Using three-point bending to evaluate tibia bone strength in ovariectomized young mice

It is well known that estrogen deficiency induces a deterioration of bone strength in aged females. The aim of this study is to determine the effect of estrogen depletion on tibia bone strength in sexually mature mice that are still undergoing skeletal maturation. At 8 weeks of age, C57BL/6 female mice underwent an ovariectomy (OVX) or sham (SHAM) surgery. Mice were killed at 2, 4, or 8 weeks post-surgery. Tibia length and cross-sectional area continued to increase in both treatment groups until 4 weeks post-surgery. Compared to SHAM mice, OVX mice demonstrated a significant reduction in uterine weight and plasma estrogen levels. Three-point bending was used to quantify the mechanical properties (breaking point, stress, stiffness, and elasticity) of the tibia. The tibias from the SHAM mice had a higher breaking point than all the age-matched OVX mice. At 8 weeks post-surgery, the tibias from the SHAM mice demonstrated higher elasticity, stress, and stiffness than the younger SHAM mice and the age-matched OVX mice. Compared to the SHAM mice, our study suggests that (1) there is a reduction in the mechanical strength of tibias from young OVX mice, and (2) the greatest decline in tibia strength of the OVX mice was once they reached skeletal maturity.     

Membrane-associated 41-kDa GTP-binding protein in collagen-induced platelet activation

Initially we established that the binding of collagen to human blood platelets stimulates both the rapid loss of PIP2 and the generation of inositol-4,5-bisphosphate (IP2) and inositol-1,4,5-triphosphate (IP3). These results indicate that the binding of collagen stimulates inositol phospholipid-specific phospholipase C during platelet activation. The fact that GTP or GTP-gamma-S augments, and pertussis toxin inhibits, collagen-induced IP3 formation suggests that a GTP-binding protein (or (or proteins) may be directly involved in the regulation of phospholipase C-mediated phosphoinositide turnover in human platelets. We have used several complementary techniques to isolate and characterize a platelet 41-kDa polypeptide (or polypeptides) that has a number of structural and functional similarities to the regulatory alpha i subunit of the GTP-binding proteins isolated from bovine brain. This 41-kDa polypeptide (or polypeptides) is found to be closely associated with at least four membrane glycoproteins (e.g., gp180, gp110, gp95, and gp75) in a 330-kDa complex that can be dissociated by treatment with high salt plus urea. Most important, we have demonstrated that antilymphoma 41-kDa (alpha i subunit of GTP-binding proteins) antibody cross-reacts with the platelet 41-kDa protein (or proteins) and the alpha i subunit of bovine brain Gi alpha proteins, and blocks GTP/collagen-induced IP3 formation. These data provide strong evidence that the 41-kDa platelet GTP-binding protein (or proteins) is directly involved in collagen-induced signal transduction during platelet activation.     

Novel C-terminal gastrin antagonists. Synthesis and biological activity

The C-terminal tetrapeptide, Trp-Met-Asp-Phe-NH2, is a full agonist of gastrin, but des-Phe analogues, including Boc-Trp-Met-Asp-NH2, are antagonists. To ascertain the minimum structural requirement for an antagonist, we used conventional solution phase methodology to synthesize analogues with further modifications including removal of the alpha-amino group of Trp, conversion of the indole to a phenyl ring, and methylation of amide bonds. These analogues were tested for their effect on pentagastrin-stimulated acid release in dogs surgically prepared with a gastric fistula. When infused intravenously at a dose of 20 pmol kg-1 h-1, the peptides significantly inhibited acid secretion. The extent of inhibition ranged from 12% to 60%. Thus, tripeptide analogues based on the C-terminal sequence of gastrin act as potent and specific antagonists of gastrin-stimulated acid secretion.     

Menopause in female rhesus monkeys

Fifteen female rhesus monkeys (Macaca mulatto), ranging in age from 8 to 34 years, were studied for one year to characterize the endocrine and menstrual changes associated with menopause in this species. Five monkeys were premenopausal; these younger monkeys, ages 8–11 years, menstruated and showed cyclic ovarian activity during the 12–month study period, as evidenced by menses and periodic elevations of serum estradiol (E₂) and luteinizing hormone (LH) concentrations. Four females, ages 24–26 years, were in transition to menopause. Two of these perimenopausal females menstruated and secreted E₂ and LH in a periodic fashion; the other two females showed elevated LH concentrations, consistently low E₂ levels, and no evidence of menstruation. Six females, ages 27–34 years, were clearly postmenopausal; LH concentrations were high, whereas E₂ concentrations were uniformly low. There was a significant inverse correlation between basal E₂ concentrations and age, and a significant positive correlation between age and LH concentrations across all 15 animals. Hormonal changes indicative of ovulation, when they occurred, were generally restricted to the winter and early spring months. Histological analysis of ovaries from four postmenopausal females revealed little or no evidence of active folliculogenesis. These data indicate that menopause in female rhesus monkeys does not occur until the second half of thethird decade of life. © 1995 Wiley-Liss, Inc.