bluuebunny/crossref_metadata_2025_split huggingface dataset:
Comparison of the effects of prostaglandin E2, prostacyclin and 1–24 adrenocorticotrophin on plasma cortisol levels of fetal sheep
Authors: Liggins G. C. , Scroop G. C. , Haughey K. G. 
Published: December 2008

The changes in plasma cortisol levels in response to intravenous infusions of prostaglandin E2 (PGE2), prostacyclin and 1–24 ACTH have been studied in chronically catheterized fetal sheep during the last third of gestation.
All three drugs increased plasma cortisol levels with prostacyclin being significantly more potent than either PGE2 or 1–24 ACTH. No interaction between the steroidogenic actions of 1–24 ACTH and either PGE2 or prostacyclin could be demonstrated. The steroidogenic action of PGE2 was not significantly modified by fetal hypophysectomy.
It is concluded that neither PGE2 nor prostacyclin is likely to be involved in the enhanced adrenal responsiveness to 1–24 ACTH observed in fetal sheep in the period immediately before birth.
Is there a cholinergic circadian rhythm throughout the oestrous cycle related to ovulation in the rat?
Authors: Dominguez Roberto , Riboni Laura , Zipitria Domingo , Revilla Rodolfo 
Published: December 2008

Rats with a 4-day oestrous cycle were given a single dose of atropine (100, 300, 500 or 700 mg/kg body wt) at 13.00 h on the days of oestrus, dioestrus 1, dioestrus 2 or pro-oestrus and were autopsied on the next expected day of oestrus. The doses of atropine (in mg/kg body wt) necessary to block ovulation during the cycle were 300 at oestrus, 100 at dioestrus 1 or 2 and 700 at pro-oestrus. A single dose of atropine (100 mg/kg) at oestrus, dioestrus 1 or dioestrus 2 was given at 09.00, 13.00, 17.00 or 21.00 h, autopsy again being performed on the next expected day of oestrus. The ability of atropine to block ovulation appeared to have a circadian rhythm, with a maximum blockade at 13.00 h on dioestrus 1 and dioestrus 2 and a minimum at 21.00 h on the same days. Hormone replacement (human chorionic gonadotrophin at oestrus, dioestrus 1 or 2, oestradiol benzoate at dioestrus 2 or progesterone at pro-oestrus) re-established normal ovulation in rats whose ovulation was blocked with atropine (100 mg/kg) on dioestrus 1 at 13.00 h. When ovulation was blocked with atropine but no hormone replacement had been given, rats ovulated 24 h after the next expected day of oestrus.
Results obtained in these experiments suggest the existence of a circadian rhythm of gonadotrophin secretion thoughout the oestrous cycle and a close relationship between that rhythm and the cholinergic system.
Role of the subcommissural organ in the control of gonadotrophin secretion in the female rat
Authors: Limonta Patrizia , Maggi Roberto , Martini Luciano , Piva Flavio 
Published: December 2008

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.
Collagen solubility and tensile properties of the rat uterine cervix in late pregnancy: effects of arachidonic acid and prostaglandin F2α
Authors: Hillier Keith , Wallis R. M. 
Published: December 2008

The collagen concentration in rat uterine cervix was less on day 18 of pregnancy than in the non-pregnant animal but did not diminish further as pregnancy proceeded.
The solubility of cervical collagen in warm acetic acid (0·5 mol/l) was increased on day 22 compared with days 19, 20 and 21 of pregnancy, and there was a positive correlation of increasing solubility with the tissue rate of creep (a measure of reducing stiffness of the cervix).
Treatment of rats subcutaneously with arachidonic acid or prostaglandin F2α (PGF2α) on day 18 of pregnancy decreased the stiffness of the tissue when assessed on day 19 and this was accompanied by increased solubility in cold saline (0·45 mol/l), cold acetic acid and warm acetic acid and a reduction in collagen concentration.
These results suggest that collagen properties rather than concentration are important in determining the stiffness of the rat uterine cervix at term and that exogenous PGF2αand arachidonic acid cause biochemical changes in collagen structure unlike those seen at term in untreated animals.
Role of histamine in the increased secretion of prolactin induced by ether in adult male rats
Authors: Alvarez E. O. 
Published: December 2008

The purpose of the present work was to determine the possible role of the histamine receptors located in the rostral zone of the hypothalamus in the control of the prolactin surge induced by ether stress. Cannulae were implanted into the preoptic anterior hypothalamic area or the third ventricle of several groups of adult male rats under ether anaesthesia. On the following day the rats were cannulated in the jugular vein so that they could be bled frequently. Twenty-four hours later saline, metiamide (an antagonist of H2 histamine) or pyrilamine (an antagonist of H1 histamine) were injected into the brain. Fifteen minutes after the injection all rats were subjected to an ether stress. Blood samples were taken at regular times after the stress and prolactin levels determined by radioimmunoassay. A prolactin surge was observed in rats injected with saline which extended up to 15–30 min after the stress. When the histamine antagonists were administered directly in the rostral hypothalamus both pyrilamine and metiamide inhibited the prolactin surge. When the histamine antagonists were administered into the third ventricle only metiamide was able to block the prolactin response completely.
The present results suggest that histamine receptors in the rostral hypothalamus of the rat are involved in the control of prolactin secretion induced by stress.
Influence of gonadal steroids on the time-course of release and synthesis of luteinizing hormone, follicle-stimulating hormone and prolactin from rat pituitary glands in vitro
Authors: Apfelbaum Marta E. 
Published: December 2008

The effect of the gonadal steroids on the time-course of release and synthesis of LH, FSH and prolactin was studied in vitro. Pituitary glands from ovariectomized rats were incubated for four sequential periods of 1 h in the presence or absence of 1·84 μmol oestradiol-17β/l, 3·44 μmol 5a-dihydrotestosterone/l or 31·80 μmol progesterone/l.
The rate of release of LH was not affected by oestradiol or dihydrotestosterone, but was enhanced by progesterone after the third period of incubation. Synthesis of LH was increased by the three steroids tested, from 1 to 4 h of incubation, the effect being more marked for oestradiol than for the other steroids. The rate of release of FSH was depressed after 3 h whereas its synthesis was increased between 1 and 2 h, only in the presence of dihydrotestosterone. Synthesis of FSH was also stimulated by oestradiol after 2 h incubation but its release was not affected. Progesterone showed no effect on either the release or the synthesis of FSH. Although oestradiol and dihydrotestosterone induced a rise in both LH and FSH synthesis, the onset, magnitude and duration of the responses were different, indicating separate regulatory mechanisms. Oestradiol stimulated the rates of both release and synthesis of prolactin. The effect was already evident after 1 h of incubation and increased thereafter. On the contrary, progesterone treatment inhibited the release and synthesis of prolactin. The rate of synthesis decreased after 1 h of incubation, whereas release was depressed after 3 h. Dihydrotestosterone had no effect on the release and synthesis of prolactin.
The evidence provided by this study indicates that the effect of the steroid hormones in vitro was predominantly on the synthesis of LH, FSH and prolactin. When changes in release of LH, FSH and prolactin occurred they were always preceded by alterations in hormone synthesis.
Thyrotrophin and the differential expression of proliferation and differentiation in dog thyroid cells in primary culture
Authors: Roger P. P. , Dumont J. E. 
Published: December 2008

Cell proliferation and the expression of differentiated functions are generally considered to be mutually exclusive states of the cell.
Thyrotrophin activates the expression of differentiated functions in dog thyroid cells by means of cyclic AMP. We have recently shown that thyrotrophin also acts through the same intracellular signal molecule to enhance proliferation of dog thyroid cells in primary cultures. In this work we showed that such primary cultures exhibit three successive phases: a latency period during which the expression of differentiated functions (iodide trapping and organification) declined, the cells still being associated with structures derived from the seeded follicles; a cell-proliferation phase with little expression of these functions, the cells being spread in a monolayer; a stationary phase with cell density reaching a plateau but no re-expression of the functions. Thyrotrophin promoted proliferation during the multipli-cation phase, but induced redifferentiation during the stationary phase. These effects were mimicked by cholera toxin and dibutyryl cyclic AMP, which suggested that they were mediated by cyclic AMP. Iodide uptake was also stimulated by cortisol.
Thyrotrophin therefore has a different action in dog thyroid cells depending on the state of the cells. The spontaneous arrest of multiplication appears to make the cells competent to respond to thyrotrophin by the induction of redifferentiation.
Action of some luteinizing hormone derivatives in ovaries from pseudopregnant rats: dissimilarities between their activities on this organ and on Leydig cells
Authors: de la Llosa-Hermier M.P. , Tertrin-Clary C. , Evrard-Hérouard M. , Hermier C. , de la Llosa P. 
Published: December 2008

Biological activities of several derivatives of ovine LH obtained by chemical modification of the amino groups were investigated using ovaries from pseudopregnant rats. Binding-inhibition activities and steroidogenic potencies of ethylated, isopropylated and guanidinated LH were in good agreement, whereas adenylate cyclase activities were relatively greater. When compared with previous results on binding-inhibition activities and steroidogenic potencies using isolated rat Leydig cells, the ovaries from pseudopregnant rats appeared to be more discriminating. Ethylated and isopropylated derivatives exhibited lower binding-inhibition activities and steroidogenic potencies in female gonads. This difference was particularly evident in the case of guanidinated LH which exhibited a very low binding-inhibition activity and consequently was unable to act as an inhibitor of the action of LH on the ovaries.
Guanidinated porcine LH (in which all the lysine residues of the α-subunit were transformed into homoarginine, without modification of the β-subunit which does not contain lysine) showed similar biological activities to guanidinated ovine LH in the isolated Leydig cells as well as in pseudopregnant ovaries. It can, consequently, act as an inhibitor of LH action on Leydig cells but not on the ovary of the pseudopregnant rat. Thus, the inhibitory properties of this derivative can be ascribed to the modification introduced in the α-subunit.
Hormone treatments and pregnancy alter myosin light chain kinase and calmodulin levels in rabbit myometrium
Authors: Matsui K. , Higashi K. , Fukunaga K. , Miyazaki K. , Maeyama M. , Miyamoto E. 
Published: December 2008

Myosin light chain kinase activity and the amount of calmodulin were measured in rabbit myometrium after the rabbits had been treated with oestrogen, progesterone and human chorionic gonadotrophin, and also during pregnancy. Injections of oestrogen and progesterone produced significant increases of 2·8- and 2·1-fold in the enzyme activity/mg protein and of 1·4- and 1·2-fold in the calmodulin content/mg protein respectively. The increases seen with oestrogen treatment were inhibited by cycloheximide administration, suggesting that protein synthesis is involved in the process. Calmodulin increased about twofold in the particulate fraction under conditions of oestrogen and progesterone treatments and the raised level of calmodulin detected in the cytosol fraction was not due to translocation from the particulate fraction.
During pregnancy the specific enzyme activity significantly increased in comparison with the values seen in samples from the non-treated rabbits.
These findings suggest that myosin light chain kinase and calmodulin in the myometrium are under hormonal regulation and may play a role in expulsion of the fetus at the latter phase of pregnancy.
Changes in oestradiol, progesterone and testosterone concentrations in follicular fluid and in the micromorphology of preovulatory bovine follicles relative to the peak of luteinizing hormone
Authors: Dieleman S. J. , Kruip Th. A. M. , Fontijne P. , de Jong W. H. R. , van der Weyden G. C. 
Published: December 2008

Preovulatory bovine follicles (n = 58) were collected at different times after the onset of standing oestrus when cows would allow mounting until shortly before ovulation, which occurred 24 ± 1·4 h after the peak level of LH in the peripheral blood. Non-atretic antral follicles (n = 71) of 3–20 mm were also collected from cows during the luteal phase of the oestrous cycle. The follicular fluid was aspirated for the radioimmunoassay of oestradiol-17β, progesterone and testosterone. The follicular wall was examined micromorphologically. Follicular fluid steroid levels were compared in 2-h periods relative to the LH peak. The development of the preovulatory follicles from onset of oestrus to ovulation can be divided into four phases. Phase 0 (after onset of oestrus but before LH surge) was characterized by a high level of oestradiol (6·05 μmol/l); the levels of progesterone and testosterone were lower (0·387 and 0·165 μmol/l respectively) but higher than in non-atretic luteal follicles of similar size. The theca interna (TI) was wider and the membrana granulosa (MG) cells were larger than those of non-atretic antral follicles. During phase 1 (0–6 h after the LH peak) oestradiol remained constant but at a lower level, progesterone increased (0·727 μmol/l) and testosterone was higher from 0 to 2 h after the LH peak (0·241 μmol/l). The TI was 40% wider, whereas the size of the MG cells remained the same. In phase 2 (6–20 h after the LH peak) the level of oestradiol dropped rapidly during the period from 6 to 10 h, that of progesterone decreased to the same level as in phase 0 and that of testosterone was low (0·031 μmol/l). The width of the TI decreased to that of preovulatory follicles in phase 0 and the MG cells were slightly larger. In phase 3 (20 h after the LH peak until ovulation) the level of oestradiol decreased further (0·461 μmol/l) and that of testosterone remained low. Progesterone increased to the highest levels observed (1·51 μmol/l), however, and this coincided with a 39% increase in the size of the MG cells, whereas the width of the TI remained the same as in the preceding phases 0 and 2. In phase 3 the basement membrane began to disintegrate and phagocytic cells could be observed. This points to a simultaneous functional and morphological luteinization.
It is suggested that these changes in follicular steroid levels and micromorphology are regulated by the preovulatory LH peak.
Identification and measurement of testosterone in plasma and follicular fluid of the mare, using gas chromatography–mass spectrometry associated with isotope dilution
Authors: Silberzahn P. , Dehennin L. , Zwaïn I. H. , Leymarie P. 
Published: December 2008

Testosterone has been identified by mass spectrometry in blood and follicular fluid aspirated from mature Graafian follicles of mares. Quantitative measurements made by gas chromatography–mass spectrometry have validated the determination of plasma testosterone made by radioimmunoassay. However, because of high levels of epitestosterone (17α-hydroxyandrost-4-en-3-one) in the follicular fluid, radioimmunoassay overestimates the true concentrations of testosterone.
The occurrence of testosterone in mare follicular fluid at a concentration which is two orders of magnitude higher than that in peripheral plasma suggests that the follicle may contribute to the production of circulating testosterone.
A biosynthetic pathway for oestradiol-17β which involves testosterone is therefore likely to occur in the mare ovary as in many other mammalian species.
Reduction of 5-day cycle length of female rats by treatment with bromocriptine
Authors: van der Schoot P. , Uilenbroek J. Th. J. 
Published: December 2008

Rats with 5-day ovarian cycles were injected daily with 1 mg bromocriptine. This treatment resulted in a change of cycle length from 5 to 4 days and a rapid increase in ovarian weight. The increase in ovarian weight resulted from the accumulation of large numbers of corpora lutea. Normal numbers of corpora lutea were formed during each cycle but luteal bodies did not disappear subsequently. Luteolysis affected only minor foci of luteal tissue and the majority of luteal tissue remained histologically intact throughout the further period of study. The reduction of cycle length from 5 to 4 days occurred when bromocriptine was administered from the day of ovulation only. If treatment was commenced at a later time during the cycle it was not effective.
Treatment with bromocriptine appeared to affect the concentrations of progesterone in the blood during dioestrus. During treatment the rats showed the pattern characteristic for 4-day cycles: typically, the high concentrations of progesterone on the day after metoestrus remained absent. These data suggest (1) that the latter part of the production of progesterone during dioestrus by 'non-functional corpora lutea' is dependent on prolactin and (2) that prolongation of high progesterone production after metoestrus plays an important role in changing the length of the cycle from 4 to 5 days.
Treatment with bromocriptine did not significantly affect the rate of maturation of follicles destined for the next ovulation. It is possible that follicular maturation is not among the critical variables which determine whether normal ovulatory cycles will last for 4 or 5 days.
Episodic secretion of luteinizing hormone and androgen in male rats
Authors: Södersten P. , Eneroth P. , Pettersson A. 
Published: December 2008

Sequential blood samples were obtained at hourly intervals from intact male rats during various phases of the light: darkness cycle. Measurement of the serum concentrations of LH and androgen showed that both hormones were secreted episodically, with a secretory episode defined as an increment and subsequent decrement in the serum hormone level exceeding the analytical intra-assay imprecision. Episodes of androgen secretion varied greatly in amplitude (from 1·04 to 30·90 nmol/l) in individual males, occurred during any phase of the light: darkness cycle and were preceded by one or two episodes of LH secretion. Individual males could show more than one episode of androgen secretion during an 18-h sampling period (mean ± s.e.m. = 1·7 ± 0·7 pulses/10 h). Mean values of serum LH and androgen in groups of animals obscured the episodic pattern of hormone secretion shown by individual animals.
Castration reduced serum androgen to non-detectable levels within 2 h and produced a temporary decline in serum LH levels and abolition of the episodic pattern of LH secretion. These effects were prevented by testosterone treatment at the time of castration. There was a gradual increase in serum LH levels and in the amplitude of the LH secretory episodes for 1 week after castration.
Treatment of castrated rats with testosterone-filled constant-release implants (10 or 20 mm long) produced high and stable serum androgen levels and episodes of LH secretion of low amplitude 1 week after castration. A constant concentration of serum androgen comparable to the mean level of intact rats, produced by implantation of 5 mm long testosterone implants 3 weeks earlier, resulted in a pattern of episodic LH secretion which was similar to that of intact rats.
Subcutaneous injection of various doses of testosterone (5, 15 or 45 μg) in castrated rats produced a dose-dependent increase in serum androgen levels within 30 min of injection and thereafter the levels declined. Injection of 15 μg testosterone produced a pulse-like increase in serum androgen concentrations with an amplitude within the range of that observed in intact rats. Injection of this amount of testosterone in castrated rats in which serum LH levels had been suppressed by prior implantation of 20 mm long testosterone implants produced no change in serum LH levels. It is suggested that androgen primarily modifies the amplitude of the LH secretory episodes and that episodic fluctuations in serum androgen levels have no immediate effect on the pattern of LH secretion. Constant serum androgen levels comparable to the mean level of intact rats are sufficient for maintenance of the normal episodic pattern of LH secretion.
Plasma prolactin and gonadotrophins during gonadal development and the onset of photorefractoriness in male and female starlings (Sturnus vulgaris) on artificial photoperiods
Authors: Dawson A. , Goldsmith A. R. 
Published: December 2008

Previous studies have shown that an increase in prolactin secretion coincides with the beginning of the photorefractory phase in starlings (Sturnus vulgaris). To determine how closely this increase is associated with the onset of refractoriness, we kept starlings on photoperiods which would induce refractoriness at different rates. Four groups of males and females were transferred from 8 h light: 16 h darkness (8L : 16D) to either 18L : 6D, 13L : 11D, 11L : 13D or 8L : 16D. Weekly blood samples were assayed for LH, FSH and prolactin and the males were frequently laparotomized to determine testis volume.
In males, both 18L and 13L induced marked increases in plasma gonadotrophin levels and rapid gonadal maturation. A photoperiod of 18L induced an earlier onset of refractoriness (2–4 weeks) than 13L (6 weeks). In both cases prolactin levels began to increase immediately before the onset of refractoriness. Males on 11L showed a slight increase in gonadotrophin levels and slow gonadal maturation. There was no increase in prolactin levels and these birds did not become refractory. Hormonal data from the females were similar to those from males. These results confirm that increased prolactin secretion is associated, in some way, with the onset of photorefractoriness in this species, although whether it is a cause or consequence of photorefractoriness, or simply of gonadal regression, remains unclear.