Alterations in steroid binding plasma proteins in Macaca nemestrina during pregnancy.

Abstract

We measured the corticosterone and dihydrotestosterone steroid binding capacities of corticosteroid-binding globulin (CBG) and sex steroid plasma binding protein (SBP) throughout pregnancy in seven Macaca nemestrina. The nSBP binding capacity rises significantly by 28 days of pregnancy, remains elevated through 56 days, tends to fall through midpregnancy, and then decreases dramatically to very low values 130-153 days after conception. In contrast, nCBG rises slightly (1.2-fold) in early pregnancy, is elevated in midpregnancy, but is similar to nonpregnant values during the last trimester of pregnancy. Our data indicate that factors controlling the plasma concentration of nCBG and nSBP are not identical. The results are in sharp contrast to those observed in human pregnancies in which both hSBP and hCBG are increased severalfold during pregnancy, including at term. Because the changes of nCBG and nSBP during pregnancy do not paralle the changes observed in human beings even though their steroid binding characteristics are similar, the M. nemestrina may serve as a valuable model for defining the physiologic function of SBP and CBG and the mechanism(s) controlling their concentrations in blood.

Regulation of Plasma Sex-Steroid-Binding Protein in Adult Cynomolgus Monkeys (Macaca Fascicularis) during Different Reproductive States

“…I t appears unlikely that plasma dilution during gestation affects the mSBP concentration since total plasma protein concentration is sustained. Moreover, as Schiller et al (1978) and Stanczyk et al (1986) have shown in rhesus monkeys, we have shown that estradiol gradually increased throughout pregnancy while total testosterone was maintained.…”

“…mulatta, and Koritnik and Marschke (1986) in M. fasciculans have shown by binding assay that in nonhuman primates, the mSBP concentration is not elevated at term. These results have been confirmed by Schiller et al (1978), who investigated the possibility of the synthesis of a new binding protein by using steadystate polyacrylamide gel electrophoresis. We confirmed here that the concentration of the protein as an antigenic determinant was also reduced in 3 of the 4 pregnant females studied.…”

“…Schiller et al (1978) in M. nemestrina, Stanczyk et al (1986) in M . mulatta, and Koritnik and Marschke (1986) in M. fasciculans have shown by binding assay that in nonhuman primates, the mSBP concentration is not elevated at term.…”

“…Thus, all of the data discount the hypothesis that a modified form of mSBP has been generated or that the binding capacity of the protein has decreased. I t is interesting to notice that another binding globulin, the corticosteroidbinding globulin (CBG), does not increase during pregnancy in M. nemestrzna (Schiller et al, 1978) and in M . mulatta (Stanczyk et al, 1986) as it does in women.…”

“…Testosterone implantation markedly reduces mSBP levels (Heinrichs et al, 1979;Burry et al, 1980;Winters et al, 1981). Decreasing SBP levels during pregnancy have been reported in M. nemestrinu (Schiller et al, 1978), M. muluttu (Stanczyk et al, 1986), and M . fusciculuris (Koritnik and Marschke, 1986).…”