bluuebunny/crossref_metadata_2025 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.
Effects of oestradiol-17β and hypophysectomy on hepatic mixed function oxidases in rainbow trout
Authors: Förlin Lars , Hansson Tiiu
Published: December 2008

The effects of oestradiol-17β and/or hypophysectomy on the metabolism of benzo(a)pyrene (BP), paranitroanisole (PNA), ethylmorphine (EM) and 7-ethoxycoumarin by liver microsomes from juvenile rainbow trout, Salmo gairdnerii, were studied. Administration of oestradiol-17β caused significant decrease in the liver microsomal metabolism of BP, PNA and EM while hypophysectomy had no effect. The suppressive effect of oestradiol-17β on the mixed function oxidases was as pronounced in hypophysectomized as in sham-operated fish, indicating that this effect of oestradiol-17β is mainly direct and independent of the pituitary gland. Administration of oestradiol-17β caused a significant increase in the apparent Km values of the PNA-O-demethylase whereas no alteration was seen in the apparent Vmax values of the enzyme. The results indicate that oestradiol-17β may play a role in the regulation of hepatic mixed function oxidases in rainbow trout.
Relationships between methoxyindoles and hydroxyindoles formed from 5-hydroxytryptamine in rat pineal gland
Authors: Morton D. J. , Potgieter B.
Published: December 2008

5-Hydroxytryptophol, 5-methoxytryptophol, 5-hydroxyindole-3-acetic acid, 5-methoxyindole-3-acetic acid, N-acetylserotonin and N-acetyl-5-methoxytryptamine produced in pineal gland culture from [14C]serotonin were measured after thin-layer chromatographic separation. A correlation between the amounts of hydroxy- and corresponding methoxyindoles was sought. The results showed a correlation between N-acetylserotonin levels and the production of N-acetyl-5-methoxytryptamine, whereas no correlation between the other hydroxy- and methoxyindoles was found.
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.
Ovarian follicle dynamics in mice: a comparative study of three inbred strains and an F1 hybrid
Authors: Faddy M. J. , Gosden R. G. , Edwards R. G.
Published: December 2008

The rates of follicle growth and death have been estimated by a mathematical method in A, CBA, RIII and A × CBA strains of mice for which differential follicle counts were available. These rates were not uniform throughout life but were specific for the immature and mature phases of life. Significant heterogeneity of the rate estimates for particular follicle stages was also identified between strains and between intact and hypophysectomized mice, which explained the differing life-time patterns of follicular utilization in these animals.
Accumulation of thiourylene antithyroid drugs in mouse salivary gland
Authors: Connell J. M. C. , McCruden D. C. , Small M. , Ferguson M. M. , Alexander W. D.
Published: December 2008

[35S]Methimazole and [35S]propylthiouracil were shown to accumulate in mouse sub-mandibular gland in vivo, with maximal tissue: plasma ratios being achieved at the lowest dose of drug studied (0·1 μg/animal). Autoradiography of submandibular glands showed that the drugs were localized to the intralobular ductal epithelium and within the lumen of the convoluted granular tubule, which was identical to the localization of radiolabelled iodide. Histochemical studies indicated that this was the site of peroxidase activity within the gland. Drug accumulation persisted when iodide trapping was competitively inhibited using perchlorate. These data suggest that antithyroid drug accumulation by this tissue is not dependent on the anion trap; the localization of drug and iodide at the site of peroxidase activity suggest that this may be an important factor in the mechanism of drug accumulation, possibly related to subsequent drug metabolism.
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.
Sex steroid concentrations in plasma from the canine deferential vein
Authors: Boulanger P. , Desaulniers M. , Bleau G. , Roberts K. D. , Chapdelaine A.
Published: December 2008

Sex steroid concentrations in plasma collected from the canine deferential vein were measured, after separation, by radioimmunoassay. The concentrations found were compared with those in the peripheral plasma. The mean concentrations of androstenedione, testosterone, 5α-dihydrotestosterone, 5α-androstane-3α,17β-diol, 5α-androstane-3β,17β-diol and oestradiol-17β were 13·2, 14·7, 8·9, 4·6, 8·0 and 7·5 fold higher respectively in plasma from the deferential vein than in peripheral plasma. A close anatomical relationship was found between the vasa deferentia, the deferential vein and the peripheral plasma as well as between the deferential vein and the prostate gland. These findings emphasize and extend earlier conclusions that high levels of sex steroids present in the deferential vein could have a local influence on the growth of the prostate.
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.
Peripheral plasma progesterone and oestradiol concentrations associated with successful and unsuccessful recovery of uterine embryos in rhesus monkeys with and without intra-uterine devices
Authors: Wheeler A. G. , Hurst P. R. , Eckstein P.
Published: December 2008

Concentrations of progesterone and oestradiol were measured in peripheral plasma samples collected at the time when the uteri of rhesus monkeys with an intra-uterine device (IUD) and those without an IUD were flushed in attempts to recover uterine embryos. The proportion of successful attempts in IUD-bearing monkeys was much lower than in the non-IUD-bearing animals. Steroid measurements indicated that this reduced success rate was not due to an effect of the IUD on the timing of ovulation within the menstrual cycle or to a steroid-mediated disturbance in the rate of embryo transport to the uterine lumen. Successful embryo recoveries were associated with a higher progesterone concentration, suggesting that one reason for failure was that the attempt had been made too close to ovulation. There was no evidence of any asymmetry between the left or right ovaries in their ovulatory or steroidogenic activity.
Evidence for glucocorticosteroid receptors in the erythroid cell line of fetal rat liver
Authors: Mayeux P. , Billat C. , Felix J. M. , Jacquot R.
Published: December 2008

A role for glucocorticosteroids in the evolution of the rat fetal liver erythropoiesis in vivo has been proposed; accordingly suppressible binding of [3H]dexamethasone by intact liver erythroid cells at 4 °C has been described. The nature of this binding was further investigated in the present paper. Suspensions of cells of the erythroid line were prepared from liver erythropoietic tissue obtained from fetuses aged 15 or 16 days. Suppressible binding of [3H]dexamethasone was studied on these suspensions. After incubation at 4 °C, approximately 89 per cent of this binding was located in the cytosol (100 000 g supernatant fraction), was excluded from Sephadex G-50 columns and was not adsorbed on activated charcoal; 11·3 ± 2·6 (s.d.) per cent (n = 4) of the suppressible binding was present in the nucleus. When cells prelabelled with [3H]dexamethasone at 4 °C were warmed to 37 °C, 52 ± 10 per cent (n = 5) of the suppressible binding was rapidly transferred to the nucleus. The suppressible radioactivity present in the cytosols at 4 °C was eluted from diethylaminoethyl (DEAE)–cellulose columns, in the presence of molybdate, as a single peak (peak II) at phosphate concentrations between 200 and 250 mmol/l. When these cytosols were warmed at 25 °C before chromatography, the radioactivity was eluted from DEAE-cellulose as a major peak (peak I) at phosphate concentrations between 50 and 70 mmol/l, and as a smaller peak corresponding to peak II. The presence of molybdate during the incubation at 25 °C prevented the formation of peak I. The suppressible binding present in the cytosols of cells incubated at 37 °C was eluted from DEAE–cellulose columns in two equivalent peaks corresponding to peaks I and II. It was concluded that [3H]dexamethasone was bound to a macromolecular component sharing the properties generally ascribed to the receptor of glucocorticosteroids.
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.
Effects of prolactin on testosterone-induced growth and protein synthesis in rat accessory sex glands
Authors: Jones R. , Riding P. R. , Parker M. G.
Published: December 2008

The relative importance of testosterone and prolactin in regulating growth and protein synthesis in rat accessory sex glands has been investigated. Protein synthesis was measured by incubating tissue minces in vitro with [35S]methionine and analysing labelled proteins on polyacrylamide gels containing sodium dodecyl sulphate. Plasma prolactin was assayed by radioimmunoassay. Results showed that castration for 8 days significantly reduced wet weights and total protein synthesis in the ventral prostate, dorsolateral prostate and caput epididymidis, but that these effects could be reversed by exogenous testosterone. Similarly, the specific incorporation of [35S]methionine into four polypeptides in the ventral prostate, two polypeptides in the dorsolateral prostate and two polypeptides in the caput epididymidis was lowered by castration but markedly stimulated by testosterone. Acute or chronic administration of 2-bromo-α-ergocryptine to animals in combination with testosterone had no significant effect on any of the parameters measured, although the drug reduced circulating prolactin to undetectable levels. In addition, exogenous prolactin given alone, or in combination with testosterone, to hypophysectomized rats had no effect on general or specific protein synthesis. The induction of hyperprolactinaemia in immature or mature rats with pituitary homographs had no effect on testosterone-stimulated growth of any accessory gland, although it caused a significant stimulation of total protein synthesis in the dorsolateral prostate and coagulating glands. However, this was a generalized effect as it did not increase the specific incorporation of [35S]methionine into androgen-dependent proteins. The results do not indicate a major role for prolactin in regulating androgen responsiveness of male accessory sex glands in the rat.
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.
Control of plasma sex steroid-binding protein in the bat Myotis lucifugus lucifugus: induction of steroid-binding activity in immature males
Authors: Damassa D. A. , Gustafson A. W. , Chari G. C.
Published: December 2008

Concentrations of sex steroid-binding protein (SBP) in plasma of immature male little brown bats (Myotis lucifugus lucifugus) were found to be low (15 ± 2·8 (s.e.m.) nmol/l) and stable throughout the period of hibernation which immediately precedes the onset of the first spermatogenic cycle (sexual maturity). In contrast, plasma SBP titres in spermatogenically active adults (summer) were markedly raised (238 ± 26 nmol/l). When immature males were removed from hibernation and maintained on a long photoperiod of 16 h light: 8 h darkness at a constant temperature of 25 °C to accelerate the onset of sexual maturity, these animals exhibited a rapid rise in circulating SBP. Plasma levels of SBP in immature males maintained on a long photoperiod increased significantly after 2 weeks, and by 3 weeks reached values (234± 20 nmol/l) that were indistinguishable from those seen in spermatogenically active adults. These high plasma SBP titres at 3 weeks were accompanied by increases in testicular and epididymal weights and the onset of spermatogenesis. However, no stimulation of the sex accessory glands was observed, possibly reflecting the effects of increased plasma SBP on the biological activity of circulating androgens. The ability of immature male Myotis to exhibit a pubertal increase in plasma SBP following simple environmental manipulation should provide a valuable model for the study of the control and action of sex steroid-binding protein.
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.
A photoperiodic response in gonadectomized Japanese quail exposed to a single long day
Authors: Nicholls T. J. , Follett B. K. , Robinson J. E.
Published: December 2008

Gonadectomized male Japanese quail maintained on short daylengths (8 h light: 16 h darkness) showed a reliable and repeatable response, in terms of increased gonadotrophin secretion, to a single long photoperiod (20 h light) followed by continuous darkness. Plasma levels of LH were significantly increased within 4 h of the end of the long day. Secretion continued to increase with time and LH and FSH concentrations reached a maximum some 24 h later, thereafter decreasing only slowly over the next 8–10 days. Quail could be used repeatedly at fortnightly intervals and gave a consistent response for at least 15 months. The size of the photoperiodic response and its considerable duration were much greater than found in intact quail. The birds showed a similar (though reduced) response if a short daylength was followed by a single 4-h light pulse interrupting the 16-h dark period. Using this system the time of maximum responsivity to the inductive effects of light lies 10–16 h from 'dawn'. The marked and rapid effects described provide an excellent experimental system in which to study how photoperiodic changes are recognized and how consequent neural activation is translated into enhanced secretion rates of hormones in the peripheral endocrine system.
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.
Milk-fat synthesis by lobules prepared from rabbit mammary gland: response to insulin, corticosterone, prolactin and progesterone
Authors: Carrington C. A. , Hosick H. L. , Forsyth I. A. , Dils R.
Published: December 2008

Multi-alveolar mammary structures (mammary lobules) were prepared from mammary glands of pseudopregnant rabbits by controlled digestion with collagenase and hyaluronidase. The overall rate of fatty acid synthesis and the proportion of milk-specific fatty acids (C8:0 and C10:0) synthesized by these lobules when cultured with insulin, corticosterone and prolactin were measured. Maximum response to physiological concentrations of prolactin (1·1 or 2·2 nmol/l) occurred in the presence of insulin (1·7 μmol/l) and corticosterone (0·58 μmol/l). In general, the results obtained on the effect of progesterone were negative. Though explants showed a ninefold greater response to prolactin per mg DNA than did mammary lobules, the latter have the advantage of being easily prepared for culture in large numbers. Reduction to below 500 μm diameter and culture in conditions which allow cell outgrowth onto plastic limited their response to prolactin. The probable roles of membrane damage by digesting enzymes and of tissue architecture in limiting prolactin response are discussed.
Patterns of progesterone, melatonin and prolactin secretion in ewes maintained in four different photoperiods
Authors: Kennaway D. J. , Sanford L. M. , Godfrey B. , Friesen H. G.
Published: December 2008

Twenty-four-hour patterns of serum melatonin and prolactin levels were determined in ewes on nine occasions during a year. The sheep were maintained in four different photoperiods: room 1, simulated natural photoperiod; room 2, normal daylength extremes twice in 12 months, changes occurring in a regular fashion; room 3, alternating long (16 h) and short (8 h) days for 90 days; room 4, constant light. Cyclic ovarian activity, determined by twice-weekly determinations of serum progesterone, commenced in rooms 1, 2 and 3 after a transition from long to short daylength and terminated during long daylength. Thus in rooms 2 and 3 there were two periods of ovarian activity. In room 4 (constant light) ovarian activity began earlier than in room 1 and was of greater duration (240 days v. 190 days). Basal prolactin levels were highest (50–134 μg/l) during periods of long daylength and lowest (< 10 μ/l) in short daylength. Ewes maintained in constant light had an intermediate level (21–62 μg/l) throughout the study. Melatonin secretion was lowest during daylight (< 78 pmol/l) and highest during darkness. Night-time melatonin levels varied markedly from hour to hour and between individuals in rooms 1, 2 and 3. There was, however, no consistent seasonal change in the absolute levels of melatonin, although the duration of melatonin secretion did closely follow the length of the dark phase. There were no significant changes in melatonin levels during the oestrous cycle. Ewes kept in constant light had < 78 pmol melatonin/l throughout the period of study. If the pineal gland is involved in transmitting photoperiodic information to the endocrine system, then it is most likely to be by means of an interaction between duration of melatonin secretion and an underlying change in sensitivity of end organs to melatonin.
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.
Evaluation of changes in the secretion of corticotrophin releasing activity using the isolated rat hypothalamus incubated in vitro
Authors: Kamstra G. S. , Thomas P. , Sadow Janet
Published: December 2008

The secretion of corticotrophin releasing activity (CRA) from the isolated rat hypothalamus incubated in vitro was investigated under various conditions of incubation and of pretreatment of donor animals providing hypothalami. Media from hypothalamic incubations were assayed for CRA by a validated double in-vitro bioassay technique which differentiates CRA from vasopressin.

A circadian rhythm was found in the secretion of CRA in vitro from isolated hypothalami obtained from animals killed at different times of the day. Secretion of CRA increased significantly at 19.00 h (dusk) compared with the secretion rate at 07.00 h, in synchrony with a rise in plasma corticosterone levels. In addition, both plasma corticosterone concentrations and CRA secretion in vitro were higher at 07.00 h than at 19.00 h after exposure of the donor animals to a reversed light cycle for 7–10 days.

Hypothalami obtained from animals chronically treated with betamethasone in the drinking water showed a diminished secretion of CRA in vitro. Exposure of untreated animals to ether vapour for 2 min immediately before death significantly increased the subsequent secretion of CRA in vitro. Ether exposure did not significantly affect the secretion of CRA in vitro from hypothalami of betamethasone-treated rats. There was a close correlation between plasma corticosterone levels and in-vitro CRA release after these treatments. The results suggest that the secretion of CRA examined in this way is a phenomenon which can reflect the changes which occur in the activity of the hypothalamo-pituitary-adrenal system in vivo during the 24-h cycle, after glucocorticoid treatment and after ether stress.
Binding of oestradiol, progesterone and prolactin in rat lung
Authors: Ben-Harari R. R. , Amit Tamar , Youdim M. B. H.
Published: December 2008

Binding of [3H]oestradiol and of [3H]progesterone in the cytosol from lungs of adult male rats was suppressible, dependent on incubation time and on protein concentration and was protein in nature. Suppressible binding of oestradiol consisted of a high affinity site (dissociation constant (Kd), 1 × 10−9±0·2 × 10−9 mol/l; maximum number of binding sites (Bmax), 0·7±0·2 pmol/mg protein) and a lower affinity site (Kd, 2·4× 10−8±0·6 × 10−8 mol/l; Bmax, 6·3±0·4 pmol/mg protein) and showed evidence of positive co-operation. Suppressible binding of progesterone consisted of a single site with a Kd of 6× 10−9± 1 × 10−9 mol/l and Bmax of 44·5±8 fmol/mg protein. Binding of 125I-labelled ovine prolactin was found in homogenates of fetal lung (20 days of gestation) but not of adult lung (80 days of age). Treatment of adult rats with ovine prolactin was associated with an increase in the number of binding sites of high affinity for 125I-labelled ovine prolactin but these sites showed an altered specificity. This 'up-regulation' of the prolactin binding may provide a mechanism by which prolactin stimulates surfactant production in lung. These results, together with the known effects of these hormones on certain lung functions, provide further evidence that lung is a target organ for oestradiol, progesterone and prolactin.
Oestrogen–bromocriptine interaction in the control of luteinizing hormone and prolactin secretion in the neonatally oestrogenized female rat
Authors: Aguilar E. , Galaz C. Fernández , Vaticón M. D. , Tejero A. , Oriol A.
Published: December 2008

Neonatally oestrogenized female rats showed hyperprolactinaemia (prolactin, 230 μg/l), normal LH levels and absence of a positive feedback effect of oestrogen on secretion of LH at 5 months of age. Bromocriptine treatment for 13 days (1 mg/kg per day) caused no changes in LH levels and prolactin levels decreased to normal values (33 μg/l). This decrease in prolactin concentration was not followed by the recovery of phasic LH response to oestrogens. The effectiveness of oestrogens to induce prolactin secretion was greater in the neonatally oestrogenized rats than in the control group. In both cases the effect diminished after bromocriptine treatment. These results indicate that hyperprolactinaemia is not the cause of the anovulatory state in oestrogenized rats and that neonatal treatment with oestrogens alters oestrogen–prolactin relations, probably involving dopamine.
Evidence that the hypothalamus may be a source of a circulating Na+-K+-ATPase inhibitor
Authors: Alaghband-Zadeh J. , Fenton S. , Hancock K. , Millettt J. , de Wardener H. E.
Published: December 2008

Acetone extracts from a variety of rat tissues were tested for their ability to stimulate renal glucose-6-phosphate dehydrogenase (G6PD) activity at 2 min in an in-vitro cytochemical assay which is a marker of the sodium potassium-dependent adenosine triphosphatase (Na+-K+-ATPase) inhibiting activity. Extracts of the hypothalamus were the only ones found to be active in this system. Acetone extract of hypothalamus also inhibited renal Na+-K+-ATPase activity in vitro. The G6PD-stimulating activity from one hypothalamus was about 10000 to 100 000 times greater than that of 1 ml plasma. The G6PD-stimulating activity of hypothalamic extracts from rats which had been on a high sodium intake for 4 weeks were approximately 150 times more active than those obtained from rats which had been on a low sodium diet. The G6PD-stimulating activity of the corresponding plasma was sixfold more active. These findings suggest that a circulating sodium transport inhibitor(s) may be secreted from the hypothalamus.
Effect of adrenalectomy on the regulation of the secretion of gonadotrophins and prolactin in the lactating rat
Authors: van der Schoot P. , de Greef W. J.
Published: December 2008

The suckling stimulus exerts an inhibitory action on the release of gonadotrophins during lactation. The possible involvement of the adrenal glands in this process was examined by studying the plasma levels of gonadotrophins in lactating rats ovariectomized on the day after parturition. It appeared that the suppression, throughout suckling, of the rise in levels of gonadotrophins in blood after ovariectomy occurred to the same extent in adrenalectomized and in sham-operated animals. It thus seems unlikely that adrenocortical hormones, albeit secreted in larger quantities during lactation, exert an inhibitory effect on the release of gonadotrophins.

Adrenalectomy had a marked effect on the plasma concentrations of prolactin during the second half of lactation. Whereas plasma concentrations of prolactin in the first half of lactation were similar in adrenalectomized and sham-operated rats, the concentrations in adrenalectomized rats did not undergo the reduction found in sham-operated rats. Adrenal hormones may thus be involved in the reduction of blood levels of prolactin observed in rats and in other mammals as lactation progresses.
Changes in serum concentration of luteinizing hormone in the female rat approaching puberty
Authors: Meijs-Roelofs H. M. A. , Kramer P. , Sander H. J.
Published: December 2008

Concentrations of LH in the serum were estimated in rats bled either once or twice during a 15-day period preceding first ovulation. In rats bled once (between 09.00 and 17.00 h) serum concentrations showed little change between 15 and 9 days before first ovulation and averaged 16 μg/l (days −15 to −9). A shift in LH level, to a mean of 31 μg/l, was seen on day −8, whereafter LH concentrations increased gradually. Basal LH values of < 10 μg/l were only found until day −4.

The finding that LH values increased with age was confirmed by data from rats bled twice with an interval of ≥ 3 days between bleedings. Furthermore, both in rats bled twice at 11.00 h and in rats bled twice at 15.00 h LH concentrations were significantly higher in the second sample.

Both morning (11.00 h) and afternoon (15.00 h) LH concentrations in rats bled once also indicated a rise in LH concentrations with age but it became apparent that only morning values showed a shift in LH concentration (from ∼ 15 to ∼42 μg/l) from day −9 to day −8. In contrast, mean afternoon values showed a gradual increase from day −15 on. From day −8 on the number of rats with LH values ≥50 μg/l increased, and from day −5 on they were more frequent at 15.00 than at 11.00 h.

Thus a clear increase in LH secretion, most likely of a pulsatile nature, was found in the female rat approaching puberty. The correlation in time and possible functional relationship with late-prepubertal follicular growth is discussed.