bluuebunny/crossref_metadata_2025_split huggingface dataset:
Endocrine changes associated with the termination of photorefractoriness by short daylengths and thyroidectomy in starlings (Sturnus vulgaris)
Authors: Dawson A. , Goldsmith A. R. , Nicholls T. J. , Follett B. K. 
Published: December 2008

ABSTRACT
When starlings (Sturnus vulgaris) are transferred from short to long days, hypothalamic content of gonadotrophin-releasing hormone (GnRH) and pituitary gonadotrophin content eventually decrease, as birds become photorefractory, to values lower than they were on short days. This implies that both should increase as photorefractoriness is terminated some time after transfer from long to short days. Further, since thyroidectomy causes termination of photorefractoriness in birds held on long days, this should also result in an increase in hypothalamic GnRH and pituitary gonadotrophin contents. This study tests these hypotheses.
Male starlings were transferred from short to long days for 10 weeks, by which time they should have become photorefractory. One group of birds was then killed; blood was collected, hypothalami and pituitaries were excised, and the stage of moult and testicular weights recorded. The remaining birds were then kept on long days, transferred to short days or thyroidectomized and kept on long days. Groups of birds in each treatment group were killed and sampled 2, 8 and 14 weeks later. Hypothalamic content of GnRH, and pituitary and plasma FSH and prolactin concentrations, were measured by radioimmunoassay.
In birds sampled after 10 weeks of long days, hypothalamic content of GnRH was quite low, pituitary and plasma levels of FSH were very low, testes were small and pituitary and plasma prolactin levels were high. In intact birds kept on long days, hypothalamic GnRH content decreased further and remained low. Pituitary and plasma FSH levels remained low, testes remained small and pituitary and plasma prolactin levels decreased slowly. In intact birds transferred to short days, hypothalamic GnRH content increased to values significantly (P<0·01) higher than in birds kept on long days. Pituitary FSH content increased (P<0·01) but plasma FSH levels remained low and testes remained small in most birds. Pituitary and plasma prolactin levels decreased rapidly. In thyroidectomized starlings kept on long days, hypothalamic GnRH content increased to the same values as in birds on short days, pituitary FSH content increased markedly and testes grew although plasma FSH remained low. Pituitary and plasma prolactin levels decreased slowly.
These results demonstrate that short days activate the hypothalamus to a state of 'readiness to function' and confirm that the thyroid glands are involved in this response.
J. Endocr. (1986) 110, 73–79
Development and steroidogenic activity of preantral follicles in the neonatal rat ovary
Authors: Carson R. , Smith J. 
Published: December 2008

ABSTRACT
The neonatal rat ovary is completely devoid of antral follicles until the twelfth day of age. During this period the ovary becomes steroidogenically active and responsive to gonadotrophins. The aim of this study was to correlate the onset of ovarian androgen and oestrogen production in vitro with the first appearance of distinct granulosa and theca cells. Although ovarian aromatase activity increased significantly on day 7 of age, ovarian oestrogen production was limited by low progesterone and testosterone production until day 12 of age. Increased aromatase activity on day 7 and androgen production on day 12 were coincident with the first appearance of granulosa and theca cells respectively. These functional and morphological changes were not associated with significant alterations in ovarian weight or concentrations of LH or FSH in serum.
J. Endocr. (1986) 110, 87–92
Somatostatin immunoneutralization stimulates thyroid function in fowl
Authors: Lam S.-K. , Harvey S. , Hall T. R. , Spencer G. S. G. 
Published: December 2008

ABSTRACT
The influence of somatostatin on thyroid function has been examined in immature domestic fowl passively immunized with somatostatin antiserum. Plasma thyroxine (T4) and tri-iodothyronine (T3) concentrations were markedly increased within 10 min of antisomatostatin administration and remained raised for at least 5 h. The increases in the T3 and T4 concentrations following somatostatin immunoneutralization were directly related to the volume of antisera administered. The increase in the T3 concentration exceeded the increase in the T4 concentration, resulting in a T3: T4 ratio greater than unity. While the raised T4 concentration began to decline 30 min after antisomatostatin administration, raised T3 concentrations were sustained for at least 2 h, and further increased the plasma T3: T4 ratio.
These results demonstrate that somatostatin immunoneutralization stimulates thyroid function in fowl. The magnitude and rapidity of the thyroidal responses to somatostatin immunoneutralization suggests that they occur independently of the hypothalamic-pituitary-thyroid axis. Somatostatin appears to exert a tonic inhibitory control on avian thyroid function, possibly by effects mediated at the thyroid gland to inhibit T4 release and by peripheral effects to suppress the conversion of T4 and T3.
J. Endocr. (1986) 110, 127–132
Changes in ornithine decarboxylase activity in ovarian follicles of the laying hen (Gallus domesticus) during the ovulatory cycle
Authors: Armstrong D. G. 
Published: December 2008

ABSTRACT
Fowl ovarian ornithine decarboxylase activity was measured at 20, 10 and 3 h before an expected ovulation in granulosa and thecal tissues from follicles at various stages of development. An increase in the enzyme activity between 10 and 3 h before an expected ovulation was assumed to be caused by preovulatory increase in plasma LH concentration.
The activity in granulosa tissue increased with increasing size of the follicle. In the largest (F1) follicle there was an 11-fold increase in granulosa ornithine decarboxylase specific activity between 10 and 3 h before ovulation. In the third (F3) and fifth (F5) largest follicles there was a 1·9- and 2-fold increase respectively.
The enzyme activity in thecal tissue from the follicular hierarchy decreased with increasing size of the follicle and the F3 thecal preparation was the only tissue to respond to the preovulatory LH surge. In contrast, ornithine decarboxylase activity in thecal tissue from small (< 5 mm) non-atretic follicles increased by two- to threefold after the preovulatory LH surge. The activity in atretic follicles of the same size was low and remained unchanged throughout the ovulatory cycle.
J. Endocr. (1986) 110, 211–216
Inhibitory effects of bromocriptine on mammary development and function in lactating mice
Authors: Knight C. H. , Calvert D. T. , Flint D. J. 
Published: December 2008

ABSTRACT
Five experiments were conducted. In the first, the plasma prolactin concentration of lactating mice was significantly reduced 3, 6 and 12 h after a single injection of 0·2 mg bromocriptine at 09.00 h, but recovered to normal levels at 24 h. A second injection at 17.00 h (i.e. total dose of 0·4 mg) completely prevented this recovery. Prolactin concentration was also reduced after the s.c. implantation of a solid pellet of bromocriptine.
Once daily injections of bromocriptine for 7 days starting 1-day prepartum (early lactation group) or on day 5 of lactation (established lactation group) significantly reduced milk yield, assessed from the weight gain of the litter or estimated by a tritiated water dilution procedure. In early lactation the degree of inhibition was positively related to the size of the suckling litter (three pups, no inhibition; nine pups, 16·4% inhibition; 14 pups, 40·8% inhibition), but in established lactation an inhibition of 25–30% was observed, regardless of litter size. Twice-daily injections and s.c. implants of bromocriptine both reduced milk yield by a greater amount (approximately 45%), but in no case was secretion completely suppressed. The inhibitory effect of bromocriptine was prevented by the simultaneous administration of ovine prolactin (0·4 mg).
Lactogenesis was apparently not affected by bromocriptine treatment. At the end of the early lactation treatment period, the mammary glands of bromocriptine-treated animals were significantly smaller and contained fewer cells than those of controls, but this was not the case in animals treated during established lactation.
It is suggested that suppression of prolactin secretion by bromocriptine treatment may reduce milk yield both indirectly, by inhibiting development of the gland and thereby reducing the size of the secretory cell population, and directly, by reducing the activity of individual secretory cells. The observation that lactation was not completely inhibited suggests that prolactin may not be the only galactopoietic hormone in the mouse.
J. Endocr. (1986) 110, 263–270
A comparison of the effects of gonadal steroids on naloxone-induced LH secretion in gonadectomized rats
Authors: Spencer G. M. , Whitehead S. A. 
Published: December 2008

ABSTRACT
The effects of the opiate antagonist naloxone on serum LH concentrations was investigated in gonadectomized rats given different regimes of steroid pretreatment. Two injections of testosterone given 48 and 24 h before naloxone treatment failed to reinstate LH responses to this drug in castrated rats while subcutaneous testosterone-filled silicone elastomer capsules implanted for a week were effective in this respect. Injections of oestrogen, oestrogen plus progesterone or progesterone alone all restored LH responses to naloxone in ovariectomized rats when given 48 and/or 24 h before drug treatment, although the magnitude of these responses varied according to the precise steroid treatments. The hypothalamic-pituitary axis was also responsive to naloxone just before the progesterone-induced LH surge in oestrogen-primed ovariectomized rats. Results show that gonadal steroids are permissive to the effects of opiate drugs, but they suggest that endogenous opioid systems do not necessarily mediate the negative feedback effects of steroids. Some other factor(s), as yet unidentified in the rat, may control the opioid modulation of gonadotrophin secretion or exert an independent inhibitory effect on gonadotrophin release.
J. Endocr. (1986) 110, 327–334
An in-situ isolated rat adrenal perfusion system for study of neurally mediated catecholamine secretion: effects of morphine, a Met-enkephalin analogue, and naloxone on catecholamine secretion
Authors: Bouloux P.-M. G. , Perrett D. , Sopwith M. , Besser G. M. 
Published: December 2008

ABSTRACT
An in-situ isolated rat adrenal perfusion technique has been devised to study the opioid control of neurally mediated adrenomedullary catecholamine release. Adrenomedullary catecholamine secretion was induced by electrical stimulation of the cut end of the left descending thoracic sympathetic chain on platinum electrodes. The half-maximal stimulatory potential (ED50) of the system was 8 V, 20 Hz, with 300μs pulse width. Basal release of catecholamine from the adrenal was constant using a perfusion flow rate of 100–300μl/min, but increased significantly with increasing perfusion temperature over the range 36–38 °C. Following repetitive 30-s stimulation of the left thoracic sympathetic chain, and 3-min fraction collections, the total amount of catecholamine released per fraction remained within 80–100% of the maximum release for up to eight consecutive stimuli. The release of catecholamines was completely blocked by hexamethonium (0·1 mmol/l), but recovered to preblockade values within two further stimuli. Using the ED50 and the first three stimuli as control, the effects of morphine (10 nmol/l–1 mmol/l), d-Ala2-MePhe4-Met-enkephalin-(O5)-ol (DAMME; 10 nmol/l–0·1 mmol/l) and naloxone (10 nmol/l– 10 μmol/l) on the response to the next three stimuli were compared. Morphine, DAMME or naloxone did not significantly alter the amount of catecholamine released by this form of stimulation. Therefore in the rat, under the conditions used, there is no evidence for mu (μ) or delta (†) opiate modulation of neurally mediated catecholamine release from the rat adrenal medulla.
J. Endocr. (1986) 111, 7–15
Evidence of gonadal steroid-independent changes in activity of the central LH-releasing hormone pulse generator in developing bull calves
Authors: D'Occhio M. J. , Gifford D. R. , Weatherly T. , Setchell B. P. 
Published: December 2008

ABSTRACT
To ascertain whether temporal changes in activity of the hypothalamo-pituitary axis in prepubertal bulls may occur independently of shifts in sensitivity to steroid feedback, the acute post-castration rise in serum gonadotrophins was monitored in bull calves castrated at monthly intervals from 4 to 9 months of age. Since a major feature of the gonadotrophin profiles of developing bulls is a change in LH pulse frequency early in life, pulsatile LH secretion after castration was used as an index of activity of the central LH-releasing hormone (LHRH) pulse generator. Relative to the day of castration (day 0) bull calves (n = 4) were bled at 20-min intervals for 8 h on day −3 and at 10-min intervals for 4 h on days 3, 5 and 7. During the first week after castration, 4-month-old bulls showed a higher (P<0·05) frequency of LH pulses compared with bulls at 8 and 9 months (1·13, 0·88 and 0·75 pulses/h respectively; pooled s.e.m.= 0·13). Mean LH levels before castration were higher (P<0·05) in 4-month-old bulls than in bulls at 7, 8 and 9 months (0·92, 0·37, 0·31, 0·38 μg/l respectively; pooled s.e.m. = 0·12). After castration mean LH levels did not differ with age. Mean FSH levels did not differ among age groups either before or after castration. Increased serum LH levels in 4-month-old bulls confirmed the transient rise in LH secretion that occurs at this time in developing bull calves. Age-related differences in LH pulse frequency observed after castration suggested that in prepubertal bulls changes in activity of the central LHRH pulse generator can occur independently of steroid feedback mechanisms.
J. Endocr. (1986) 111, 67–73
Relaxin acts centrally to inhibit oxytocin release during parturition: an effect that is reversed by naloxone
Authors: Jones S. A. , Summerlee A. J. S. 
Published: December 2008

ABSTRACT
Experiments were carried out to establish whether infusion of relaxin prolongs gestation and labour in the rat by suppressing release of oxytocin, and whether the effects of relaxin on birth could be reversed by the opioid antagonist naloxone. Female rats were implanted with subcutaneous osmotic minipumps for the infusion of purified porcine relaxin into the jugular vein for 84 h from either day 19 or day 20 of gestation. Infusion of relaxin delayed the onset of labour and in those animals which delivered during relaxin infusion, delivery was longer by approximately 45 min. Plasma oxytocin levels 40 min after delivery of the first fetus were 45·25 ± 3·6 pmol/l (mean ± s.d.) in unoperated controls and significantly (P < 0·01) depressed (23·89 ± 3·9) in rats that delivered during infusion of relaxin. Rats that delivered after the infusion of relaxin had finished, gave birth significantly (P < 0·05) faster than controls and plasma oxytocin levels were significantly (P < 0·01) raised (77·87 ±15·9 pmol/l). Naloxone treatment (1 mg/kg; i.m.) given immediately after the delivery of the first fetus reversed the inhibitory effect of relaxin and the interval between successive deliveries was slightly faster than that of controls. Plasma oxytocin levels in relaxin-infused naloxone-treated rats were significantly (P < 0·01) higher than values in unoperated control rats. The results confirm that relaxin suppresses oxytocin release possibly through an opioid system and this may be important in the control of the timing of birth.
J. Endocr. (1986) 111, 99–102
Induction of ovulation during anoestrus in two breeds of sheep with multiple injections of LH alone or in combination with FSH
Authors: Wallace J. M. , McNeilly A. S. , Baird D. T. 
Published: December 2008

ABSTRACT
The gonadotrophic requirements for the induction of ovulation and formation of a viable corpus luteum in two breeds of seasonally anoestrous sheep of differing fecundity was investigated.
Welsh Mountain (n = 20) and Damline ewes (n = 19) were given LH or FSH either alone or in combination. Luteinizing hormone was injected i.v. at an increasing frequency for 72 h (one injection every 3 h for 24 h, one every 2 h for 24 h, and one every hour for 24 h) and FSH was injected in an identical manner for the first 36 h of treatment.
Exogenous LH alone and in combination with FSH induced a preovulatory LH surge in all 19 ewes and ovulation in 18 out of 19 ewes of both breeds. However exogenous FSH alone was ineffective. The incidence of normal corpus luteum function in ewes induced to ovulate was low and not related to treatment, timing or magnitude of the LH/FSH surge. It is concluded that in both breeds studied (a) it is the infrequency of LH pulses which limits the development of preovulatory follicles during seasonal anoestrus, (b) that the requirement for FSH remains unknown, and (c) that the induction of inadequate corpora lutea during seasonal anoestrus reflects either defects in hormonal priming of the preovulatory follicle and/or inappropriate luteotrophic support after ovulation.
J. Endocr. (1986) 111, 181–190
Sexual dimorphism in immunoneutralization of bioactivity of rat and ovine inhibin
Authors: van Dijk S. , Steenbergen J. , Gielen J. Th. , de Jong F. H. 
Published: December 2008

ABSTRACT
Inhibin was partially purified from bovine follicular fluid using chromatography on immobilized Procion Red 3B and anion-exchange chromatography. Ovariectomized Texel ewes were immunized against the inhibin-containing fraction from the Procion Red 3B column and the immune response was subsequently boosted with similar fractions or with the preparation obtained from the anion-exchange column. The potencies of the resulting antisera were evaluated in an invitro bioassay system for estimating inhibin activity, using dispersed rat pituitary cells. The antisera were found to inhibit the bioactivity of inhibin preparations from ovarian follicular fluid of bovine, porcine, ovine or human origin, as well as inhibin activity in ovine testicular lymph and rete testis fluid, in culture media from rat granulosa and rat Sertoli cells and in homogenates of rat ovaries and testes. These results indicate that the inhibin molecules from several species contain a common bioactive moiety. The results also showed that the antiserum was more effective in neutralizing inhibin activity from ovarian than from testicular sources in both sheep and rat, indicating a sex-related difference in the inhibin molecules within a species.
J. Endocr. (1986) 111, 255–261
Differential effects of catecholoestradiol-17β and oestradiol-17β on concentrations of plasma LH in the fetal pig
Authors: Parvizi N. 
Published: December 2008

ABSTRACT
The effects of 2-hydroxyoestradiol-17β and oestradiol-17β on the concentration of serum LH was studied in fetal pigs. 2-Hydroxyoestradiol-17β (5 μg/fetus; n = 6), oestradiol-17β (5 μg/fetus; n = 7) or vehicle (n = 6) were injected i.v. into chronically catheterized fetal pigs at gestational ages of 105–108 days. Seven additional fetuses at the same age served as untreated controls. 2-Hydroxyoestradiol-17β but not oestradiol-17β resulted in a rapid decline in plasma LH levels from 0·82 ± 0·21 (s.e.m.) to 0·21 ± 0·05 μg/l within 20 min of injection. Baseline concentrations of plasma LH in the mothers were low (0·72 ±0·2 μg/l) and were not affected by catecholoestrogen or oestrogen treatment of fetuses. The results suggest that catecholoestrogens do not modulate LH secretion in fetal pigs through an oestrogenic action. It is possible that they act by modifying catecholamine metabolism or neurotransmission.
J. Endocr. (1986) 111, 297–300
Developmental changes in gonadotrophins and testicular gonadotrophin receptors in the pig, from neonatal to adult life
Authors: Vandalem J. L. , McNamara M. , Petit R. , Hennen G. 
Published: December 2008

ABSTRACT
Changes in the concentrations of LH and FSH testicular receptors have been studied in the pig, from neonatal to adult life, and correlated with blood LH, FSH and testosterone concentrations.
Quantification of gonadotrophin receptors was performed in equilibrium binding studies, using homologous systems. The presence of high-affinity binding sites for LH and FSH (association constant (Ka): LH ∼ 20 litres/nmol; FSH ∼ 10 litres/nmol) was demonstrated in the testes of all animals studied. The apparent affinity of LH and FSH receptors did not change significantly with age.
During the first weeks of life, there was a transient rise in LH receptor content, reaching a maximum of 8·7 ± 2·2 (mean ± s.e.m.) pmol/g testis at 24 days of age. This was correlated with a peak in testosterone secretion and reflects the second wave of interstitial cell proliferation in the pig. A second increase in the number of LH receptors occurred after 12 weeks of age and corresponds to pubertal maturation and final differentiation of adult Leydig cells. During this period, circulating concentrations of testosterone markedly increased without any significant variation in LH blood levels, suggesting a change in testicular sensitivity to LH in the maturing pig.
A continuous increase in FSH receptor content was observed from the neonatal to the adult pig. This increase occurred in two phases. During the first 2 months of life, the increase in the number of FSH receptors exceeded that of testis growth rate and resulted in an increase in FSH receptor concentrations which reached a peak at 12·1 ± 1·8 pmol/g testis, at week 9. After this time the increase in the amount of FSH receptors was slower than that of testis weight gain, leading to a decrease in receptor concentration.
Since changes in the amounts of LH and FSH receptor concentrations were not correlated with variations in gonadotrophin concentrations in the blood, an inductive role for FSH on LH receptors, as has been shown in the rat, could thus not be demonstrated in the pig.
J. Endocr. (1986) 111, 301–308
Angiogenesis in reproductive tissues
Authors: Findlay J. K. 
Published: December 2008

ABSTRACT
Angiogenesis is the process of generating new capillaries and leads, therefore, to vascularization of tissues. This process occurs during embryological development and during pathological and physiological conditions in adult life, including those involving the reproductive organs. Recent studies, in the field of tumour biology in particular, have led to the identification of several factors responsible for inducing angiogenesis and the elucidation of ways of modulating their activity. This review summarizes our knowledge of angiogenesis in the ovary, testis, endometrium and placenta, and suggests ways in which further research might contribute to a better understanding of the processes controlling reproduction and identify new approaches to the regulation of fertility.
J. Endocr. (1986) 111, 357–366