Characterization of the MTR in Male Reproductive Tract Tissues
Scatchard plots of 125I-OTA binding to matched samples of adult tammar prostate and testis were linear, indicating a single class of binding site that was confirmed by analysis with the Ligand program. The mean binding affinities (Ka) were similar in the prostate (2.1 ± 0.18 L/nmol: mean ± SEM, n = 8) and testis (1.3 ± 0.4 L/nmol). The specificity of 125I-OTA binding was assessed by competitive displacement studies with various OT and vasopressin receptor agonists and antagonists (Fig. 5). In the prostate gland and myometrium, MT and OT showed relatively high and equal binding affinities for the 125I-OTA-binding site, whereas AVP, LVP, and MC had much lower binding affinities. proventil inhaler
In general, the ligand-binding affinity was in the order of decreasing affinity OTA > MT = OT > MC > AVP = LVP. which is indicative of binding to an OT-like receptor. In the testis, however, LVP, AVP, and the vasopressin receptor antagonist MC had much higher binding affinities for the 125I-OTA-binding site compared with MT and OT (Fig. 5c), suggesting binding to vasopressin-like receptors but not MTR. Concentrations of MTR in the adult prostate gland (27.7 ± 3.0 fmol/mg protein: n = 4) were 8-fold lower than those in the myometrium of the Day 22 pregnant female tammar but were higher than receptor concentrations in the median vagina and endometrium at the same stage of pregnancy. MTR concentrations were marginally higher, although not statistically different (ANOVA, p = 0.08), in the central portion of the prostate as compared with the anterior region.
FIG. 5. Competitive displacement of 125I-OTA binding in the tammar gravid myometrium (a), prostate (b), and testis (c) by MT, OT, AVP, LVP, and MC.