Induction of Lactogenic Binding Sites in the Liver of the Snell Dwarf Mouse

Publisher Website
Google Scholar
Abstract
Lactogenic binding sites were shown to be absent in the livers of Snell dwarf mice (dw/dw). Phenotypically normal littermates (DW/?), bound o[ovine]PRL [prolactin] with an apparent affinity constant, Ka, 15 .times. 109 M-1 and possessed quantities of binding sites equivalent to 25 and 8 fmol [femtomoles]/mg liver protein in females and males, respectively. Lactogenic binding sites were induced in livers of dw/dw mice upon transplantation of intact DW/? pituitaries under the kidney capsule, induction occurring in a biphasic manner. Detectable binding sites could not be reinduced by daily single oPRL injections into dw/dw after the transplanted pituitary had been excised. I.p. injections of b[bovine]GH [growth hormone] + oPRL + thyroxine (T4) every 4 or 8 h induced detectable binding sites that were maximally detectable 8-12 h after the final injection. Injection of bGH alone every 8 h for 2 days also induced the lactogenic binding sites in an amount approaching that of the female DW? DW/? males exhibited a 6.5-fold or 2-fold increase in the number of lactogenic binding sites when treated every 4 h with bGH or oPRL, respectively. Addition of oPRL + T4 to the bGH injections lowered the increase to 2-fold. [125I]bGH did not bind nor did bGH compete with [125I]-oPRL bound to the membrane preparations. The inability of bGH to bind to the membrane preparations suggests either the necessity of an intermediate bGH-responsive tissue for induction of the lactogenic receptor or the presence of a bGH binding site in the liver, undetectable by receptor assays currently in use. The Snell dwarf mouse provides a convenient and naturally occurring model system to study the induction of lactogenic binding sites.