Hormone receptors of the baboon cardiovascular system. Biochemical characterization of aortic cytoplasmic androgen receptors.

Abstract

Cytoplasmic androgen receptors were identified in the aorta of the baboon (Papio sp.)-Using the synthetic androgen R1881 (17/?-hydroxy-17a-methyl-estra-4,9,11-trien-3-one) as probe, androgen receptors were demonstrated only when the incubation mixtures contained 1.0 nM triamcinolone acetonide (TA). The relative binding affinity of selected steroids for the aortic androgen receptor was R1881, 100%; 5a-dihydrotestosterone, 46.1%; testosterone, 60.7%; progesterone, 9.1%; R5020, 3.1%; and estradlol-17/3, 7.5%. The androgen receptor migrated on low-ionic-strength linear sucrose density gradients as a macromolecule with a sedimentation coefficient of 8.0S. Saturation analysis performed at 2°C (available sites) showed that the androgen receptor content of baboon aortic cytoplasmic extracts was 12.9 ± 2.4 fmoles/mg protein and that the dissociation constant for R1881 was 1.47 ± 0.07 nM. The observation that TA was required in the cytoplasmic extracts in order to identify androgen receptor indicates the presence of progesterone receptor-like binding components. These aortic cytoplasmic androgen receptors are indicated to be physiologically functional by previous autoradiographic studies that showed localization of radioisotope in the nuclei of aortic smooth muscle cells following injection of baboons with 5a-dihydrotestosterone. (Arteriosclerosis 1981; 1:257-264) E strogens 1 " 5 and androgens 6 " 9 alter blood flow rates in accessory reproductive organs. Clinical observations and epidemiologic studies have repeatedly confirmed that women have lower rates of coronary heart disease (CHD) and less severe coronary atherosclerosis than do males of equivalent age. 10 These studies imply a possible role for sex steroid hormones as modulators of vascular tissue cell function.

Androgen Receptors Mediate Hypertrophy in Cardiac Myocytes

“…19 To date, there has been no unequivocal evidence that androgens can produce a hypertrophic effect directly on cardiac myocytes independent of other neurohormonal or hemodynamic effects that alter preload and/or afterload, although there is immunohistochemical evidence that androgen receptors are present in some cell types within the myocardium. 20,21 Therefore, we undertook the present study to determine whether in adult mammalian heart, and specifically in cardiac myocytes, androgen receptors are present in a molecular context that permits regulation of cardiac hypertrophy by exogenous androgens. We now report that the androgen receptor gene is expressed specifically in cardiac myocytes and that androgens can mediate a significant hypertrophic response directly in cardiac myocytes.…”

Hormone receptors of the baboon cardiovascular system. Biochemical characterization of aortic and myocardial cytoplasmic progesterone receptors.

“…atrial and ventricular myocardial fibers following injection of radiolabeled 5a-dihydrotestosterone and documented limited capacity nuclear localization of radioisotope in smooth muscle cells of the major muscular and elastic arteries following injection of either tritiated 5a-dihydrotestosterone or estradiol-17/?. In previous biochemical studies, we have provided evidence for the presence of cytoplasmic androgen receptors in the aorta (Lin et al, 1981a) and myocardium (Lin et al, 1981b) of the baboon. In the course of those studies, we obtained preliminary evidence for the presence of aortic and myocardial cytoplasmic progesterone receptor-like binding components (Lin et al, 1981a(Lin et al, , 1981b).…”

“…In previous biochemical studies, we have provided evidence for the presence of cytoplasmic androgen receptors in the aorta (Lin et al, 1981a) and myocardium (Lin et al, 1981b) of the baboon. In the course of those studies, we obtained preliminary evidence for the presence of aortic and myocardial cytoplasmic progesterone receptor-like binding components (Lin et al, 1981a(Lin et al, , 1981b). In the current study, we report the identification and characterization of baboon myocardial and aortic progesterone receptors.…”

“…The heart was removed, and right and left ventricles and atria were separated and cut into blocks of 0.8-1.0 g. The aorta was removed and cut into blocks of 0.8-1.0 g. Tissue samples were immediately placed into polypropylene screw top cryotubes (Vangard International, Inc.), frozen by immersion in liquid nitrogen, and transferred, without delay, to a -90°C freezer where they were stored until used. Cytoplasmic extracts were prepared by a slight modification of methods previously described (Lin et al, 1981a(Lin et al, , 1981b. In brief, tissue was thawed on ice and subsequent procedures were performed at 2°C.…”

“…(Radioinert R5020 was prepared in buffer T50E0.1D10G2 containing 1 mg/ml BSA.) Separation of bound and free radioligand was by the dextran-y-globulin coated charcoal (DGCC) procedure previously used by us (Lin et al, 1981a(Lin et al, , 1981b, with the exception that EtOH was eliminated. After correction for nonspecific binding, as previously described (Boesel et al, 1977), data were analyzed by the method of Scatchard (1949).…”