bluuebunny/crossref_metadata_2025 huggingface dataset:
Stimulation of milk secretion with inhibition of milk ejection by corticosteroids during extended lactation in the rat
Authors: Flint D. J. , Clegg R. A. , Knight C. H.
Published: December 2008

Milk yield declined significantly between days 22 and 28 of lactation in rats, when lactation was extended by frequent replacement of older litters with younger ones. Corticosterone implants but not cortisol injections or implants prevented this decline. Cortisol, however, appeared to inhibit milk ejection since the mammary glands became engorged with milk and milk yield was improved dramatically by oxytocin injections. In both cases corticosteroid concentrations increased approximately threefold above basal concentrations.

Both corticosteroids increased total mammary gland RNA content and lipoprotein lipase (LPL) activity of the mammary gland but were without effect on insulin binding. They also decreased LPL activity, lipogenesis and the number of insulin receptors on adipose tissue.

Serum prolactin and insulin concentrations were unaffected by any of the treatments.

The results suggest that corticosteroids (1) inhibit milk ejection under certain conditions, (2) may be circulating in lower concentrations, which thereby limit milk production, during prolonged lactation and (3) may improve milk yield during extended lactation in part by suppressing anabolic activity in adipose tissue.

J. Endocr. (1984) 103, 213–218
Differential effects of cryptorchidism and short photoperiod on testicular prolactin and LH/human chorionic gonadotrophin receptors in the golden hamster
Authors: Bartke A. , Klemcke H. G. , Amador A. G. , Talamantes F.
Published: December 2008

Gonadal atrophy induced by short photoperiods in male golden hamsters is accompanied by a decrease in the total content of testicular prolactin and LH/human chorionic gonadotrophin (LH/hCG) receptors and a concomitant rise in the concentration of LH receptors. Atrophic testes are typically abdominal. In this study, we have compared the effects of experimentally induced cryptorchidism and the effects of a short photoperiod on testicular prolactin and LH/hCG receptors. Cryptorchidism produced the expected decrease in testicular weight and an increase in plasma FSH concentrations, without altering plasma concentrations of LH or prolactin and with a relatively small decrease in plasma testosterone. It also produced an increase in the concentration of prolactin and LH/hCG receptors without significant changes in their total content. Exposure to a short photoperiod decreased weights of testes and seminal vesicles and plasma levels of prolactin and testosterone, with no significant effects on plasma gonadotrophin levels. Short photoperiod also increased the concentration of LH/hCG receptors but, in contrast to the effects of cryptorchidism, it produced a precipitous decline in the total content of testicular receptors for both prolactin and LH/hCG. We conclude that changes in prolactin and hCG binding measured in membrane preparations from decapsulated testes of hamsters exposed to a short photoperiod cannot be explained by the abdominal position of the gonads, abnormalities of Sertoli cell function or changes in the relative proportion of Leydig cells in the atrophic testes.

J. Endocr. (1984) 103, 227–231
Central effects of photoperiod on reproduction in the ram revealed by the use of a testosterone clamp
Authors: Lincoln G. A.
Published: December 2008

Over a 3-year period eight adult Soay rams were exposed to an artificial lighting regimen of alternating 16-week periods of long days (16 h light:8 h darkness; 16L:8D) and short days (8L:16D) to induce a seasonal cycle in reproduction and wool growth every 32 weeks. Early in the study the rams were castrated (four during long days and four during short days) and 48 weeks later the castrated animals were each given an s.c. implant of testosterone to increase the blood plasma concentration of testosterone to 14–20 nmol/l. The changes in the concentrations of LH, FSH and testosterone were measured in blood samples collected once or twice weekly while records were made of the changes in the size of the testes (before castration), the intensity of the sexual skin flush, the expression of aggressive and sexual behaviour and the rate of wool growth.

The results showed that in the castrated rams there were only minor changes in the blood levels of LH, FSH and the expression of aggressive behaviour related to the 32-week light cycle, while the sexual skin flush was permanently absent. However, after the commencement of the constant testosterone therapy, there were major changes in all the reproductive parameters related to the lighting regimen with a similar temporal relationship as observed in the rams before castration. Cyclic variation in wool growth occurred throughout the study related to the changes in photoperiod but this was not markedly affected by castration and testosterone replacement.

The conclusion is that photoperiod acts centrally within the brain to dictate the cyclic changes in reproduction and wool growth in the ram, but testosterone is required for the full expression of the effects on reproduction. In the normal seasonal sexual cycle, photoperiod affects both the secretion of testosterone and the responsiveness to testosterone, resulting in a peak of sexuality in autumn.

J. Endocr. (1984) 103, 233–241
Androgen-binding proteins in sheep epididymis: age-related effects on androgen-binding protein, cytosolic androgen receptor and testosterone concentrations. Correlations with histological studies
Authors: Carreau S. , Drosdowsky M. A. , Courot M.
Published: December 2008

The androgen-binding protein (ABP) and the cytosol androgen receptor (Rc) were measured in the epididymis of sheep aged 50, 120 and 200 days. Specific binding protein was not detected at 50 days (infantile); near puberty (120 days), ABP was more concentrated in caput and cauda epididymal cytosols (117 and 183 fmol/mg protein respectively) than in corpus (53 fmol/mg) although Rc levels were low (3–5 fmol/mg). In postpubertal rams (200 days), ABP and Rc concentrations were higher in caput and cauda than in corpus epididymis. Testosterone concentrations at 50 days were not statistically different along the epididymis and varied from 0·3 to 0·8 pmol/mg protein. In 120-day-old animals, testosterone was more concentrated in caput and corpus (0·45 and 0·41 pmol/mg) than in cauda (0·17 pmol/mg); at 200 days, the testosterone contents were low (0·10–0·17 pmol/mg) in all parts of the epididymis. A ten-fold increase in plasma testosterone concentrations was observed between 50 and 200 days (1·31 to 11·71 nmol/l). Histological studies of the epididymis in the three groups of animals showed that the cell differentiation started in the cauda where the principal epithelial cells were higher (47–56 μm) than in the caput (31–38 μm) at 50 days. The principal cells of the caput were two- to threefold higher in postpubertal rams than in infantile lambs, a finding which is correlated with the levels of ABP and Rc. This may suggest an important physiological role of this region in the induction of sperm maturation.

J. Endocr. (1984) 103, 281–286
Effects of long-term administration of high doses of medroxyprogesterone acetate on hormone receptors and target organs in the female rat
Authors: Di Carlo F. , Racca S. , Conti G. , Gallo E. , Muccioli G. , Sapino A. , Bussolati G.
Published: December 2008

The changes in oestrogen, progesterone and prolactin receptor levels in target organs, and the macroscopic and microscopic modifications of uterus, ovary, adrenal and pituitary gland induced by long-term administration of high doses of medroxyprogesterone acetate (MPA) were investigated in female rats. Medroxyprogesterone acetate was injected i.m. for 30 days at daily doses of 7·5, 15 and 75 mg/kg. Oestrogen and/or progesterone-binding capacities were remarkably reduced at all doses of MPA used both in the uterus and pituitary gland. Furthermore, MPA caused a very evident reduction in the weight of pituitary glands, ovaries, adrenals and uterus.

In all MPA-treated rats corpora lutea were absent from the ovaries, whereas the adrenals showed a significant reduction in the thickness of the cortex. In accordance with this, there was no evidence of ACTH-producing cells in the pituitary glands. Prolactin-producing cells were also absent, while GH-producing cells were present. Serum prolactin levels were significantly reduced at all doses of MPA used. A dramatic reduction of prolactin receptor concentrations was observed in the liver and the ovaries of MPA-treated rats.

The results suggest that MPA acts as an antioestrogenic drug both by reducing the number of oestrogen receptors in target tissues and by changing the structure (and perhaps the function) of those organs (pituitary glands, ovaries and adrenals) which are, directly or indirectly, a source of oestrogens. The decreased synthesis of prolactin and the reduction of the number of prolactin receptors (which, on the contrary, are both increased by oestrogens) might be considered as additional antioestrogenic effects of MPA.

J. Endocr. (1984) 103, 287–293
Maintenance of neonatal rat B cells in glucose-depleted medium: effect of medium with galactose and 2-deoxyglucose
Authors: Wakabayashi S. , Kagawa S. , Nakao K. , Mimura K. , Matsuoka A.
Published: December 2008

Monolayer cultures of the pancreas of the neonatal rat were maintained for 7 days in glucose-depleted TCM 199 medium, supplemented with 5·5 mmol galactose/l, with or without 0·1 mmol 2-deoxyglucose/l. Under culture conditions without 2-deoxyglucose, the responsiveness of B cells supported on galactose was totally abolished by day 7 of culture, and islets degenerated. In contrast, the addition of 2-deoxyglucose to the galactose-supplemented medium promoted the survival and the function of B cells even in a glucose-depleted environment and, in addition, yielded the monolayers mostly consisting of endocrine cells by destroying fibroblasts selectively. On day 7 the recovery of insulin in the cells was higher than that of the cells grown in medium with galactose alone (10·7-fold), and than the initial level at day 0 (twofold). Furthermore, the response to an acute challenge with 16·7 mmol glucose/1 was 3·3-fold, to 10 mmol leucine/1 it was 8·5-fold, and to 10 mmol 2-ketoisocaproate/l it was 10·9-fold above each value observed on day 1. In summary, the above data indicate that morphologically intact, functionally competent endocrine B cells can be grown in medium free from glucose.

J. Endocr. (1984) 103, 377–381
Dopamine enters lactotrophs and reaches their secretory granules
Authors: Gallardo M. G. P. , Bilinski M. , Chiocchio S. R. , Tramezzani J. H.
Published: December 2008

The presence of dopamine in the lactotroph cell, as well as in isolated prolactin secretory granules, was demonstrated by means of an histochemical reaction for electron microscopy. Biochemical assays further confirmed the presence of dopamine in the secretory granules.

Autoradiographic preparations examined by light microscopy showed dopamine internalization in dispersed anterior pituitary cells.

Isolated anterior pituitary lactotroph cells incorporated more [3H]dopamine than a fraction containing other anterior pituitary cells.

J. Endocr. (1985) 104, 23–28
Intravenous growth hormone: growth responses to patterned infusions in hypophysectomized rats
Authors: Clark R. G. , Jansson J.-O. , Isaksson O. , Robinson I. C. A. F.
Published: December 2008

Young hypophysectomized rats were maintained with chronic indwelling i.v. cannulae attached via swivels to a multichannel pumping system programmed to deliver GH in a continuous or pulsatile pattern for several days. Continuous i.v. infusions of human GH for 5 days produced dose-dependent increases in body weight and tail length, without increasing food intake. A comparison of GH infusions by the s.c. or i.v. route showed that the direct i.v. route was threefold more effective. Pulsatile i.v. infusions of human or bovine GH at two doses (12 or 36 mu./day, eight pulses/day, 5-min duration, every 3 h) produced greater increases in body weight than continuous i.v. infusions of GH at the same daily dose. Continuous infusions of bovine GH produced a lower growth rate in the second of two consecutive 5-day treatment periods, whereas the responses to pulsatile GH did not diminish with time. Both body weight gain and long-bone growth were affected by the frequency of GH pulses; nine pulses per day were more effective than three pulses per day which in turn produced larger growth responses than one pulse per day. Keeping GH pulse frequency constant and varying pulse duration (4, 16 or 64 min) did not affect growth rates. In conclusion, long-term pulsatile i.v. infusions of GH mimic the endogenous secretory pattern, and are most effective when given at the physiologically appropriate pulse frequency.

J. Endocr. (1985) 104, 53–61
Hormone concentrations, mammary development and milk yield in goats given long-term bromocriptine treatment in pregnancy
Authors: Forsyth I. A. , Byatt J. C. , Iley S.
Published: December 2008

Ten British Saanen goats were treated daily with 5 mg bromocriptine intramuscularly from week 8 of pregnancy until week 20 (day 140). By comparison with untreated control goats (n = 8), concentrations of prolactin in plasma were suppressed throughout the treatment period and remained significantly lower until 3 days prepartum, parturition occurring on day 153 ± 0·7 (mean ± s.e.m., n = 10). Growth hormone concentrations were low, but the incidence of levels exceeding 1 μg/l was increased in bromocriptine-treated goats. Plasma concentrations of placental lactogen, progesterone and oestrone sulphate were unaffected. The accumulation of pre-colostrum in the udder (lactogenesis stage I) was not affected by bromocriptine treatment in goats carrying twin fetuses, but in goats with single kids it was delayed by about 4–6 weeks to week 17 of pregnancy. Secretion could not be expressed from the udder and the concentration of α-lactalbumin in plasma remained low. Udder volume was significantly reduced in week 15–16 but not week 20–21 of pregnancy by bromocriptine treatment. Milk yields after 50 or 203 days of lactation were not significantly different from those in control goats. Placental lactogen concentrations in late pregnancy and udder volume in week 20–21 were the only variables measured which correlated with milk yield post partum. It is concluded that in vivo placental lactogen is an effective mammotrophic hormone, although less potent than prolactin as evidenced by the delay in lactogenesis stage I in bromocriptine-treated goats bearing single kids.

J. Endocr. (1985) 104, 77–85
Menstrual cycle and exposure to oestrogens unopposed by progesterone: relevance to studies on breast cancer incidence
Authors: Metcalf M. G. , Mackenzie J. A.
Published: December 2008

It is claimed that the exposure of women to oestrogens unopposed by progesterone increases the risk of breast cancer. Despite indirect evidence in support of this claim, the impracticability of monitoring oestrogen and progesterone levels in large numbers of women for prolonged periods of time has meant that no direct demonstration of the effect has been made. A possible technique is suggested.

The ratio (R) of oestrogens to pregnanediol in urine has been used as an index of oestrogen exposure relative to progesterone. Samples were collected at weekly intervals on 700 occasions from 30 perimenopausal women, and on 519 occasions from 66 women with a history of regular menstrual cyclicity. Unusually prolonged episodes of unopposed high oestrogen excretion (R ≥ 100 for ≥ 2 successive weeks) were observed on 30 occasions in 15 of the perimenopausal women and on four occasions in the other women. In the perimenopausal group, these episodes occurred in 46·9% of the 32 menstrual cycles which were longer than 50 days compared with 6·9% of the 72 cycles which were shorter than 35 days (P < 0·001). The association of prolonged episodes of unopposed high oestrogen excretion with long menstrual cycles suggests the possibility of using menstrual cycle length as an index of oestrogen exposure during the menopausal transition.

J. Endocr. (1985) 104, 137–141
Lack of direct inhibitory action of oxytocin on progesterone production by dispersed cells from human corpus luteum
Authors: Richardson M. C. , Masson G. M.
Published: December 2008

Suspensions of luteal cells were prepared from samples of human corpora lutea obtained during the luteal phase of menstrual cycles. Addition of oxytocin (1 μmol/l) to the various cell preparations had no effect on either basal production of progesterone or on steroidogenic responses to a range of concentrations of gonadotrophin.

J. Endocr. (1985) 104, 149–151
Peripubertal changes in the nature of LH
Authors: Buckingham J. C. , Wilson C. A.
Published: December 2008

Administration of pregnant mare serum gonadotrophin (PMSG) to peripubertal rats, aged 27 days, induces ovulation provided the animals weigh more than 60 g at the time of the injection. In an attempt to determine whether the apparent immaturity of the ovaries in smaller rats is associated with an inability of the pituitary gland to secrete LH, the biological and immunological properties of LH in peripubertal PMSG-treated rats were examined. A single injection of PMSG caused a marked hypersecretion of LH in rats aged 27 days. The LH in the plasma of rats weighing more than 60 g was active in both the radioimmunoassay and the cytochemical bioassay but that in smaller rats was active only in the former. Plasma from both groups of rats stimulated the release of testosterone from dispersed Leydig cells.

Luteinizing hormone-releasing hormone stimulated the secretion, in vitro, of immunoreactive, cytochemically active LH by pituitary tissue from rats weighing over 60 g. The LH released in vitro from tissue from the smaller animals, like that in their plasma, was active in the radioimmunoassay but not in the cytochemical system. The results suggest that an abrupt change in the nature of LH occurs at puberty and that ovulatory cycles commence only when the pituitary gland secretes the adult form of LH with a full spectrum of biological activity.

J. Endocr. (1985) 104, 173–177
Drinking-induced changes in fowl adrenocortical activity: effect of visual and non-visual stimuli
Authors: Harvey S. , Klandorf H. , Lam S.-K.
Published: December 2008

The deprivation of drinking water for 30 h resulted in increased corticosterone concentrations in the plasma of 8- to 10-week-old chickens. When water-deprived birds were allowed to drink ad libitum the corticosterone concentration declined within 45 min, to the level in hydrated controls, and remained suppressed thereafter. Similar reductions in the corticosterone concentrations were also observed in water-deprived chicks which were allowed to drink for only 5 min, 1 min or 5 s. The involvement of visual stimuli in mediating this adrenocortical response was demonstrated by a comparable decline in the corticosterone concentration in water-deprived birds which were presented with water but not allowed access to it. Non-visual stimuli also appeared to be causally involved in the adrenocortical suppression after drinking, since the intraperitoneal injection of tap water (40 ml per bird) also resulted in a lowering of the corticosterone level. However, in the absence of appropriate reinforcement from metabolic stimuli, a rebound in the corticosterone concentration was observed in birds prevented from drinking, in birds unable to satiate their thirst and in birds rehydrated (orally or intraperitoneally) without feeding.

These results demonstrate adrenocortical suppression in water-deprived chickens after free access to food and water and the involvement of visual and non-visual stimuli in mediating this response. The maintenance of adrenocortical suppression is dependent upon metabolic stimuli associated with food and water intake.

J. Endocr. (1985) 104, 225–231
A phylogenetic study of the structural and functional characteristics of corticosteroid binding globulin in primates
Authors: Robinson P. A. , Hawkey C. , Hammond G. L.
Published: December 2008

A monospecific antiserum against human corticosteroid binding globulin (hCBG) has been used to identify structural similarities between hCBG and CBG in the blood of other primates and representative species of different vertebrate classes. Double immunodiffusion analysis indicated that only CBG in Old World monkeys and apes cross-react with the hCBG antiserum. This was confirmed by a solid-phase radioimmunoassay for hCBG which also demonstrated that CBG in apes is immunologically identical to hCBG and that Old World monkey CBG comprises most, but not all, of the hCBG epitopes. The electrophoretic mobilities of human, gorilla and gibbon CBG were similar (RF 0·50–0·51), but differed from Old World monkey CBG (RF 0·44–0·49) and chimpanzee CBG (RF 0·47). Although serum/plasma cortisol binding capacities were similar in Old World primates, the dissociation half-times (t½) of cortisol were higher from human and ape CBG (18–25 min) than from Old World monkey CBG (14–18 min). The steroid binding specificities of human and ape (CBG corticosterone > cortisol > progesterone ≥ testosterone) were also different from those of Old World monkey CBG (corticosterone >> cortisol ≃ progesterone > testosterone). Lemur plasma cortisol binding capacity and CBG dissociation t½ of cortisol were similar to hCBG, but its steroid binding specificity was different (cortisol > corticosterone > progesterone ≥ testosterone) and it did not cross-react with the hCBG antiserum. We could not detect high affinity cortisol binding activity in blood samples from New World monkeys, and they did not cross-react with the hCBG antiserum. These results suggest that considerable modification in the steroid binding activity and structure of CBG has occurred since the evolutionary appearance of the primates, but that the rate of change decreased after the cladogenesis of Catarrhine primates.

J. Endocr. (1985) 104, 251–257
Identification and characterization of a human corticosteroid binding globulin variant with a reduced affinity for cortisol
Authors: Robinson P. A. , Hammond G. L.
Published: December 2008

A corticosteroid binding globulin variant (CBGv) has been identified in a serum sample taken from an apparently healthy woman during late pregnancy. Identification was based on the observation that it exhibited approximately half the cortisol binding capacity expected when compared to its concentration measured by radioimmunoassay (RIA). Affinity purification of CBGv excluded the possibility that this anomaly was caused by assay interference, and demonstrated that immunoreactive CBGv was capable of binding cortisol. The CBGv had a molecular weight (63 800) similar to normal CBG, and no evidence of molecular aggregation was found by gel filtration. Although the electrophoretic mobility, isoelectric profile and immunochemical identity of CBGv appeared to be similar to normal CBG, it focussed as two distinct bands (pI 5·48 and pI 5·53) after desialylation with neuraminidase, unlike normal CBG which focusses only at pI 5·48. Investigation of the steroid binding characteristics of CBGv revealed a reduced association-rate constant (Ka = 1·05 × 109 1/mol) and dissociation half-time (12·5 min) when compared with normal CBG (Ka = 1·39 × 109l/mol and 25 min at 0 °C) but an apparently normal steroid binding specificity. Although the physiological significance of this variant is not known, the cortisol concentration in the variant serum was within the normal range of women during late pregnancy. No other CBG variants were identified among other normal controls (n = 66) or nine patients with Cushing's syndrome. It is suggested that comparisons between cortisol binding capacity and RIA will reveal other variants of CBG, and lead to greater understanding of their physiological significance.

J. Endocr. (1985) 104, 269–277
Human thyroid cells in monolayer retain the ability to secrete tri-iodothyronine in response to thyrotrophin
Authors: Ollis C. A. , Fowles A. , Brown B. L. , Munro D. S. , Tomlinson S.
Published: December 2008

Confluent monolayer cultures of human thyroid cells secreted low levels of immunoassayable triiodothyronine (T3) and this process could be stimulated by TSH in a concentration-dependent manner. The characteristics of the response to TSH were related to the age of the thyroid cell culture both in terms of the relative sensitivity to TSH and the quantity of T3 released. Cells which had been in culture for 2–3 days (primary cultures) secreted high levels of T3 under unstimulated and TSH-stimulated conditions with a median effective dose (ED50) for TSH of 0·030 mu. TSH/ml. However, cells which had been subcultured and consequently had been in culture for a longer period of 6–7 days secreted lower levels of T3 under basal and stimulated conditions. This was approximately 30% of that released from primary cultures with an ED50 for TSH of 0·1 mu. TSH/ml. Reorganization of human thyroid cells into follicular structures was seen during growth with TSH but these cultures showed little response to subsequent acute stimulation by TSH; the return of a diminished, less sensitive response to TSH was seen after a recovery period of 8 h. The time-course of T3 release was dependent on the TSH concentration with low TSH concentrations stimulating T3 secretion after increased incubation periods. Human thyroid cells had lost the ability to concentrate and organify free iodide after several days in culture but were still secreting T3. This indicates the presence of intracellular stores of T3 which are released on stimulation with TSH, rather than new synthesis of T3.

J. Endocr. (1985) 104, 285–290
Blood pressure and metabolic effects of 9α-fluorocorticosterone and 9α-fluorodeoxycorticosterone in sheep
Authors: Scoggins B. A. , Coghlan J. P. , Denton D. A. , McCarthy P. J. , Mason R. T. , Tresham J. , Whitworth J. A.
Published: December 2008

9α-Fluorocortisol has been postulated to have 'hypertensinogenic' as well as 'mineralocorticoid' and 'glucocorticoid' activity. The present study examined the blood pressure and metabolic effect in sheep of the structurally related steroids 9α-fluorodeoxycorticosterone (9α-FDOC) and 9α-fluorocorticosterone (9α-FB). Infusions of these fluorinated steroids at 0·63 and 0·67 mg/day respectively for 5 days produced falls in plasma potassium, but only 9α-FB increased urine volume. 9α-FDOC raised mean arterial pressure by 11 mmHg and 9α-FB raised it by 14 mmHg. Addition of a 9α-fluoro group appears to increase both 'mineralocorticoid' and 'hypertensinogenic' steroid potencies.

J. Endocr. (1985) 104, 291–294
Increase in plasminogen activator in the involuting uterus of the postpartum rat
Authors: Shimada H. , Okamura H. , Espey L. L. , Mori T.
Published: December 2008

Plasminogen activator (PA) activity in the rat uterus was measured at fixed intervals post partum in order to determine whether this serine protease increases during the acute remodelling of tissue which occurs in the involuting uterus. Plasminogen activator activity was measured by an indirect method based on the hydrolysis of the chromogenic substrate S-2251 by PA-generated plasmin. At the time of parturition the control level of PA activity was 0·033 ± 0·018 (s.d.) μmol/4 mg uterine wet weight per 30 min. This activity increased fourfold to a peak of 0·131 ±0·036 at 3 days post partum, and then it declined steadily towards the control level during the next 7 days. Concomitantly, uterine weight decreased to 25% of the control weight by 3 days post partum, and it continued to decrease until day 15. In the 30 days post partum during which PA activity was monitored there was no significant change in plasmin inhibitors in the uterine extracts. The results suggest a correlation between PA activity and the process of tissue remodelling which occurs during involution of the rat uterus. This increase in PA might serve to activate a latent collagenase since the measured peak in PA activity happens to coincide with a reported increase in collagenolytic activity in the involuting rat uterus.

J. Endocr. (1985) 104, 295–298
Thyroid function in pyridoxine-deficient young rats
Authors: Dakshinamurti K. , Paulose C. S. , Thliveris J. A. , Vriend J.
Published: December 2008

In pyridoxine-deficient young rats hypothalamic serotonin was decreased with no changes in the dopamine and noradrenaline content. Serum thyroxine and tri-iodothyronine concentrations were much lower in the deficient rats as compared to pyridoxine-supplemented controls. No significant difference between deficient and control groups in the serum TSH concentration was detected. Highly significant decreases in the content of pituitary TSH and in the number of pituitary thyrotroph secretory granules were found. These results suggest that the hypothyroidism of pyridoxine-deficient young rats might be of hypothalamic origin.

J. Endocr. (1985) 104, 339–344
Responses to prolactin secretagogues in oestrogen-treated rats suggest that the defect in prolactin regulation produced by oestrogen is at the level of the pituitary gland
Authors: Willoughby J. O. , Pederick H. , Jervois P. , Menadue M. , Judd S. J.
Published: December 2008

Prolactin responses to pharmacological agents were used to characterize the defect in prolactin regulation which occurs after administration of high doses of oestrogen to rats.

Animals with chronically implanted venous cannulae were injected with 2 mg oestradiol benzoate in oil and 2–3 days later prolactin concentrations were measured after injections of saline, thyrotrophin-releasing hormone (TRH), fenfluramine, apomorphine and butaclamol. The responses were compared with those in oil-injected animals.

Hyperprolactinaemia in oestrogen-treated animals was unresponsive to apomorphine, but was even more sensitive to dopamine receptor blockade than controls. These results suggest that the lactotrophs in oestrogen-treated animals are already maximally suppressed by endogenous dopamine, though ineffectively.

Although there was an increased prolactin response to TRH in oestrogen-treated animals, there was an impaired response to fenfluramine, indicating suppressed serotonergic prolactin-releasing factor mechanisms.

Maximal endogenous dopaminergic activity and suppressed prolactin-releasing factor mechanisms are appropriate hypothalamic responses to hyperprolactinaemia. The operation of these responses in the earliest stages of the development of pituitary hyperplasia indicates that oestrogen induces a disturbance of prolactin regulation in the lactotroph, independent of hypothalamic control.

J. Endocr. (1985) 104, 447–452
Medroxyprogesterone acetate does not perturb the profile of steroid metabolites in urine during pregnancy
Authors: Yovich J. L. , Willcox D. L. , Wilkinson S. P. , Poletti V. M. , Hähnel R.
Published: December 2008

The plasma concentrations of medroxyprogesterone acetate (MPA) in 14 women administered the progestagen for threatened abortion during the first 6 weeks of pregnancy were measured by specific radioimmunoassay. Treatment (52 nmol orally every 6 h) was continued to 18 weeks of gestation. The mean plasma concentration of MPA rose rapidly during day 1 of treatment to 14·1 ±1·84 nmol/l. It reached 21·5 ± 2·3 nmol/l by 7 days and subsequently stabilized at around 26·8±5·0 nmol/l by the end of week 2. Urinary steroid profiles were determined by gas–liquid chromatography and mass spectrometry for six of the MPA-treated women and compared with those of six untreated women of similar gestational age. No differences were detected between the two groups of women, suggesting that the administration of MPA during pregnancy did not alter qualitatively or quantitatively the metabolism and excretion into urine of progesterone and oestrogens.

J. Endocr. (1985) 104, 453–459
Spermatogenesis, seminal characteristics and reproductive hormone levels in mature rams with induced hypothyroidism and hyperthyroidism
Authors: Chandrasekhar Y. , Holland M. K. , D'Occhio M. J. , Setchell B. P.
Published: December 2008

Mature Merino rams were made hypothyroid by daily oral drenching with methylthiouracil or hyperthyroid by daily subcutaneous injections of thyroxine for 8 weeks. Neither hypothyroidism nor hyperthyroidism had any apparent effect on either spermatogenesis or daily sperm production, but motility of ejaculated spermatozoa and circulating testosterone concentrations were reduced in both conditions. The ratio of testosterone concentrations in plasma from the internal spermatic vein to those in peripheral blood plasma was higher in hyperthyroid (21·2 ± 3·5) than in control (11·1 ±4·4 and hypothyroid (7·6±1·4) rams. The basal secretion rate for testosterone was slightly lower in hypothyroid rams and testosterone responses to human chorionic gonadotrophin and after LH-releasing hormone (LHRH) were very much reduced. Basal serum LH levels were low in both hypothyroid and hyperthyroid rams compared with controls whereas there were no differences in FSH levels. The LH response to exogenous LHRH was reduced in hypothyroid rams but not in hyperthyroid rams. Serum prolactin levels on the other hand were higher than control in both hypothyroid and hyperthyroid rams.

Reduced testosterone secretion in hypothyroid rams indicates that the normal function of Leydig cells depends on an adequate level of thyroid hormones. The decrease in circulating testosterone concentrations in hyperthyroid rams with normal secretion rates suggests an increased testosterone clearance rate in these animals. The decreased spermatozoal motility in hypo- and hyperthyroid rams suggests that the lowered testosterone level in these animals has altered the androgen-dependent maturation of spermatozoa in the epididymis. Changes in testis function together with decreased LH secretion in hypothyroid rams indicate that thyroid hormones can act at both the pituitary gland and testes to influence reproductive function in mature rams.

J. Endocr. (1985) 105, 39–46
Levels of dopamine and thyrotrophin-releasing hormone in hypophysial stalk blood during an oestrogen-stimulated surge of prolactin in the ovariectomized rat
Authors: de Greef W. J. , Klootwijk W. , Karels B. , Visser T. J.
Published: December 2008

The changes in hypothalamic release of dopamine and thyrotrophin-releasing hormone (TRH) into the hypophysial portal vascular system during an oestrogen-stimulated surge of prolactin in ovariectomized rats were investigated.

A single injection of 5 μg oestradiol benzoate resulted in a reliable increase in the plasma levels of prolactin during the afternoon 3 days later. Anaesthesia did not block this afternoon surge of prolactin, although its magnitude was only half of that of unanaesthetized rats. Before and during this surge, hypophysial stalk blood was collected into methanol to analyse the hypothalamic release of dopamine and TRH. Immunoreactive TRH in these methanolic extracts eluted as a single peak with the same retention time as authentic TRH on reverse-phase high performance liquid chromatography. In comparison to the morning values, levels of dopamine decreased and those of TRH increased in hypophysial stalk blood by 50 and 240% respectively. These data indicate that hypothalamic dopamine and TRH may be involved in the afternoon surge of prolactin.

Daily treatment with parachlorophenylalanine, an inhibitor of serotonin synthesis, reduced the hypothalamic release of TRH by 50%, but did not prevent the afternoon surge of prolactin and TRH induced by oestradiol benzoate.

J. Endocr. (1985) 105, 107–112
Reappraisal of the influence of mammary distension on the frequency of milk ejection in the rat
Authors: Riggs C. M. , Sutherland R. C. , Wakerley J. B.
Published: December 2008

Experiments were performed to reinvestigate the importance of mammary engorgement for activation of the milk-ejection reflex in the rat. Reflex milk ejection (measured by intramammary pressure recordings during a 2-h suckling test under anaesthesia) was compared in rats with engorged mammary glands (15-h separation from the pups, followed by sham-removal of milk) and in rats with drained mammary glands (15-h separation, followed by milk removal using a foster litter and exogenous oxytocin).

In experiment 1, multiple small (2 mu.) doses of oxytocin were used for milk removal: these were effective in emptying the mammary glands and caused no subsequent impairment or change in sensitivity of the mammary response to oxytocin. Using this draining procedure, no significant differences were observed in either the number or relative amplitude of the milk ejections, or the occurrence of pup stretch reactions between engorged and drained rats. Similar results were seen in experiment 2, where an identical draining protocol was used, but the rats were pretreated with propranolol before the suckling test. In experiment 3, large (250 mu.) oxytocin doses were used for milk removal, as in previous studies. Again mammary draining had no effect on milk ejection in a subsequent suckling test (with propranolol pretreatment). However, the number of stretch reactions shown by the pups was significantly (P < 0·001) reduced from 8·6 ± 1·4/2 h to 1·9 ± 0·6/2 h. This effect probably related to long-term impairment of the oxytocin response of the mammary glands following the draining procedure, and could not be attributed to the draining per se. The dissociation of milk ejections and pup behavioural responses using this method of draining the glands explains previous reports, based on behavioural observations, that mammary draining profoundly disrupts milk ejection. It is concluded that mammary engorgement in fact has little influence on the activation of the milk-ejection reflex in the rat.

J. Endocr. (1985) 105, 127–132
Immunocytochemical localization of vasopressin-binding sites in the rat kidney
Authors: Ravid R. , Swaab D. F. , Pool Chr. W.
Published: December 2008

The rat kidney and brain are major target organs for vasopressin (VP). A procedure was developed for immunocytochemical staining of VP and its binding sites in the kidney. This procedure involved preincubation of kidney sections with the ligand, followed by immunocytochemical detection of VP.

The staining in renal tubules from Wistar rats was enhanced by preincubation of tissue sections with increasing concentrations of VP (6–6000 nmol/l). Staining was present in the epithelium of distal convolutions and collecting ducts (medullary and cortical portions) and more pronounced in the apical zone of the tubular epithelium. With high concentrations of VP in the preincubation, staining was also obtained in the thick ascending limb of the loop of Henle. There was no staining under any circumstances in proximal tubules. In the kidney of the Brattleboro rat homozygous for hypothalamic diabetes insipidus (DI) which congenitally lacks VP but responds to the peptide, exactly the same staining pattern was observed after preincubation with VP, but the maximal staining was less intense. The VP binding to the DI rat kidney, after 2 weeks treatment with VP (using Accurel implants), reached levels seen in the Wistar kidney after in-vitro preincubation with high doses of VP.

J. Endocr. (1985) 105, 133–140
Androgen feedback-dependent and -independent control of photoinduced LH secretion in male tree sparrows (Spizella arborea)
Authors: Wilson F. E.
Published: December 2008

Photoperiodic control of gonadotrophin secretion in male tree sparrows was studied by examining changes in plasma LH in castrated birds retained on short daylengths and in castrated birds transferred to long daylengths. Plasma LH concentrations were markedly higher in photostimulated birds than in non-photostimulated birds throughout the 25-day experiment, and implantation of the antiandrogen cyproterone (free alcohol), which should have blocked the action of castration-resistant androgens, did not increase plasma LH in either group. Such results, obtained from birds in which testosterone feedback was inoperative, indicate that the gonadostimulatory effect of long daylengths in intact males must be mediated, at least in part, by an androgen feedback-independent mechanism. To determine whether changes in testosterone feedback facilitate gonadotrophin secretion during photostimulation, two feedback performance characteristics (i.e. set point (minimum concentration of testosterone that suppresses plasma LH) and sensitivity (change in plasma LH per unit change in testosterone)) were quantified by evaluating plasma LH responses of non-photostimulated castrated birds and of photostimulated castrated birds to replacement testosterone (0–4·16 μmol). The data indicate that, in addition to stimulating LH secretion by an androgen feedback-independent mechanism, long daylengths reduce feedback inhibition of LH secretion by increasing the putative set point and decreasing the sensitivity of the testosterone feedback mechanism. The feedback-independent effect is the predominant effect of photostimulation on LH secretion in male tree sparrows.

J. Endocr. (1985) 105, 141–152
Nuclear retinoic acid binding protein in human prostate adenomas
Authors: Boyd D. , Chisholm G. D. , Habib F. K.
Published: December 2008

A retinoic acid binding protein has been detected in salt extracts of nuclei obtained from human prostate adenoma. The binding was characterized by competition experiments, temperature/time studies and saturation analysis.

Substantial binding was only observed after sonication of nuclei and charcoal-pretreatment of a salt extract. The binding of radiolabelled all-transretinoic acid was displaced by all-trans-retinoic acid, retinol and to a lesser extent retinal and two synthetic retinoids, RO 10-1670 and RO 13-7410. Testosterone and dihydrotestosterone, at a 100-fold excess, had little effect on the binding.

The association between retinoic acid and nuclear protein was both temperature and time dependent. At 37 °C, equilibrium was rapidly reached (30 min) whereas at 4 and 25 °C, ligand binding occurred at a slower rate. Saturation analysis performed under steady-state conditions yielded a dissociation constant of 15 ±2 nmol/l.

Metabolism studies failed to show conversion of either radiolabelled all-trans-retinol or [3H]retinoic acid in vitro; these data suggest that both acid and alcohol forms of vitamin A are recognized by the extracted nuclear protein.

The effect of three enzyme inhibitors on [3H]retinoic acid binding was studied. Binding was unaltered in the presence of aprotinin and phenylmethylsulphonyl fluoride but sodium molybdate (10 mmol/l) increased binding by 18%.

The presence of a specific retinoid binding protein in prostate nuclei suggests that retinoids may play some role in the function of the gland.

J. Endocr. (1985) 105, 157–162
Effects of low phosphorus and low calcium diets on the production and metabolic clearance rates of 1,25-dihydroxycholecalciferol in pigs
Authors: Fox J. , Ross R.
Published: December 2008

Severe dietary calcium (Ca) or phosphorus (P) deficiency leads to a similar degree of stimulation of (1) plasma and intestinal 1,25-dihydroxycholecalciferol (calcitriol) levels and (2) intestinal Ca absorption. In contrast, P depletion causes a much smaller increase in the renal 25-hydroxycholecalciferol-1-hydroxylase enzyme activity than does Ca depletion. To test the hypothesis that a reduced metabolic clearance rate (MCR) during P depletion might, in part, account for the observed increase in calcitriol levels, we have developed a simple primed-infusion technique to determine the MCR and production rate (PR) of calcitriol, in vivo, in pigs fed low Ca and low P diets. The MCR of calcitriol was unchanged (0·92 ml/min per kg metabolic body size (MBS)) when low P diets were fed, but showed a significant 15% increase (1·06 ml/min per kg MBS) during the feeding of low Ca diets. The PR of calcitriol increased by 2·3-fold when low P diets were fed and by fourfold during Ca depletion. Thus the increase in plasma calcitriol levels during P depletion of pigs is caused by an increase in production rather than a decrease in clearance. In contrast, Ca depletion is associated with a slightly higher PR than indicated by measurement of plasma calcitriol levels because of the increased MCR.

J. Endocr. (1985) 105, 169–173
Pituitary and gonadal response to exogenous LH-releasing hormone in the male domestic cat
Authors: Goodrowe K. L. , Chakrabortyt P. K. , Wildt D. E.
Published: December 2008

To determine the influence of exogenous LH-releasing hormone (LHRH) on serum LH and testosterone, ten adult male domestic cats received three treatments on a rotating schedule at 10-day intervals as follows: (I) 0·1 ml saline i.m. (control); (II) 10 μg LHRH i.m., single injection; (III) 10 μg LHRH i.m., two injections given at a 2-h interval. Serial blood samples collected over a 360-min interval were analysed by radioimmunoassay for LH and testosterone. Although baseline serum LH values in saline-treated animals (treatment I) varied markedly among individual cats (2·2–29·2 μg/l), there was no evidence of pulsatile LH release or alterations in testosterone over time within individual males. In treatment II, the single injection of LHRH induced a rapid rise in mean serum LH within 30 min in all cats (mean peak, 88·2 ±9·8 μg/l), which returned to baseline by 120 min after LHRH. Mean testosterone increased within 30 min in this group (from 6·03 ±2·18 to 18·55 ±3·36 nmol/l), peaked at the 60-min collection (19·76 ± 2·77 nmol/l) and returned to baseline by the 150-min sample. After treatment III, serum LH peaked at 131·6±13·6μg/l within 30 min of the initial LHRH injection. A second injection of LHRH produced another LH surge within 30 min, but in all cats this second response was of a lower magnitude (mean peak, 69·0±14·5μg/l) and shorter duration (P<0·05). The second LHRH injection sustained peripheral testosterone levels for approximately 1 additional h. The increase in testosterone response was negatively correlated with pretreatment serum testosterone concentrations in both treatment groups (treatment II, r = −0·46; treatment III, r = −0·72). These results which provide an endocrinological data base for the male domestic cat: (1) demonstrate the acute sensitivity of the male pituitary-gonadal axis to a single injection of LHRH; (2) indicate that an additional LHRH challenge within 2 h results in a more attenuated LH surge, suggesting pituitary refractoriness to repeated LHRH administration; (3) suggest that gonadal sensitivity to LHRH administration is influenced by circulating testosterone.

J. Endocr. (1985) 105, 175–181
Effect of inhibition of prostaglandin synthesis on cervical softening and uterine activity during ovine parturition resulting from progesterone withdrawal induced by epostane
Authors: Ledger W. L. , Webster M. A. , Anderson A. B. M. , Turnbull A. C.
Published: December 2008

The effects of an inhibitor of 3β-hydroxysteroid dehydrogenase (epostane) on uterine activity and cervical softening have been studied in eight sheep during late pregnancy. Treatment with epostane led to a rapid decline in the concentration of progesterone measured in utero-ovarian venous plasma, to less than 10% of the pretreatment value within 30 min of bolus injection. This was followed by a significant (P<0·02) increase in the concentrations of metabolites of prostaglandins E and F in utero-ovarian venous plasma and uterine activity similar to that seen in the final stages of normal labour. Measurements of cervical tissue extensibility made ex vivo showed the cervix to have softened considerably. These changes occurred without any significant change in the concentration of oestradiol-17β in utero-ovarian venous plasma. Infusion of mefenamic acid, an inhibitor of prostaglandin synthesis, prevented the changes in uterine activity and cervical softening that occurred after injection of epostane alone. Mefenamic acid also reduced the increase in concentrations of metabolites of prostaglandins E and F in plasma, although the concentration of progesterone in these animals showed the same abrupt fall which occurred in sheep after injection of epostane alone. These results suggest that progesterone withdrawal, in the absence of any subsequent rise in circulating oestrogen concentrations, is sufficient stimulus to induce cervical softening in the ewe. Cervical softening following progesterone withdrawal can be prevented by inhibition of prostaglandin synthesis.

J. Endocr. (1985) 105, 227–233