The thyroid C cells of ovariectomized rats treated with estradiol

The structure and function of thyroid C cells were studied in ovariectomized (Ovx) adult female rats without and after chronic treatment with estradiol dipropionate (EDP). A peroxidase–antiperoxidase method was applied for localization of calcitonin (CT) in the C cells. Morphometric changes in their volume, nuclei, and relative volume density were evaluated in comparison with sham-operated control rats using a stereological method. The number of C cells was calculated. CT content in the sera was determined by radioimmunoassay. Ovariectomy (Ovx) led to a 21% increase in body weight (P<0.005), while treatment of Ovx rats with EDP decreased body weight by 25% (P<0.01). The immunoreactivity for CT in C cells of the Ovx rats was markedly increased. Significant decreases in the volume of C cells (by 13%; P<0.05) and serum CT (by 45%) were recorded, while the C cell number increased by 59% (P<0.05) in relation to the corresponding controls. The treatment of Ovx rats with EDP caused conspicuous degranulation of the C cells. The cellular volume was increased by 11% and serum CT by 36% in comparison with Ovx animals. At the same time a decrease in C cell number by 29% (P<0.05) was evident. It may be concluded that estradiol deficiency after Ovx reduced the synthesis and release of CT, while chronic treatment of these animals with EDP had a positive effect on the secretory activity of thyroid C cells.     

Effects of ovariectomy and chronic estradiol administration on pituitary-thyroid axis in adult rats

The effects of ovariectomy (Ovx) and of ovariectomy followed by chronic estradiol dipropionate administration (Ovx EDP) on the structure and function of the pituitary-thyroid axis were examined in the rat. Pituitary TSH cells and thyroid tissue were histologically, immunohistochemically and stereologically investigated. Serum TSH and T(4) levels were determined by RIA. Ovx did not affect pituitary weight, but subsequent treatment with EDP led to its more than two-fold increase (p<0.05). After ovariectomy, the cellular volume of pituitary TSH-immunoreactive cells increased by 28%, p<0.05 compared to sham-operated animals (SO). Treatment of Ovx rats with EDP partially reversed this change. However, the relative volume density of thyrotrophs decreased in comparison to the Ovx and SO groups (by 18% and 23%, p<0.05, respectively). No statistically significant differences in serum TSH levels were observed between the experimental groups. In thyroid tissue both peripheral and central follicles responded to Ovx and EDP treatments. Compared to SO rats, the relative volume densities of the follicles and colloid were increased (by 14% and 30%, p<0.05, respectively) in Ovx rats. Chronic EDP treatment of Ovx rats reversed these changes to the pre-ovariectomy state. Hyperplasia of thyroid follicular cells and a significant reduction (by 21%, p<0.05) of the serum level of T(4) were detected. In conclusion, estradiol deficiency and chronic treatment affected pituitary TSH cells and thyroid tissue. The sum effect of Ovx on the pituitary-thyroid axis was slightly stimulatory. Subsequent EDP treatment decreased thyroid functioning but at the same time preserved serum TSH at the control level.     

Thyroid C cells of middle-aged rats treated with estradiol or calcium

 The structure and function of C cells of middle-aged female rats (14-months old) treated with estradiol dipropionate (EDP), calcium (Ca) or a combination of EDP+Ca were studied. A stereological method was used to determine the volume of calcitonin (CT)-immunoreactive C cells and their nuclei, and the relative volume density and mean number of the C cells per section were calculated. Serum levels of CT, osteocalcin, parathyroid hormone (PTH), and β-estradiol were also measured. A significant decrease in body weight of the rats treated with EDP or EDP+Ca was observed. These treatments led to a significant decrease in cellular and nuclear volumes, relative volume density, and mean number of C cells per section, in comparison with the corresponding controls. A reduction of the serum level of CT, PTH, and osteocalcin was also recorded in EDP- and EDP+Ca-treated animals. No statistically significant differences between Ca- and vehicle-injected rats, with regard to all morphometric C cell parameters and biochemical values determined, were seen. However, a conspicuous degranulation of the C cells and decreased immunoreactivity for CT in the Ca-receiving group, which could be interpreted as the signs of increased activity of these cells, were noticed. This effect of Ca was also observed in rats injected with EDP and Ca in combination, when the inhibitory effect of EDP on C cell function was less noticeable than in the group treated with EDP alone. Accepted: 29 July 1997     

Chronic estradiol exposure modulates thyroid structure and decreases T4 and T3 serum levels in middle-aged female rats

OBJECTIVES: In human medicine, estrogen is applied in prevention and treatment of health problems associated with the menopause. The aim of this study was to examine the effects of chronic estradiol dipropionate (EDP) treatment on thyroid gland structure and function in middle-aged female rats. METHODS: At 14 months of age, Wistar rats received 0.625 mg EDP/kg b.w./day intraperitoneally for 2 weeks. The peripheral and central zones of the thyroid were stereologically analyzed and the following morphometric parameters determined: volume density of follicles, follicular epithelium, interstitium and colloid, epithelial height and the index of activation rate. Serum levels of TSH, T4 and T3 were determined by ELISA. RESULTS: EDP treatment led to significant decreases in volume densities of follicles and follicular epithelium, epithelial height and index of activation rate (by 11%, p < 0.05; 23%, p < 0.005; 11%, p < 0.05 and 21%, p < 0.05, respectively) in comparison to control values. Hyperplasia of thyroid follicular cells was noticed in 25% of EDP-treated animals. Serum levels of T4 and T3 were decreased (by 33%, p < 0.005 and 28%, p < 0.001, respectively), but TSH concentration was not significantly different from that of the controls. CONCLUSION: Chronic estradiol treatment significantly decreased volume density and height of centrally located follicular epithelium, follicular activation index and serum level of total thyroid hormones in middle-aged rats.     

The effects of synthetic salmon calcitonin on thyroid C and follicular cells in adult female rats

Structural and morphometric features of thyroid C and follicular cells were studied in adult rat females after treatment with synthetic salmon calcitonin (CT). The animals were chronically treated with either a low (10 IU/kg b.w) or a high (100 IU/kg b.w) dose of CT. A stereological method was applied to determine the volume density and the number of immunoreactive C cells. The height and volume density of follicular epithelium, colloid, interstitium and the follicles (epithelium plus colloid), as well as the index of activation rate were calculated. A significant decrease in body weight, as well as the volume density of immunoreactive C cells and the number of C cells per mm2, was observed in rats treated with both doses of CT. The height and volume density of follicular epithelium and follicles, as well as the index of activation rate were significantly increased in the animals given the high CT dose, while the volume densities of colloid and interstitium were reduced. No significant changes in the examined morphometric parameters were detected after treatment with the low CT dose. According to these results it can be concluded that the structural features of thyroid C and follicular cells were affected by the high dose CT treatment in the opposite manner, while the low dose CT treatment influenced only C cells.     

Effect of estrogen on global myocardial ischemia-reperfusion injury in female rats

We investigated the effects of estrogen on global myocardial ischemia-reperfusion injury in rats that were ovariectomized (Ovx), sham-operated, or ovariectomized and then given 17beta-estradiol (E(2)beta) supplementation (Ovx+E(2)beta). Hearts were excised, cannulated, perfused with and then immersed in chilled (4 degrees C) cardioplegia solution for 30 min, and then retrogradely perfused with warm (37 degrees C), oxygenated Krebs-Henseleit bicarbonate buffer for 120 min. The coronary flow rate, first derivative of left ventricular pressure, and nitrite production were all significantly lower in Ovx than in sham-operated or Ovx+E(2)beta hearts. However, coronary flow rates or nitrate production were not consistently different throughout the entire reperfusion period. Ca(2+) accumulated more in Ovx rat hearts than in sham-operated or Ovx+E(2)beta hearts, and mitochondrial respiratory function was lower in Ovx hearts than in hearts from the other two groups. Marked interstitial edema and contraction bands were seen in hematoxylin-eosin-stained sections of Ovx rat hearts but not in hearts from either of the other groups. Hematoxylin-basic fuchsin-picric acid-stained sections revealed fewer viable myocytes in hearts from the Ovx group than from the sham or Ovx+E(2)beta group. Transmission electron microscopy demonstrated more severely damaged mitochondria and ultrastructural damage to myocytes in Ovx rat hearts. Our results indicate that estrogen plays a cardioprotective role in global myocardial ischemia-reperfusion injury in female rats.     

Daidzein but not other phytoestrogens preserves bone architecture in ovariectomized female rats in vivo

Ovariectomy of immature female rats, results in significant decrease of trabecular bone volume and in cortical bone thickness. Previously, we found that estradiol-17beta (E(2)) restored bone structure of ovariectomized (Ovx) female rats to values obtained in intact sham-operated female rats. E(2) also selectively stimulated creatine kinase (CK) specific activity a hormonal-genomic activity marker. In the present study, we compared the effects of E(2) and the phytoestrogens: daidzein (D), biochainin A (BA), genistein (G), carboxy-derivative of BA (cBA), and the SERM raloxifene (Ral) in Ovx, on both histological changes of bones and CK, when administered in multiple daily injections for 2.5 months. Bone from Ovx rats, showed significant disrupted architecture of the growth plate, with fewer proliferative cells and less chondroblasts. The metaphysis underneath the growth plate, contained less trabeculae but a significant increased number of adipocytes in the bone marrow. D like E(2) and Ral but not G, BA, or cBA, restored the morphology of the tibiae, similar to that of control sham-operated animals; the bony trabeculeae observed in the primary spongiosa was thicker, with almost no adipocytes in bone marrow. Ovariectomy resulted also in reduced CK, which in both epiphysis and diaphysis was stimulated by all estrogenic compounds tested. In summary, only D stimulated skeletal tissues growth and differentiation as effectively as E(2) or Ral, suggesting that under our experimental conditions, D is more effective in reversing menopausal changes than any of the other isolated phytoestrogens which cannot be considered as one entity.     

Effects of ovariectomy on duodenal calcium transport in the rat: altered ability to adapt to low-calcium diet

Studies were undertaken to determine whether ovariectomy (ovx) would alter the ability of female rats to adapt to low dietary Ca intake by exhibiting an in duodenal active Ca transport. Intact and ovx female rats were fed diets containing 1.5, 0.50, or 0.02% Ca prior to measuring active Ca transport using everted duodenal sacs in vitro. In some experiments, ovx animals were pair-fed to intact animals of the same age consuming the same diet. When ovx animals were allowed to eat ad lib, we found that both growth rate and duodenal active Ca transport increased relative to age-matched, intact controls. However, when growth of ovx animals was maintained at the control rate by pair-feeding, ovx per se did not affect intestinal active Ca transport. Ovx did not alter circulating levels of 1,25-dihydroxyvitamin D (1,25(OH)2D). We found that intact females responded to the low-Ca (0.02%) diet with increased circulating 1,25(OH)2D levels and increased intestinal active Ca transport. Ovx animals exhibited the same increase in circulating concentrations of 1,25(OH)2D in response to low-Ca diet, but did not demonstrate increased duodenal active Ca transport. When ovx animals consumed the diet ad lib, they became larger and exhibited higher Ca transport rates than intact animals fed the high-Ca diet, but there was no difference in Ca transport between ovx animals fed diets containing different Ca contents. The results of these experiments demonstrate that in female rats, the ability to adapt to altered dietary Ca intake is dependent on intact ovarian function and is not necessarily directly related to circulating concentrations of 1,25(OH)2D.     

Chronic exposure to constant light affects morphology and secretion of adrenal zona fasciculata cells in female rats

The effect of chronic exposure to light of adult Wistar rats on growth and function of adrenal zona glomerulosa (ZG) and zona fasciculata (ZF) were examined. The females were exposed to continuous light of 600 lux for 95 days, starting on day 30 of age. The controls were kept under a 12:12 h light-dark cycle, at ambient temperature. The rats were sacrificed by decapitation and the left adrenal gland of each animal was dissected out and prepared for morphometric analyses. In animals exposed to chronic lighting, the absolute and relative volume of ZG were insignificantly increased by 5% (p>0.05) compared to controls. The volume of ZG cells and their nuclei were insignificantly changed by 1% (p>0.05) in comparison with corresponding controls. The absolute and relative volume of ZF were significantly increased (by 14 and 9%, respectively; p<0.05), as compared to controls. The volume of ZF cells and their nuclei were significantly increased (by 12 and 9%, respectively; p<0.05). Serum concentration of corticosterone was also significantly (p<0.05) increased by 13% in light-exposed group in comparison with control rats. These findings suggest that continuous exposure of female rats to constant light increased growth and secretory activity of ZF cells.     

Effect of calcium stress on the skeleton mass of intact and ovariectomized rats

Female rats were ovariectomized (Ovx) or sham-operated (control) at 18 weeks and the entire skeleton obtained at 24 weeks (baseline) or after an additional 31 day (28 week) interval on a normal (1.0%) or deficient (0.02%) calcium diet. Ovx rats showed a 42% increase in whole body bone resorption (3H-tetracycline loss) in the absence of calcium stress (1.0% calcium diet) and a 70% increase in resorption with morphological evidence of dramatic loss of cancellous bone mass when placed on calcium-deficient (0.02%) diets. Ovx rats kept on the 1.0% calcium diet showed a significant increase in both their body weight (30.2%) and total bone mass (11.6%) compared to baseline sham-operated controls. However, the total skeleton mass of these animals was significantly reduced (-20%) from that predicted by calculations based on body weight. Maintaining animals on calcium-deficient diets had no significant effect on the total skeleton mass of either control or Ovx rats in comparison with age-matched controls on 1.0% diets. It was further determined that an increase in bone mass between 24 and 28 weeks in rats receiving 1.0% dietary calcium occurred in both the axial and appendicular skeleton and was proportionately similar between control and Ovx groups. However, in animals subjected to dietary calcium stress during this interval, the decreased skeletal growth noted was confined primarily to the axial skeleton. The data indicate that ovariectomy or ovariectomy plus calcium stress does not result in loss of total bone mass during the interval of dramatically increased resorption and rapid loss of cancellous bone. The results suggest that the deterioration in individual bone structural and mechanical integrity due to ovariectomy or dietary calcium deficiency may not be attributed to overt loss in total bone mass but may involve a redistribution of bone mass.     

Morphometric study of the LH-immunoreactive gonadotrophic cells of rats following treatment with methoclopramide.

The LH-immunoreactive cells of the adult rat hypophysis were studied morphometrically after chronic treatment with methoclopramide. The morphological features of these cells showed modifications in both male and female rats, after treatment. Additionally, morphometric changes revealed a significant decrease (p less than 0.05) in both cytoplasmic area, which was more evident in the female rats, and nuclear area, with respect to the normal and control animals. These findings suggest that chronic inhibition of the dopaminergic system in rats atrophies LH-immunoreactive gonadotrophic cells of rats.     

Multiple dexamethasone treatment affects morphometric parameters of gonadotrophic cells in adult female rats

Exposure to glucocorticoids leads to numerous changes in various biological systems including the reproductive system. The aim of the present work was to find out whether dexamethasone (Dx) treatment of adult female rats would influence the histological and morphometric characteristics of the pituitary gonadotrophic cells (luteinizing--LH cells and follicle stimulating--FSH cells). One group of female Wistar rats received Dx injections on three consecutive days in doses 1.0, 0.5 and 0.5 mg/kg b.w. respectively, while the control rats were treated with equivalent volumes of saline. Experimental and control animals were sacrificed 24 h and 72 h after the last injection. The peroxidase-antiperoxidase (PAP) immunocytochemical procedure was used to study the LH and FSH cells. The stereological and morphometric analyses showed that multiple Dx treatments of female rats significantly decreased the volume of LH cells and the volume of their nuclei 24 h and 72 h after the last Dx injection in comparison with control values. At 24 h after Dx treatment, the volume density of LH cells was significantly increased, but at 72 h differences between the experimental and control groups were insignificant. The increase in number of LH cells per unit area (mm2) was significant at both timepoints (24 h and 72 h). Stereologic and morphometric characteristics of FSH cells was changed after Dx treatment in the same manner as that of LH cells, except for the volume density, where a significant increase was established 24 h and 72 h after the last Dx application. These results clearly demonstrate that 24 h and 72 h after the last of three Dx injections there were changes in the immunocytochemical and morphometric features of gonadotrophic cells.     

Nascent EDHF-mediated cerebral vasodilation in ovariectomized rats is not induced by eNOS dysfunction

In estrogen-depleted [i.e., ovariectomized (Ovx)] animals, an endothelium-derived hyperpolarizing factor (EDHF)-like mechanism may arise to, at least partially, replace endothelial nitric oxide (NO) synthase (eNOS)-derived NO in modulating cerebral arteriolar tone. Additional findings show that eNOS expression and function is restored in estrogen-treated Ovx female rats, while the nascent EDHF-like activity disappears. Because NO has been linked to repression of EDHF activity in the periphery, the current study was undertaken to examine whether the nascent EDHF role in cerebral vessels of Ovx females relates to a chronically repressed eNOS-derived NO-generating function. We compared the effects of chronic NOS inhibition with Nomega-nitro-L-arginine-methyl ester (L-NAME; 100 mg. kg-1. day-1 for 3 wk) on EDHF-mediated pial arteriolar vasodilation in anesthetized intact, Ovx, and 17beta-estradiol-treated (0.1 mg. kg-1. day-1 ip, 1 wk) Ovx (OVE) female rats as well as in male rats that were prepared with closed cranial windows. In the chronic NOS inhibition groups, pial arteriolar responses were monitored in the absence (all groups) and presence (females only) of indomethacin (Indo; 10 mg/kg iv). Finally, the gap junction inhibitory peptide Gap 27 (300 muM) was applied to block EDHF-related vasodilation. NO donor (S-nitroso-N-acetyl-penicillamine) responses were similar in all rats studied. Acetylcholine (ACh) reactivity was virtually absent in control Ovx rats and chronically NOS-inhibited intact female, OVE, and male rats. However, a partial recovery of ACh reactivity was seen in L-NAME-treated Ovx females. In addition, in the presence of L-NAME, a normal CO2 reactivity was observed in all females, whereas a 50% reduction in CO2 reactivity was seen in males. In intact and OVE rats, both chronic and acute (NG-nitro-L-arginine suffusion) NOS inhibition, combined with Indo, depressed ADP-induced dilation by > or =50%, and subsequent application of Gap 27 had no further effect on ADP-induced vasodilation. ADP reactivity was retained in Ovx rats after combined chronic NOS inhibition and acute Indo, but was attenuated significantly by Gap 27. In males, Gap 27 had no effect on arteriolar reactivity. Taken together, our data demonstrate that in the cerebral microcirculation, NO does not have an inhibitory effect on EDHF production or action. The increased EDHF-like function in chronic estrogen-depleted animals is not due to eNOS deficiency, suggesting a more direct effect of estrogen in modulating EDHF-mediated cerebral vasodilation.     

Blueberry prevents bone loss in ovariectomized rat model of postmenopausal osteoporosis

The objective of the present study was to explore the bone protective role of blueberry in an ovariectomized rat model. Thirty 6-month-old female Sprague-Dawley rats were either sham-operated (Sham) or ovariectomized (Ovx) and divided into three groups: Sham, Ovx (control), Ovx+blueberry (5% blueberry w/w). After 100 days of treatment, rats were euthanized, and blood and tissues were collected. Bone mineral density (BMD) and content of whole body, right tibia, right femur and fourth lumbar vertebra were assessed via dual-energy X-ray absorptiometry. As expected, Ovx resulted in loss of whole-body, tibial, femoral, and 4th lumbar BMD by approximately 6%. Blueberry treatment was able to prevent the loss of whole-body BMD and had an intermediary effect on prevention of tibial and femoral BMD when compared to either Sham or Ovx controls. The bone-protective effects of blueberry may be due to suppression of Ovx-induced increase in bone turnover, as evident by lowered femoral mRNA levels of alkaline phosphatase, collagen type I and tartrate-resistant acid phosphatase to the Sham levels. Similarly, serum osteocalcein levels were also lower in the blueberry group when compared to the Ovx control group, albeit not significantly. In summary, our findings indicate that blueberry can prevent bone loss as seen by the increases in BMD and favorable changes in biomarkers of bone metabolism.     

Thyroid C cells in male and female rats with chronic renal failure

The kidneys are responsible for iodine and of thyroid hormone biodegradation. The aim of this study was the histomorphological and immunohistochemical evaluation of the influence of sex on parafollicular thyroid C cells in rats with chronic renal failure. The experiment included 40 Wistar rats after subtotal nephrectomy, after sham operation, and without any surgical procedure. Two weeks after nephrectomy, fragments of thyroids were collected from the examined animals. Paraffin sections were stained with H+E and by silver impregnation. Calcitonin (CT), synaptophysin (SPh), somatostatin (ST), and neuron-specific enolase (NSE) were detected immunohistochemically in C cells. In rats with experimental uremia, immunostaining for the examined substances increased significantly in comparison to the controls. We also observed higher number of C cells with a stronger reaction in the group of males, compared to the female rats.     

Effects of dietary phytoestrogen on global myocardial ischemia-reperfusion injury in isolated female rat hearts

We investigated the effects of phytoestrogen on global myocardial ischemia-reperfusion injury in five groups of female rats. A high-phytoestrogen group (HPE) was ovariectomized (Ovx) and fed a diet containing soybean protein and a high-isoflavone soy extract. Another Ovx group of rats was fed the same diet as the HPE group but treated with the estrogen receptor blocker ICI-182,780 (HPE + ICI). A third group of Ovx rats was fed a diet containing soybean protein alone (low-phytoestrogen content; LPE). A fourth Ovx group was fed a diet free of phytoestrogen (Ovx). The fifth group of rats was sham ovariectomized (sham). Hearts from all rats were subjected to 30 min of global, hypothermic (4 degrees C), cardioplegic ischemia and 120 min of normothermic (37 degrees C) reperfusion with oxygenated Krebs-Henseleit buffer. Compared with either the sham or the HPE group, the Ovx and HPE + ICI groups had significantly decreased first derivative of left ventricular pressure (dP/dt), coronary flow rate (CFR), nitrite production and mitochondrial respiratory function and significantly increased Ca2+ accumulation and myocardial histological and ultrastructural injury. The CFR of the LPE group was significantly different from that of either Ovx or HPE + ICI group but the dP/dt, nitrite production, Ca2+ accumulation, and mitochondrial function were not. Our results indicate that diets containing phytoestrogen extract play a cardioprotective role in global myocardial ischemia-reperfusion in female rats.     

Differential modulation by estrogen of alpha2-adrenergic and I1-imidazoline receptor-mediated hypotension in female rats.

We have recently shown that estrogen negatively modulates the hypotensive effect of clonidine (mixed alpha2-/I1-receptor agonist) in female rats and implicates the cardiovascular autonomic control in this interaction. The present study investigated whether this effect of estrogen involves interaction with alpha2- and/or I1-receptors. Changes evoked by a single intraperitoneal injection of rilmenidine (600 microg/kg) or alpha-methyldopa (100 mg/kg), selective I1- and alpha2-receptor agonists, respectively, in blood pressure, hemodynamic variability, and locomotor activity were assessed in radiotelemetered sham-operated and ovariectomized (Ovx) Sprague-Dawley female rats with or without 12-wk estrogen replacement. Three time domain indexes of hemodynamic variability were employed: the standard deviation of mean arterial pressure as a measure of blood pressure variability and the standard deviation of beat-to-beat intervals (SDRR) and the root mean square of successive differences in R-wave-to-R-wave intervals as measures of heart rate variability. In sham-operated rats, rilmenidine or alpha-methyldopa elicited similar hypotension that lasted at least 5 h and was associated with reductions in standard deviation of mean arterial pressure. SDRR was reduced only by alpha-methyldopa. Ovx significantly enhanced the hypotensive response to alpha-methyldopa, in contrast to no effect on rilmenidine hypotension. The enhanced alpha-methyldopa hypotension in Ovx rats was paralleled with further reduction in SDRR and a reduced locomotor activity. Estrogen replacement (17beta-estradiol subcutaneous pellet, 14.2 microg/day, 12 wk) of Ovx rats restored the hemodynamic and locomotor effects of alpha-methyldopa to sham-operated levels. These findings suggest that estrogen downregulates alpha2- but not I1-receptor-mediated hypotension and highlight a role for the cardiac autonomic control in alpha-methyldopa-estrogen interaction.     

Effect of serum estradiol and leptin levels on thyroid function, food intake and body weight gain in female Wistar rats

We evaluated the interplay among estrogen, leptin and thyroid function in the regulation of body mass in female rats. Adult female rats were divided into four groups: control (C, sham-operated), ovariectomized (OVX), ovariectomized treated with estradiol benzoate (Eb) 0.7 or 14 μg/100 g bw per day, during 21 days. OVX led to an increase in body mass, food intake and food efficiency (change in body mass as function of the amount of food ingested) which were normalized by the lower Eb dose, and decreased significantly when the higher dose was given. Serum leptin levels were increased more than two-fold in all ovariectomized groups. Serum T4 levels of the Eb treated OVX were significantly lower than in the controls. Serum T3 and TSH were unaffected by OVX or by Eb treatment. Uterine type 2 iodothyronine deiodinase (D2) activity changed in parallel with serum estradiol: decreased after OVX, returned to control levels after the lower E2 treatment, and increased significantly after the high Eb dosage. The hypothalamic D2 activity was reduced around 30% in all castrated groups, treated or not with estrogen, whereas in the brown adipose tissue the enzyme was not changed. Interestingly, although estrogen-treated OVX rats had lower body weight, serum leptin was high, suggesting that estrogen increases leptin secretion. Our results show that estradiol is necessary for the hypothalamic action of leptin, since the increase in leptin levels observed in all ovariectomized rats was associated with a decrease in food intake and food efficiency only in the rats treated with estrogen.     

Involvement of cAMP but not PKA in the increase of corticosterone secretion in rat zona fasciculata-reticularis cells by aging

The effects and mechanisms of aging on corticosterone secretion in zona fasciculata-reticularis (ZFR) cells of ovariectomized (Ovx) rats were studied. Young (3-month) and old (24-month) female rats were Ovx for 4 days before decapitation. ZFR cells were isolated and incubated with different hormones or reagents at 37 degrees C for 30 min. Aging increased the basal secretion of corticosterone both in vivo and in vitro. The adrenocorticotropin (ACTH)-, forskolin-, 3-isobutyl-l-methylxanthine (IBMX)-, 8-bromo-adenosine 3',5'-cyclic monophosphate (8-Br-cAMP)-, and ovine prolactin (oPRL)-stimulated release of corticosterone by ZFR cells was greater in old than in young Ovx rats. H89, an inhibitor of protein kinase A (PKA), decreased the production of corticosterone in ZFR cells from young but not old Ovx rats. Forskolin-, or IBMX-induced production of cAMP was greater in old than in young Ovx animals, which correlated with the increase of corticosterone production by aging. The activity of 11 beta-hydroxylase that converts deoxycorticosterone (DOC, 10(-9) or 10(-8) M) to corticosterone in rat ZFR cells was decreased by age. However, the corticosterone production in response to high dose of DOC (10(-7) M) was indifferent between young and old groups. These results suggest that aging increases corticosterone production in Ovx rats via a mechanism in part associated with an increase of adenylyl cyclase activity and a decrease of phosphodiesterase activity, and then an increase of the generation of cAMP, but not related to either PKA activity or 11 beta-hydroxylase.