bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of elevated blood insulin-like growth factor-I (IGF-I) concentration upon IGF-I in bovine mammary secretions during the colostrum phase
Authors: Hadsell D. L. , Baumrucker C. R. , Kensinger R. S.
Published: December 2008

The objectives of these studies were to determine if the concentration of insulin-like growth factor-I (IGF-I) in mammary colostrum secretions could be altered through manipulation of IGF-I concentrations in blood and to compare the temporal changes of IGF-I in mammary secretions to those occurring for IgG1. Milking of 15 pregnant Holstein cows was stopped at 8 weeks prepartum and they were randomly assigned to one of three treatments. A control (C) treatment consisted of feeding the animals 100% of NRC requirements for protein and energy. A second group of cows was fed as the control group and injected with 1·8 μmol bovine GH/day. The third group was fed at 70% of NRC requirements for protein and energy to cause a moderate nutrient restriction (NR). Body weight was measured weekly. Blood was collected by tail venepuncture at 4 h intervals for 24 h. Mammary secretions were collected and pooled among contralateral front and rear quarters (diagonal) for measurement of volume, IGF-I and IgG1 concentrations. Samples were collected at −7, −5, −2, 0 and 1 week postpartum. Cows on the NR treatment failed to gain weight during the dry period compared with C cows (P < 0·05). Blood GH and IGF-I concentrations (P > 0·1) were unaffected by NR treatment. Cows treated with GH had higher (P < 0·01) serum GH and IGF-I levels throughout the entire treatment period, and higher serum IgG1 at 5 and 2 weeks prepartum (P < 0·01). Total mass of IGF-I secreted per diagonal averaged 3·6-fold greater for GH-treated cows during the prepartum period than C and NR cows (P < 0·01). The concentration of IGF-I in mammary secretions was not affected by treatment during the prepartum period, but was 40% greater (P < 0·05) in GH-treated cows than C and NR cows at parturition. Analysis of a selective index comparing IGF-I secretion with that of IgG1 suggested that IGF-I does not enter mammary secretions by passive diffusion from blood.

Journal of Endocrinology (1993) 137, 223–230
Influence of N-methyl-d-aspartate on the reproductive axis of male Syrian hamsters
Authors: Urbanski H. F. , Fahy M. M. , Collins P. M.
Published: December 2008

The influence of excitatory amino acids (EAAs) on reproductive neuroendocrine function was investigated in adult male Syrian hamsters of the LSH/Ss Lak strain. Before the study, the animals were maintained in a sexually regressed condition, under short days (SD) and subsequently were either transferred to long days (LD) or kept under SD, for a further 4 weeks. In the former group, photostimulation produced a predictable elevation in the hypophysial contents and serum concentrations of FSH and LH. This was accompanied by an increase in testicular size, an elevation in serum testosterone levels and an increase in spermatogenic activity; the SD hamsters remained sexually quiescent throughout the study. In contrast, SD hamsters that were given daily injections of the EAA agonist, N-methyl-d,l-aspartate (NMA: 50 mg/kg body weight, s.c.), showed stimulatory responses that were generally even more pronounced than those shown by the LD group. Surprisingly, an identical NMA treatment paradigm failed to cause a similar activation of the reproductive axis in LD hamsters that were given daily afternoon injections of melatonin (25 μg, s.c), even though the inhibitory effect of this melatonin treatment is generally regarded as being comparable with that produced by exposure to SD. Although EAAs can acutely stimulate the neurocircuitry that controls LH-releasing hormone secretion, the present findings suggest that EAAs might also exert a long-term stimulatory action by acting further upstream in the photoneuroendocrine pathway.

Journal of Endocrinology (1993) 137, 247–252
Rapid clearance of insulin-like growth factor (IGF)-binding protein species from blood and an associated fall in circulating IGF-I following partial hepatectomy in the rat
Authors: Phillips I. D. , Arany E. , Strain A. J. , Han V. K. M. , Hill D. J.
Published: December 2008

The presence of insulin-like growth factors (IGFs) in blood is regulated by their association with specific IGF-binding proteins (IGFBPs). In turn, the level of IGFBPs in the blood is likely to depend on a dynamic equilibrium between peptide production and clearance to extravascular tissues or organ-specific degradation. Since circulating IGFBPs may largely derive from liver we have employed partial hepatectomy in the rat to study the clearance rate of endogenous IGFBPs from blood once a major site of production is removed. Adult male rats were partially hepatectomized and serum and the remaining liver removed between 30 min and 7 days after surgery. Ligand blot analysis revealed two major species of IGFBP, of 28–30 kDa and 40–44 kDa in sera from control rats or sham-operated rats respectively. The larger species corresponded in size to rat IGFBP-3, but the smaller form was not recognized by antisera against rat IGFBP-1, bovine IGFBP-2 or human IGFBP-5 following Western immunoblot. Following hepatectomy, the levels of both IGFBP forms in the serum declined within 30 min and were barely detectable after 3 h or 6 h. They began to increase again in serum 24 h following surgery. The reduction in IGFBPs following hepatectomy was not primarily due to degradation by specific proteases in serum. Circulating levels of insulin were increased fivefold 3 h after hepatectomy but subsequently returned to control values. The rise in insulin was accompanied by a significant (P < 0·05) reduction in circulating IGF-I after 3 h which persisted at 24 h. Glucose levels in serum showed a transient but non-significant reduction between 90 min and 6 h after hepatectomy. Total RNA was extracted from remnant liver and subjected to Northern blot hybridization with 32P-labelled cDNAs encoding rat IGFBP-1, -2 or -3. Messenger RNA encoding IGFBP-1 was barely detectable in liver from control or sham-operated animals, but increased within 30 min of partial hepatectomy and peaked at 3 h. It subsequently declined and was again barely detectable after 24 h. No expression of IGFBP-2 or -3 mRNAs was found by Northern blot analysis in the liver of control animals or following partial hepatectomy. These results suggest that both IGF-I and IGFBPs in rat serum decreased rapidly following partial hepatectomy, and that this was due largely to the rapid clearance of the peptide and its binding proteins once the major source of production was removed. A rapid induction of IGFBP-1 in the remaining liver may be unrelated to the circulating IGFBPs since immunoreactive IGFBP-1 was not detected in rat serum.

Journal of Endocrinology (1993) 137, 271–280
The paraventricular nucleus and corticotrophin-releasing hormone are not critical in suppressing pulsatile LH secretion in ovariectomized lactating rats
Authors: Tsukamura H. , Ohkura S. , Coen C. W. , Maeda K.-I.
Published: December 2008

Various types of hypothalamic roof deafferentation (RD) (i.e. large anterior (LARD), large posterior (LPRD), small anterior (SARD) or middle (MRD)), electrolytic lesions of the paraventricular nucleus (PVN) or intracerebroventricular (i.c.v.) injection of α-helical corticotrophin-releasing factor(9–41) (α-helical CRF(9–41)) were performed in ovariectomized lactating rats in order to determine the afferent pathway of the suckling stimulus and whether the PVN and corticotrophin-releasing hormone (CRH) are involved in suppressing pulsatile LH secretion during lactation. Animals were ovariectomized on day 2 of lactation (day 0 = the day of parturition). Deafferentations and electrolytic lesions were made on day 7. On the following day, blood samples were taken via an indwelling atrial cannula every 6 min for 3 h. Pulsatile LH secretion with high frequency and amplitude was present in rats with LARD or LPRD despite the suckling. In rats with MRD, LH pulses with a small amplitude were observed when the cut was on or under the ventral margin of the PVN, but there were few LH pulses when the cut passed through the PVN. Electrolytic lesioning of the PVN, however, did not affect the suppression of pulsatile LH secretion during lactation. In addition, i.c.v. injection of α-helical CRF(9–41) (26·1 nmol/10 μl) into the third ventricle on day 8 of lactation did not reverse the suppression of LH secretion by the suckling stimulus. These results suggest that the pathway associated with this inhibition may be rather diffuse and that the PVN region and CRH are not critical in conveying the inhibitory inputs of the suckling stimulus.

Journal of Endocrinology (1993) 137, 291–297
Dopamine D1 receptor analogues act centrally to stimulate prolactin secretion in ewes
Authors: Curlewis J. D. , Clarke I. J. , McNeilly A. S.
Published: December 2008

It is well known that prolactin secretion is inhibited by dopamine acting via the pituitary dopamine D2 receptor. Dopamine D1 receptor analogues also affect prolactin levels although the mechanisms and physiological significance are poorly understood. The present study of the ewe was undertaken to characterize the effects of the D1 receptor agonist SKF 38393 and antagonist SCH 23390 on prolactin in this species and to determine whether the prolactin response to both drugs requires an intact hypothalamo-pituitary axis. Ovariectomized ewes were injected intravenously with vehicle, 0·2, 2 or 20 mg SKF 38393 (D1 agonist) or SCH 23390 (D1 antagonist). At the 20 mg dose, plasma prolactin concentrations were significantly (P <0·01) increased by each drug and returned within an hour to control levels. When injected directly into the lateral ventricles of the brain (intracerebroventricular (i.c.v.) injection), a 100-fold lower dose of SKF 38393 (0·2 mg; P <0·05) was sufficient to stimulate prolactin secretion. In contrast, i.c.v injection of SCH 23390 (0·02 and 0·2 mg) had no effect on prolactin levels and at no dose was there evidence for suppression of prolactin levels. These results are in accord with earlier studies in the rat which suggested that the D1 agonist stimulated prolactin secretion via a direct effect on central dopamine D1 receptors whereas the

D1 antagonist interacted with the pituitary dopamine D2 receptor to increase prolactin secretion. In a further experiment this hypothesis was tested in hypothalamo-pituitary disconnected ewes which were infused with dopamine (0·5 μg/kg per min) for 3 h. After 2 h of the dopamine infusion, animals were challenged with intravenous injections of the vehicle, 20 mg SKF 38393, 20 mg SCH 23390 or 2 mg domperidone (dopamine D2 antagonist). Infusion of dopamine was followed by a significant (P <0·05) decline in prolactin concentrations so that after 2 h prolactin levels were 40% of the preinfusion value. Following injection of the vehicle, SCH 23390 or SKF 38393, prolactin levels continued to decline for the remainder of the experiment. As expected, injection of domperidone was followed by a significant (P <0·05) increase in prolactin to reach peak levels after 30 min. These results demonstrate that peripheral injections of the dopamine D1 agonist SKF 38393 or antagonist SCH 23390 increase prolactin secretion in the ewe. The prolactin response to either drug requires an intact hypothalamo-pituitary axis indicating that SKF 38393 and SCH 23390 act at some central site(s) which is linked with hypothalamic secretion of prolactin-releasing or -inhibiting factors.

Journal of Endocrinology (1993) 137, 457–464
Transient reduction in trabecular bone formation after discontinuation of administration of oestradiol-17β to ovariectomized rats
Authors: Tobias J. H. , Chambers T. J.
Published: December 2008

While the osteopenia associated with oestrogen deficiency is thought to arise from a relative defect in bone formation with respect to resorption, oestrogen administration itself leads to a decrease, rather than an increase, in bone formation. This decrease in bone formation, which arises from oestrogen's inhibitory effect on bone turnover, presumably masks any underlying tendency of oestrogen treatment towards stimulation of bone formation. To investigate this further, we have examined the early effect of discontinuing the administration of oestradiol-17β (OE2; 40 μg/kg on bone formation indices in ovariectomized 13-week-old rats, before the turnover-induced increase in formation occurs. Histomorphometric indices were assessed at the proximal tibial metaphysis 0, 7, 10, 13 and 16 days following discontinuation of OE2 treatment. Measurements of body weight, uterine weight and longitudinal growth rate confirmed that there were rapid effects of OE2 deficiency on these parameters.

We could detect no significant increase in bone resorption, as measured by osteoclast surface and number, until 16 days after ending treatment with OE2; this was coincidental with a reduction in bone volume. Shorter periods of OE2 deficiency were associated with a marked decrease in bone formation, as assessed by dynamic histomorphometric indices. This inhibition of bone formation was largely due to a reduction in double fluorochrome-labelled trabecular surfaces, which were decreased by approximately 70%. We conclude that ending OE2 administration in ovariectomized rats caused a striking decrease in trabecular bone formation, if such indices are assessed prior to the subsequent turnover-induced increase in formation. This suggests that oestrogen treatment in ovariectomized rats is associated with a stimulatory effect on bone formation, in addition to its recognized anti-resorptive action.

Journal of Endocrinology (1993) 137, 497–503
Response to short photoperiod and spontaneous sexual recrudescence in the lesser mouse lemur: role of olfactory bulb removal
Authors: Perret M. , Schilling A.
Published: December 2008

The body weight and sexual activity of the male lesser mouse lemur, a prosimian primate, undergo cyclic changes that are photoperiod-dependent. Exposure to long daylength (LD; 14 h light/day) led to sustained sexual activity, fully developed testes and high plasma testosterone concentrations (228 ±25 nmol/l, n = 10). After 14 weeks under LD, a marked decrease in testosterone levels occurred. Gonadal regression was completed within 20 weeks under LD without concomitant changes in body weight. Exposure to short daylength (SD; 8 h light/day) reinforced the sexual quiescence and was associated with a high ponderal gain (from 60 to 110 g). However, independent of the date of gonadal arrest, the sexual activity of males spontaneously resumed at a fixed time after exposure to SD. The testes developed, testosterone concentrations increased to 155 nmol/l and the body weight decreased (from 110 to 80 g) within 20 weeks under SD exposure. The timing for refractoriness appeared very similar under inhibitory and stimulatory photoperiods. This is consistent with the hypothesis that the perception of a critical daylength is used to regulate the timing of the following sexual phase through a mechanism involving photorefractoriness.

Contrary to cricetid rodents, a direct response to photoperiodic signals for both body weight and sexual activity were not prevented by olfactory bulb removal in male mouse lemurs. In bulbectomized males (n = 12), sexual activity was stimulated by LD and inhibited by SD. Their plasma testosterone levels, however, significantly differed from those of controls in both photoperiods. Likewise, ponderal cycles remained intact but the fattening phase was delayed and reduced. Finally, whereas the sexual recrudescence of bulbectomized males occurred under SD with a delay of only 2–4 weeks, spontaneous testicular regression under exposure to LD did not appear in our experimental photoperiodic conditions.

Journal of Endocrinology (1993) 137, 511–518
Constant low-dose oestradiol replacement accelerates skeletal maturation and growth in ovariectomized adolescent rhesus monkeys
Authors: Wilson M. E. , Gordon T. P. , Tanner J. M.
Published: December 2008

The effects of oestradiol (OE2) on adolescent growth in female rhesus monkeys were evaluated by testing the hypothesis that, upon removal of the ovary, the increase in growth normally seen at the time of puberty would be abolished and that treatment with OE2 would restore it. Juvenile monkeys (n= 12) were ovariectomized and were given either an OE2-bearing silicone elastomer capsule implanted subcutaneously to simulate mid-pubertal concentrations ('treated = ', n = 8) or no steroid treatment ('control = ', n = 4). Females were studied from 18 to 42 months of age which, in intact females, typically encompasses the prepubertal period to the occurrence of first ovulation. Over the whole period, growth in body weight, crown–rump (CR) length and tibia length for control females were less than the 95% confidence limits of females treated with OE2. However, significant spurts of growth in both CR and tibia length occurred in the control as well as treated animals, although the peak velocities were somewhat lower for non-OE2-treated animals. Peak growth velocities occurred at an earlier chronological age in treated females, although at the same degree of skeletal maturity as found in control females. Skeletal maturity was significantly advanced in treated females from 27 months onward. Serum concentrations of nocturnal GH increased significantly with advancing age in both groups, with greater increases observed in treated females. Serum concentrations of IGF-I were higher in treated females until some 30 months of age, at which point concentrations increased in a similar fashion in both groups. IGF-I concentrations were elevated in the months preceding and following the peak CR growth velocity in treated females whereas concentrations of IGF-I rose coincidently with peak CR growth in control females. These data indicate that, in the absence of OE2, growth in female monkeys has periods of acceleration and that OE2 may enhance this pre-set pattern. Furthermore, the growth-promoting effects of OE2 are determined by the degree of skeletal maturity. Once a certain degree of skeletal maturity is attained, bones may be primed for maximal growth, but, as skeletal maturity continues to advance, the effect of OE2 on growth diminishes.

Journal of Endocrinology (1993) 137, 519–527
Endogenous opioid regulation of oxytocin release during parturition is reduced in ovariectomized rats
Authors: Way S. A. , Douglas A. J. , Dye S. , Bicknell R. J. , Leng G. , Russell J. A.
Published: December 2008

Pregnant rats were ovariectomized (or shamovariectomized) on days 17, 18 or 21 of pregnancy and oestradiol-17β and progesterone were replaced. Prepartum oxytocin concentrations were significantly lower in ovariectomized steroid-treated rats than in intact controls, and on day 21 of pregnancy injection of relaxin into acutely ovariectomized rats significantly increased plasma oxytocin concentrations. During parturition, injection of the opioid antagonist naloxone induced significant increases in plasma oxytocin concentration compared with salineinjected rats. The naloxone-induced increase was significantly less in ovariectomized steroid-treated rats than in rats with intact ovaries, indicating that endogenous opioid activity is less in ovariectomized rats than in intact rats. The progress of parturition in the ovariectomized steroid-treated rats was severely disrupted compared with sham-ovariectomized rats despite similar plasma oxytocin levels at the birth of pup number 2; this disruption was not overcome by injection of naloxone or by the consequent increase in oxytocin secretion, indicating deficient preparation of the uterus and birth canal in the absence of relaxin. We conclude that the decreased oxytocin concentrations prepartum, the prolongation of parturition and the decrease in opioid tone in ovariectomized steroid-treated rats may be partly due to a lack of relaxin produced by the ovary.

Journal of Endocrinology (1993) 138, 13–22
pGlutamylglutamylprolineamide modulation of growth hormone secretion in domestic fowl: antagonism of thyrotrophin-releasing hormone action?
Authors: Harvey S. , Trudeau V. L. , Ashworth R. J. , Cockle S. M.
Published: December 2008

Pyroglutamylglutamylprolineamide (pGlu-Glu-ProNH2) is a tripeptide with structural and immunological similarities to thyrotrophin-releasing hormone (TRH; pGlu-His-ProNH2). Since TRH stimulates GH secretion in domestic fowl, the possibility that pGlu-Glu-ProNH2 may also provoke GH release was investigated. Unlike TRH, pGlu-Glu-ProNH2 alone had no effect on GH release from incubated chicken pituitary glands and did not down-regulate pituitary TRH receptors. However, pGlu-Glu-ProNH2 suppressed TRH-induced GH release from pituitary glands incubated in vitro and competitively displaced [3H]methyl3-histidine2-TRH from pituitary membranes. Systemic injections of pGlu-Glu-ProNH2 had no significant effect on basal GH concentrations in conscious birds, but promptly lowered circulating GH levels in sodiumpentobarbitone anaesthetized fowl. Submaximal GH responses of conscious and anaesthetized birds to systemic TRH challenge were, however, potentiated by prior or concomitant administration of pGlu-Glu-ProNH2. These results demonstrate, for the first time, that pGlu-Glu-ProNH2 has biological activity, with inhibitory and stimulatory actions within the avian hypothalamo-pituitary axis. These results indicate that pGlu-Glu-ProNH2 may act as a TRH receptor antagonist within this axis.

Journal of Endocrinology (1993) 138, 137–147
Glucagon-like peptide-1(7–36)amide and glucose-dependent insulinotropic polypeptide secretion in response to nutrient ingestion in man: acute post-prandial and 24-h secretion patterns
Authors: Elliott R. M. , Morgan L. M. , Tredger J. A. , Deacon S. , Wright J. , Marks V.
Published: December 2008

The acute effects of different macronutrients on the secretion of glucagon-like peptide-1(7–36)amide (GLP-1(7–36)amide) and glucose-dependent insulinotropic polypeptide (GIP) were compared in healthy human subjects. Circulating levels of the two hormones were measured over a 24-h period during which subjects consumed a mixed diet. In the first study, eight subjects consumed three equicaloric (375 kcal) test meals of carbohydrate, fat and protein. Small increases in plasma GLP-1(7–36) amide were found after all meals. Levels reached a maximum 30 min after the carbohydrate and 150 min after the fat load. Ingestion of both carbohydrate and fat induced substantial rises in GIP secretion, but the protein meal had no effect. In a second study, eight subjects consumed 75 g glucose or the equivalent portion of complex carbohydrate as boiled brown rice or barley. Plasma GIP, insulin and glucose levels increased after all three meals, the largest increase being observed following glucose and the smallest following the barley meal. Plasma GLP-1(7–36)amide levels rose only following the glucose meal. In the 24-h study, plasma GLP-1(7–36)amide and GIP concentrations were increased following every meal and remained elevated throughout the day, only falling to fasting levels at night. The increases in circulating GLP-1(7–36)amide and GIP levels following carbohydrate or a mixed meal are consistent with their role as incretins. The more sustained rises observed in the daytime during the 24-h study are consistent with an anabolic role in lipid metabolism.

Journal of Endocrinology (1993) 138, 159–166
Human recombinant inhibin A and testosterone act directly at the pituitary to suppress plasma concentrations of FSH in castrated rams
Authors: Tilbrook A. J. , de Kretser D. M. , Clarke I. J.
Published: December 2008

The roles of inhibin and testosterone in the negative feedback control of the secretion of FSH were explored in experiments using castrated rams administered human recombinant inhibin A (hr-inhibin) and testosterone propionate (TP). Two experiments were conducted in the non-breeding season. In experiment 1, two groups of long-term castrated rams (wethers) were treated with an i.v. injection of either vehicle or hr-inhibin in two doses (25 and 50 μg) given 2 weeks apart. Plasma concentrations of FSH, measured by radioimmunoassay, were suppressed significantly (P<0·01) and equally by both doses of hr-inhibin with a mean (± s.e.m.) maximal suppression of FSH of 19·9 ± 2·60% occurring 6–10 h after injection. In experiment 2, hypothalamo-pituitary disconnected (HPD) wethers given 125 ng gonadotrophin-releasing hormone (GnRH) every 2 h, were treated with vehicle or 25 or 50 μg hr-inhibin before or after treatment (32 mg/day) with TP. A cross-over design was used so that each wether was treated with vehicle and hr-inhibin. Treatment with TP significantly (P<0·001) suppressed plasma concentrations of FSH by 56%. Both doses of hr-inhibin were similarly effective in significantly (P<0·05) suppressing plasma concentrations of FSH causing a mean suppression of 31·1 ± 5·60% 6–10 h after injection. The suppressive effect of hr-inhibin was significantly (P<0·05) increased when the wethers were treated with TP to a mean suppression of 50·7 ± 5·6% 6–10 h after injection. These data indicate that both inhibin and testosterone exert negative feedback control on FSH secretion in rams and that the suppressive effects of inhibin may be enhanced by testosterone. Furthermore, both inhibin and testosterone acted directly on the pituitary to suppress FSH secretion in rams. The inhibition of FSH by a direct pituitary action of testosterone in this study is at variance with our previous findings with HPD wethers during the breeding season when it was shown that testicular steroids have minimal feedback effects at this level. These discrepancies suggest that the sensitivity of the pituitary to negative feedback by testicular steroids may change with the breeding season independent of an input from the hypothalamus. Finally, the greater suppressive effects of hr-inhibin in HPD wethers in experiment 2 compared with the hypothalamo-pituitary intact wethers in experiment 1 suggests that the sensitivity of the pituitary to inhibin may be increased by limiting the GnRH stimulus to the pituitary.

Journal of Endocrinology (1993) 138, 181–189
Characterization of a novel non-peptide vasopressin V1 receptor antagonist (OPC-21268) in the rat
Authors: Burrell L. M. , Phillips P. A. , Stephenson J. , Risvanis J. , Hutchins A.-M. , Johnston C. I.
Published: December 2008

A non-peptide, orally effective, vasopressin (AVP) V1 receptor antagonist 1-{1-[4-(3-acetylaminopropoxy) benzoyl]-4-piperidyl}-3,4-dihydro-2(1H)-quinolinone (OPC-21268) has recently been described. This paper reports the in-vitro and in-vivo characterization of OPC-21268 binding to vasopressin receptors in rat liver and kidney.

OPC-21268 caused a concentration-dependent displacement of the selective V1 receptor antagonist radioligand, 125I-labelled [d(CH2)5,sarcosine7]AVP to V1 receptors in both rat liver and kidney medulla membranes. The concentration of OPC-21268 that displaced 50% of specific AVP binding (IC50) was 40±3 nmol/l for liver V1 and 15±2 nmol/l for kidney V1 receptors (mean ± s.e.m.; n = 3). OPC-21268 had little effect on the selective V2 antagonist radioligand [3H]desGly-NH29[d(CH2)5,d-Ile2,Ile4] AVP binding to V2 receptors in renal medulla membranes (IC50 >0·1 mmol/l).

After oral administration to rats, OPC-21268 was an effective V1 antagonist in a time- and dose-dependent manner. Binding kinetic studies showed that OPC-21268 acted as a competitive antagonist at the liver V1 receptor in vitro and in vivo, in addition to its in-vitro competitive effects at the renal V1 receptor. OPC-21268 shows promise as an orally active V1 antagonist.

Journal of Endocrinology (1993) 138, 259–266
Plasma clearance and tissue distribution of labelled insulin-like growth factor-I (IGF-I) and an analogue LR3IGF-I in pregnant rats
Authors: Bastian S. E. P. , Walton P. E. , Wallace J. C. , Ballard F. J.
Published: December 2008

To determine whether the changes in insulin-like growth factor-binding proteins (IGFBPs) and IGF-I levels during pregnancy in rats affect the clearance of IGFs from the circulation, we have measured pharmacokinetic parameters and the tissue distribution of radiolabelled IGF-I and LR3IGF-I, a potent analogue which has a markedly reduced affinity of binding to the IGFBPs. Intravenous boluses of radiolabelled growth factors were administered to catheterized virgin and age-matched pregnant rats on day 18 of gestation when plasma IGFBPs, in particular IGFBP-3, are dramatically reduced. IGF-I was cleared more rapidly from plasma in pregnant rats compared with the virgins; metabolic clearance rate (MCR) = 2·88±0·12 (s.e.m.) and 0·90±0·05 ml/min per kg respectively. Although LR3IGF-I was cleared more rapidly than IGF-I from plasma, similar clearance rates for the analogue were obtained in both pregnant and virgin animals, MCR = 9·19±0·15 and 9·84±0·28 ml/min per kg respectively. In virgin rat plasma, labelled IGF-I was mainly associated with the 150 kDa complex, whereas in pregnant rat plasma IGF-I was predominantly associated with lower Mr IGFBPs (approximately 30–50 kDa). The majority of LR3IGF-I was detected as free peptide. A larger proportion of the tracer was detected as small Mr breakdown products in plasma from rats under conditions of reduced binding to IGFBPs, e.g. during pregnancy or when LR3IGF-I was the labelled tracer, suggesting greater rates of IGF degradation. More LR3IGF-I tracer was detected in kidneys, ovaries and adrenals of virgin rats and in the ovaries and adrenals of pregnant rats, compared with IGF-I tracer. IGF-I radioactivity was greater than LR3IGF-I in caecum, brain, liver and heart in virgin rats and in kidneys, caecum, brain, liver, heart, placenta, fetus and fetal plasma of the pregnant rats. These results show that the reduction in IGFBP during pregnancy dramatically increased the clearance of IGF-I from the circulation towards that obtained with LR3IGF-I. The observation that less LR3IGF-I was detected in placenta, fetus and fetal plasma compared with IGF-I raises the possibility that the ability to bind IGFBPs during pregnancy may enhance IGF uptake by the conceptus.

Journal of Endocrinology (1993) 138, 327–336
The involvement of vasopressin in the renal actions of atrial natriuretic peptide in conscious fluid-balanced rats
Authors: Burgess W. J. , Balment R. J.
Published: December 2008

The renal and endocrine actions of atrial natriuretic peptide (ANP) administered at a rate to induce plasma concentrations within the physiological range have been re-examined in conscious rats in which body fluid volume was maintained by infusion of replacement fluid at a rate to match spontaneous urine losses (servo-controlled replacement) throughout experimentation. The involvement of vasopressin in the actions of ANP was assessed by comparing the responses induced in Brattleboro (DI) and Long–Evans (LE) rats.

A rate of ANP administration inducing a less than twofold increment in circulating ANP concentration evoked a small but significant diuresis and natriuresis. In contrast to previous studies during which body fluid balance had not been maintained and the response to ANP was transient, renal responses were rapid in onset and sustained over the period of hormone administration. The change in renal excretion occurred without concomitant changes in mean arterial blood pressure, haematocrit or glomerular filtration rate, and without consistent alterations in the circulating concentrations of angiotensin II, vasopressin, aldosterone or corticosterone. Furthermore, although small differences between the two strains in the character of the response could be demonstrated, the evoked response was of similar magnitude in vasopressin-replete and -deficient animals.

In summary, in conscious rats in which body fluid volume was maintained, the profile of the diuretic and natriuretic responses evoked by low-rate ANP administration was different from that previously observed in anaesthetized and/or constantly infused preparations; being rapid in onset and sustained. The similarity in the renal effects observed following ANP administration in LE and DI rats in the present study suggests that vasopressin is not a prerequisite for the renal actions of ANP evoked by plasma concentrations within the physiological range.

Journal of Endocrinology (1993) 138, 413–420
Clearance of exogenous parathyroid hormone-related protein in pregnant, non-pregnant and fetal sheep, goats and pigs
Authors: Ratcliffe W. A. , Abbas S. K. , Care A. D.
Published: December 2008

In the sheep, goat and pig, radiolabelled parathyroid hormone related protein (PTHRP) and immunoreactive PTHRP(1–34) and (1–86) were rapidly cleared from the circulation. Metabolic clearance rates (MCR) were in the range of 1·25–7·5 ml/min per kg and were slightly slower than that of intact PTH in man (10 ml/min per kg); while the mean MCR of labelled PTHRP(1–86) in fetal sheep and goats was significantly faster than that in their respective mothers (14·4 vs 4·0 ml/min per kg respectively). This may reflect increased metabolism of PTHRP by fetal tissues, e.g. the placenta. Similar rates of clearance of radiolabelled PTHRP(1–141), (1–86) and (1–34) suggest that clearance involves the amino terminus of the molecule.

Journal of Endocrinology (1993) 138, 459–465
Protein kinase in rat adipocytes: influence of androgenic status and regional fat distribution
Authors: Lacasa D. , Agli B. , Mur B. , Dieudonné M. N. , Giudicelli Y.
Published: December 2008

The effects of castration and testosterone treatment on insulin- and phorbol ester (TPA)-stimulated lipogenic responses, phorbol dibutyrate-specific binding to protein kinase C (PKC) in the cytosol and the β-PKC isoform level quantified by immunoblotting were compared in rat fat cells from femoral subcutaneous (SC) and deep intra-abdominal (epididymal) fat deposits.

In control rats, the PKC content was lower in SC than in epididymal fat cells. After castration, the difference in PKC content between SC and epididymal fat cells was reduced and restored by testosterone treatment. However, androgenic status failed to modify the PKC content in SC fat cells. The lipogenic response to insulin was also differently regulated by the androgenic status in the two fat deposits. After castration, the response was increased in SC fat cells, while it was blunted in epididymal fat cells. These effects were corrected by testosterone administration.

These results demonstrate that, in white adipocytes, PKC is an additional biological parameter which varies according to the anatomical origin of the fat cells. They also provide evidence that PKC is controlled by androgens in vivo and emphasize the regional site specificity of such a control.

Journal of Endocrinology (1993) 138, 493–501
The effect of tri-iodothyronine on the membrane potential and intracellular sodium and potassium activities of rat soleus and extensor digitorum longus muscles
Authors: MacDermott M.
Published: December 2008

Tri-iodothyronine (T3) induces a considerable increase in the number of Na/K pump units in rat skeletal muscles, but this effect is more pronounced in red muscles, such as soleus, than in white muscles such as extensor digitorum longus (EDL). In the present study, the effect of T3 on the membrane potential (Em) and the intracellular activities of K+ and Na+ (aKi and aNai) in the two muscle types has been studied using microelectrodes. Hyperthyroidism was induced by seven subcutaneous injections of 50 μg T3 per 100 g body weight on alternate days. Following treatment of rats with T3, the mean T3 concentration in the serum was 8·4 ± 0·46 nmol/l (s.d.) compared with 1·1 ± 0·16 nmol/l in the serum of untreated control rats, and the heart weight/body weight ratio of the treated rats had increased from 0·29 ± 0·01 in control rats to 0·39 ± 0·02. In soleus muscle fibres from the T3-treated rats, the Em, aKi and aNai were unchanged, whereas, in EDL muscle fibres from these rats, the Em had depolarized by 2 mV (P<0·01) and aNai had increased by 2 mmol/l (P<0·05). Since T3 induces not only an increase in the number of pump units and active movement of Na+ and K+ but also an increase in the passive fluxes of these ions, the results are discussed in terms of these two opposing ionic movements.

Journal of Endocrinology (1993) 138, 503–507
Concentration-dependent effects of adrenaline on the profile of insulin secretion from isolated human islets of Langerhans
Authors: Lacey R. J. , Cable H. C. , James R. F. L. , London N. J. M. , Scarpello J. H. B. , Morgan N. G.
Published: December 2008

The effects of the mixed α/β-agonist adrenaline on insulin secretion from isolated human islets of Langerhans were studied. In static incubation experiments, adrenaline (0·1 nmol/l to 10 μmol/l) caused a concentration-dependent inhibition of glucose-induced insulin secretion from isolated human islets. However, perifusion experiments revealed that the time-course of the secretory changes induced by adrenaline was complex. When employed at a high concentration (1 μmol/l), adrenaline caused a sustained inhibition of glucose-induced insulin secretion, which could be relieved by the addition of the α2-antagonist yohimbine (10 μmol/l). By contrast, infusion of adrenaline at a lower concentration (10 nmol/l), produced a large initial potentiation of glucose-induced insulin secretion. This response was, however, short-lived and followed by sustained inhibition of secretion, which could be relieved by yohimbine (10 μmol/l). The initial stimulation of insulin secretion provoked by 10 nmol adrenaline/l was abolished when islets were incubated in the presence of the β-antagonist, propranolol (1 μmol/l), consistent with activation of β-adrenoceptors. In support of this, treatment of human islets with the selective β2-agonist clenbuterol, was also associated with marked stimulation of insulin secretion. By contrast, each of two selective β3-agonists tested failed to alter insulin secretion from human islets. The results indicate that human pancreatic B-cells are equipped with both α2-and β2-adrenoceptors which can affect insulin secretion. Adrenaline interacts with both of these but the α2-response is predominant and can overcome the tendency of β2-adrenoceptors to potentiate insulin release.

Journal of Endocrinology (1993) 138, 555–563
Isolation and characterization of a cytostatic histone H2B-like protein from fetal lungs of non-diabetic and diabetic rats
Authors: Conliffe P. R. , Bennett H. P. J. , Mulay S.
Published: December 2008

It was observed in the course of other studies that rat fetal lung extracts inhibited proliferation of fetal lung cells in culture. The purpose of the present study was to isolate and characterize this cytostatic factor. It was found that fetal lungs contained a 16 kDa cytostatic factor and its concentration was twofold greater in fetal lungs of diabetic rats compared with control rats. This fetal lung cytostatic protein (FLCP) was purified by reversed-phase, heparin-affinity and gel filtration high-performance liquid chromatography and SDS-PAGE. The purified protein was electroblotted onto polyvinylidene difluoride membrane and subjected to sequence analysis. The amino-terminal sequence of this fetal lung cytostatic protein was PEPAKSAPAPXKGIGKQXXKAX XKA... and showed significant homology with histone H2B; however, the amino acid composition of FLCP suggested that it may be structurally distinct from histone H2B. Ion-spray mass spectrometry suggested that FLCP was made up of at least two species of the protein with molecular weights of 13 776·1 and 14 007·3 and was different from the molecular weight of rat histone H2B predicted by its cDNA sequence. The concentration of FLCP, based on amino acid compositions, was 0·32 nmol/g and 0·83 nmol/g wet fetal lung from non-diabetic and diabetic rats respectively. These findings suggest that the fetal rat lung produces a regulatory factor bearing considerable homology with but possibly different from histone H2B and that fetal lung immaturity during diabetic pregnancy might be contributed to by an increase in this factor.

Journal of Endocrinology (1993) 139, 97–105
Localization, characterization and activity of pituitary adenylate cyclase-activating polypeptide in the frog adrenal gland
Authors: Yon L. , Feuilloley M. , Chartrel N. , Arimura A. , Fournier A. , Vaudry H.
Published: December 2008

Pituitary adenylate cyclase-activating polypeptide (PACAP) has recently been isolated from the frog brain and the sequence of the peptide appears to be strikingly similar to that of mammalian PACAP. In the present study, we have investigated the localization of PACAP in the frog interrenal (adrenal) gland by immunocytochemistry using antisera directed against PACAP 38 or PACAP 27. Two types of PACAP-immunoreactive fibres were observed: thick varicose fibres coursing between adrenal cells and thin processes located in the walls of blood vessels irrigating the gland. Bilateral transection of the splanchnic nerves did not affect the intensity and distribution of PACAP immunoreactivity. The mean ± s.e.m. concentration of PACAP, measured by radioimmunoassay in crude adrenal extracts, was 0·65 ± 0·16 nmol/g wet tissue. Two molecular forms of PACAP in the adrenal gland were characterized by reversed phase high-performance liquid chromatography combined with radioimmunoassay quantification. The elution profiles revealed the existence of two peaks exhibiting the same retention times as synthetic frog PACAP 38 (fPACAP 38) and PACAP 27, the predominant form being PACAP 38. The possible involvement of PACAP in the regulation of adrenal steroidogenesis was investigated in vitro using a perifusion system for frog adrenal slices. Graded doses of fPACAP 38 (0·1–10 μmol/l) increased the secretion of both corticosterone and aldosterone in a dose-dependent manner. Administration of repeated pulses of fPACAP 38 (1 μmol/l), at 120-min intervals, led to a reproducible stimulation of corticosteroid secretion without any tachyphylaxis. Prolonged infusion (2 h) of the peptide induced a rapid increase in corticosterone and aldosterone output, followed by a gradual decline in the secretion rate, suggesting the occurrence of a desensitization phenomenon. Synthetic porcine vasoactive intestinal peptide, which is structurally related to PACAP, was about ten times less potent than fPACAP 38 in stimulating steroidogenesis while the [Des-His1]-fPACAP 38 analogue was 100 times less effective. These results demonstrate that a peptide closely related to fPACAP 38 is present in fibres innervating the frog adrenal gland and could participate in the regulation of corticosteroid secretion, particularly during neurogenic stress.

Journal of Endocrinology (1993) 139, 183–194
Urinary epidermal growth factor is excreted from the rat isolated perfused kidney in the absence of plasma
Authors: Jørgensen P. E. , Hilchey S. D. , Nexø E. , Poulsen S. S. , Quilley C. P.
Published: December 2008

Large amounts of epidermal growth factor (EGF) are excreted in urine and the majority of this urinary EGF appears to be of renal origin. EGF is synthesized in the kidneys as a membrane-bound 160 kDa precursor, in the thick ascending limb of Henle and in the early part of the distal convoluted tubule. Very little is known about how EGF is released from cell membranes into urine but proteolytic cleavage of the membrane-bound EGF precursor seems likely. The purpose of this study was to examine whether plasma constituents are necessary for urinary excretion of EGF. In the rat isolated kidney perfused at a pressure of 90 mmHg with a modified Krebs–Henseleit buffer containing oncotic agents, the quantity of EGF excreted into the ureteral effluent was 67% of the amount excreted by the rat kidney in vivo. The EGF excreted by the isolated kidney behaved like urinary EGF upon gel filtration. Administration of the proteinase inhibitor aprotinin reduced urinary EGF excretion from the rat isolated perfused kidney by approximately 50%.

In conclusion, the rat isolated perfused kidney excreted significant amounts of urinary EGF without having access to plasma, and EGF excretion was reduced by aprotinin. This is further evidence suggesting an intrarenal source of urinary EGF and suggests that the EGF precursor in the rat kidney is processed by enzyme(s) of renal origin.

Journal of Endocrinology (1993) 139, 227–234
A novel angiotensin I isolated from an elasmobranch fish
Authors: Takei Y. , Hasegawa Y. , Watanabe T. X. , Nakajima K. , Hazon N.
Published: December 2008

It is believed that the renin-angiotensin system evolved initially in primitive bony fishes and is absent from elasmobranchs. We have isolated angiotensin I from the incubates of plasma and kidney extracts of an elasmobranch fish, Triakis scyllia, using eel vasopressor activity as an assay system. Its sequence was determined to be H-Asn-Arg-Pro-Tyr-Ile-His-ProPhe-Gln-Leu-OH. Dogfish angiotensin I is teleost-like because of an asparagine residue at position 1 but it is mammalian-like because of an isoleucine residue at position 5. The unique and most important substitution in dogfish angiotensin I is a proline residue at position 3 which may cause significant changes in its tertiary structure. A glutamine residue at position 9 is also unique among all angiotensin Is sequenced to date. Dogfish angiotensin I is more potent than rat angiotensin I in its vasopressor activity in the dogfish but the relationship is reversed in the rat. Thus angiotensin receptors as well as the hormone molecules appear to have evolved during vertebrate phylogeny. Our findings establish the elasmobranch renin-angiotensin system and support the hypothesis that the renin-angiotensin system is a phylogenetically old hormonal system which plays important roles in cardiovascular and fluid homeostasis.

Journal of Endocrinology (1993) 139, 281–285
Effect of fasting on serum insulin-like growth factor-I (IGF-I) levels and IGF-I-binding activity in cockerels
Authors: Morishita D. , Sasaki K. , Wakita M. , Hoshino S.
Published: December 2008

White Leghorn male chicks of 40 days of age were fasted for 5 days and then refed. Blood samples were collected from these chicks before, during and after fasting and serum levels of GH and insulin-like growth factor-I (IGF-I) and serum IGF-I-binding activity were determined. The fasting-induced reduction in body weight was accompanied by a significant rise in circulating GH and fall in IGF-I, coupled with increased serum IGF-I-binding activity. When pooled serum was chromatographed under neutral conditions, IGF-I binding activity and IGF-I immunoreactivity were mainly associated with a large (Mr= 150 000) and a small protein (Mr=30 000). Fasting induced a marked increase in the IGF-I-binding activity of the 30 kDa IGF-I-binding protein (IGFBP) and refeeding restored activity to the normal levels seen before fasting. Ligand blotting of serumbinding proteins with 125I-labelled IGF-I, after first subjecting the samples to polyacrylamide gel electrophoresis and transfer to nitrocellulose, revealed that four IGFBPs (Mr=20 000, 30 000, 35 900 and 41 000) were present in chicken serum, and that the 125I-labelled IGF-I binding of the 30 kDa monomer was increased by fasting and restored to normal by refeeding in agreement with gel filtration profiles of IGF-Ibinding activity. Western blot analysis suggested that the 30 kDa IGFBP is homologous to IGFBP-2 found in mammalian blood plasma. The results show that IGFBPs in chicken serum and their responses to fasting are similar to those in mammals.

Journal of Endocrinology (1993) 139, 363–370