bluuebunny/crossref_metadata_2025 huggingface dataset:
Neonatal exposure to a progestin via milk alters subsequent LH cyclicity in the female rat
Authors: Holzhausen C. , Murphy S. , Birke L. I. A.
Published: December 2008

Medroxyprogesterone acetate (MPA; 5 μg/g body wt) or norethisterone oenanthate (NET-OEN; 4 μg/g body wt) was given to lactating female rats by subcutaneous injection 1 day after parturition. Each female suckled ten female pups which had been randomly allocated to her and at 21 days of age the pups were weaned. In this way female pups were exposed to either MPA or NET-OEN via milk during suckling. The patterns of LH and progesterone secretion at pro-oestrus were investigated using radioimmunoassay. When these pups reached adulthood it was found that neonatal exposure to MPA via milk significantly reduced the pro-oestrous LH peak by 45% as well as the total amount (by 27%) of LH secreted during pro-oestrus. Neonatal exposure via milk to NET-OEN had no effect on LH secretion during pro-oestrus. Pro-oestrous progesterone secretion was unaffected by either MPA or NET-OEN treatment.

J. Endocr. (1984) 100, 149–154
Studies on the control of gonadotrophin release in the gonadectomized male rat: evidence for a lack of involvement of the hypothalamic noradrenergic system in the long-term castrated rat
Authors: Herdon H. J. , Everard D. M. , Wilson C. A.
Published: December 2008

The effects of castration with or without testosterone replacement in the adult male rat were studied to investigate possible hypothalamic mechanisms by which changes in gonadotrophin secretion occur at different times after castration, with particular reference to the continuing LH rise and its lack of suppression by testosterone in the long-term castrated rat. Castrated rats received either subcutaneous silicone elastomer implants containing testosterone or empty implants at the time of castration, and a sham-operated group served as controls.

At 1, 10 and 40 days after castration, there were six-, 15- and 25-fold rises respectively in LH and 1·5-, two-and fivefold rises in FSH. However, there were no significant changes in hypothalamic noradrenaline concentration and turnover or in α-adrenoceptor density and affinity at any time after castration. Testosterone implants were effective in suppressing gonadotrophin release at 1 and 10 days, but not at 40 days after castration, and did not significantly affect hypothalamic noradrenaline turnover or α-adrenoceptors at any time.

Neither acute inhibition of the noradrenergic system, using either the α-adrenoceptor blockers phenoxybenzamine and phentolamine or the synthesis inhibitor α-methyl-p-tyrosine, nor chronic depletion of hypothalamic noradrenaline by 6-hydroxydopamine had any significant effect on the normal rise in LH levels seen on days 10 and 40 after castration, and did not alter the ability of testosterone to suppress LH levels. This indicates that, in the long-term castrated rat, the noradrenergic system may not be involved in the control of gonadotrophin release. However, at 16 h after castration, α-adrenoceptor blockers and α-methyl-p-tyrosine did reduce LH levels, indicating that the noradrenergic system is likely to be involved in the short-term response to castration.

J. Endocr. (1984) 100, 235–244
Sex differences in behavioural androgen sensitivity: possible role of androgen metabolism
Authors: Mode A. , Gustafsson J.-Å. , Södersten P. , Eneroth P.
Published: December 2008

Masculine sexual behaviour was induced in castrated sexually inactive but experienced male rats by testosterone-filled constant-release implants or daily injections of the synthetic androgen 17β-hydroxy-17α-methyl-estra-4,9,11-triene-3-one (methyltrienolone, R 1881), which resists metabolism by target organs. Feminization of the hepatic androgen metabolism by subcutaneous implantation of osmotic minipumps, which delivered a constant amount of human GH, did not affect the behavioural response of castrated rats to testosterone. Testosterone implants were only minimally effective in inducing male behaviour in ovariectomized female rats, but R 1881 was as effective in stimulating male behaviour in females as in males. Testosterone-treated but not R 1881-treated females showed pronounced female sexual behaviour in response to progesterone treatment despite the absence of measureable amounts of oestradiol-17β in peripheral blood. The results provide evidence that masculine sexual behaviour can be activated by an androgen in the absence of oestrogenic stimulation and suggest that the sex difference in the behavioural response to testosterone may be due to a sex difference in the metabolism of androgens by the brain.

J. Endocr. (1984) 100, 245–248
Inhibitory effect of androgen on the synthesis of proteinase F in the male mouse submandibular gland
Authors: Hosoi K. , Tanaka I. , Murai T. , Ueha T.
Published: December 2008

Androgenic regulation of one of the esteroproteinases (proteinase F) in the mouse submandibular gland was studied using specific antiserum. In contrast to esteroproteinases such as proteinases A, D or P-esterase, proteinase F content in male but not in female mice was increased by gonadectomy and decreased by the injection of various androgens. In-vivo incorporation of [3H]leucine into proteinase F in males was increased after castration and decreased by the injection of testosterone propionate; androgens inhibited the denovo synthesis of proteinase F in male mice. The dose–response curves for testosterone propionate and time-courses following castration or after the injection of testosterone propionate were reciprocal between proteinase F and total esteroproteinase activity. Proteinase F, like other esteroproteinases in the submandibular gland of the mouse, was localized in granular convoluted tubular cells. These data indicate that granular convoluted tubular cells of the male mouse submandibular gland synthesize both androgen-inducible proteinases and androgen-inhibitory proteinase (proteinase F).

J. Endocr. (1984) 100, 253–262
Effect of stress on tissue and plasma levels of immunoreactive β-endorphin in ovariectomized rats primed with oestrogen and progesterone
Authors: Hulse G. K. , Coleman G. J.
Published: December 2008

The aim of this study was to investigate the effect of oestrogen and progesterone on levels of immunoreactive β-endorphin (Ir-β-EP) in the hypothalamus, anterior pituitary gland, neurointermediate lobe and plasma under normal conditions and conditions of stress. The injection of oestrogen + progesterone into ovariectomized rats increased Ir-β-EP levels in extracts of anterior pituitary tissue and in plasma, under both normal and stressed conditions. Exposure to a stress reduced the content of anterior pituitary Ir-β-EP in ovariectomized rats treated with oestrogen + progesterone and also with sesame oil. Such treatment only resulted in increments in plasma Ir-β-EP in oil-treated but not in oestrogen + progesterone-treated overiectomized rats. It was concluded (1) that oestrogen and progesterone are involved in the regulation of resting levels of anterior pituitary Ir-β-EP during the rat oestrous cycle, (2) that stress reduces levels of anterior pituitary Ir-β-EP and (3) that increased levels of plasma oestrogen + progesterone inhibit plasma Ir-β-EP increments which normally accompany exposure to stress.

J. Endocr. (1984) 100, 277–280
Simultaneous production of monoclonal antibodies to dehydroepiandrosterone, oestradiol, progesterone and testosterone
Authors: Fantl V. E. , Wang D. Y.
Published: December 2008

Mice were immunized with a mixture of four steroid antigens: dehydroepiandrosterone (DHA), oestradiol, progesterone and testosterone linked to bovine serum albumin through the 7, 6, 11α and 17β positions respectively. The response to immunization varied widely with no one mouse producing an optimal response to all four steroids. In the two fusion experiments performed, antibodies to all four antigens were developed. Data are presented which show that the immune response of the spleen donor is related to the relative numbers and quality of the antibodies produced to each steroid. Despite the structural identity of the progesterone and testosterone haptens, antibodies elicited in response to their respective antigens could readily be distinguished from each other.

From the large number of monoclonal antibodies obtained those most useful for radioimmunoassay were three high affinity antibodies to oestradiol and two antibodies raised against DHA but with high affinity for DHA sulphate.

J. Endocr. (1984) 100, 367–376
Induction of germinal vesicle breakdown in Xenopus laevis oocytes: synergistic action of progesterone and insulin
Authors: Le Goascogne C. , Hirai S. , Baulieu E.-E.
Published: December 2008

Progesterone is the hormone that reinitiates the meiotic division of amphibian oocytes and insulin and insulin-like growth factors are also active on defolliculated oocytes in vitro. We have studied Xenopus laevis oocytes (stage 5–6) of different hormonal sensitivities, obtained from unstimulated and from human chorionic gonadotrophin-stimulated females. Some oocytes from unstimulated females were also precultured with a subthreshold level of progesterone. A dose-dependent potentiating effect of the action of progesterone was observed with insulin, and this was particularly remarkable in low-sensitivity oocytes. Since in the presence of insulin, the optimally effective concentration of progesterone was much reduced (as an example from 1 μmol/l to 50 nmol/l), it is suggested that an insulin-like growth factor may play a physiological role in the reinitiation of meiosis in ovaries.

J. Endocr. (1984) 101, 7–12
Involvement of prolactin in the onset of puberty in female rats
Authors: Gonzalez M. D. , López F. , Aguilar E.
Published: December 2008

Pimozide (1 mg/kg per day), bromocriptine (1 mg/kg per day) or domperidone (0·1 mg/kg per day) administered daily to rats from day 21 did not change the age at which vaginal opening occurred, nor did they affect the body weight at that age. Therefore the evolution of prolactin levels was different in these three groups. The pimozide-treated group showed high prolactin levels measured on day 23, at vaginal opening and at first oestrus. In the bromocriptine-treated group, levels were undetectable on the day of vaginal opening. Chronic treatment with domperidone failed to increase prolactin levels on day 23 and at vaginal opening. Nevertheless, large increases were observed after a single injection of domperidone at both 21 and 30 days of age.

A significant increase in LH observed on day 23 in the pimozide-treated group was the only effect on gonadotrophin levels which was detected. Ovarian weights were unaffected by the treatments, whereas adrenal weight was increased in the bromocriptine-treated group and decreased in the pimozide- and domperidone-treated groups.

Female rats grafted on day 21 with one additional pituitary gland from adult (90 days) or young (21 days) donors showed a similar advancement in the time of vaginal opening, although the animals bearing an adult pituitary gland showed higher prolactin levels than those observed in animals grafted with young pituitary glands.

This study suggested that the onset of puberty is not closely linked with the evolution of prolactin levels and that the hormone itself is not indispensible for the process.

J. Endocr. (1984) 101, 63–68
Effect of changes in litter size at mid-lactation on lactation in rats
Authors: Grigor M. R. , Sneyd M. J. , Geursen A. , Gain K. R.
Published: December 2008

The effect of altering the number of pups per litter from ten to two or two to ten at day 14 of lactation in rats was investigated. Reducing litter size had no effect on the daily live weight gain whereas increasing the litter size resulted in an initial weight loss followed by an impaired weight gain. Maternal food consumption decreased to values appropriate for rats feeding two pups within 2 days after litter reduction, but required at least 5 days after the increase in litter size to increase to values appropriate for rats feeding large litters from parturition. Altering the litter size resulted in maternal serum insulin concentrations that were intermediate between those expected for rats feeding two or ten pups from parturition. Maternal serum prolactin concentrations increased after litter sizes were increased and decreased initially after litter reduction before being restored to normal levels. The activities of the lipogenic enzymes, fatty acid synthase, glucose-6-phosphate dehydrogenase and 'malic' enzyme in the mammary gland all decreased within 72 h of litter reduction to levels appropriate for rats feeding two pups. Although all three enzymes increased in activity after litter size increase, only fatty acid synthase had reached values appropriate for rats feeding ten pups by 72 h.

J. Endocr. (1984) 101, 69–73
Effects of continuous administration of oxytocin by an Accurel device on parturition in the rat and on development and diuresis in the offspring
Authors: Boer G. J. , Kruisbrink J.
Published: December 2008

A controlled-delivery module based on microporous Accurel polypropylene tubing, implanted subcutaneously in the rat, was used to release oxytocin for at least 40 days both in vitro and in vivo. Using a dosage rate of approximately 650 ng oxytocin per day and implanting the device in rats on day 17 of pregnancy, the known physiological action of oxytocin in advancing labour was confirmed. The increased concentrations of oxytocin in the mothers gave rise to adverse effects; the course of labour was protracted during expulsions of the first pups and the birth weight was reduced. Postnatally, body development of the pups was also affected, although there was partial recovery when the pups started to feed independently. Both pre- and postnatal exposure of pups to an oxytocin-treated mother reduced their body water turnover measured at 1 month of age.

The effects on the course of parturition and during lactation might be explained by a blockade of uterine and mammary gland oxytocin receptors respectively, thereby inhibiting a proper response to pulsatile endogenous oxytocin secretion. The changes in water metabolism, which are opposite to those described for the heterologous hormone vasopressin, are less easy to explain since maternal oxytocin is not supposed to pass the placenta. The results may indicate that clinical use of oxytocin for induction of labour and lactation may have hitherto unrecognized side-effects.

J. Endocr. (1984) 101, 121–129
Relationship between glucose and 20α-hydroxysteroid dehydrogenase in fetal sheep erythrocytes
Authors: Nancarrow C. D. , Connell P. J. , Stevens D.
Published: December 2008

We have examined whether glucose supply to fetal sheep erythrocytes limits the rate of 20α-reduction of progesterone in blood and as such is associated with the progressive loss of 20α-hydroxysteroid dehydrogenase activity which has been observed from 30 days before term.

Enzyme activity in erythrocytes depleted of glucose by washing was regained in the presence of at least 0·167 mmol glucose/l. The cofactor NADPH was necessary to support the reaction in lysed cells. Addition of glucose to whole blood diluted 20-fold for assay of 20α-hydroxysteroid dehydrogenase did not increase the rate of reaction. Infusion of dextrose to increase fetal plasma glucose concentrations had no effect on 20α-hydroxysteroid dehydrogenase activity. Over the period from 114 to 137 days of gestation, both dextrose- and saline-infused fetuses showed a decline in enzyme activity from a combined mean of 1·45 ± 0·21 (s.e.m.) to a mean of 0·78 ± 0·18 μmol/ml erythrocytes per h. Fetal leucocytes did not contribute significantly to the activity of 20α-hydroxysteroid dehydrogenase in whole blood.

The rate of 20α-reduction of progesterone in the blood of eight fetuses with indwelling carotid catheters declined from 2·31 ± 0·09 μmol/ml erythrocytes per h at 90–95 days of gestation to 0·73 ± 0·04 μmol/ml per h at 141–145 days. However, a consistent decline was only observed after 116–120 days. The apparent equilibrium position for progesterone reduction to 20α-dihydroprogesterone varied between 83·9 ± 1·8 and 65·7 ± 4·2%.

Thus, it appears that the decline in 20α-hydroxysteroid dehydrogenase activity which occurs in whole blood of sheep fetuses during the last 30 days of gestation is due to dilution of the fetal erythrocytes with adult-type erythrocytes rather than development of limiting concentrations of plasma glucose.

J. Endocr. (1984) 101, 131–139
Decrease of morphine-induced prolactin release by a procedure causing prolonged stress
Authors: Fekete M. I. K. , Kanyicska B. , Szentendrei T. , Simonyi Á. , Stark E.
Published: December 2008

The effects of morphine and fentanyl on plasma prolactin levels in rats have been measured. It was found that a prolonged immobilization stressful procedure for 5 h inhibited the response to morphine and fentanyl to increase prolactin secretion, but did not influence the increase in plasma prolactin caused by haloperidol. The injection of a large dose of cortisol (25 mg/kg, s.c.) also evoked an inhibition of morphine-induced prolactin release. The inhibition was maximal 24 h after the administration of the glucocorticoid. These results indicate that stress may induce prolonged alteration in endogenous opioid-mediated neuro-modulation via a prolonged release of glucocorticoids.

J. Endocr. (1984) 101, 169–172
Inhibitory action of chemically deglycosylated human chorionic gonadotrophin on hormone-induced steroid production by dispersed cells from human corpus luteum
Authors: Richardson M. C. , Masson G. M. , Sairam M. R.
Published: December 2008

The biological activity of deglycosylated human chorionic gonadotrophin (hCG) prepared by treatment of the native hormone with anhydrous hydrogen fluoride was evaluated using suspensions of dispersed cells from biopsies of human corpus luteum obtained during the luteal phase of normal menstrual cycles. A reproducible pattern of response to hCG in terms of progesterone production by luteal cells was established for a range of luteal ages. Deglycosylation of hCG led to a diminished level of maximum response to the hormone. Co-incubation of luteal cells with a level of hCG just sufficient to elicit a maximum response and increasing concentrations of deglycosylated hCG led to a progressive inhibition of the hormonal response; at a concentration of 103 ng deglycosylated hCG/ml (a tenfold excess of deglycosylated hCG over the native hormone), hCG-induced progesterone production was reduced by about 50%. Deglycosylated hCG therefore acts as a partial antagonist for the action of hCG on human luteal cells.

J. Endocr. (1984) 101, 327–332
Plasma LH concentrations in the ewe in response to repeated injections of low doses of gonadotrophin releasing hormone during the follicular phase of the oestrous cycle
Authors: McLeod B. J. , Haresign W.
Published: December 2008

Oestrus was synchronized in 15 naturally cyclic ewes by the administration of a prostaglandin F2α analogue. Groups of five ewes were then treated i.v. with either small doses of gonadotrophin releasing hormone (GnRH; 125 or 250 ng/injection) or saline, at 2-h intervals from day 14 of the subsequent cycle until 24 h after the onset of oestrus.

Treatment with GnRH induced episodic LH release which continued until the onset of a preovulatory LH surge. Mean plasma LH concentrations over this period were significantly (P< 0·001) higher in animals receiving 250 ng GnRH (2·44±0·11 μg/l) than in those receiving either 125 ng GnRH (1·17±0·06 μg/l) or saline (1·14±0·05 μg/l). However, GnRH treatment did not influence the timing of oestrus or mean ovulation rates.

J. Endocr. (1984) 101, 365–370
Interaction between prolactin and zinc in the human prostate gland
Authors: Leake A. , Chisholm G. D. , Habib F. K.
Published: December 2008

The interaction between prolactin and zinc was examined in vitro in the human prostate gland. The results indicated that prolactin did not modulate the acute uptake of zinc into benign prostatic hypertrophy tissue whereas zinc, in contrast, increased the uptake of prolactin into the prostate gland. Our study further showed that the augmented uptake of prolactin by zinc was partly due to an increase in the non-specific binding properties of the peptide hormone. We were also able to demonstrate that the specific binding of 125I-labelled human prolactin to the receptor was reduced in the presence of zinc by a competitive mechanism.

J. Endocr. (1984) 102, 73–76
Effects of exposure to pups on maternal behaviour, sexual behaviour and serum prolactin concentrations in male rats
Authors: Södersten P. , Eneroth P.
Published: December 2008

Male rats showed maternal behaviour within 72 h after the onset of continuous exposure to newborn rat pups. The latency of the behavioural response could be reduced by daily treatment with the dopamine receptor antagonist domperidone (2 × 2·5 mg/rat), which increased serum prolactin concentrations (241·4 ± 26·5 (s.e.m.) μg/l) above those of vehicle-treated males exposed to pups (25·3 ± 11·7 μg/l). Male rats did not respond to exposure to pups by secreting prolactin; keeping endogenous prolactin concentrations at a minimum (2·8±0·1 μg/l) by daily treatment with the dopamine receptor agonist bromocriptine (0·5 mg/rat) did not affect the behavioural response of male rats to newborn pups. Neither exposure to pups nor the modest hyperprolactinaemia induced by daily domperidone treatment affected the display of male sexual behaviour by male rats.

J. Endocr. (1984) 102, 115–119
Suckling and serum prolactin and LH concentrations in lactating rats
Authors: Södersten P. , Eneroth P.
Published: December 2008

The frequency of pup sucking behaviour was related to serum concentrations of prolactin and LH in rats during various phases of lactation. Sucking frequency and prolactin levels decreased and LH levels increased as lactation progressed. There was no clear relationship between sucking frequency and either prolactin or LH levels. Serum prolactin concentrations were highest when the rats spent most of their time away from their pups and lowest when the rats spent most of their time with the pups attached to their nipples. Prolactin was secreted episodically during prolonged continuous nipple stimulation. Removal of the pups in late lactation and replacement with a newborn litter increased sucking frequency but did not affect serum LH levels and only marginally increased serum prolactin levels. Injection of the dopamine receptor antagonist domperidone produced a far more pronounced release of prolactin from the pituitary gland in early than in late lactation. A circadian control mechanism and an episodic pattern of release may contribute to the great variation in serum prolactin concentrations seen in early lactation; decreased pituitary sensitivity to dopamine receptor blockade may be related to the low concentration of serum prolactin found in late lactation.

J. Endocr. (1984) 102, 251–256
Adrenal changes in genetically hypothyroid mice
Authors: Shire J. G. M. , Beamer W. G.
Published: December 2008

The adrenocortical X-zone was very poorly developed in young female mice homozygous for the hypothyroid, hyt, mutation, Feeding the mice thyroid powder resulted in the development of an X-zone. This subsequently degenerated in the same way as the X-zone found in the normal litter-mates of the mutants. We suggest that the adrenocortical effects may be due to changes in prolactin stimulation consequent upon the lack of response to thyrotrophin of the mutants.

J. Endocr. (1984) 102, 277–280
Oestradiol and somatomedin-C influence body weight patterns in premenarchial rhesus monkeys housed outdoors
Authors: Wilson M. E. , Schwartz S. M. , Walker M. L. , Gordon T. P.
Published: December 2008

The influence of gonadal status on the pattern of changes in body weight was examined in three groups of outdoor-housed premenarchial rhesus monkeys (Macaca mulatta) from 1 to 2 years of age. Gonadally intact (n=8) and ovariectomized oestradiol-treated females (n=5) gained significantly more weight than ovariectomized untreated females (n=5). The overall larger weight gains for the intact and ovariectomized oestradiol-treated groups were associated with significantly higher fasting levels of serum insulin. All subjects exhibited two periods of significant weight gain from 12 to 16 months of age between May and September and from 21 to 24 months of age between February and May. Serum GH and somatomedin-C levels were also raised during these periods of accelerated growth. Although the pattern of serum GH was similar among groups, serum somatomedin-C levels were significantly higher in both intact and ovariectomized oestradiol-treated subjects from 21 to 24 months of age, suggesting physiological levels of oestradiol may facilitate somatomedin-C production during periods of increased GH secretion. Thus, absolute changes in body weight in outdoor-housed premenarchial rhesus monkeys are influenced by gonadal status, possibly mediated through increases in serum insulin. Furthermore, dynamic changes in body weight occur during prepubertal development, with the largest increments associated with increased somatomedin-C levels at specific ages synchronized with natural changes in the environment.

J. Endocr. (1984) 102, 311–317
Increase in Leydig cell responsiveness in the unilaterally cryptorchid rat testis and its relationship to the intratesticular levels of testosterone
Authors: Sharpe R. M. , Cooper I. , Doogan D. G.
Published: December 2008

Adult rats were made unilaterally cryptorchid (UCD) and 6–7 weeks later Leydig cells were isolated from the scrotal and abdominal testes and their capacity to secrete testosterone in vitro was compared. Basal testosterone production by Leydig cells from the abdominal testes of UCD rats was lowered, compared with cells from the contralateral scrotal testes, whilst their responsiveness to both human chorionic gonadotrophin and an LH releasing hormone agonist was enhanced two- to threefold (P< 0·001) compared both with cells from the contralateral scrotal testes and with cells isolated from untreated rats of the same age. In the UCD rats, concentrations of testosterone in testicular interstitial fluid (IF) were reduced (P< 0·001) by 70–90% in abdominal, compared with scrotal, testes. A similar reduction was evident in the levels of testosterone in spermatic venous blood, and both this decrease and that in IF levels of testosterone varied according to the degree of testicular involution.

The ontogeny of the above changes was investigated. After induction of unilateral cryptorchidism, the weight of the abdominal compared with the scrotal testis declined slowly, such that by day 5 there was only a 25% reduction in weight compared with a 70% reduction by day 40. In contrast, the levels of testosterone in IF from abdominal testes declined rapidly, such that by day 5 an 80% reduction was attained, compared with scrotal testes, with little further change by day 40. Hormone-stimulated testosterone production by Leydig cells isolated from the abdominal testes was unchanged or marginally reduced over the first 3 days compared with cells from the scrotal testes, but by day 5 there was a significant increase in responsiveness; this increase was of smaller magnitude than that evident at day 40. These results suggest a possible association between the fall in intratesticular levels of testosterone induced by unilateral cryptorchidism and the Leydig cell hypertrophy and hyper-responsiveness that occurs in the same testes. The implications with respect to altered Sertoli–Leydig cell interaction are discussed.

J. Endocr. (1984) 102, 319–327
Oxytocin secretion during milking in dairy cows with regard to the variation and importance of a threshold level for milk removal
Authors: Schams D. , Mayer H. , Prokopp A. , Worstorff H.
Published: December 2008

Oxytocin secretion in dairy cows was measured during milking by means of a specific radioimmunoassay. Basal oxytocin concentrations before milking recorded from 147 milkings from 21 cows, where an assay method with enhanced sensitivity was employed, were 1·5 ± 0·6 pmol/l and there was no evidence for any conditioned release of oxytocin. A 1-min manual stimulation before milking evoked a variable but distinct increase in oxytocin concentrations in 188 out of 195 milkings performed using 29 cows. Despite the high variation in absolute concentrations five types of typical secretion pattern could be distinguished. There was no obvious relationship between patterns or absolute concentrations of oxytocin and milk-flow characteristics. Evidence is given that milk ejection seems to follow the threshold principle in that small releases of oxytocin up to a range of 3–5 pmol/l plasma are sufficient to evoke maximum milk ejection.

J. Endocr. (1984) 102, 337–343
Changes in plasma prolactin in male starlings during testicular regression under short days compared with those during photorefractoriness
Authors: Goldsmith A. R. , Nicholls T. J.
Published: December 2008

Male starlings which had fully developed testes under 11-h daily photoperiods were subjected for 10 weeks to daylengths either increasing or decreasing by 30 min per week. In both cases testicular regression occurred; in the former case this was complete due to photorefractoriness, and was accompanied by a postnuptial moult and a marked (P <0·01) rise in plasma prolactin concentration. In the latter case the rate of gonadal regression was slow and variable and no moulting was observed. Plasma prolactin remained very low. Eventually the birds which had experienced decreasing photoperiods were transferred to long (16 h) days; they were shown to be photosensitive since their testes redeveloped rapidly. There was also a rise in plasma prolactin, the birds eventually showed the full testicular regression characteristic of photorefractoriness, and moulting occurred. These results show that raised prolactin secretion is not associated with short-day-induced testicular regression but only with long-day-induced photorefractoriness.

J. Endocr. (1984) 102, 353–356
Seasonal testosterone profile and testicular responsiveness to pituitary factors and gonadotrophin releasing hormone during two different phases of the sexual cycle of the frog (Rana esculenta)
Authors: Pierantoni R. , Iela L. , d'Istria M. , Fasano S. , Rastogi R. K. , Delrio G.
Published: December 2008

Plasma and testicular testosterone concentrations in the frog, Rana esculenta, were studied by radioimmunoassay and showed similar seasonal fluctuations. The increase in testicular androgen during November preceded that occurring in the plasma by 2 months. Pituitary products and gonadotrophin releasing hormone, and the responsiveness of the testis to these substances play an important role in determining the hormone profile.

J. Endocr. (1984) 102, 387–392
Early effects of pinealectomy on LH and testosterone secretion in white-tailed deer
Authors: Plotka E. D. , Seal U. S. , Letellier M. A. , Verme L. J. , Ozoga J. J.
Published: December 2008

The early effects of pinealectomy on LH and testosterone secretion were studied in 11 white-tailed bucks. Six bucks were pinealectomized and three were sham-operated in early March at 9 months of age. Two unoperated bucks of the same age were also followed. The response of the pituitary gland and testis to LH releasing hormone (LHRH) was monitored for 2 h each month for 1 year by radioimmunoassay of serum LH and testosterone. Prestimulation levels of LH (expressed as μg NIH-oLH-S7) exhibited a cosinor curve pattern over the year (P < 0·002) with levels ranging between 0·1 and 3·9 μg/l. Highest levels in pinealectomized males occurred in May 2 months after surgery and in control (sham-operated and unoperated) males in August. Maximal LH response to LHRH was characterized by a double-peaked curve in serum LH with the early peak around 20 min and a later peak at about 2 h after injection. Maximal response to LHRH occurred in May in pinealectomized bucks and in August in control bucks. Baseline testosterone concentrations and testosterone response to LHRH varied in a seasonal fashion throughout the 12-month period in control bucks (P < 0·001 ) but not in pinealectomized bucks. Baseline testosterone concentration and testosterone response to LHRH rose within 2 months after surgery in pinealectomized bucks and remained relatively constant for the next 10 months. These data demonstrate an early effect of pinealectomy on LH and testosterone secretion in 9-month-old animals kept under conditions of natural photoperiod and suggest differences in the response to pinealectomy by the pituitary gland and testes. Furthermore, the effect appears to be a release from suppression early after pinealectomy followed by a disruption of the normal sequence of events related to the autumn rut.

J. Endocr. (1984) 103, 1–7
Ovarian–splenic autotransplantation: evidence that oestrogen does not inhibit hepatic somatomedin generation
Authors: Clark R. G. , Holder A. T.
Published: December 2008

This study was designed to test the hypothesis that oestrogens inhibit growth by reducing hepatic somatomedin generation. We have attempted to deliver oestrogen preferentially to the liver by transplanting ovarian tissue into the spleen. Four groups of rats were compared: intact, ovariectomized, ovariectomized with successful ovarian transplants, and animals where due to adhesions between the transplant and body wall and/or viscera oestrogens reached the general circulation. Plasma levels of LH and FSH, uterine weights, ovarian weights and vaginal smears supported this classification of animals. Ovariectomy increased body weight, body length, bioassayable serum somatomedin levels and 35SO42− uptake into costal cartilage in vivo compared with intact rats and animals with adhesions. Preferentially exposing the liver to oestrogen did not suppress the increased growth, serum somatomedin activity or uptake of 35SO42− in vivo observed in ovariectomized animals. The results suggest that the presence of oestrogen in the general circulation is associated with growth suppression and lowered somatomedin bioactivity while the presence of oestrogen in the hepatic portal circulation has little effect on body growth. We conclude that oestrogen does not appear to inhibit growth in the rat by influencing the release of somatomedin from the liver. It also seems that serum somatomedin concentration may not reflect liver somatomedin generation but overall production throughout the body.

J. Endocr. (1984) 103, 43–47
Adrenal/parathyroid regulation of DNA, collagen and protein synthesis in rat epiphysial cartilage and bone
Authors: Russell J. E. , Walker W. V. , Simmons D. J.
Published: December 2008

Young, growing rats which had been chronically (2 weeks) adrenalectomized or parathyroidectomized were used to define the roles of the adrenal and parathyroid glands on the maintenance of normal circadian rhythms of DNA, collagen and non-collagen protein synthesis in the skeleton. The animals were conditioned to food being available ad libitum and to 12 h light: 12 h darkness (lights on from 08.00 to 20.00 h). The pace of DNA, collagen and non-collagen protein synthesis in different regions of the tibia (tibial growth cartilage, metaphysial bone and diaphysial bone) was measured by the in-vivo incorporation of tritiated thymidine (1 h) and radioactive proline (48 h). In intact rats there were no regional differences in the phasing of the circadian profiles; peak DNA and non-collagen protein synthesis occurred at the onset of the dark period while peak collagen synthesis occurred during the middle of the period of light. Adrenalectomy selectively abolished the regional DNA synthesis rhythms without altering the phases of the serum Ca and phosphorus (P) rhythms, which peak at mid-day and at the onset of darkness respectively. Parathyroidectomy abolished the regional rhythms for collagen and non-collagen protein synthesis and serum Ca rhythms, without altering the phase of the serum P and corticosterone rhythms. Dietary Ca-lactate supplements, which raised serum Ca levels towards normal in parathyroidectomized rats, were able to correct serum corticosterone values but did not normalize bone collagen and non-collagen protein synthesis values. These data indicate that the adrenal rhythm governs the proliferative activities of bone and cartilage cells, and that parathyroid hormone is essential to maintain normal collagen and non-collagen protein synthesis rhythms.

J. Endocr. (1984) 103, 49–57
Inhibin-like activity in media from cultured rat granulosa cells collected throughout the oestrous cycle
Authors: Sander H. J. , van Leeuwen E. C. M. , de Jong F. H.
Published: December 2008

Granulosa cells of antral ovarian follicles from adult 5-day cyclic rats were cultured on each day of the cycle. The rat granulosa cell conditioned medium (rGCCM) was harvested and renewed on each day of a 4-day culture period. Inhibin-like activity and progesterone were estimated in rGCCM using an in-vitro bioassay system with dispersed rat anterior pituitary cells and radioimmunoassay respectively. Removal of steroids from rGCCM with dextran-coated charcoal was effective and did not significantly change the inhibin-like activity of the treated samples.

On day 1 of culture the inhibin-like activity of rGCCM for each day of the oestrous cycle was 20–90% higher than on days 2, 3 and 4 of culture when low and constant levels were observed. Media collected after culture on days 1 and 2 from pro-oestrous cells contained larger amounts of inhibin-like activity than media collected on the other days of the cycle.

On day 1 of culture, rGCCM from pro-oestrous cells contained higher concentrations of progesterone than that from cells collected on the other days of the cycle. On days 2, 3 and 4 progesterone levels in rGCCM were undetectable (< 320 pmol/l) except in media from pro-oestrous cultures on day 2. Addition of FSH (62 μg/l) to granulosa cell cultures in medium with or without 10% fetal calf serum (FCS) did not alter the inhibin-like activity of rGCCM from pro-oestrous cells. The presence of FCS maintained the production of inhibin-like activity since rGCCM from cells cultured without FCS was devoid of FSH-suppressing activity after 3 days of culture.

It is concluded that material with inhibin-like activity is secreted at a higher rate by granulosa cells collected on the day of pro-oestrus than on any other day of the cycle. However, on the day of pro-oestrus, transport of inhibin-like activity from the follicle to the circulation is apparently impeded since this increased inhibin production is not reflected in a reduction in plasma FSH concentration.

J. Endocr. (1984) 103, 77–84
Effect of ageing on cyclic AMP output by renal medullary cells in response to arginine vasopressin in vitro in C57BL/Icrfat mice
Authors: Goddard C. , Davidson Y. S. , Moser B. B. , Davies I. , Faragher E. B.
Published: December 2008

The effect of age on the cyclic AMP (cAMP) response to increases in the concentration of arginine vasopressin in the presence of isobutyl methylxanthine (100 μmol/l) was studied in an in-vitro renal cell suspension prepared from C57BL/Icrfat mice at 6, 12, 18, 24, 29 and 35 months of age. Comparison of the response of the preparation to vasopressin, calcitonin and parathyroid hormone suggested that it was enriched with renal medullary cells. Basal cAMP output was similar throughout but the threshold dose of vasopressin increased from 1 × 10−11 mol/l (6, 12 and 18 months of age) to 1 × 10−10 mol/l (24, 29 and 35 months of age). The dose–response curve in 35-month-old mice was shifted to the right with the concentration of vasopressin required to give half maximal cAMP increased from 9·4 ± 0·37 × 10−11 mol/l (6 months) to 3·5±1·6 × 10−10 mol/l (35 months). Maximum cAMP output at 1 × 10 −9 mol/l was also reduced in the same animals (stimulated:basal ratio, 51·22±19·12 at 6 months; 11·50 ± 6·02 at 35 months). The results suggest that the lack of renal response to vasopressin in terms of cAMP metabolism may play a role in the well-documented age-related decline in urine-concentrating ability in experimental animals and elderly people.

J. Endocr. (1984) 103, 133–139
Effect of intravenous administration of growth hormone-releasing factor (hpGRF-44) and Tyr-d-Trp-Ala-Trp-d-Phe-NH2 on plasma hormones and metabolites in goats
Authors: Hart I. C. , James S. , Perry B. N. , Simmonds A. D.
Published: December 2008

It has recently been demonstrated that human pancreatic GH-releasing factor (hpGRF-44) and Tyr-d-Trp-Ala-Trp-d-Phe-NH2 (subsequently referred to as 'the peptide') release GH from rat pituitary glands maintained in vitro and, in the former case, increase circulating GH in rats and man. The commercial importance of discovering an agent capable of specifically enhancing GH secretion in ruminants stimulated the present study which examined: (1) the intravenous administration of both peptides on plasma GH, prolactin, insulin, glucose, urea and non-esterified fatty acids in goats and (2) the effect of the peptide on the release of GH from sheep pituitary glands maintained in vitro.

The peptide was injected into the jugular vein of goats in three different forms and at several concentrations (dispersal by shaking, 0·07 μg/kg; 0·7 μg/kg; ball-milled, 7·0 μg/kg, 70 μg/kg; dimethyl sulphoxide (5%), 7·0 μg/kg, 70 μg/kg). None of the treatments stimulated a significant increase in circulating GH. Nevertheless the peptide (20 μg/ml medium) was found to stimulate a 50–60% increase in the production of GH from sheep pituitary glands maintained in vitro.

The effect of intravenously injecting hpGRF-44 (1·0 pg/kg) was investigated in the present and absence of passive immunization with sheep anti-somatostatin immunoglobulin G (IgG) (a bolus of 600 mg, 3 h before treatment with hpGRF-44). Plasma GH was increased (P<0·001) within 15 min of treatment and the magnitude of the response was the same for both the immunized and non-immunized goats. A second peak was measured after approximately 75 min which was only significant (P < 0·05) in the immunized group. Although circulating insulin tended to increase after treatment with sheep anti-somatostatin IgG, neither passive immunization, nor hpGRF-44 nor the peptide stimulated any change in the plasma concentrations of the other parameters which were measured.

J. Endocr. (1984) 103, 173–178
Corticosterone availability in male rats at rest and during shock avoidance: differences among individuals, temporal patterns and effects of dexamethasone
Authors: Wade S.
Published: December 2008

Repeated measurement of the time-integral of interstitial fluid free corticosterone concentration (corticosterone availability) under home-cage conditions, during exposure to recently unfamilar apparatus, and during active shock avoidance over 3 days, demonstrated extreme stability within individuals, and consistent differences among individuals, in corticosterone availability under home-cage conditions. These consistent differences among individuals were preserved, while mean levels were doubled, during exposure to apparatus and during shock avoidance after treatment with dexamethasone. However, this persistent pattern of differences among individuals was not apparent during shock avoidance in the absence of dexamethasone.

Shock avoidance provoked up to fourfold increases in corticosterone availability. Repeated measurements over 3 days showed consistent hour-to-hour increases within days and a gradual decline over days. Dexamethasone given 4 h before shock avoidance resulted in corticosterone availability intermediate between that in home-cage and that in the previous shock-avoidance session.

The situation-dependent loss of consistent interindividual differences is proposed to signal a qualitative change in regulation of corticosterone availability within individuals, and a tactic for using interindividual differences to study some aspects of complex regulatory systems is suggested.

The hour-to-hour increase in corticosterone availability during shock avoidance may be attributable to slow achievement of full adrenal output; the decline over days may be due to behavioural factors.

J. Endocr. (1984) 103, 187–194
Platelet-derived growth factor and multiplication-stimulating activity II, but not multiplication-stimulating activity III-2, stimulate [3H]thymidine and [35S]sulphate incorporation by fetal rat costal cartilage in vitro
Authors: Hill D. J. , Milner R. D. G.
Published: December 2008

The actions of partially purified porcine platelet-derived growth factor (PDGF) and highly purified multiplication-stimulating activity (MSA) II and MSA III-2, which are somatomedins, were investigated on the incorporation of [3H]thymidine and [35S]sulphate by fetal rat costal cartilage in vitro. This was compared with their effects in the presence of 1% fetal calf serum (FCS) on the uptake of thymidine by growth-arrested fetal rat fibroblasts. Platelet-derived growth factor at concentrations of 0·21–21 μg/l enhanced the incorporation of both isotopes by fetal cartilage in the presence of 1% FCS, but had an inconsistent action on thymidine uptake and no significant action on sulphate uptake in serum-free medium. Platelet-derived growth factor promoted thymidine uptake by growth-arrested, isolated fetal rat fibroblasts. Multiplication-stimulating activity II (10–100 μg/l) stimulated the uptake of thymidine and sulphate by fetal cartilage in medium containing 1% FCS but had no consistent action in serum-free medium, although MSA II and PDGF had a synergistic effect on thymidine uptake in the absence of serum. Multiplication-stimulating activity III-2 had no consistent action on thymidine or sulphate incorporation by fetal cartilage in either serum-free or serum-supplemented medium. However, the same preparation of MSA III-2 stimulated the uptake of [3H]thymidine into fetal rat fibroblasts with a half-maximal response at a concentration of 5–10 μg/l. The results identify PDGF as a possible mitogenic agent for fetal rat connective tissues in vitro and show a differential sensitivity of fetal cartilage to MSA peptides.

J. Endocr. (1984) 103, 195–203
Secretory dynamics of 1α-hydroxycorticosterone in the elasmobranch fish, Scyliorhinus canicula
Authors: Hazon N. , Henderson I. W.
Published: December 2008

Peripheral plasma concentrations, metabolic clearance rates (MCR) and blood production rates (BPR) of 1α-hydroxycorticosterone (1-OH-B) were determined in female dogfish (Scyliorhinus canicula) under varying environmental conditions. The constant-infusion technique, using high specific activity tritiated 1-OH-B, was applied to measure the MCR, and BPR were derived from the product of plasma concentration and MCR at equilibrium. Urea plasma clearances and apparent BPR were assessed in a similar manner. Fish were adapted stepwise to 140, 120, 90, 80, 70, 60 and 50% normal sea water (about 1000 mosmol/l). In all cases 1-OH-B was the major corticosteroid, cortisol and corticosterone were sought but never detected.

In environments of reduced osmolarity, plasma osmolarity, sodium, chloride and urea concentrations all declined, alongside increases in plasma concentrations, MCR and BPR of 1-OH-B. In fish held in environments at concentrations greater than normal sea water, plasma osmolarity, sodium, chloride and urea concentrations all increased. Plasma clearance of urea increased in fish held in environments more dilute than sea water, while it decreased in the more hyperosmotic waters. It is tentatively concluded that homeostasis of plasma composition, with particular respect to urea, is in part regulated by 1-OH-B in the dogfish.

J. Endocr. (1984) 103, 205–211