Determination of triiodothyronine concentration in human serum

A simplified method has been described for the measurement of triiodothyronine (T3) in human serum. The sensitivity was sufficient for determinations on hypothyroid as well as normal and thyrotoxic sera. The values obtained have been in reasonable agreement with a double isotope derivative assay. The normal T3 concentration in human serum approximates 0.2 mug/100 ml; the mean +/-SD of 31 normal sera was 220 +/-27 ng/100 ml. Elevations were observed in sera from 40 patients with thyrotoxicosis (752 +/-282 ng/100 ml), and diminutions were found in sera from 10 hypothyroid patients (98+/-48 ng/100 ml). In rare instances thyrotoxicosis may be due to elevated serum T3 with normal thyroxine (T4) concentration. The incidence of this condition remains to be determined. In approximately half the cases with low serum T4 after (131)I therapy, the eumetabolic state may be maintained by normal or elevated T3 concentration. From these data and kinetic studies indicating a rapid turnover it may be inferred that T3 rather than T4 may be the more important hormone in health and in disease.

Luteinizing hormone-releasing hormone binds to enriched human placental membranes and stimulates in vitro the synthesis of bioactive human chorionic gonadotropin

Partially purified cell membranes were prepared from midterm and term placentas after sedimentation on a sucrose density gradient. Biochemical characterization showed that the sucrose density pellet was enriched 8-fold in alkaline phosphatase activity and also contained the majority of [125I]LHRH binding sites. This enrichment was also confirmed by electron microscopy. Specific binding of LHRH was then determined by incubating iodinated LHRH or two of its superanalogs with increasing doses of the corresponding radioinert ligand. Scatchard representation of the data showed curvilinear plots whose first component revealed, for both stages of pregnancy, saturable binding of [125I]LHRH and its agonists with similar association constants (Ka) that ranged between 5.5 X 10(5) M-1 and 1.1 X 10(7) M-1. When standardized per milligram of DNA content, the number of binding sites ranged between 225 and 310 X 10(-12) M. Specificity was evidenced by the inability of a biologically active LHRH antagonist, oxytocin, and TRH to inhibit [125I]LHRH binding. Short term placental cultures incubated with 1.5 X 10(-6)M LHRH had increased production rates of both immunoassayable and bioassayable hCG, and this effect was 4-fold higher in midterm placental cultures. Placental incubations with either buffer or equimolar concentrations of oxytocin or TRH had no effect on hCG production. These observations expand information on extrapituitary binding sites of LHRH and suggest a role for this peptide in the physiology of the human placenta.

Functional opioid receptor sites in human placentas

We characterized the presence of opioid peptide receptor sites in plasma membranes and cells from human midterm and term placentas. Incubations with [3H]ethylketo-cyclazocine (EKC) at increasing doses revealed the presence of high affinity, low capacity, opioid peptide receptor-specific binding of the kappa-type. Scatchard analysis of the binding data showed, in the plasma membranes, linear plots at both stages of pregnancy with similar mean equilibrium association constants of 1.31 +/- 0.29 (+/- SE) X 10(9) mol/L-1 (n = 4) at midterm and 0.52 +/- 0.63 X 10(9) mol/L-1 at term (n = 4). In placental cells (n = 4) from term gestations, the binding plots were curvilinear; the first component had a Ka of 5.51 +/- 0.50 X 10(9) mol/L-1, and the second component had a Ka of 1.33 +/- 0.81 X 10(8) mol/L-1 (P less than 0.01). When standardized per mg tissue protein, the number of binding sites in plasma membranes increased from 13.8 +/- 9.8 fmol at midterm to 50.0 +/- 18.6 fmol at term (P less than 0.05). For term placental cells, the concentration of binding sites was 81.2 +/- 36.0 fmol for the high affinity sites and 713 +/- 390 fmol for the lower affinity sites. Specificity for the kappa-type of OPR was found based on the inability of mu- or delta-opioid peptides, as well as LHRH and TRH, to compete for [3H]EKC binding. Term placental cells incubated with various doses of opioid peptides had a 50% increase in placental lactogen production. The increase was significantly higher than controls only with kappa-agonists (P less than 0.05), maximal with 10(-9) mol/L EKC, and completely inhibited by 5 X 10(-6) mol/L naloxone. These results expand on previous data demonstrating the presence of opioid peptide receptor in placental plasma membranes and suggest a role for opioid peptides in regulating secretion of placental lactogen by placental cells.

Angiotensin II stimulates both inositol phosphate production and human placental lactogen release from human trophoblastic cells

We studied the functional significance of the binding of angiotensin-II (AII) to human placentas. Human trophoblastic cell suspensions were prepared by trypsin digestion of minced tissue. Cell incubations with increasing doses of [125I](SAR1)AII, ranging from 0.01-2.5 nmol/L, were carried out for 20 min at 37 C. The results indicated the presence of specific low capacity [4300 +/- 1300 (+/- SE) sites/cell], high affinity (Kd = 0.38 +/- 0.06 nmol/L) binding sites for [125I](Sar1)AII. This binding was specific for AII analogs. When placental cells were preloaded with 40 microCi/mL [3H]myoinositol for 2 h at 37 C, AII stimulation resulted in a dose-dependent increase in inositol phosphate (InsP) production [EC50 = 1.4 +/- 0.4 (+/- SE) nmol/L], as measured by ion exchange chromatography. (Sar1)AII also stimulated InsP production, with an EC50 of 0.3 +/- 0.2 nmol/L. AII-stimulated production of InsP was completely blocked by the antagonist (Sar1,Ala8)AII. AII also stimulated human placental lactogen release from trophoblastic cells in a dose-dependent fashion. The EC50 was 18 +/- 9 pmol/L, and the stimulation was blocked by (Sar1,Ala8)AII, as found for AII-stimulated InsP production. These results suggest that stimulation of human placental lactogen release by AII may be mediated by activation of phospholipase-C, which, in turn, produces phosphoinositide breakdown. The results, therefore, provide evidence of a physiological role for the renin-angiotensin system within the human placenta.

Labelling of D2-dopaminergic and 5-HT2-serotonergic binding sites in human trophoblastic cells using [3H]-spiperone

We previously reported that dopamine (DA) inhibited the release of human placental lactogen (hPL) from human placental cells. We also demonstrated the presence of D2-dopamine receptors in membrane preparations of human term placenta. The aim of the present study was to characterize these D2 receptors on freshly isolated human trophoblastic cells. The binding of [3H]-spiperone to these cells showed a curvilinear Scatchard plot suggesting the presence of two classes of binding sites (Kd1 = 1.26nM; Kd2 = 44.3nM). Competition experiments showed the following inhibitory binding potencies: serotonin-2 (5-HT2) > or = D2 >>> alpha-adrenergic, beta-adrenergic, D1-dopamine, thus suggesting the presence of 5-HT2 binding sites. We have examined this possibility by blocking [3H]-spiperone binding to 5-HT2 receptors in the presence of 50nM ketanserin, a selective antagonist of 5-HT2 sites. Under this condition, the linear Scatchard plot obtained suggested a single population of homogeneous binding sites for [3H]-spiperone with a Kd of 0.55nM. To further characterize placental D2 receptors we conducted binding experiments with [3H]-raclopride, an more selective D2 antagonist. The linear Scatchard plot obtained with this ligand suggested one class of binding sites for [3H]-raclopride (Kd = 6nM) with the following inhibitory potencies: D2 >>> beta-adrenergic >> 5-HT2, D1, alpha-adrenergic. These results suggest an important paracrine function for DA in human placenta and show for the first time that [3H]-spiperone binds putative 5-HT2 receptors in human placenta.

Effect of aging on the dissociation kinetics and estradiol receptor nuclear interactions in mouse uteri: correlation with biological effects

The dissociation kinetics of uterine estradiol receptor (UER) from young, middle-aged, and old mice have been studied in vitro and correlated with interactions of the steroid receptor with nuclear suspensions in a cell-free system. Furthermore, we have determined in these various age groups of mice the concentration of uterine cytosolic progesterone receptors and the activity of glucose-6-phosphate dehydrogenase. Compared to UER from young mice, the receptor from middle-age and old mice displayed similar first order dissociation kinetics, but a significantly reduced fraction of the slow component resulting from transformation of the receptor into a state of higher affinity for estradiol. In all age groups, sodium molybdate markedly inhibited this heat activation of UER. Recombination studies using heat-treated cytosolic UER and enriched nuclear fractions of various age groups suggested a markedly reduced ability for nuclear binding with advancing age, despite unchanged affinity of activated UER for nuclear acceptor sites that ranged from 3-5 X 10(9) M-1. Cross-incubation studies of heat-activated cytosolic UER with nuclei from young, middle-aged, and old mice suggested that the activation defect of cytosolic UER was already present at middle age and that a reduced nuclear ability to support receptor binding followed the onset of reproductive acyclicity. In parallel with these endocrine defects, we observed, with aging, decreases in mean baseline progesterone receptor concentrations and glucose-6-phosphate activity in uteri of both intact and castrated mice. The diminution of these two parameters was present at middle age, further increased at old age, and persisted after administration of low (0.2 mg) or high (2.0 mg) doses of estradiol for 3 days before study. Our observations suggest that decreased receptor activation is primarily responsible for the decreased effects of estrogen in aging mice.

Long-standing goiter and hypothyroidism: an unusual presentation of a TSH-secreting adenoma

A 63-year-old female patient was referred to our hospital in February 1994 for a pituitary tumor. On a previous examination, in 1973, she had a goiter, nonspecific symptoms and only an elevated serum T3. In 1984 she had become hypothyroid, her goiter had increased, serum T4 was 69 nmol/L, TSH 34.4 mU/L, and TPO antibodies were positive. Hypothyroidism due to autoimmune thyroiditis was diagnosed and she received L-T4 100 micrograms/day. In 1985 and 1986, serum TSH had decreased but remained slightly elevated, while T4 was at the upper limits of normal. From 1987 to 1989 her serum TSH rose from 9 to 20 mU/L and remained at that level for the ensuing 4 years in spite of increasing L-T4 up to 150 micrograms/day. In October 1993, after discontinuing L-T4 for 6 weeks, TSH was 23.7 mU/L, T4 170 nmol/L, 131I thyroid uptake 52%, and the CT scan showed a large pituitary tumor with suprasellar extension. On preoperative investigation TSH was 40-51 mU/L with no response to TRH or GnRH. The alpha-subunit was increased at 6.33 micrograms/L with the alpha-TSH/TSH molar ratio of 1.23. Prolactin was elevated, but plasma cortisol, FSH, and LH were low. At surgery, we found a large chromophobe adenoma with few PAS-positive granules and with immunostaining positive for TSH and prolactin. From the clinical and biological data, we can conclude that the patient had probably a TSH-secreting adenoma since the goiter was first detected. The development, however, of autoimmune thyroiditis with hypothyroidism considerably modified the presentation of the disease and may have accelerated the growth of the tumor.

Ca2+, but not membrane lipid hydrolysis, mediates human chorionic gonadotropin production by luteinizing hormone-releasing hormone in human term placenta

We postulated a role for lipid metabolism and Ca2+ in the LHRH-induced release of hCG by human placentas. Term placental cells in suspension prelabeled with [3H]myoinositol were stimulated without or with increasing concentrations of LHRH in the presence of 10 mM LiCl, and total inositol phosphate (IP) was measured by ion exchange chromatography; a nonsignificant 0.9 +/- 0.08-fold increase over the control value was observed. In contrast, placental cells stimulated with equimolar concentrations of angiotensin II (AII) induced a 4.6 +/- 0.9-fold increase in total IP (P less than 0.01), while rat pituitary cells showed 1.9 +/- 0.2- and a 2.4 +/- 0.07-fold increases in total IP production after stimulation with LHRH or AII, respectively (P less than 0.05). These increases were blocked by coincubation with specific LHRH and AII antagonists. When 1 x 10(6) placental cells were incubated with 45Ca2+ without and with increasing doses of LHRH for 0-75 s and then filtered under negative pressure, we observed significant incorporation of 45Ca2+. This influx was linear with incubation time, significantly more pronounced in cells exposed to LHRH than in control cells, and showed a dose-response curve to LHRH that reached maximal influx rates of 3.6 +/- 0.3 nM/min.1 x 10(6) cells with 10(-5) M LHRH. This response was completely blocked by coincubation with 10(-5) M LHRH antagonists; cobalt chloride and verapamil reduced it by 60% and 80%, respectively. Compared to placental cells stimulated with LHRH alone, those coincubated with LHRH and specific LHRH or Ca2+ antagonists released from 10-100% less hCG. We conclude that Ca2+ participates in the LHRH action in human placentas, but uncoupled to PI turnover.

An islet-activating protein-sensitive G-protein is involved in dopamine inhibition of both angiotensin-stimulated inositol phosphate production and human placental lactogen release in human trophoblastic cells

In isolated human trophoblastic cells, dopamine (DA) significantly inhibited the angiotensin-II (AII)-stimulated inositol phosphate (IP) accumulation by 44 +/- 8% (EC50, 0.5 +/- 0.2 microM) and human placental lactogen (hPL) release by 85 +/- 5% (EC50, 1.0 +/- 0.8 microM). These effects were blocked by sulpiride, a specific D2 antagonist. On the contrary, scherring 23390 (a specific D1 antagonist) and propranolol (a specific beta-adrenergic antagonist) were ineffective, suggesting that these DA effects are mediated through a DA receptor of the D2 subtype. The mechanism by which DA inhibited AII-stimulated inositol phosphate production implicates a GTP-binding protein sensitive to the islet-activating-protein (IAP), since DA's effects on IP accumulation and hPL release were blocked by this toxin. To further characterize this GTP-binding protein, particulate fractions of placental cells were incubated with [alpha-32P]NAD and IAP. Solubilized extracts were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Two proteins of 40 and 41 kDa mol wt were specifically ADP ribosylated. They were probably involved in the DA inhibitory processes, since IAP treatment, known to suppress the effects of DA, also reduced the labeling of these two molecules by around 40%. The effects of AII and DA on hPL release appear to be insensitive to the external calcium concentration, since the results were not significantly different in normal (1.8 mM Ca2+) and low Ca2+ (10(-5) M Ca2+) concentrations. On the other hand, increasing the intracellular concentration of cAMP by adding forskolin did not modify the effect of DA on either IP accumulation or hPL release, suggesting that cAMP is not implicated in hPL release from freshly isolated human trophoblastic cells.

On the presence of nonfunctional uterine estrogen receptors in middle-aged and old C57BL/6J mice

The nuclear binding kinetics of uterine 17 beta-estradiol (E2) receptors (UER) were studied throughout aging in intact and castrated (OVX) mice. When compared to young animals, 15- to 18-month-old mice showed a significant reduction in their total cytosolic (0.526 vs. 0.405 pmol/uterus; P less than 0.05) and nuclear (0.37 vs. 0.16 pmol/uterus; P less than 0.01) UER content, whereas the affinity (Ka) for estrogens remained constant (0.8-1.6 X 10(9) M-1). This age-related decrease in UER was preceded by a blunted and retarded nuclear binding of UER at 10-14 months of age, which was further accentuated after transition from perimenopause. Ovariectomy (OVX), whether performed neonatally or in adulthood, reduced the total concentration of cytosolic and nuclear UER in each age group studied, but did not prevent this reduced nuclear binding observed in middleaged mice. However, when standardized per tissue protein, the mean number of cytosolic UER from young and middle-aged, but not old, mice was reduced by 50% after neonatal OVX (176.5, 178.4, and 218.8 fmol/mg protein, respectively), whereas it remained unchanged when OVX was performed in adulthood and the animals subsequently studied at peri- and postmenopausal ages (326.3 and 283.3 fmol/mg protein, respectively). Daily administration of a physiological dose of E2 for 7 days to OVX mice of each age group induced maximal synthesis of UER in young animals, but not in peri- and postmenopausal ones; in peri- and postmenopausal animals, this was paralleled by reduced uterotropic responses despite similar increments in plasma E2. These results suggest an age-related, gonad-independent decline in the number of functional UER early in reproductive aging.

Hypothalamic-pituitary axis during reproductive aging in mice

We correlated the content of hypothalamic (HT) GnRH and pituitary (PT) GnRH receptor sites with PT and plasma gonadotropin levels throughout aging in C57BL/6J mice. Female mice of 4-6 months (young), 10-12 months (middle-age) or 15-18 months (old) of age were studied either intact or 15 days post-ovariectomy (OVX) with or without E2 therapy. In intact mice, HT GnRH content increased twofold during aging while GnRH receptor sites in PT remained unchanged. PT content of both FSH and LH gradually rose during aging while plasma concentration rose even more. OVX resulted in a significant decrease in both HT GnRH content and PT receptor sites and no age difference was observed. OVX also resulted in a significant increase in both PT content and plasma levels of gonadotropin in young and middle-age mice while old mice showed a blunted response. After E2 therapy for 7 days, HT GnRH content and PT GnRH receptor sites returned to normal levels in all age groups. By contrast, E2 therapy resulted in no change in PT content of FSH:LH in any age group. Whereas plasma FSH:LH levels returned to intact levels in young mice, they remained elevated to OVX levels in middle-age and old ones. Our results demonstrate an age related dichotomy in the PT production of FSH:LH unrelated to changes in either HT GnRH content or its PT receptor sites, thus suggesting cellular defects in post-receptor binding events within the pituitary.

Effect of ACTH on cholesterol and steroid synthesis in adrenocortical tissues

Previous studies have established that under normal conditions, adrenal HMG-CoA reductase activity is higher in hamsters than in rats and humans. The hamster reductase activity follows a diurnal rhythm corresponding to that of plasma ACTH and glucocorticoids [Endocrinology 107 (1980) 215] but not to that of aldosterone. ACTH treatments to hamsters increased reductase activity after a latency of 60 min; this enhancement was prevented by cycloheximide [J. steroid Biochem. 24 (1986) 325]. Immunotitration and immunoblotting studies confirmed that ACTH caused an increase in reductase protein synthesis. In rats, long-term (1-9 days) and short-term (3 h) treatments with ACTH also induced increase in adrenal HMG-CoA reductase activity and reductase protein. In the presence of iodoacetamide and inhibitors of proteolytic enzyme, a main specific band of enzyme was evinced in the area of 102 +/- 6 kDaMr, by Western blotting, for both hamster homogenate and microsomal preparations (Endocrinology, 120 (1987]. Similarly Mr values were found with rat adrenal preparations. The concentration of mRNA, analyzed using the c-DNA pRed-10 coding for the Chinese hamster ovary reductase, was increased in adrenals of hamsters treated with ACTH. The reductase mRNA levels also fluctuated during the day in parallel with those of reductase activity and reductase protein. In conclusion, these results indicate that ACTH and other conditions inducing a change in hamster adrenal HMG-CoA reductase activity provoke parallel changes in reductase mRNA and reductase protein content. ACTH acts on the adrenal reductase of species synthesizing large as well as small quantities of cholesterol, thus indicating the general importance of this hormonal control.

Effect of thyroid hormones on G proteins in synaptosomes of chick embryo

We have described a thyroid hormone receptor in synaptosomes of the chick embryo brain. To understand how the hormones exert their actions at this level, we performed a series of studies to demonstrate that this receptor could be linked to G proteins. Guanosine 5'-[gamma-thio]triphosphate (GTP gamma S)(100 muM) lowered the binding capacity of the receptor high affinity site from 8.9 +/- 1.3 to 3.4 +/- 1.3 ng T3/mg protein, a finding consistent with the coupling of receptor to G proteins. Furthermore, ADP ribosylation with pertussis toxin showed that thyroid hormones induced a dose-dependent increase in the inactive alpha 0-subunit of the G0 protein. This effect was detected at 10 pM, with a maximal increase (mean +/- SEM, 50 +/- 3.6%) at 100 nM, and T4 was as effective as T3. Both hormones also decreased the intrinsic guanine triphosphatase activity of G proteins by lowering the binding of GTP to the alpha-subunit and their rate of hydrolysis. This inhibition was greater with T4 (25 +/- 5%) than with T3 (14 +/- 2%), suggesting that the former could be the more active hormone at the synaptosomal level. The effect on guanine triphosphatase activity confirms that the synaptosomal thyroid hormone receptor is coupled to a G(zero) protein. These results demonstrate that thyroid hormones increase or favor the ADP ribosylation of G alpha(zero) by pertussis toxin. Thus, they enhance the alpha(zero)-GDP form of the G(zero) protein, namely its inactive conformation. By decreasing the activity of this protein, these hormones may modulate the formation of second messengers in synaptosomes and intervene in the regulation of neuronal proliferation and differentiation induced by several factors. Therefore, thyroid hormones may exert their action on brain maturation at least in part by modulating G alpha(zero) through their synaptosomal receptor.

Dynamics of LHRH binding to human term placental cells from normal and anencephalic gestations

In order to improve our knowledge on human placental hCG production, we studied the binding of an LHRH agonist (N-Ac-Pro1,D-Leu6)-LHRH to third trimester intact placental cells from normal and anencephalic fetuses. In normal pregnancies, specific and saturable binding was found for both LHRH and its analogs with two classes of binding sites. Association constants were 4.7 +/- 2.2 (mean +/- SEM) X 10(5) M-1 for the low affinity sites and 1.7 +/- 0.8 X 10(8) M-1 for the higher affinity sites (P less than 0.01), and the estimated number of sites was 1.71 +/- 0.52 nmol/mg of cell protein and 2.79 +/- 0.54 pmol/mg of cell protein, respectively. Preincubation with increasing concentrations of LHRH agonist induced a progressive decrease in specific binding sites and manifested by a reduction in hCG production which paralleled the concentration of the agonist in preincubation buffer. Studies with placental cells from three anencephalic fetuses showed a decreased binding capacity for LHRH and its agonist, when compared to normal trophoblastic cells, as well as a reduced capacity to produce hCG. Our results suggest that mechanisms dependent upon LHRH binding to its receptor are required for placental hCG production in normal pregnancies. Furthermore our investigation suggests a role for the endocrine feto-placental milieu in the manifestation of these placental LHRH binding sites.

Corticosteroid receptors in the kidney of chick embryo. I. Nature and properties of corticosterone receptor

Cytosol from kidney of chick embryo (age 16-18 days) contained a corticosterone-binding site with the features of a putative receptor. This receptor was a thermolabile protein, readily digested by proteolytic enzymes, with a sedimentation coefficient of 7-8 S and with an apparent molecular weight greater than 100,000. Simultaneous studies with transcortin (CBG) revealed several differences between the renal- and serum-binding protein pertaining to the effect of temperature, the sedimentation coefficient, the charcoal "stripping" and, finally, the binding and competition of various steroids for the two proteins. Kinetic analysis showed a rapid association (10 min), which followed second-order reaction kinetics, and a dissociation of pseudo-first-order reaction kinetics with a t1/2 of 168 min at 0 degrees. The analysis of the Scatchard plot showed the presence of a single class of binding sites with an association constant (KA) of 1.3 X 10(8)M-1 and a binding capacity (nmax) of 500-700 fmol/mg protein. We obtained similar results when we used dexamethasone as a ligand. The association (ka) and dissociation (kd) rate constants were respectively 2.9 X 10(6)M-1 sec-1 and 6.86 X 10(-5) sec-1. From their ratio a KA value of 4.2 X 10(10) M-1 was obtained. Studies with various steroids demonstrated that only dexamethasone and, to a lesser degree, progesterone competed for the binding site. These data showed that the kidney of chick embryo possessed one type of receptor for the glucocorticoids, which was similar to the type II described in rat kidney.

Hormonal regulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase mRNA in the rat adrenal gland

We studied the effect of ACTH on 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase enzyme. Reductase activity and reductase mass were enhanced by 22- and 6.2-fold respectively in one series of experiments, whereas in another the levels of reductase activity, reductase mass, and reductase mRNA were increased 6.6-, 3.6- and 2.2-fold respectively, following daily administration of exogenous ACTH for 3 days. Daily injection of 4-aminopyrazolopyrimidine (4-APP) to rats for 3 days increased circulating ACTH level 5.4-fold, whereas adrenal HMG-CoA reductase activity, reductase mass and reductase mRNA levels were greatly increased 36-, 10- and 16-fold, respectively. To counteract the effect of elevated plasma ACTH, dexamethasone acetate (Dex) was administered to 4-APP treated rats. At 3 h post Dex administration, plasma ACTH and corticosteroids levels were effectively decreased by 58 and 59%, respectively. The levels of adrenal HMG-CoA reductase mRNA, reductase activity and reductase mass were also diminished by 38, 31 and 40%, respectively. Our results show that rat adrenal HMG-CoA reductase can respond rapidly to hormonal changes, presumably through variations in circulating ACTH levels.

Age-dependent, ovary-independent decrease in the nuclear binding kinetics of estrogen receptors in the brain of the C57BL/6J mouse

To further define the role of aging of the brain in the induction of reproductive acyclicity, we put to death intact as well as castrated female C57BL/6J mice of various ages before and from 0.5 to 24 hours after subcutaneous injection of 0.2 micrograms of 17 beta-estradiol. Pooled hypothalamic and pituitary tissues were dissected and cytosolic/nuclear estrogen receptors were assayed in buffer that consisted of 10 mmol/L Tris(hydroxymethylaminomethane) hydrochloride, 1.5 mmol/L ethylenediaminetetraacetic acid, and 0.5 mmol/L dithiothreitol and contained molybdate (25 mmol/L) and inhibitors of proteases. Our results in intact animals indicated that baseline cytosolic concentration of estrogen receptors remained constant at 60 to 77 fmol/mg of protein (range) throughout aging, whereas nuclear levels of estrogen receptors decreased from 1.2 to 1.6 fmol/micrograms of deoxyribonucleic acid (range) to nondetectable levels after the onset of ovarian acyclicity. No age-related changes in the Ka were observed. After subcutaneous challenge with estrogen, nuclear binding of hypothalamic-pituitary axis estrogen receptors revealed a significant age-related decrease which was already evident at 10 to 14 months of age and prior to the onset of anestrous. Castration, whether performed neonatally or at 8 months of age, reduced the hypothalamic-pituitary axis concentration of estrogen receptors in middle-aged and aged animals, but did not prevent this blunted kinetics of nuclear binding. One week of daily injection of 17 beta-estradiol to intact and castrated mice of all age groups prior to binding kinetic studies induced maximal (five fold) increases in the content of hypothalamic-pituitary axis estrogen receptors in young animals which readily bound to the nucleus. After similar therapy to middle-aged and aged mice, minimal changes or even no changes were observed in both cellular estrogen receptor contents, despite similar increments in plasma levels of estrogen. These findings suggest an age-dependent decrease in the kinetics of hypothalamic-pituitary axis estrogen receptors manifested by a reduced synthesis of functional estrogen receptors in the brain of mice.

Corticosteroid receptors in the kidney of chick embryo. II. Ontogeny of corticosterone receptor and cellular development

In this study the ontogeny of cytosol receptors for corticosterone in the chick embryo kidney was examined and then this ontogenic profile was compared with that of an index of cellular development, i.e., the enzyme ornithine decarboxylase (ODC). The corticosterone receptor concentration (nmax) increased by sevenfold from Day 12 to Day 15 of embryogenesis and then declined to its lowest level by the time of hatching (Day 21). Similar results were obtained when dexamethasone was used as ligand, except that the baseline values at Day 9 and 21 were higher than those found with corticosterone. An identical ontogenic profile was obtained when the results were corrected for the endogenous glucocorticoids present in the cytosol. This increase of the corticosterone receptor occurred simultaneously with the enhanced adrenal corticoid synthesis. The ODC also showed a marked increase and a rapid fall during chick embryogenesis, but the enzyme activity was at its maximum when the corticosterone receptor number was still low (Days 12 and 13) and quickly decreased by the time the receptors had reached their highest levels (Days 14 and 15). The lowest level of ODC was observed immediately before hatching. These results indicate that during chick embryogenesis adrenal corticoids may induce the development of the corticosteroid receptor and that such development may cause a suppression of ODC activity. This suppressive effect of glucocorticoids could represent a mechanism of hormonal action on the kidney.