bluuebunny/crossref_metadata_2025 huggingface dataset:
Plasma progesterone levels in the pregnant and non-pregnant tammar, Macropus eugenii
Authors: Hinds L. A. , Tyndale-Biscoe C. H.
Published: December 2008

The plasma progesterone concentrations were measured in one group of tammars undergoing non-delayed oestrous cycles and pregnancy, and in another group undergoing pregnant and non-pregnant cycles which had been inhibited by lactation and initiated by removal of the pouch young. The basal concentrations of progesterone during lactation and for the first 5 days of the cycle were less than 200 pg/ml. In all animals there was a transient peak of about 450 pg/ml lasting 1–2 days, on days 5–8, and this was followed by a return to the basal concentrations. From day 10 the concentration rose and remained at 500 pg/ml until the day of parturition and/or oestrus when it again returned to the basal concentration. There was no difference in pattern of the early peak associated with pregnancy but the peak concentration in the delayed pregnant cycles was just significantly higher than in the non-pregnant cycles of the same animals. These data do not support the hypothesis for the maternal recognition of early pregnancy in the tammar.
A procedure for the purification of somatotrophs isolated from rat anterior pituitary glands using Percoll density gradients
Authors: Hall Marianne , Howell S. L. , Schulster D. , Wallis M.
Published: December 2008

We have used fractionation on density gradients of Percoll to separate the cell types in the rat anterior pituitary gland and to produce a purified preparation of somatotrophs. The method differs from those described previously which used, for example, albumin or Ficoll gradients, in being more rapid and avoiding low temperatures, and therefore gives cells with improved viability. Anterior pituitary glands from male rats were dispersed with trypsin to produce 1·5 × 106–2·0 × 106 cells/gland. These were fractionated on hyperbolic density gradients of Percoll. Two bands of cells containing somatotrophs were detected, one of which (band A; density 1·075–1·082 g/cm3) contained approximately 90% somatotrophs, whereas the other (band B; density 1·055–1·068 g/cm3) contained about 70% somatotrophs mixed with other cells, especially lactotrophs. Cells in band A appeared more responsive to secretagogues than those in band B; growth hormone secretion was stimulated markedly by cyclic AMP derivatives and prostaglandin E2, and inhibited by somatostatin. Such purified somatotrophs are well suited to biochemical studies on the mechanism of the control of growth hormone secretion.
Effects of gonadal steroid hormones on the hypothalamo-pituitary-liver axis in the control of sex differences in hepatic steroid metabolism in the rat
Authors: Mode Agneta , Norstedt Gunnar
Published: December 2008

The site of action of gonadal hormones in the regulation of hepatic steroid metabolism was investigated by measuring the effects of (i) implantation of oestradiol into the pituitary gland or anterior hypothalamus of males and (ii) subcutaneous injection of a synthetic androgen in deafferentated male and female rats. The hepatic responses measured in vitro were 5α-reduction, and 6β- and 16α-hydroxylation of androstenedione.

After intrapituitary or intrahypothalamic implantation of oestradiol, 5α-reductase activity increased and 6β- and 16α-hydroxylase activity decreased in males relative to the enzyme activities of cholesterol-implanted animals, indicating a feminizing effect of the oestrogen. This effect could not be accomplished by subcutaneous injection of the same oestrogen preparation.

Deafferentation had no effect on hepatic steroid metabolism in females, but caused a feminization in males. In addition, subcutaneous treatment of intact females with the synthetic androgen caused masculinization of hepatic steroid metabolism, but was without effect in deafferentated animals. Treatment with synthetic androgens had no effect on the hepatic steroid metabolism in deafferentated male animals. Subcutaneous injection of a potent synthetic progestagen had little effect on hepatic steroid metabolism in intact females.

It is concluded that oestrogen feminizes hepatic steroid metabolism by an action at the hypothalamic-pituitary level and that an intact hypothalamic-pituitary axis is required for the masculinizing action of the synthetic androgen on hepatic steroid metabolism. It is possible that the site of action of androgens is in the anterior hypothalamus or in adjacent areas of the brain.
Influence of olfactory signals on the reproductive behaviour of social groups of rhesus monkeys (Macaca mulatta)
Authors: Michael R. P. , Zumpe Doris
Published: December 2008

Olfactory influences are important in the control of reproductive function in many mammalian species including primates. Previous studies have shown that a mixture of volatile aliphatic acids (copulins), normally present in the vaginal secretions of rhesus monkeys, can exert a stimulatory effect on the sexual behaviour of males when pairs are tested in small cages. The present study deals with the role of these substances when tested in social groups of rhesus monkeys housed in a large testing arena, the purpose being to assess the effectiveness of olfactory signals under more nearly naturalistic conditions. Each group consisted of one male with four long-term ovariectomized females from which the male could choose. A counter-balanced experimental design was used in which each female of a testosterone-treated pair was given applications to the sexual skin of either copulins or control ether immediately before each 1-h behaviour test. After 16 tests, the procedure was repeated with the previously untreated pair in each group, and nine groups were separately studied. Testosterone was used here simply to enhance female proceptivity. The results showed that females received significantly more ejaculations (P <0·05). mounting attempts (P <0·01) and mounts (P <0·05) when bearing copulins than when bearing control ether. There were positive responses to copulins in 12 of the 36 male–female pairs, involving all males, and positive responses to ether in five of 36 pairs, involving four males. Copulins resulted in a change in the choice of sexual partner in five males, but there were no changes in the choice of partner with ether. Social factors, such as dominance, could override the responses to olfactory signals, and there was a significant treatment order effect, but this was eliminated by the counter-balanced design. These findings indicate a significant role for olfactory communication in mate selection in a socially living higher primate.
Concentrations of epidermal growth factor in mouse milk throughout lactation
Authors: Beardmore J. M. , Richards R. C.
Published: December 2008

A radioimmunoassay was used to measure the concentration of epidermal growth factor (EGF) in mouse milk throughout lactation.

The EGF content of mouse milk increased steadily from birth to a concentration of 427 μg/l at day 8 of lactation. These high levels were maintained until the approach of weaning, when values decreased from day 17 to 130 μg/l at day 22.

Milk samples chromatographed on a Biogel P10 column gave a major peak of immunoreactivity at the point at which pure standard EGF was eluted.

The origin of milk EGF is unknown, but the high concentrations of this peptide identified in mouse milk suggest that it must play a role in the neonate.
Plasma immunoreactive gastric inhibitory polypeptide in obese hyperglycaemic (ob/ob) mice
Authors: Flatt P. R. , Bailey C. J. , Kwasowski P. , Page T. , Marks V.
Published: December 2008

Gastric inhibitory polypeptide (GIP), a recognized component of the enteroinsular axis, is raised in the plasma and intestine of obese hyperglycaemic (ob/ob) mice. To evaluate the control of plasma GIP and its role in the hyperinsulinaemia of the ob/ob syndrome, GIP and insulin were determined at different ages in fed mice, and at 10–12 weeks of age after fasting/refeeding and administration of GIP, different nutrients and insulin to mice fasted for 18 h. Plasma GIP and insulin were raised in adult (10- and 20-week-old) compared with younger (3- and 5-week-old) mice, although GIP was not increased in the presence of hyperinsulinaemia at 3 weeks of age. Fasting suppressed and refeeding promptly restored plasma GIP and insulin concentrations. Administration of GIP to mimic postprandial concentrations evoked a marked but transient insulin response which was protracted in the presence of rising hyperglycaemia. Orally administered fat, glucose and amino acids raised GIP concentrations with fat having a particularly strong effect. Glucose and amino acids also evoked prominent increases of insulin, but fat produced only a small rise in insulin in the absence of increasing glucose concentrations. Consistent with glucose-potentiation, a mixture of all three nutrients greatly augmented the insulin response without further increase of plasma GIP. Glucose-induced increase in endogenous insulin and doses of exogenous insulin up to 100 units/kg did not suppress basal, fat-stimulated or glucose-stimulated GIP release. The results indicate that raised GIP concentrations make an important contribution to the hyperinsulinaemia and related metabolic abnormalities of the ob/ob syndrome.

J. Endocr. (1984) 101, 249–256
Effects of background adaptation on the pituitary and plasma concentrations of some pro-opiomelanocortin-related peptides in the rainbow trout (Salmo gairdneri)
Authors: Rodrigues K. T. , Sumpter J. P.
Published: December 2008

Radioimmunoassays for α-MSH, β-MSH, ACTH and endorphin were used to measure pituitary concentrations of these peptides in rainbow trout during adaptation to black and white backgrounds. There was no difference in the pituitary content of any of these peptides between long-term black- and white-adapted trout. Plasma levels of α-MSH immunoreactivity were significantly higher in black-adapted trout than in white-adapted trout. Time-course studies revealed that although the body colour of trout showed an initial rapid adaptation to background colour, this was not paralleled by a corresponding change in plasma α-MSH levels. These only showed significant changes after 7 or more days of background adaptation, when melanophore recruitment or degradation occurred on black or white backgrounds respectively. Intravenous administration of mammalian α-MSH, salmon β-MSH I or antibodies to these peptides did not affect short-term background adaptation. However, long-term administration of mammalian α-MSH via osmotic minipump maintained melanophore numbers in grey-adapted trout transferred to a white background, although this observation was based on only two fish. It is concluded that peptides derived from pro-opiomelanocortin do not appear to be involved in controlling physiological colour change but may be involved in regulating morphological colour change of the rainbow trout.

J. Endocr. (1984) 101, 277–284
Effects of hypophysectomy and growth hormone treatment on renal hydroxylation of 25-hydroxycholecalciferol in rats
Authors: Wongsurawat N. , Armbrecht H. J. , Zenser T. V. , Forte L. R. , Davis B. B.
Published: December 2008

Growth hormone stimulates intestinal calcium absorption. This action has been linked to vitamin D metabolism. We have investigated the effects of hypophysectomy and GH treatment on renal metabolism of 25-hydroxycholecalciferol (25-OH-D3). Renal hydroxylation of 25-OH-D3 was measured in vitro using the renal slice technique. Experiments were performed in young F344 rats fed a vitamin D-replete, low calcium diet for 4 weeks. In hypophysectomized rats, renal conversion of 25-OH-D3 to 1,25-dihydroxycholecalciferol (1,25-(OH)2D3) was markedly reduced compared with sham-operated rats. Renal conversion of 25-OH-D3 to 24,25-(OH)2D3 was markedly increased in hypophysectomized rats compared with sham-operated rats. Treatment of hypophysectomized rats with rat GH (rGH) for 10 days resulted in a significant increase in renal conversion of 25-OH-D3 to 1,25-(OH)2D3 and a significant decrease in conversion to 24,25-(OH)2D3. Rat GH treatment caused no significant changes in serum levels of immunoreactive parathyroid hormone. Serum calcium concentrations were similar in all groups, and serum phosphorus was low in hypophysectomized rats. Treatment of hypophysectomized rats with ovine GH for 6 days caused changes which were much less pronounced than those induced by rGH. Renal conversion of 25-OH-D3 to 1,25-(OH)2D3 and 24,25-(OH)2D3 correlated well with growth rate (weight gain). These results suggest that GH, either directly or indirectly, modulates renal metabolism of 25-OH-D3.

J. Endocr. (1984) 101, 333–338
In-vitro effects of corticosterone, synthetic ovine corticotrophin releasing factor and arginine vasopressin on the release of adrenocorticotrophin by fetal rat pituitary glands
Authors: Dupouy J. P. , Chatelain A.
Published: December 2008

The in-vitro release of ACTH by fetal rat pituitary glands on days 17, 19 and 21 of pregnancy was measured using radioimmunoassay.

The spontaneous release of ACTH, expressed in pg ACTH/gland per h, increased with fetal age, in correlation with the sharp rise in pituitary ACTH content. However, since pituitary ACTH content was nearly sevenfold higher at term than on day 17, while basal release of ACTH was only threefold higher, one can speculate that the spontaneous release of ACTH was proportionally greater on day 17 than on day 21 of gestation.

As corticosterone, at a physiological concentration (865 nmol/l), reduced ACTH release, it was concluded that the pituitary gland was one site of the negative feedback action of the corticosteroids during fetal life.

Quantities of synthetic ovine corticotrophin releasing factor (CRF) which gave concentrations of 0·3–30 nmol/l in the incubation medium induced a sharp rise in ACTH release which was log-dose dependent between 0·3 and 3 nmolCRF/1 on day 17 and between 0·3 and 30 nmolCRF/1 on days 19 and 21. The response to CRF increased with fetal age.

Quantities of arginine vasopressin (AVP) which gave concentrations of 2–200 nmol/l stimulated ACTH release at all stages of gestation investigated. However, the response to AVP was much lower than that to CRF.

Potentiation of CRF-induced ACTH release was not observed when whole pituitary glands from 21-day-old fetuses were incubated with AVP (20 nmol/l) + CRF (3 nmol/l).

Such results were correlated with the ontogenesis of immunoreactive vasopressin- and CRF-containing fibres in the median eminence of the rat fetus, as well as with the CRF-like immunoreactivity present in adult rat pituitary portal plasma and the AVP content of the fetal rat hypophysis.

J. Endocr. (1984) 101, 339–344
Further characterization of the second oestrogen-binding species of the rat granulosa cell
Authors: Kudolo G. B. , Elder M. G. , Myatt L.
Published: December 2008

Rat granulosa cell cytosol contains a second oestrogen-binding species (SOB) distinguished from the classical oestrogen receptor by its lower dissociation constant (approx. 45 nmol/l) and the ability to bind oestrogens, antioestrogens, androgens and progesterone but not diethylstilboestrol. The SOB and the oestrogen receptor can be further distinguished by their differential adsorption to spheroidal hydroxylapatite and Concanavalin A–Sepharose. Addition of chaotropic salts or molybdate to granulosa cell cytosol did not alter the concentration of SOB or oestrogen receptor measured, indicating that there are no 'masked' binding sites in the two species caused by aggregation phenomena. The association rate of oestradiol with SOB at 4°C (1·72 ± 0·27(s.e.m.) × 108 mol/h) and 25°C (4·50 ± 0·36 × 108 mol/h) was faster than with the oestrogen receptor (7·20 ± 0·15 × 107 mol/h and 1·23 ± 0·15 × 108 mol/h respectively). The biphasic dissociation kinetics of [3H]oestradiol from the oestrogen receptor at 25°C (rate constants k−1 = 0·30±0·07/min and k−2 = 3·73±0·57 × 10−3/min) were similar to those reported in other target tissues but the dissociation of [3H]oestradiol from SOB appeared to be much more rapid and could not be measured by the Sephadex LH-20 separation method employed for determining receptor kinetics. Using sucrose density-gradient (SDG) analysis and Sephacryl S-200 gel chromatography the oestrogen receptor fractionated in an aggregated form (10·3S, Stokes radius >5·2 nm) in low ionic strength buffers and as a small species (4·4S, Stokes radius 3·5 nm) in buffers containing 0·4 m-KCl. However, the SOB fractionated as 2–3S, Stokes radius 3·7–4·0 nm at low ionic strength and as 5·8S, Stokes radius 3·5 nm in 0·4 m-KCl. In contrast to the receptor from other target tissues the granulosa cell oestrogen receptor did not bind to the artificial acceptor matrix oligo(dT)-cellulose and heat activation did not promote a 4S to 5S conversion when analysed on SDG. The salt-extracted form of nuclear receptor sedimented at 4·6S, mol. wt 69–72 000 on SDG.

J. Endocr. (1984) 102, 93–102
Activity of the genital tract and plasma levels of oxytocin and cortisol at the time of mating in the ewe
Authors: Garcia-Villar R. , Schams D. , Alvinerie M. , Laurentie M. P. , Toutain P. L.
Published: December 2008

Experiments were conducted in the ewe to determine the effects of mating on the activity of the genital tract and on blood levels of oxytocin and cortisol. The activity of the uterus and cervix was recorded by electromyography, oxytocin was measured by radioimmunoassay, and cortisol by high performance liquid chromatography. Mating itself did not increase circulating oxytocin or cortisol; uterine motility remained unchanged during and after copulation but the cervix was significantly stimulated during teasing and after copulation. It is suggested that increased cervical activity resulting from adrenergic mechanisms may facilitate the generation of a cervical reserve of spermatozoa.

J. Endocr. (1985) 105, 323–329
Release of oxytocin during suckling and parturition in the rat
Authors: Higuchi T. , Honda K. , Fukuoka T. , Negoro H. , Wakabayashi K.
Published: December 2008

A highly sensitive and specific radioimmunoassay (RIA) for oxytocin was developed and used to measure oxytocin concentrations during both suckling and parturition in individual rats. In urethane-anaesthetized rats, the suckling stimuli, provided by ten pups, induced intermittent increases in intramammary pressure of about 10 mmHg. This was associated with a significant (P < 0·01) increase in serum oxytocin levels from 19·5 ± 4·5 (s.e.m., n = 9) to 49·1 ± 7·4 pmol/l (n = 9) in the samples taken within 30 s from the time of the peak in the pressure. These rises in serum oxytocin returned rapidly to the basal levels as expected from the short half-life (1·46 min) of oxytocin in general circulation.

On day 22 or 23 of gestation, serum oxytocin levels remained stable until 0–0·5 h before the first fetus was expelled. They then increased significantly (P < 0·01) from 27·6± 4·6 pmol/l (n = 19) in samples taken 0–0·5 h before to 45·1 ± 5·6 pmol/l in samples taken after the expulsion of the first fetus and gradually increased until the last fetus was expelled. Serum oxytocin concentrations then declined but remained higher than those observed before the first fetus had been born until at least 1–1·5 h after the expulsion of the last fetus. Thus, this oxytocin RIA revealed increased concentrations of the hormone in blood during both suckling and parturition in the rat.

J. Endocr. (1985) 105, 339–346
Calcium-independent stimulation of glycogenolysis by arginine vasotocin and catecholamines in liver of the axolotl (Ambystoma mexicanum) in vitro
Authors: Janssens P. A. , Kleineke J. , Caine A. G.
Published: December 2008

Arginine vasotocin (AVT) caused a concentrationdependent increase of glycogen phosphorylase a activity, breakdown of glycogen and release of glucose, when added to pieces of axolotl liver in organ culture. The concentration causing half-maximal response (EC50) was about 1 nmol/l. These actions of AVT were unaffected by the adrenergic antagonists propranolol, yohimbine and prazosin, but were blocked by equimolar amounts of d(CH2)5Tyr(Me)AVT, a synthetic antagonist of vasopressin. Arginine vasotocin similarly caused glycogenolysis in isolated perfused axolotl liver where the EC50 was about 0·1 nmol/l.

The glycogenolytic action of AVT (10 nmol/l) was sustained for at least 3 h in Ca2+ -free perfusion and longer in organ culture. No increase in Ca2+ concentration in the effluent perfusion medium was apparent during AVT-induced glucose release. Omission of Ca2+ from the medium, together with addition of EGTA (2·5 mmol/l) to the organ culture, had only a slight inhibitory effect upon the rate of glycogenolysis brought about by AVT and did not inhibit the glycogenolytic action of catecholamines.

Addition of the calcium ionophore A23187 (5 μmol/l) neither caused glucose release nor abolished the glycogenolytic action of AVT added subsequently. Nevertheless, A23187 caused increased loss of 45Ca from Ca2+-loaded liver pieces whereas AVT was without effect.

There was a slight accumulation of cyclic AMP (cAMP), but not cGMP, in axolotl liver pieces cultured in the presence of 0·1 μmol AVT/l and this was accentuated in the presence of phosphodiesterase inhibitors.

We conclude that, in contrast to the position in mammals, Ca2+ is not involved in the glycogenolytic actions of AVT or catecholamines in axolotl liver. Preliminary experiments suggest that the same is true in the carp and we suggest that the involvement of Ca2+ in regulation of hepatic glucose release may not have evolved until after the amphibians separated from the ancestors of the mammals.

J. Endocr. (1986) 109, 75–84
Single channel recordings of potassium currents in an insulin-secreting cell line
Authors: Sturgess N. C. , Ashford M. L. J. , Carrington C. A. , Hales C. N.
Published: December 2008

Using the patch-clamp technique we observed three distinct classes of K+ channels which were spontaneously active in excised 'inside-out' membrane patches from an insulin-secreting rat pancreatic islet cell line (CRI-G1). Two of these occurred infrequently, one with a conductance of approximately 7 pS, and the other a conductance of 220 pS. The activation of the 220 pS K+ channel was dependent upon the membrane voltage and was sensitive to the concentration of calcium ions at the cytoplasmic surface of the membrane. The third, and by far the most common class of K+ channel, was characterized by its sensitivity to ATP. Application of ATP to the cytoplasmic side of the membrane reversibly inhibited this K+ channel in a dose-dependent manner, but had no effect when applied to the external side. The properties of the ATP-sensitive K+ channel appear to be indistinguishable from those of a channel found in rat neonatal β cells. Thus this insulin-secreting cell line should prove valuable in the investigation of the role of K+ channels in the regulation of insulin secretion.

J. Endocr. (1986) 109, 201–207
Autocrine tumour growth regulation by somatomedin C: an in-vitro model
Authors: Pavelić K. , Vrbanec D. , Marušić S. , Levanat S. , Čabrijan T.
Published: December 2008

A human primary haemangiosarcoma was derived from a patient with severe hypoglycaemia. Cell line established from that tumour secreted somatomedin C in serum-free culture media. Immunoreactive somatomedin from the media eluted from Sephacryl S-200 in two peaks of 160 000 and 8000 molecular weights. Similar results were obtained when medium was acidified and chromatographed on Sephadex G-50. Binding of tracer concentrations of 125I-labelled somatomedin C to human haemangiosarcoma cells was much higher than that of 125I-labelled insulin. Half-maximal displacement of 125I-labelled somatomedin C binding occurred at an unlabelled somatomedin C concentration of 0·7 nmol/l. Insulin competed with 125I-labelled somatomedin for binding to this receptor, but 150-fold more insulin was required for half-maximal displacement. Somatomedin secreted by human haemangiosarcoma cells and purified from serum-free media strongly stimulated [methyl-3H]thymidine incorporation into the DNA of these cells. Inhibition of somatomedin C secretion by cortisol resulted in the inhibition of tumour cell proliferation but stimulation of somatomedin secretion by human GH stimulated the cell proliferation rate. It appears that production of somatomedin C in human haemangiosarcoma cells plays a part in the regulation of tumour growth by an autocrine mechanism.

J. Endocr. (1986) 109, 233–238
Reduced adrenal cortical sensitivity to ACTH in lambs with cut splanchnic nerves
Authors: Edwards A. V. , Jones C. T. , Bloom S. R.
Published: December 2008

The possibility that the sensitivity of the adrenal cortex to endogenous ACTH may be affected by splanchnic nerve activity has been investigated in conscious, weaned, 5- to 8-month-old lambs. The animals were atropinized (0·5 mg/kg) and tested with an i.v. infusion of noradrenaline (333 ng/kg per min for 10 min), which produced a significant rise in the mean concentration of both ACTH and cortisol in the arterial plasma. In lambs tested at least 7 days after section of both splanchnic nerves, just below the diaphragm, the rise in plasma ACTH concentration was significantly greater, and that in plasma cortisol significantly less, than in control lambs. The mean plasma ACTH and cortisol concentrations were linearly related to one another in both groups (r = 0·93 and 0·92) but the sensitivity of the adrenal cortex to the steroidogenic action of ACTH appeared to have been roughly halved 1 week after bilateral splanchnic nerve section.

J. Endocr. (1986) 110, 81–85
LH and testosterone cause the development of seminiferous tubule contractile activity and the appearance of testicular oxytocin in hypogonadal mice
Authors: Nicholson H. D. , Worley R. T. S. , Charlton H. M. , Pickering B. T.
Published: December 2008

Immunoreactive oxytocin is present in the testis and it has been shown that this hormone increases the contractility of seminiferous tubules. We have investigated the relationship between testicular oxytocin, tubular movements and the effects of LH and testosterone using, as a model, the hypogonadal (hpg/hpg) mouse, which is deficient in hypothalamic LH-releasing hormone (LHRH). Whilst both testicular oxytocin and seminiferous tubule movements, resembling those seen in the rat, can be found in normal adult mice, neither can be found in hypogonadal mice. After 2 weeks of treatment with LH (200 ng to 100 μg daily) low levels of testicular oxytocin and tubular movements were observed. Treatment with large doses of testosterone for 2–12 weeks led to higher concentrations of testicular oxytocin and tubular movements resembling those seen in the normal adult mouse. The results support the evidence that testicular oxytocin modulates seminiferous tubule movements. We suggest that testosterone may play a part in the accumulation of oxytocin in the testis.

J. Endocr. (1986) 110, 159–167
Reappearance of the thymus in old rats after orchidectomy: inhibition of regeneration by testosterone
Authors: Greenstein B. D. , Fitzpatrick F. T. A. , Adcock I. M. , Kendall M. D. , Wheeler M. J.
Published: December 2008

The thymus is a critically important organ during development, but atrophies progressively during the ageing process after puberty and is often considered to be unimportant in adult life. We have found that the thymus, which is grossly atrophied in 12- to 15-month-old male rats, is markedly restored in size 30 days after orchidectomy. The organ then appears normal histologically, having a well-defined cortex and medulla, is vascularized and filled with thymocytes. The regeneration of the thymus after orchidectomy was inhibited in a dose–related fashion by testosterone implants which produced serum concentrations of testosterone within the physiological range. The thymus was also increased in size after orchidectomy of 10-week-old rats, and testosterone inhibited the enlargement of the thymus. These results have important implications for the possible enhancement of the immune system with associated improvement of health during ageing and disease. They also point to an important physiological link between the endocrine and immune systems.

J. Endocr. (1986) 110, 417–422
Automated repetitive microsampling of blood: growth hormone profiles in conscious male rats
Authors: Clark R. G. , Chambers G. , Lewin J. , Robinson I. C. A. F.
Published: December 2008

A system is described for the automatic collection of small samples of blood from conscious rats. Rats bearing chronic indwelling i.v. catheters were connected via swivels to a multichannel peristaltic pump, solenoid valves and a fraction collector. A microcomputer controlled the operations involved in the removal of blood and its deposition into a fraction collector for subsequent direct radioimmunoassay for GH. Blood samples of 10–20 μl could be collected, into a total volume of 100 μl heparinized saline, from up to eight rats simultaneously every few minutes for many hours. This collection method avoided major blood loss and did not require transfusions of donor blood to maintain blood volume. Using a doublelumen cannula it was possible to inject or infuse into the animals while sampling blood. The system was used to investigate in detail the secretion of GH in conscious male rats. The 3-hourly endogenous secretory rhythm of GH was maintained for up to 44 h with episodes of GH secretion being multicomponent. Endogenous secretion was suppressed by constant i.v. infusions of somatostatin, with repetitive sampling showing in detail a rapid rebound secretion of GH after terminating the somatostatin infusions. Four injections of a fragment of GH-releasing factor, given at 3-hourly intervals, produced entrained GH responses, but the subsequent recovery of endogenous GH pulsing was delayed for up to 12 h. This method for the automatic microsampling of blood in small animals gives a very detailed description of the blood levels of hormones secreted in a highly episodic fashion, and could be widely applicable to other endocrine studies.

J. Endocr. (1986) 111, 27–35
Arginine infusion blocks the action of parathyroid hormone but not arginine vasopressin on the renal tubule in man
Authors: O'Reilly D. St.J. , Fraser W. D. , Penney M. D. , Logue F. C. , Cowan R. A. , Williams B. C. , Walters G.
Published: December 2008

Six male volunteers were infused with arginine (0·5 g/kg body weight) over 30 min, after an overnight fast and water deprivation. There was a significant decrease in renal phosphate clearance (P<0·025) and urinary cyclic adenosine monophosphate (cAMP) output (P<0·025) during the 60- to 90-min period after the beginning of the infusion; both returned to the preinfusion basal levels within 150 min. The plasma levels of parathyroid hormone (PTH) were not affected by the infusion and remained unchanged during the subsequent 150 min. Plasma levels of arginine vasopressin (AVP) were also not significantly affected although plasma osmolality increased by 6–9 mmol/kg in all subjects. The infusion resulted in a diuresis, and a fall in urine osmolality but a decrease in free-water clearance; creatinine clearance was not affected. Six other subjects were given a bolus of 230 i.u. PTH intravenously, and 20 days later this was repeated during an infusion of arginine (0·5 g/kg body weight). There was a significant decrease in urinary phosphate (P< 0·025) and cAMP excretion (P<0·05) when PTH was given with arginine. It is suggested that arginine blocks the action of PTH on the proximal renal tubule but not that of vasopressin on the distal nephron and collecting ducts.

J. Endocr. (1986) 111, 501–506
Inhibitory effect of various radiographic contrast agents on secretion of thyroxine by the dog thyroid and on peripheral and thyroidal deiodination of thyroxine to tri-iodothyronine
Authors: Laurberg P. , Boye N.
Published: December 2008

In previous studies we have found that the cholecystographic contrast agent ipodate induced a rapid, sustained and reversible inhibition of thyroxine (T4) secretion from perfused dog thyroid lobes. This type of inhibition of thyroid secretion has not been observed previously. To evaluate whether this effect is unique for ipodate, ten other iodine-containing radiographic contrast agents were tested. The four agents used for cholecystography (iocetamate, iodipamide, ioglycamate and iotroxate) all induced rapid inhibition of T4 secretion from TSH-stimulated perfused dog thyroid lobes, while none of six agents predominantly excreted through the kidneys (amidotrizoate, metrizamid, metrizoate, iodamide, diodone and ioxithalamate) influenced T4 secretion significantly. All the cholecystographic agents inhibited T4 deiodinases from dog thyroid and liver. Diodone also inhibited the deiodinases while none of the other compounds tested had any effect.

The results indicate that the structure necessary to inhibit thyroid secretion is common to a number of cholecystographic agents and that it could be related to the structure responsible for the inhibitory effect of cholecystographic agents on T4 deiodinases.

J. Endocr. (1987) 112, 387–390
Naloxone stimulates sexual behaviour in lactating rats
Authors: Forsberg G. , Eneroth P. , Södersten P.
Published: December 2008

During lactation the display of sexual receptivity in response to treatment with oestradiol benzoate (OB; 2 or 10 μg) and progesterone (0·5 mg) was inhibited, but the behaviour could be activated by i.p. (5 mg) or intracerebroventricular (i.c.v.; 100 μg) but not intrathecal (i.t.; 100 or 500 μg) injections of the opioid peptide receptor antagonist naloxone. The behaviour was also inhibited in ovariectomized rats in which serum progesterone and prolactin levels had been raised by treatment with progesterone implants and the dopamine receptor antagonist domperidone, and the uterine cervix had been stimulated. Intraperitoneal injections of naloxone (1 mg) reactivated the behaviour of cervically stimulated rats. The concentration of β-endorphin-like immunoreactivity in the serum of lactating rats (42·8± 9·2 pmol/l) was not raised above that of ovariectomized rats (35·8 ± 8·4 pmol/l) nor was the concentration of β-endorphin-like immunoreactivity altered in the pituitary gland (22·5 ± 2·5 pmol/l), midbrain central grey (6·3 ± 2·2 pmol/l) or hypothalamus (5·6± 2·6 pmol/l) of lactating rats in comparison with ovariectomized rats (24·8 ± 4·4, 4·0 ± 2·0 and 4·7 ± 1·4 pmol/l respectively). Adrenalectomy facilitated the display of sexual behaviour in lactating rats treated with OB plus progesterone and caused a slight increase in serum β-endorphin-like immunoreactivity (30·5± 2·7 pmol/l) compared with that in non-adrenalectomized lactating rats (26·1 ± 2·1 pmol/l). It is suggested that an opioid peptide, but probably not β-endorphin, inhibits sexual behaviour during lactation and after cervical stimulation.

J. Endocr. (1987) 113, 423–427
Effects of injecting growth hormone or thyroxine on milk production and blood plasma concentrations of insulin-like growth factors I and II in dairy cows
Authors: Davis S. R. , Gluckman P. D. , Hart I.C. , Henderson H. V.
Published: December 2008

Three cows received injections of thyroxine (T4; 20 mg/day), four cows GH (40 mg/day) and three cows saline (control; 10 ml/day) on days 5–8 of a 16-day experimental period during peak lactation. Milk yield increased 13% in cows given GH (from 14·6 to 16·5 kg/day) and 15% in cows given T4 (from 15·8 to 18·2kg/day) but did not change in control cows. Injection of T4 increased milkfat and lactose content but reduced milk protein content. Injection of GH was without effect on milk composition during the injection period but milk protein rose after injections ceased.

Injection of T4 increased plasma concentrations of T4 and tri-iodothyronine six- to sevenfold, with maxima occurring on day 9. Injection of GH increased the plasma concentration of GH five- to tenfold 5 h after injection. The plasma concentration of insulin-like growth factor I (IGF-I) was increased in cows given GH in both morning (08.30 h) and afternoon (14.30 h) blood samples, the difference being greatest in afternoon samples in which plasma IGF-I content increased from 3·3 to 6·8 nmol/l. Injection of T4 reduced the plasma concentration of IGF-I in morning samples but the concentration in afternoon samples remained relatively constant throughout the 16-day experimental period. The plasma concentration of IGF-II rose in morning samples in all treatment groups to reach a maximum of 200–250 nmol/l by day 9.

The galactopoietic response to injection of GH but not T4 was associated with an increase in plasma concentration of IGF-I. Changes in plasma concentration of IGF-II were not associated with changes in milk yield.

J. Endocr. (1987) 114, 17–24
Effect of different photoperiods on concentrations of 5-methoxytryptophol and melatonin in the pineal gland of the Syrian hamster
Authors: Skene D. J. , Pevet P. , Vivien-Roels B. , Masson-Pevet M. , Arendt J.
Published: December 2008

Specific, sensitive and direct radioimmunoassays have been used to determine the daily patterns of 5-methoxytryptophol (ML) and melatonin in the pineal glands of Syrian hamsters kept in different photo-periods: 8 h light: 16 h darkness (8L:16D), 14L: 10D and 16L: 8D. A rhythm in pineal ML was evident in animals in all the photoperiods, with high daytime levels (641±35 (s.e.m.) fmol/gland; n=162) which dropped to 119±16 fmol/gland (n = 44) 7·1– 7·5 h after lights out. The duration of low night-time ML levels was proportional to the length of the dark phase (1·2 h in 16L:8D, 5·4 h in 14L: 10D and 8·4 h in 8L: 16D). A marked daily rhythm in melatonin was also present in hamsters in the different photoperiods, with daytime levels of 323 ± 34 fmol/gland (n = 129) and night-time peak concentrations of 3676 ± 336 fmol/gland (n = 22). The duration of high nocturnal melatonin levels was dependent upon the length of the dark phase (4·1 h in 16L: 8D, 4·5 h in 14L: 10D and 12·5 h in 8L: 16D). Linear regression analysis revealed a statistically significant inverse relationship between pineal ML and melatonin levels in 8L: 16D (P< 0·001), 14L: 10D normal (P<0·05) and 14L: 10D shifted (P<0·001) photoperiods. After advancing the lighting schedule by 10 h (14L: 10D, lights off at 04.00 h), pineal ML and melatonin rhythms became entrained to the new lighting regimen.

The daily rhythms in pineal ML and melatonin in the Syrian hamster thus depend on the prevailing photoperiod, a reciprocal relationship existing between pineal ML and melatonin concentrations.

J. Endocr. (1987) 114, 301–309
Secretion rates and short-term patterns of gonadotrophin-releasing hormone, FSH and LH throughout the periovulatory period in the mare
Authors: Alexander S. L. , Irvine C. H. G.
Published: December 2008

We have developed a non-surgical technique for longterm collection of pituitary venous blood which consists of slightly diluted hypophysial portal blood into which pituitary hormones have been secreted. In these experiments jugular and pituitary venous blood samples were collected from five unmedicated, ambulatory mares at 5-min intervals for 2–6 h on 11 occasions during the 6 days surrounding the ovulatory LH peak. Jugular blood only was collected from another five periovulatory mares without pituitary cannulae. The duration of oestrus was similar in mares with and without pituitary cannulae and all mares ovulated, showing that the procedure did not affect the reproductive axis. In all pituitary-cannulated mares the secretion of gonadotrophin-releasing hormone (GnRH), FSH and LH occurred almost continuously with broad, concurrent pulses of the three hormones superimposed upon this tonic background. Only 9% of the GnRH pulses appeared to be ineffective in inducing a rise in gonadotrophin levels. When measured in pituitary blood, gonadotrophin pulse frequency varied from 0·45 pulses/h early in the LH surge to 1·87 pulses/h at the time of ovulation. In contrast, mean pulse frequency measured in jugular blood did not exceed 1 pulse/h throughout the periovulatory period in cannulated or non-cannulated mares. The low amplitude of jugular pulses (< 50% fractional increase) may have caused problems in identifying the pulses. In the two mares in which pituitary venous blood was sampled during more than one period before ovulation, GnRH secretion tended to be lower on the day of ovulation (day 0) than earlier in oestrus (ratio day 0:day −1; mare WV = 0·58, mare LS = 0·66), whereas LH secretion rate was higher on the day of ovulation (ratio day 0:day −1; mare WV = 1·54, mare LS = 6·68). These studies show that the painless and non-invasive collection of pituitary venous blood, which is possible only in horses, can provide a useful tool for studying hypothalamic-pituitary interactions under completely physiological conditions.

J. Endocr. (1987) 114, 351–362
Cholecystokinin peptides as local modulators of thyroidal calcitonin secretion in the dog?
Authors: Laurberg P. , Rehfeld J. F.
Published: December 2008

Cholecystokinin (CCK) is a heterogeneous gut hormone which is also synthetized in extra-intestinal endocrine cells and neurones. In order to examine the possibility that CCK peptides are local modulators of calcitonin secretion, we have studied the structure– activity relationship on calcitonin secretion from perfused canine thyroid lobes as well as the presence and molecular nature of CCK in the thyroid. Peptides containing the intact COOH-terminal tetrapeptide amide of CCK (CCK-4, CCK-5, pentagastrin, CCK-8 and gastrin-17) all induced dose-dependent (0·1, 3 and 100 nmol/l) increases in calcitonin release (P<0·05, n =4) with biphasic secretion during 6-min infusion periods. The deamidated tetrapeptide and the COOHterminal tripeptide were without effect. Gel chromatography of neutral water and acid–ethanol extracts of thyroid tissue, monitored by sequence-specific CCK and gastrin radioimmunoassays, disclosed a variety of CCK and gastrin peptides of which a predominant form resembled small molecular forms like CCK-4 and CCK-5. The presence in the thyroid of small CCK-like peptides and the pronounced effect of such peptides on calcitonin secretion suggest that calcitonin secretion is modulated by local release of small CCK peptides. They could originate from intrathyroidal nerves or from sub-populations of C-cells.

J. Endocr. (1987) 115,77–82
Endogenous opioid control of pulsatile LH secretion in rams: modulation by photoperiod and gonadal steroids
Authors: Lincoln G. A. , Ebling F. J. P. , Martin G. B.
Published: December 2008

The role of endogenous opioid peptides in the inhibitory control of pulsatile LH secretion was studied in adult Soay rams at different stages of the seasonal reproductive cycle, entrained by an artificial lighting regimen of alternating 16-week periods of long and short days. The LH responses to the acute administration of naloxone (opioid antagonist) and morphine (opioid agonist) were measured in intact rams (n = 7), testosterone-implanted castrated rams (n = 8) and castrated rams (n = 8) to assess the interaction between photoperiod and gonadal steroids in the opioid control of LH secretion.

In the intact and testosterone-implanted castrated rams, naloxone (1·7 mg/kg i.v.) increased and morphine (1·0 mg/kg i.v.) decreased mean LH concentrations and LH pulse frequency during the sexually active phase under short days, but these effects were reduced or absent during the inactive phase under long days. The changes in the LH responses occurred in close parallel with the photoinduced changes in endogenous LH secretion. In the castrated rams receiving no supplementary testosterone, plasma LH concentrations were permanently raised and there were only minor changes related to the photoperiod. Naloxone (1·7 mg/kg) induced transient increases in LH secretion at all stages, and morphine (1·0 mg/kg) failed to suppress LH levels under both short and long days. LHRH stimulation tests revealed that there were changes in LH release related to the induced reproductive cycle in the intact and testosterone-implanted rams but not in the castrated rams; these changes in the responsiveness of the pituitary gonadotrophs to LHRH could not account for the changes in the LH response to the opiate drugs.

These results illustrate that an endogenous opioid mechanism is involved in the tonic inhibition of LH secretion acting to regulate the pulsatile release of LHRH from the hypothalamus. This system can be shown to be functional in a steroid-dependent manner in the sexually active phase of the seasonal cycle, but not in the inactive phase of the cycle when non-opioidergic mechanisms are presumed to predominate in the inhibition of LH secretion.

J. Endocr. (1987) 115, 425–438
Insulin-like growth factor-I stimulates oxytocin and progesterone production by bovine granulosa cells in culture
Authors: Schams D. , Koll R. , Li C. H.
Published: December 2008

The effect of insulin-like growth factor-I (IGF-I), epidermal growth factor (EGF), fibroblast growth factor (FGF) and nerve growth factor (NGF) on production of oxytocin and progesterone by cultured bovine granulosa and luteal cells was studied. Secretion of oxytocin was stimulated, in a dose-dependent manner, by IGF-I at 48 and 120 h of culture to levels much higher than those after stimulation with LH, FSH, EGF, FGF or NGF. A similar effect of IGF-I was observed for progesterone but, in contrast to oxytocin, secretion of progesterone was not increased by EGF, NGF or FGF. During primary culture, for 4 h, of dispersed bovine luteal cells obtained from corpora lutea between days 4 and 10 of the oestrous cycle, all the growth factors tested failed to stimulate secretion of oxytocin or progesterone. The data suggest the relevance of growth factors (especially IGF-I) for ovarian physiology and their possible importance for differentiation of follicles and luteinization.

J. Endocr. (1988) 116, 97–100
Influence of parasitism on plasma concentrations of growth hormone, somatomedin-C and somatomedin-binding proteins in calves
Authors: Elsasser T. H. , Rumsey T. S. , Hammond A. C. , Fayer R.
Published: December 2008

A parasitic disease model (sarcocystosis) was used to study the effects of infection and associated plane of nutrition on GH and somatomedin-C (SM-C) patterns in plasma, and SM-C binding protein patterns in plasma from 4-month-old male Holstein calves. Calves, matched by age and rate of growth before the experiment, were divided into three treatment groups (n = 7). In the first (control), animals were uninfected and food was available ad libitum; in the second, animals were infected with Sarcocystis cruzi and food was available ad libitum. The third group consisted of uninfected animals pair-fed to the level of feed intake of the infected animals. Blood samples were obtained at various times after infection for analysis of the secretory patterns of GH (day 27 after infection, samples every 10 min for 6 h), SM-C (days 27, 35 and 58 after infection) or binding protein (day 42 after infection). Samples were analysed for GH and SM-C by radioimmunoassay. Relative molecular weights of binding proteins were assessed by elution patterns from gel permeation columns.

Clinical signs of infection were manifest abruptly on day 26 after infection. Voluntary feed intakes of infected calves as a per cent of control calves were 18, 46 and 78 on days 27, 35 and 58 after infection respectively. Plasma GH concentrations were lower in infected and pair-fed than in control calves (P < 0·05). Plasma SM-C concentrations were reduced in calves with diminished feed intakes and lower still in infected calves (P < 0·05). Plasma SM-C was positively correlated with nitrogen retention across treatment groups (r = 0·81). Two classes of binding proteins differing in molecular weight were identified. The relative amounts of each binding protein in plasma were reduced during low feed intake with some differences in the endogenous saturation affected by infection.

These data suggest that altered growth and metabolism in parasitized calves may arise in part from both nutritional and infection-mediated effects on the regulation of GH, SM-C and SM-C binding proteins.

J. Endocr. (1988) 116, 191–200