correspondence should be addressed.

Received July 24, 2000; Revision received February 2, 2001

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Specific binding of bovine somatotropin (BST) and bovine prolactin (BPRL) to cow granulosa cells from antrum-containing follicles of different diameter was studied. Scatchard analysis of the data revealed a single type of low affinity BST-binding sites on the granulosa cells with dissociation constants similar to those for the BPRL-binding sites. The number of BST-binding sites on the cells decreased with increasing follicle diameter from 3-5 to 6-10 mm. However, the binding capacity to BPRL decreased only in the case of cells from follicles 11-20 mm in diameter. The findings are discussed in relation to the “homologous binding” phenomenon.

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KEY WORDS: somatotropin, prolactin, binding sites, granulosa cells, follicle

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