Fate of human chorionic gonadotropin bound to rat corpora lutea.

The current studies were designed to ascertain the fate of hCG bound to rat corpora luteal cell receptors. Graded doses of highly purified hCG (CR119), ranging from 0.1-10.1 micrograms, were injected. Groups of pseudopregnant rats received iodinated hCG, unlabeled hCG, or both. Supraphysiological levels of hCG were used to enhance the internalization of hCG and its receptors. When ovarian membrane pellets (48,000 X g) were subjected to continuous sucrose density ultracentrifugation, two different ovarian membrane fractions (F1 and F2) bound hCG. Although an increase in hCG binding to the F2 membrane fraction was observed between 1-6 h after a single 0.1-microgram [125I]iodo-hCG injection, no subsequent enhanced binding to that fraction was observed. However, the F1 fraction bound at least 3 fold more hCG than did the F2 fraction 1, 6, 12, and 24 h after the injection of 0.1 micrograms [125I]iodo-hCG. When groups of animals were injected with 0.1, 1.0, or 10.0 micrograms unlabeled highly purified hCG, peak serum, ovarian plasma membrane, and ovarian intracellular hCG concentrations were observed at different times after hormone injection and suggested the progressive transfer of hCG from serum to ovarian fractions in a time- and dose-dependent relationship. Although no intracellular hCG was detected until 60 min after the single 0.1-microgram injection of hCG, both serum and membrane-bound levels were measurable within 15 min of that injection. From these observations, we suggest that ovarian intracellular hCG does not reflect significant contamination with serum or interstitial fluid or from significant dissociation of membrane-bound hCG during tissue handling. Finally, when intracellular hCG was subjected to continuous sucrose density gradient ultracentrifugation, a single major 135I peak was observed, and this comigrated with [125I]iodo-hCG. Our interpretation of the foregoing observations is that the major intracellular form of hCG is not receptor bound.

Characterization of a small molecular size urinary immunoreactive human chorionic gonadotropin (hCG)-like substance produced by normal placenta and by hCG-secreting neoplasms.

Urine obtained from normal pregnant women as well as from patients with hCG-secreting tumors frequently contains native hCG and free hCG subunits when separated on Sephadex G-100. In addition, a small amount of an immunoreactive, hCG-like, low molecular weight substance is usually observed in those chromatograms and represents less than 1% of the total immunoreactive hCG present. Two patients with widely metastatic hCG-secreting tumors excreted disproportionately large quantities of that low molecular weight substance, and that observation raised the possibility that this substance was a secretory and not a degradative product of the hCG molecule. The small immunoreactive hCG-like substance was subsequently characterized immunologically, biologically, and physically. The hCG fragment displayed a biphasic dose-response line in a homologous hCG RIA. The slope of the upper portion of the dose-response line was equal to that for native hCG, but the slope of the lower component of the dose-response line was significantly different from that for hCG. The immunoreactive hCG substance cross-reacted with hCG beta but not with either hCG alpha or hCG beta carboxyl-terminus. The small molecular size immunoreactive hCG-like substance bound to Concanavalin A-Sepharose 4B and eluted with 0.2 M alpha-D-methyl glucopyranoside, contained no significant intrinsic biological activity when tested in the in vitro Leydig cell bioassay and also failed to compete with labeled hCG for specific ovarian LH/hCG receptors. Consequently, that small urinary immunoreactive hCG substance behaved neither as a hCG agonist or antagonist. It exhibited a plasma half-life of 4.5 min when the appropriate Sephadex G-100 fractions were injected into immature female rats. The small molecular size immunoreactive hCG-like substance may be a secretory or breakdown product of hCG-secreting cells.

Spatial variation in the vulnerability of Norwegian Arctic counties to radiocaesium deposition.

Under the Arctic Monitoring and Assessment Programme (AMAP), studies have been undertaken to compare potential fluxes of radiocaesium via important food products. The results for three Norwegian Arctic counties are presented in this paper. The comparative importance of different foodstuffs in contributing to collective dose varies spatially due to differing rates of production and transfer. Although reindeer meat is an important contributor to the radiocaesium flux following a nuclear release, other food products such as cow milk and lamb have been identified as potentially important. Assuming an even deposition following a nuclear release the radiocaesium flux was estimated to be highest for reindeer meat in Finnmark and Troms, whereas cow milk gave the highest flux in Nordland. The total number, geographical distribution and diet composition of indigenous peoples within different Arctic regions is an important factor affecting individual and collective doses arising from a nuclear release. Finnmark has been shown to be the most vulnerable of the three counties because it has the highest flux of radiocaesium and the largest number of indigenous people. The potential contribution of foodstuffs which are known to readily accumulate radiocaesium needs further consideration, in particular, mushrooms, freshwater fish and berries.