Rabbit Growth Hormone Research Articles

Human pancreatic growth hormone-releasing factor stimulates release of growth hormone in conscious unrestrained male rabbits.

The effect on GH secretion of GH-releasing factor (GRF), a 44-amino acid peptide recently isolated from a human pancreatic tumor (hpGRF), was examined in conscious male rabbits. During a 6-h period (1030-1630 h) of the control study individual rabbits exhibited pulsatile GH release with a surge at 1030-1200 h, a trough at 1200-1400 h, and a second peak at 1400-1630 h. Intravenous bolus injections of 1 and 10 micrograms hpGRF caused significant and dose-related increases in plasma GH during both the period of the trough (1300 h) and the surge (1530 h), although the GH responses were obviously higher during the latter than the former period. Passive immunization with anti-somatostatin (SRIF) sheep serum resulted in a prompt increase in plasma GH immediately after an injection of the antiserum. When 0.1, 1, and 10 micrograms hpGRF were successively injected iv at 1215, 1345, and 1515 h, respectively, maximum levels of plasma GH after hpGRF in anti-SRIF sheep serum-treated rabbits were significantly higher than in animals given normal sheep serum. The plasma GH responses to 10 micrograms hpGRF, given iv only once at 1515 h in normal sheep serum-treated animals, were not different from those to 10 micrograms hpGRF injected at 1515 h after the prior administration either of the smaller hpGRF dose (0.1 micrograms, 1215 h; 1 microgram, 1345 h), nor of the large dose (10 micrograms, 1100 h). These findings suggest the following: 1) that the secretion of GH is pulsatile in conscious, unrestrained male rabbits; 2) that hpGRF is a potent secretagogue for GH release in rabbits as well as other species; 3) that the magnitude of plasma GH response to hpGRF is different according to timing of the injection during the course of pulsatile GH secretion but is not influenced by the prior administration of hpGRF (no priming effect); and 4) that the responsiveness of plasma GH to hpGRF is affected by circulating endogenous SRIF.

The purification and characterization of rabbit placental lactogen

Rabbit placental lactogen, a polypeptide hormone functionally related to the growth hormone/prolactin family, was isolated from placenta by (NH4)2SO4 precipitation, gel filtration and ion-exchange chromatography on DEAE-and CM-cellulose. The hormone was purified to more than 90% homogeneity, as determined by end-group analysis. On disc gel electrophoresis at pH9.0 it migrates as a pair of closely spaced bands with mobilities of 0.489 (minor band) and 0.511 (major band), and its isoelectric point is 6.1. Its mol.wt. is 20600, as determined by sedimentation--equilibrium centrifugation, and 24200, as estimated by gel electrophoresis in sodium dodecyl sulphate. Its amino acid composition resembles that of rabbit growth hormone and rat prolactin, except for a lower glutamic acid and leucine content. Like the prolactins, rabbit placental lactogen has two tryptophan and six cysteine residues, and its N-terminus, valine, is identical with that for human placental lactogen. By radioimmunoassay, it does not cross-react with antisera to either rat growth hormone or rat prolactin; in addition, it does not cross-react with antisera to bovine placental lactogen by double immunodiffusion. The similarity of the biochemical characteristics of rabbit placental lactogen to the other non-primate placental lactogens lends further support to the hypothesis that these molecules occupy a more central position in the growth hormone/prolactin "tree" than do their primate counterparts.

Radioimmunoassay of rabbit growth hormone.

Preparation of rabbit growth hormone which is suitable for trace labeling is described. The molecular weight of rabbit growth hormone as determined by polyacrylamide-gel electrophoresis i s 18,000. The assay uses purified rabbit growth hormone labeled with radioiodine-125. An enzymatic procedure which utilizes 4 µg of lactoperoxidase and 0.88 mM hydrogen peroxide was adapted for the iodination. The antiserum was prepared in rhesus monkeys and used in the assay in a final dilution of 1:100,000. The reference standard had a potency of 0.60 IU/mg by the body weight gain bioassay. Separation of antibody-bound growth hormone from free growth hormone was achieved with goat anti-monkey gamma globulin. The affinity constant of the antigen-antibody reaction of the assay equaled 109 L/M and the average standard deviation of duplicate aliquots within a single assay over the range of 2 to 50 ng was 1.9 ng (4%). Interassay variability over the same range for unknowns measured in two different assays was 2.8 ng (6%). P...

Lack of transplacental passage of growth hormone in rabbits.

Die Plasma-Verschwindungskurve des prazipitierbaren TCA in schwangeren Kaninchen zeigt nach Injektion von radiojodiertem menschlichem Wachstumshormon, dass dieses wahrend der Schwangerschaft eine kurzere Halbwertszeit besitzt (t 1/2). Kaninchen, die 2 h nach i.v. Injektion des Wachstumshormons geopfert wurden, wiesen einen Transfermangel zu den Foeten auf.

SITES OF ACTION OF GROWTH HORMONE IN CARTILAGE.

SummaryTwo experiments using added growth hormone in rabbits have been described. When supplied to explants of normal rabbit epiphysis, cultured in vitro, the hormone produced no detectable effects. However, when given to the animal in vivo before its tissues were explanted, the hormone produced a marked increase in chondrogenetic activity demonstrable in the cultured ex-plants by autoradiographs of tritiated thymi-dine incorporation. The most marked effect occurred in the germinal zone of the epi-physeal growth cartilage and the corresponding cells of the articular and anlage cartilage.