© 1986 by The Society for Integrative and Comparative Biology
Similarities and Differences Among Prolactins and Growth Hormones and Their Receptors1
Department of Physiology-Anatomy and The Cancer Research Laboratory, University of California Berkeley, California 94720
SYNOPSIS. Data from the literature and from our own studies on the receptors for prolactin (PRL) and growth hormone (GH) are reviewed and analyzed. Receptors for PRL have been studied in a wider range of species and in a greater diversity of target organs than have the binding sites for GH. Although GHs are structurally more highly conserved among the vertebrates than are PRLs, the available data indicate that there is greater diversity among GH receptors than there is among PRL receptors. In general, GH receptors show greater species specificity but less hormone specificity than do PRL receptors. The reason for the greater diversity among GH receptors as compared to PRL receptors is unknown; it bears no relationship to phylogeny.
Data on the binding of purified preparations of mammalian PRL, GH and placental lactogen (PL) to renal and hepatic receptors for PRL and GH, respectively, of several vertebrate species are reviewed. The species and hormone specificity of the binding of the hormones to the two typesof receptors showed no consistent pattern. To explain this disarray, we propose that the receptor binding domains of PRL and GH were present in their common ancestral gene and that they havebeen retained to variable degrees by all of the descendant members of the PRL-GH family. We further propose that hormone and species specificity of binding is determined by hindering features on the hormones and on the receptors, rather than by merely the presence or absence of the appropriate binding determinants.