The cation concentrations in the samples measured in this Human prostatic epithelial cells synthesize large quantities study were selected in accordance with the cation levels of citrate, which are secreted into the luminal space of the for prostatic fluid as reported by Kavanagh (11). In that prostate. Since citrate levels are significantly reduced in reinvestigation, a linear relationship between the pH and the gions of prostate adenocarcinoma, the citrate concentration citrate concentration present in prostatic fluid was found, measured by localized in vivo 1 H NMR spectroscopy may ranging from a pH value of 8.0 at low/zero citrate concentraserve as a marker to discriminate between prostate adenocartion to a pH value of 6.2 at a high citrate concentration of cinoma and benign prostatic hyperplasia (1-5). At the field 180 mM. In addition, the following linear relationships of strength of 1.5 T, which is commonly available in the clinic, various components of prostatic fluid to citrate were obthe two sets of methylene protons of citrate (Fig. 1) resonate served. By linear regression with y (mM) Å a citrate (mM) at only slightly different Larmor frequencies, resulting in a / b (mM), y Å Na / , a Å 0.03, b Å 142.3; y Å K / , a Å complex proton spectrum of the AB type. The shape of 0.52, b Å 14.2; y Å Ca 2/ , a Å 0.17, b Å 2.7; y Å Mg 2/ , such a resonance multiplet is determined by the spin-spin
, which is proportional to the applied B 0 field. The values of these two parameters also determine the com-First, for the study of the effect of the three divalent cations on the various NMR parameters, a solution of 90 plicated J modulation of the NMR signal of the AB spin system after multipulse sequences which are used in local-m M citrate was prepared, which corresponds to the mean citrate concentration found in normal prostatic fluid. The ized in vivo NMR spectroscopy (6-9).
pH was adjusted to its average value in this fluid ( i.e., Exact knowledge of the values of D and J is necessary, 7.1 ) by adding NaOH. Further, three solutions with 90 not only in order to optimize pulse sequence timing, but also m M citrate and the concentration of one of the divalent for a correct quantitation of the citrate concentration from cations calculated from the citrate concentration according NMR spectra measured in vivo. Moore and Sillerud (10) to the linear relationship mentioned above ( i.e., 8.5 m M have shown for a solution of 0.1 M sodium citrate that D, Zn 2/ , 14.7 m M Mg 2/ , or 18.0 mM Ca 2/ ) were prepared J, and also the midpoint of the chemical shifts of the citrate and adjusted to the same pH. For each divalent cation, methylene proton resonances (d Cit ) show a large pH depenfour mixtures of the solutions with and without cation dence. In that study, the influence of cations was not taken were made, resulting in cation concentrations of 0, 33, 67, into account. However, zinc, calcium, and magnesium are and 100% of the average value found in normal prostatic present in much higher concentrations in prostatic fluid than fluid. In addition, a sample was prepared which contained in other body fluids, and citrate has a high affinity for these 90 m M citrate and the corresponding concentrations of divalent cations (11). For this reason, we studied the influall three divalent cations, i.e., 8.5 m M Zn 2/ , 14.7 m M ence of cations present in prostatic fluid on the chemical-Mg 2/ , and 18.0 m M Ca 2/ ( pH 7.1 ) . shift and J-coupling parameters for the methylene protons of citrate. The results of this study show that the values of Second, for the study of the pH dependence of the NMR parameters, two solutions were prepared. The first contained the parameters D, J, and d cit all increase upon addition of divalent cations. Of the three cations mentioned above, zinc only 90 mM citrate. The second solution contained 90 mM citrate, 61 mM potassium chloride, 18 mM calcium chloride, has the largest effect on J and d cit , and calcium has the largest effect on D. Furthermore, the pH dependence of the 14.7 mM magnesium chloride, and 8.5 mM zinc chloride, according to the average cation composition of expressed hu-parameters D, J, and d cit in the presence of cations differs from the pH dependence of these parameters in the absence man prostatic fluid as reported by Kavanagh (see above). The pH values of both solutions were adjusted to the starting value of cations.