Hamster growth hormone. Species specificity and physiological changes in blood and pituitary concentrations as measured by a homologous radioimmunoassay.

Abstract

A specific and sensitive homologous radioimmunoassay (RIA) for determination of golden hamster growth hormone (GH) is described and compared to a heterologous hamster GH RIA. Using the homologous system, cross-reactivity experiments between golden hamster GH on one hand, and pituitary extracts from two other hamster species, and purified GHs from several rodent and mammalian species, suggested that hamster GH differs from other rodent and mammalian GHs to a greater extent than rat GH. Using the homologous method, we have determined that, in the golden hamster, diurnal plasma fluctuations have a mean interpeak interval of 70-80 min, that serum GH concentrations are affected by nyctohemeral differences in lighting, by ether vapors, by animal's gender, and by starvation and refeeding. Basal GH concentrations were not influenced by exposure to different photoperiods or by removal of the gonads. A heterologous hamster GH RIA, which utilizes a radioiodinated rat GH and monkey antihamster GH serum, represents the most advantageous method for the measurement of hamster GH because of its high sensitivity (0.3 ng/ml), low limit of detection (46 pg/ml), high antiserum binding to iodinated rat GH, and the ability to measure rat and mouse GHs in addition to hamster GH. Immunological differences between hamster, rodent, and other mammalian GHs are diminished when heterologous, rather than homologous, tracer is used.