EFFECTS OF AGE AND OVARIAN FUNCTION ON THE PITUITARY–THYROID SYSTEM IN FEMALE RATS

1978 ◽  
Vol 78 (2) ◽  
pp. 225-232 ◽  
Author(s):  
H. J. CHEN ◽  
P. G. WALFISH
Keyword(s):  
Ovarian Function ◽  
Female Rats ◽  
Ovariectomized Rats ◽  
Lower Percentage ◽  
Female Rat ◽  
Thyrotrophin Releasing Hormone ◽  
Young Rats ◽  
Trh Stimulation ◽  
Old Rats ◽  
Absolute Concentrations

SUMMARY The effects of ovariectomy and ovariectomy and treatment with oestradiol benzoate (OB) on the basal concentration of thyrotrophin (TSH), the total concentrations and concentrations of free tri-iodothyronine (T3) and thyroxine (T4), and the concentrations of TSH, T3 and T4 observed after treatment with thyrotrophin releasing hormone (TRH) were studied in old (16–17 months of age) constant oestrous and young (3–4 months of age) oestrous rats. The untreated old control rats had significantly (P< 0·001) lower basal total T4 concentrations and percentage and absolute concentrations of free T4 and lower percentage and absolute concentrations of free T3 than untreated young rats. The basal levels of TSH in these two groups were similar and the increases in TSH after injection of TRH were identical. Two weeks after ovariectomy, no significant additional differences in hormone concentrations between old and young rats were observed. However, release of TSH induced by TRH was increased by three- to fourfold in old rats after ovariectomy compared with nine- to tenfold in young ovariectomized rats (P<0·01). Basal T4 concentrations remained unchanged in old ovariectomized rats treated for 7 days with 2 μg OB/day compared with both intact and ovariectomized rats. However, T4 concentrations in OB-treated young rats were significantly (P<0·001) reduced. Treatment with OB significantly increased both basal and TRH-induced T3 and TSH levels in old and young rats although the young rats showed a greater response (P<0·001). Two hours after injection of TRH, serum T3 concentrations in old rats increased only after OB treatment and not after ovariectomy alone or in intact rats, whereas T3 concentrations rose in all three groups of young animals. These results indicate that (1) older female rats have lower total T4, free T4 and free T3 concentrations and a lower TSH response to TRH, (2) OB treatment in young rats suppresses serum T4 but increases serum T3 and results in a greater TSH response to TRH and (3) at least one of the mechanisms accounting for the alterations in thyroid function observed in the older female rat, in addition to possible concomitant primary thyroid gland hypofunction, is a hyporesponsiveness of pituitary thyrotrophs to both endogenous negative feedback signals from low serum thyroid hormone concentrations and exogenous TRH stimulation.

Age-related alterations in prolactin binding sites in the female rat

1991 ◽  
Vol 124 (3) ◽  
pp. 314-321 ◽  
Author(s):  
Philippe Schneiter ◽  
Marianne J. Reymond ◽  
Thérèse Lemarchand-Béraud
Keyword(s):  
Binding Sites ◽  
Mammary Glands ◽  
Female Rats ◽  
Affinity Constant ◽  
Female Rat ◽  
Binding Studies ◽  
Young Rats ◽  
Age Related ◽  
Old Rats ◽  
Nulliparous Female

Abstract. Aging is associated with various neuroendocrine alterations, including in the rat a hypersecretion of PRL with maintained ovulations (repetitive pseudopregnancy) and a reduced activity of the hypothalamic dopaminergic neurons with loss of the neuron responsiveness to PRL, suggestive of age-related alterations in PRL receptors. In this study we have investigated PRL binding sites in the hypothalamus as well as in the mammary glands, the ovaries and the liver of young and old nulliparous female rats. The old rats (26-28 months) displayed spontaneous repetitive pseudopregnancies and they were compared with young (4-6 months) pseudopregnant rats; the binding studies were performed by saturation analysis using 125I-oPRL as ligand and particulate membrane preparations. In the hypothalamus, a negligible binding of PRL was observed in all fragments studied, mediobasal hypothalamus, median eminence, in both young and old rats and no characterization of the binding sites could be achieved. In the mammary glands, the number of PRL binding sites was appreciable in spite of the nulliparity of the rats, but it was smaller in the old than in the young rats (9.0±1.4 vs 14.9±1.2 fmol/mg protein; mean ± sem; p<0.02). In the ovaries, the density of PRL binding sites was similar in the old and young rats (112.6±9.7 vs 115.0±8.9 fmol/mg protein), illustrative of a maintained luteotropic effect of PRL with age in the rat. In contrast, in the liver a greater number of binding sites was found in the old than in the young rats (261.9±36.6 vs 63.6±5.8 fmol/mg protein; p<0.001), supportive of the ability of PRL to induce its own receptors in that tissue. The affinity constant of PRL binding was not altered with age in the tissues studied. These results are illustrative of tissue-specific modifications in the number of PRL binding sites with age and they are suggestive of a sustained biological activity of PRL in the old rats.

Age-related differences in basal and calcium-stimulated plasma calcitonin levels in female rats

1992 ◽  
Vol 262 (5) ◽  
pp. E557-E560
Author(s):  
C. L. Tsai ◽  
H. F. Pu ◽  
C. P. Lau ◽  
P. S. Wang ◽  
T. K. Liu
Keyword(s):  
Ovarian Function ◽  
Estradiol Benzoate ◽  
Young Female ◽  
Female Rats ◽  
Target Tissue ◽  
Young Rats ◽  
Ovx Rats ◽  
Age Related ◽  
Old Rats ◽  
Effects Of Aging

The effects of aging on calcitonin (CT) secretion in female rats were investigated. Old (24 mo) at constant diestrus status and young (2 mo) at diestrus status rats were either ovariectomized (Ovx) or left intact as controls. Ovx rats were injected subcutaneously with estradiol benzoate (25 micrograms/kg body wt) or sesame oil one time per day for 3 days. All rats were infused with CaCl2 (10 mg/ml) at a rate of 2 ml/h for 30 min via a jugular catheter connected to a peristaltic pump. Blood samples (0.5 ml each) were collected at 0, 30, 60, and 120 min. The basal and post-CaCl2 levels of plasma Ca measured with radioimmunoassay were significantly higher (P less than 0.05-0.01) in old than in young female rats. The pre- and post-CaCl2 levels of plasma Ca and CT in young rats were not altered by Ovx or estradiol replacement. In old rats, Ovx caused a higher (P less than 0.01) level in plasma CT at 0 and 30 min after CaCl2 infusion. Both basal and stimulated levels of plasma CT were higher (P less than 0.01) in old Ovx than in young Ovx rats. These results demonstrated that 1) the increase of plasma CT in response to Ca challenge was greater in old than in young female rats, 2) the influence of estradiol and ovarian function on plasma CT concentration increases as a function of age, and 3) estradiol reduced the plasma CT in response to hypercalcemia in old Ovx rats. The sensitivity of the target tissue of young rats may be lower in response to the modulation of estrogen during hypercalcemia without compromising the secretion and hypocalcemic effect of CT in young rats. All suggested an age-related relationship between estrogen and CT secretion in minute-to-minute regulation during Ca infusion in rats.

Role of the subcommissural organ in the control of gonadotrophin secretion in the female rat

1982 ◽  
Vol 95 (2) ◽  
pp. 207-213 ◽  
Author(s):  
Patrizia Limonta ◽  
Roberto Maggi ◽  
Luciano Martini ◽  
Flavio Piva
Keyword(s):  
Subcommissural Organ ◽  
Oestrous Cycle ◽  
Female Rats ◽  
Ovariectomized Rats ◽  
Normal Female ◽  
Female Rat ◽  
Thermal Lesions ◽  
Gonadotrophin Secretion

Thermal lesions were placed in the subcommissural organ (SCO) of female rats with normal cycles and long-term ovariectomized rats. In normal female rats SCO lesions disrupted the oestrous cycle in more than half of the animals, the majority of which entered a state of prolonged dioestrus. In these animals, serum gonadotrophin levels were similar to those of rats with regular cycles on day 2 of dioestrus. In animals in which the oestrous cycle was maintained, a delayed LH surge occurred on the day of pro-oestrus and the pro-oestrous FSH surge was absent. The usual increase in FSH on the day of oestrus was present. Lesions in the SCO did not change the high gonadotrophin levels typical of ovariectomized animals. These results suggested that the SCO may play a role in the control of the cyclic but not the tonic release of the gonadotrophins. In particular, it appears that the SCO might be involved in the regulation of the hypersecretion of FSH during the day of pro-oestrus.

Estradiol attenuates the antidiuretic action of vasopressin in ovariectomized rats

1995 ◽  
Vol 268 (4) ◽  
pp. R951-R957 ◽  
Author(s):  
Y. X. Wang ◽  
J. T. Crofton ◽  
H. Liu ◽  
K. Sato ◽  
D. P. Brooks ◽  
...  
Keyword(s):  
Slow Release ◽  
Tap Water ◽  
Female Rats ◽  
Ovariectomized Rats ◽  
Sexually Dimorphic ◽  
Female Rat ◽  
Ovarian Hormone ◽  
Dose Dependent ◽  
Antidiuretic Action

To determine which ovarian hormone is involved in the sexually dimorphic antidiuretic action of vasopressin, the antidiuretic response to vasopressin was examined in sham-operated nonestrous female rats chronically treated with vehicle and in ovariectomized rats treated with vehicle, progesterone, estradiol, or the combination of estradiol and progesterone, respectively. Three-week-old female rats were sham operated or ovariectomized, and a slow-release hormone pellet was implanted at the 6th wk. The experiment was performed at the 10th to 12th wk in conscious, chronically instrumented rats hydrated with tap water (2% body wt). Infusion of vasopressin at rates of 10-1,000 pg.min-1.kg body wt-1 resulted in a dose-dependent antidiuretic response that was significantly enhanced in ovariectomized rats compared with the intact nonestrous females. Progesterone had no effect, whereas estradiol attenuated and restored the antidiuretic response to vasopressin to a level similar to that in intact nonestrous female rats. These results suggest that it is estrogen, but not progesterone, that reduces the antidiuretic response to vasopressin in the female rat.

Pituitary receptors for LH-releasing hormone (LHRH) and responsiveness to LHRH in adult female rats after neonatal monosodium l-glutamate treatment

1985 ◽  
Vol 107 (1) ◽  
pp. 9-13 ◽  
Author(s):  
S. E. Inkster ◽  
R. N. Clayton ◽  
S. A. Whitehead
Keyword(s):  
Adult Female ◽  
Female Rats ◽  
Serum Prolactin ◽  
Female Rat ◽  
Releasing Hormone ◽  
Old Rats ◽  
Lh Releasing Hormone ◽  
Ovarian Cyclicity ◽  
Pituitary Receptors

ABSTRACT The effects of neonatal monosodium l-glutamate (MSG) treatment on pituitary responsiveness to LH-releasing hormone (LHRH) and on pituitary LHRH receptors have been investigated in the intact adult female rat. Three- to four-month-old rats treated with MSG (4 mg/g body wt) on days 2, 4, 6, 8 and 10 after birth had significantly reduced ovarian and pituitary weights, showed an absence or disruption of ovarian cyclicity after puberty, and had significantly higher concentrations of serum prolactin despite normal levels of LH. In-vitro pituitary LH responses to LHRH were in the normal range for one group of treated animals whilst in a second group the LH responses were markedly enhanced. In contrast, the total number of pituitary LHRH receptors were significantly reduced in all MSG-treated animals showing that the increased pituitary responsiveness of MSG-treated animals is not attributable to an increase in pituitary LHRH receptors. J. Endocr. (1985) 107, 9–13

scholarly journals Effect of age on progesterone receptor expression, and osteoprogenitor proliferation and differentiation in female rat vertebral cell populations

2006 ◽  
Vol 190 (2) ◽  
pp. 261-270 ◽  
Author(s):  
Weidong Pei ◽  
Carlton G Bellows ◽  
Yongheng Jia ◽  
Johan N M Heersche
Keyword(s):  
Progesterone Receptor ◽  
Receptor Expression ◽  
Cell Populations ◽  
Female Rat ◽  
Progesterone Receptor Expression ◽  
Young Rats ◽  
Basal Expression ◽  
Proliferation And Differentiation ◽  
Old Rats ◽  
Effect Of Age

In the present investigation, we evaluated whether the capacity for proliferation and differentiation of progesterone (Prog)-dependent osteoprogenitors in the female rat skeleton is related to the level of Prog receptors (PRs) and/or the level of circulating estrogen. We confirmed that in rats, estrogen levels at 18 months of age are higher than those at 3 months, and higher again in rats of 22.5, 25.5, and 26 months of age. Prog levels in rats of ages between 18 and 25.5 months were lower than those at 26 and 3 months of age. PR-A levels were tenfold higher than those of PR-B in cell populations where PR-B was detectable; PR-B receptors were not detectable in all cell populations. In populations derived from 22.5 to 26 months old rats, the basal levels of PR-A were higher than those derived from 3 and 18 months old rats by five- and twofold respectively. Prog treatment enhanced PR-A expression in animals of all ages. Estrogen enhanced the effect of Prog on PR-A expression in cell populations from the 3 and 18 months old rats, but had no effect on PR-A expression in cell populations from 22.5, 25.5, and 26 months old rats. This might be related to the high basal expression of PR in 22.5–26 months old rats (the ‘persistent estrous’ phase). Our results also confirm our previous observation that in rats, the number of Prog- and dexamethasone (Dex)- dependent osteoprogenitors, and the effect of estrogen on the response to Prog do not decrease with age. In conclusion, we have shown that the basal level of PR-A was increased in old rats, and that this correlated with increased serum estrogen levels, but not with the number of detectable Prog-dependent osteoprogenitors. We also found that Prog upregulates the expression of its own receptors and that estrogen enhances this in young rats but not in rats over 22.5 months of age, in which estrogen levels are elevated.

A SEXUALLY DIMORPHIC RHYTHM IN OESTRADIOL-ACTIVATED LORDOSIS BEHAVIOUR IN THE RAT

1979 ◽  
Vol 83 (2) ◽  
pp. 267-274 ◽  
Author(s):  
S. HANSEN ◽  
P. SÖDERSTEN ◽  
P. ENEROTH ◽  
B. SREBRO ◽  
K. HOLE
Keyword(s):  
Daily Rhythm ◽  
Female Rats ◽  
Male Rats ◽  
Ovariectomized Rats ◽  
Sexually Dimorphic ◽  
Female Rat ◽  
Suprachiasmatic Nuclei ◽  
Light Darkness ◽  
Lordosis Behaviour ◽  
Neonatal Castration

Ovariectomized rats exposed to constant plasma levels of oestradiol showed a daily rhythm in lordosis behaviour, with high levels of lordosis occurring during the dark portion of the daily light: darkness cycle and low levels during the light period. Similarly treated male rats failed to show a rhythm in lordosis behaviour. However, neonatal castration permitted the expression of the lordosis rhythm in male rats; conversely, an injection of 1·25 mg testosterone propionate on day 4 of life abolished the rhythm in female rats. Pinealectomy, adrenalectomy or depletion of brain 5-hydroxytryptamine levels did not affect the periodicity in lordosis behaviour but lesions in the suprachiasmatic nuclei of the hypothalamus disrupted the rhythm. It is suggested that the daily rhythm in lordosis behaviour participates in the control of the termination of heat in the female rat and that the perinatal hormone milieu may exert permanent effects on periodic functions.

Testosterone treatment of ovariectomized rats: Effects on lipolysis regulation in adipocytes

1990 ◽  
Vol 123 (1) ◽  
pp. 61-66 ◽  
Author(s):  
Giovanni De Pergola ◽  
Agneta Holmäng ◽  
Jan Svedberg ◽  
Riccardo Giorgino ◽  
Per Björntorp
Keyword(s):  
Ovarian Function ◽  
Female Rats ◽  
Ovariectomized Rats ◽  
Fat Cell ◽  
Adrenergic Agonist ◽  
Intact Female ◽  
Testosterone Treatment ◽  
Catalytic Unit ◽  
Uk 14,304 ◽  
Intact Rats

Abstract. The effects of testosterone treatment (2 mg every 14 days, for three months) on adipocyte lipolysis of intact (250-300 g body weight) and ovariectomized female rats were studied. Testosterone treatment of intact rats had no effect. Ovariectomy was followed by an increase in fat cell size and a decrease of lipolysis stimulated by isoproterenol, norepinephrine, epinephrine, forskolin, cAMP and isobutylmethylxantine. The number of βadrenergic receptors was reduced. There was, however, no change in the antilipolytic effects of UK 14,304 (alpha2-adrenergic agonist), nicotinic acid, N6-phenylisopropyladenosine or insulin. Testosterone treatment of ovariectomized rats restored the number of β-adrenoceptors and lipolysis stimulated by cAMP and isobutylmethylxantine, but not lipolysis stimulated by catecholamines and forskolin, suggesting a remaining defect in the catalytic unit of adenylate cyclase. These results indicate that ovariectomy is followed by a profound derangement of the lipolytic pathway at several levels, from β-adrenoceptors number to the triglyceride lipase activity. This is partially restored by treatment with testosterone, which, however, has no effect on intact female rats. This study emphasizes the importance of ovarian integrity for the lipolytic regulation and the inability of testosterone to replace ovarian function in this regard or to affect lipolysis in intact female rats.

Rapid appearance of connexin 26-positive gap junctions in centrilobular hepatocytes without induction of mRNA and protein synthesis in isolated perfused liver of female rat

1994 ◽  
Vol 107 (12) ◽  
pp. 3579-3590 ◽  
Author(s):  
T. Kojima ◽  
N. Sawada ◽  
M. Oyamada ◽  
H. Chiba ◽  
H. Isomura ◽  
...  
Keyword(s):  
Gap Junctions ◽  
Rat Liver ◽  
Liver Perfusion ◽  
Female Rats ◽  
Ovariectomized Rats ◽  
Connexin 26 ◽  
Female Rat ◽  
Perfused Liver ◽  
Junction Protein ◽  
E Cadherin

In the adult rat liver, the gap junction protein connexin 32 (Cx32) is evenly distributed in hepatocytes within the liver lobules, while connexin 26 (Cx26) is preferentially localized in hepatocytes in periportal zones. We report here that Cx26-positive gap junctions rapidly appear in the centrilobular hepatocytes of adult female rat livers during a 30 minute perfusion of the liver through the hepatic portal vein with a 1:1 mixture of Dulbecco's modified Eagle's medium (DMEM) and oxygen transport FC-43 fluid at a physiological flow rate without any changes in the distribution of Cx32. The change in the localization of Cx26 was closely related to that of E-cadherin, and there was no significant increase in the amounts of Cx26 protein and mRNA. The appearance of Cx26 in the centrilobular hepatocytes was inhibited by treatment with cytoskeleton disruptors such as colchicine and cytochalasin B, and intracytoplasmic transport inhibitors such as brefeldin A. The liver perfusion induced the appearance of Cx26 in the centrilobular hepatocytes only in female rats. Estrogen treatment of ovariectomized rats caused the appearance of both Cx26 and E-cadherin in centrilobular hepatocytes not only in the perfused liver but also in the non-perfused liver. Our results indicate that in the rat liver: (a) the localization of Cx26 can be modulated by a post-translational mechanism; (b) E-cadherin may play an important role in the formation of gap junctions composed of Cx26; and (c) the formation of gap junctions is regulated by female steroid hormones.

Regulation of luteal activity in adult female rats treated neonatally with testosterone propionate

1983 ◽  
Vol 96 (3) ◽  
pp. 417-425 ◽  
Author(s):  
P. van der Schoot ◽  
W. J. de Greef
Keyword(s):  
Plasma Levels ◽  
Testosterone Propionate ◽  
Prolactin Secretion ◽  
Human Chorionic Gonadotrophin ◽  
Female Rats ◽  
Ovariectomized Rats ◽  
Normal Female ◽  
Female Rat ◽  
Lower Plasma ◽  
Decidual Tissue

The present study was concerned with the control of luteal activity in female rats which had been treated neonatally with 1·25 mg testosterone propionate (TP). Treatment of such rats in adulthood with 15 i.u. human chorionic gonadotrophin induced ovulation followed by a period of luteal activity. The two daily surges of prolactin secretion, typical for a period of luteal activity in the normal female rat, were not observed in TP-treated females. Instead, higher basal levels of prolactin were observed in TP-treated females than in normal female rats. Furthermore, uterine traumatization at 5 days after ovulation did not result in the formation of decidual tissue. In intact TP-treated females luteal activity, induced and temporarily sustained by an ectopic pituitary transplant, persisted after removal of the pituitary graft. In contrast, in TP-treated females which had been ovariectomized on day 25 of age and had received an ovarian transplant before induction of the luteal phase, luteal activity ended within a week after removal of the ectopic pituitary gland. Females treated with TP which had been ovariectomized on day 25 of life had lower plasma levels of prolactin and higher levels of dopamine in hypophysial stalk plasma than intact TP-treated females when measured at 4 months of age. Treatment of ovariectomized rats with oestradiol-17β increased levels of prolactin in plasma and lowered levels of dopamine in hypophysial stalk plasma. It is concluded that the control of luteal activity in TP-treated females shows 'male' characteristics. However, the presence of the ovaries in such rats leads to decreased hypothalamic release of dopamine and increased plasma levels of prolactin, probably due to increased oestrogen levels. These increased levels of prolactin are sufficient to maintain luteal activity.

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