Nonactivated chick progesterone receptor from hypotonic tissue extracts exists in a large complex containing the heat shock proteins hsp90 and hsp70 plus additional smaller proteins; activation of receptor to a DNA-binding form involves the dissociation of proteins from the complex. Whereas numerous attempts to reversibly bind components to the activated receptor have been unsuccessful, we now report conditions that promote the reassociation of hsp90 and hsp70 to progesterone receptor. Cytosolic receptor was dissociated from hsp90 and hsp70 by treatment with 0.5 M KCl and 10 mM ATP in the absence of progesterone. It was then purified by binding to immunoaffinity resins. After wash steps, the receptor-resin complex was incubated in rabbit reticulocyte lysate at 30 C, rewashed, and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Saturable binding of rabbit hsp90 and hsp70 to chick receptor was found after incubation with reticulocyte lysate; hsp binding was temperature dependent, but not dependent on exogenous ATP. Incubation of dissolved receptor with oviduct cytosol, from which receptor was obtained, or with purified hsp did not result in hsp binding. Furthermore, mixing oviduct cytosol with lysate inhibited hsp reconstitution, suggesting negative factors for hsp binding in oviduct cytosol. The steroid-binding domain of the receptor was required, since no hsp binding was observed in the reconstitution system using a receptor mutant lacking this domain. When the receptor was isolated in the presence of progesterone, reconstitution with hsp90 and hsp70 did not occur. This is consistent with the in vivo effects of progesterone in promoting hsp dissociation.

The protein composition of the avian progesterone receptor was analyzed by immune isolation of receptor complexes and gel electrophoresis of the isolated proteins. Nonactivated cytosol receptor was isolated in association with the 90-kilodalton (kDa) heat shock protein, hsp9O, as has been described previously. A 70-kDa protein was also observed and was shown by Western immunoblotting to react with an antibody specific to the 70-kDa heat shock protein. Thus, two progesterone receptor-associated proteins are identical, or closely related, to heat shock proteins. When the two progesterone receptor species, A and B, were isolated separately in the absence of hormone, both were obtained in association with hsp9O and the 70-kDa protein. However, activated receptor isolated from oviduct nuclear extracts was associated with the 70-kDa protein, but not with hsp9O. A hormone-dependent dissociation of hsp9O from the cytosolic form of the receptor complex was observed within the first hour of in vivo progesterone treatment, which could explain the lack of hsp9O in nuclear receptor complexes. In a cell-free system, hsp9O binding to receptor was stabilized by molybdate but disrupted by high salt. These treatments, however, did not alter the binding of the 70-kDa protein to receptor. Association of the 70-kDa protein with the receptor could be disrupted by the addition of ATP at elevated temperatures (23°C). The receptor-associated 70-kDa protein is an ATP-binding protein, as demonstrated by its affinity labeling with azido[32P]ATP. These results indicate that the two receptor-associated proteins interact with the progesterone receptor by different mechanisms and that they are likely to affect the structure or function of the receptor in different ways.

Dietary sodium and blood pressure regulation differs between normotensive men and women, an effect which may involve endothelial production of nitric oxide (NO). Therefore, we tested the hypothesis that differences in the NO component of endothelium-dependent vasodilation between low and high dietary sodium intake depend on sex. For 5 days prior to study, healthy adults consumed a controlled low-sodium diet (10 mmol/day, n = 30, mean age ± SE: 30 ± 1 yr, 16 men) or high-sodium diet (400 mmol/day, n = 36, age 23 ± 1 yr, 13 men). Forearm blood flow (FBF, plethysmography) responses to brachial artery administration of acetylcholine (ACh, 4 μg·100 ml tissue(-1)·min(-1)) were measured before and after endothelial NO synthase inhibition with N(G)-monomethyl-l-arginine (l-NMMA, 50 mg bolus + 1 mg/min infusion). The NO component of endothelium-dependent dilation was calculated as the response to ACh before and after l-NMMA accounting for changes in baseline FBF: [(FBF ACh - FBF baseline) - (FBF ACh(L-NMMA) - FBF baseline(L-NMMA))]. This value was 5.7 ± 1.3 and 2.5 ± 0.8 ml·100 ml forearm tissue(-1)·min(-1) for the low- and high-sodium diets, respectively (main effect of sodium, P = 0.019). The sodium effect was larger for the men, with values of 7.9 ± 2.0 and 2.2 ± 1.4 for men vs. 3.1 ± 1.3 and 2.7 ± 1.0 ml·100 ml forearm tissue(-1)·min(-1) for the women (P = 0.034, sex-by-sodium interaction). We conclude that the NO component of endothelium-dependent vasodilation is altered by dietary sodium intake based on sex, suggesting that endothelial NO production is sensitive to dietary sodium in healthy young men but not women.

The protein composition of the avian progesterone receptor was analyzed by immune isolation of receptor complexes and gel electrophoresis of the isolated proteins. Nonactivated cytosol receptor was isolated in association with the 90-kilodalton (kDa) heat shock protein, hsp90, as has been described previously. A 70-kDa protein was also observed and was shown by Western immunoblotting to react with an antibody specific to the 70-kDa heat shock protein. Thus, two progesterone receptor-associated proteins are identical, or closely related, to heat shock proteins. When the two progesterone receptor species, A and B, were isolated separately in the absence of hormone, both were obtained in association with hsp90 and the 70-kDa protein. However, activated receptor isolated from oviduct nuclear extracts was associated with the 70-kDa protein, but not with hsp90. A hormone-dependent dissociation of hsp90 from the cytosolic form of the receptor complex was observed within the first hour of in vivo progesterone treatment, which could explain the lack of hsp90 in nuclear receptor complexes. In a cell-free system, hsp90 binding to receptor was stabilized by molybdate but disrupted by high salt. These treatments, however, did not alter the binding of the 70-kDa protein to receptor. Association of the 70-kDa protein with the receptor could be disrupted by the addition of ATP at elevated temperatures (23 degrees C). The receptor-associated 70-kDa protein is an ATP-binding protein, as demonstrated by its affinity labeling with azido[32P]ATP. These results indicate that the two receptor-associated proteins interact with the progesterone receptor by different mechanisms and that they are likely to affect the structure or function of the receptor in different ways.

We conclude that autonomic control of HRV at rest and during mental stress is altered by dietary sodium in healthy normotensive young adult men and women.