bluuebunny/crossref_metadata_2025_split huggingface dataset:
Fetal and maternal production and metabolism of gastrin in sheep
Authors: Shulkes Arthur , Chick Patricia , Hardy K. J. 
Published: December 2008

In the sheep fetus, plasma levels of gastrin are raised above adult levels from 2 weeks before birth. This observation initiated the present study on the maternal and fetal secretion rate, metabolism and placental transfer of gastrin. The experiments were performed on conscious pregnant ewes with chronically cannulated fetuses and on newborn lambs. Metabolic clearance rate (MCR), production rate (PR) and placental transfer of gastrin were measured by alternate steady-state infusion of gastrin into the mother and fetus. Plasma levels of gastrin were measured by radioimmunoassay.
Metabolic clearance rate was similar in the pregnant and non-pregnant ewe (8·4± 1·1 (s.e.m.) and 9·0±1·4 ml/min per kg) respectively. However, fetal MCR was significantly increased. Term was 145 days. Metabolic clearance rate was 15·5 ± 1·7 at 110–125 days of gestation, 25·6 ± 2·9 at 126–135 days, 29·7 ± 4·9 at 136–145 days and remained raised in the first 2 weeks post partum.
Gastrin did not cross the placenta in either direction. Placental destruction of gastrin was not responsible for the increased fetal MCR as umbilical artery and umbilical vein levels were not significantly different during fetal gastrin infusion. Furthermore, MCR remained raised in the newborn lambs. Gastrin PR was significantly increased at all ages.
The results showed that the previously reported fetal hypergastrinaemia is from fetal sources and is not a result of immaturity of clearance mechanisms. In fact, fetal MCR was significantly increased. The increased fetal plasma gastrin levels are due to an increased rate of production from the fetus.
Effect of progesterone on the non-genomic response to oestrogen in the rat
Authors: Grunert Germana , Tchernitchin A. N. 
Published: December 2008

Different effects of oestrogen are mediated separately, by independent mechanisms of action. Accordingly, it has been shown that it is possible to dissociate these effects under various conditions which stimulate or inhibit responses selectively. The present study describes the action of progesterone on non-genomic responses to oestrogen stimulation which, it has been suggested, are mediated by eosinophils.
Oestrogen induced an increase in the number of eosinophils in the rat uterus, an increase in uterine wet weight and oedema of deep endometrial stroma (measured as decrease in cellular density). Progesterone induced a slight oedematous reaction in superficial endometrial stroma but did not induce uterine eosinophilia. Progesterone pretreatment of oestrogen-treated rats did not block oestrogen-induced uterine eosinophilia and oedema but induced an increase in the degranulation of uterine eosinophils. Therefore the number of eosinophils decreased without any change in the uterine oedema induced after 6 h of oestrogen action. The results corroborate previously published evidence of a dissociation of the action of oestrogen in independent groups of responses. Progesterone, a known blocker of some oestrogenic responses, did not block the effects mediated by eosinophils at 6 h after oestrogen administration; any change in these effects at later times can be explained by an earlier eosinophil degranulation under the action of progesterone.
Effects of pancreatectomy, tolbutamide and insulin on glucose fluxes in chickens
Authors: Danby R. W. , Martin I. K. , Gibson W. R. 
Published: December 2008

The effects of pancreatectomy and of injection of insulin or tolbutamide on glucose fluxes in chickens were examined. This was prompted by earlier observations that tolbutamide seems not to require the presence of pancreatic insulin for its acute hypoglycaemic action in this species. Rates of appearance (Ra) and disappearance (Rd) of glucose were estimated by isotope dilution using [14C]glucose in single-injection experiments and [14C]glucose and [6−3H]glucose in priming-injection + constant-infusion experiments.
Six hours after sub-total pancreatectomy (splenic lobe remained in situ), chickens were hyperglycaemic (16·7 v. 10·4 mmol glucose/l in controls), had a larger sampled glucose pool (4·41 v. 3·10 mmol) and a higher average rate of glucose utilization (41·7 v. 33·3 μmol/kg per min) than sham-operated controls as estimated in single-injection experiments. Tolbutamide (50 mg/kg injected i.v.) reduced Ra in intact chickens from 33·9 to 1·1 μmol/kg per min and reduced Ra in pancreatectomized chickens from 42·2 to 10·2 μmol/kg per min. In priming-injection + constant-infusion experiments tolbutamide again reduced Ra significantly. In all cases Rd tended to fall, apparently as a result of the developing hypoglycaemia. Tolbutamide did not affect the volume of extracellular fluid (sucrose space). In single-injection experiments, insulin (1 unit/kg injected i.v.) reduced Ra by 56% and transiently increased Rd by 39%.
It was concluded that pancreatectomy and injection of insulin or tolbutamide produce responses in glucose movements in chickens that are qualitatively similar to those in mammals. In chickens the hypoglycaemic action of tolbutamide, which persists in the absence of the pancreas, depends on an inhibition of glucose release by the liver.
Androgen and oestrogen dynamics in hyperthyroidism
Authors: Ridgway E. C. , Maloof Farahe , Longcope Christopher 
Published: December 2008

Using constant infusions of [3H]testosterone and [14C]oestradiol or [3H]androstenedione and [14C]oestrone the dynamics of androgen and oestrogen metabolism and production in patients with hyperthyroidism were measured.
The metabolic clearance rates of testosterone and oestradiol were decreased but those of androstenedione and oestrone were within the normal range. The conversion ratios of testosterone to androstenedione and of testosterone to dihydrotestosterone (DHT) were decreased whereas those of androstenedione to testosterone and androstenedione to DHT were increased. These changes could be explained by increased serum levels of sex hormone binding globulin which binds testosterone and DHT but not androstenedione.
The fraction of androstenedione infused into and measured as oestrone in the blood was normal in seven out of nine subjects and the fraction of testosterone infused and measured as oestradiol was normal in all nine subjects.
The production rates of testosterone and oestradiol were in the normal range but the production rates of androstenedione and oestrone were raised in half the subjects.
Somatomedin activity and growth hormone levels in body fluids of the fetal pig: effect of chronic hyperinsulinaemia
Authors: Spencer G. S. G. , Hill D. J. , Garssen G. J. , Macdonald A. A. , Colenbrander B. 
Published: December 2008

Chronic hyperinsulinaemia in the presence of euglycaemia was obtained in pig fetuses between 90 and 104 days gestational age (term is 114 days) by the implantation of insulin-filled osmotic minipumps. At 104 days these fetuses were compared with both saline-implanted controls and with unoperated fetuses from the same sows.
Mean plasma GH levels were the same in all three treatment groups and were much greater than in the maternal peripheral venous circulation. Levels of GH in amniotic fluid were low, and even lower levels were measured in lung fluid. Glucose and protein levels were also lower in amniotic fluid than in plasma and lower still in lung fluid. In contrast, somatomedin activity was higher in amniotic and lung fluids than in fetal plasma and, when expressed relative to protein content, was highest in lung fluid. Insulin-treated fetuses had significantly (P < 0·05) higher levels of somatomedin activity than control fetuses, but despite this were neither longer nor heavier than control fetuses. From these data it is concluded that neither insulin nor somatomedin directly affect fetal growth.
Effects of oestradiol, progesterone and androstenedione on the pulsatile secretion of luteinizing hormone in ovariectomized ewes during spring and autumn
Authors: Martin G. B. , Scaramuzzi R. J. , Henstridge J. D. 
Published: December 2008

The effects of oestradiol-17β, androstenedione, progesterone and time of the year on the pulsatile secretion of LH were tested in ovariectomized Merino ewes (n = 32). The steroids were administered by small subcutaneous implants, and the LH pulses were observed in samples taken at intervals of 15 min for 12 h in spring 1979, autumn 1980 and spring 1980, seasons corresponding to successive periods of anoestrus, breeding season and anoestrus.
During spring, oestradiol alone was able to reduce the frequency of the LH pulses, while progesterone, either alone or in combination with oestradiol, had little effect. During autumn, on the other hand, neither oestradiol nor progesterone could significantly reduce the frequency of the pulses when administered independently, whereas the combined treatment was very effective. Androstenedione had no significant effect on pulse frequency at either time of the year, either alone or in any combination with oestradiol and progesterone.
The basal levels of LH, over which the pulses are superimposed, were reduced by oestradiol alone in both seasons. Progesterone alone had no consistent effects, but interacted significantly with oestradiol and this combined treatment maintained low basal levels most effectively at all times. Androstenedione had no significant effect.
The amplitude of the pulses increased throughout the course of the experiment. Within seasons, the amplitudes were significantly higher in the presence of oestradiol and progesterone, but were not significantly affected by androstenedione.
It was concluded that certain of the ovarian steroids exert negative feedback on the tonic secretion of LH primarily by reducing the frequency of the pulses, and that the changes in LH secretion attributable to season and phases of the oestrous cycle can be accounted for entirely by the responses of the hypothalamus to oestradiol and progesterone. The role of the androstenedione secreted by the ovary in the ewe remains obscure.
Co-operation of progesterone and prostaglandins in ovulation induced by human chorionic gonadotrophin in immature rats primed with pregnant mare serum gonadotrophin
Authors: Kohda Heigo , Mori Takahide , Nishimura Toshio , Kambegawa Akira 
Published: December 2008

Serial injections of a mixture of prostaglandin (PG) E2 and F2α 0, 2, 4, and 6 h after simultaneous injection of human chorionic gonadotrophin (hCG) and indomethacin incompletely restored the ovulation that would have been blocked by indomethacin in immature rats treated with pregnant mare serum gonadotrophin followed by hCG. Serial injections of another mixture of PGE2 and PGF2α 6, 8, 10 and 12 h after simultaneous injection of hCG and indomethacin similarly reversed, in part, the inhibitory effects of indomethacin on hCG-induced ovulation. In contrast, serial injections of the mixtures of PGE2 and PGF2α 0, 2, 4, 6, 8, 10 and 12 h after simultaneous injection of hCG and indomethacin completely restored the indomethacin-blocked ovulation, suggesting that the prostaglandins mediate the action of hCG on ovulation both in the earlier and later stages of the preovulatory process.
Six hours after simultaneous injection of hCG and indomethacin serial injections of a mixture of PGE2 and PGF2α reproduced the acute and temporary increase in concentrations of progesterone and testosterone in plasma which would have been abolished by indomethacin. Progesterone given concurrently with hCG and indomethacin partially antagonized the inhibitory action of indomethacin on ovulation. Serial injections of a' mixture of PGE2 and PGF2α 6, 8, 10 and 12 h after concurrent administration of progesterone with hCG and indomethacin completely restored the indomethacin-blocked ovulation, suggesting that progesterone can substitute the action of prostaglandins injected serially in the first half of the preovulatory process.
It was concluded that the co-operation of progesterone in the earlier stage and of prostaglandins in the later stage of the preovulatory interval is required to mediate the action of hCG on ovulation.
Effects of oestradiol benzoate and progesterone on luteinizing hormone release and catecholamine turnover in the preoptic-hypothalamic brain area of ovariectomized rats
Authors: Hiemke C. , Frohne D. , Bruder D. , Ghraf R. 
Published: December 2008

At noon, long-term (4–6 weeks) ovariectomized rats were exposed for 6–78 h to a single subcutaneous injection of oestradiol benzoate (20 μg) which significantly reduced the serum levels of LH over the whole time-interval investigated. The negative feedback action of oestradiol was accompanied by reduced turnover of both noradrenaline and dopamine in the preoptic-anterior hypothalamic brain area (POAH), but not in the mediobasal hypothalamus, 6, 68 and 72 h after administration of the hormone. Between 72 and 78 h after oestradiol-priming an afternoon increase of noradrenaline turnover was observed in the POAH. In rats primed with oestradiol benzoate for 72 h, short-term exposure (6 h) to progesterone (2·5 mg) induced a marked surge of serum LH and FSH in the late afternoon. In the POAH of these rats progesterone did not interfere with the afternoon increase of noradrenaline turnover induced by oestradiol-priming. However, it markedly increased the dopamine turnover rate of primed rats, thus reversing the inhibitory action of oestradiol benzoate on the dopaminergic system of the POAH.
It is concluded that both the noradrenergic and the dopaminergic neurones of the POAH are involved in the negative and positive feedback actions of oestradiol and progesterone on LH and FSH release. The paper discusses whether the oestradiol-induced afternoon increase in noradrenaline turnover represents a prerequisite for the induction of LH surges by progesterone.
Serotonin-reinstatement of luteinizing hormone surges after loss of positive feedback in ovariectomized rats bearing subcutaneous capsules containing oestrogen
Authors: Walker R. F. 
Published: December 2008

In ovariectomized rats treated chronically with oestrogen there is a loss of positive feedback effects on LH secretion. This was not due to depletion of pituitary LH since injection of LH releasing hormone (LH-RH; 50 ng/100 g body wt) caused a significant (P < 0·01) rise in serum LH even after the loss of spontaneous LH surges. However, the magnitude of the increase in serum LH in response to LH-RH was greater (412 ± 41 μg/l) before than after (291 ± 29 μg/l) loss of the LH surges. Excessive blood sampling was also not responsible, since positive feedback responses declined comparably in rats bled daily or once every 3–4 days.
Progesterone (0·5 mg s.c.), administered for 5 consecutive days, failed to restore LH surges indicating that deficiency of this steroid after ovariectomy does not cause positive feedback responses to disappear in rats exposed chronically to oestrogen. Moreover regular daily fluctuations in serum progesterone, probably of adrenal origin, occurred before as well as after daily LH surges were lost.
Serotonin content and turnover were depressed (P < 0·05) when ovariectomized rats first received the subcutaneous capsules containing oestrogen. This change correlated temporally with the onset of daily LH surges and was eventually lost. After 30 days exposure to oestrogen, serotonin turnover increased (P < 0·01) and positive feedback responses were absent. Catecholamine levels and turnover did not show differential responses to oestrogen and were depressed after acute as well as chronic steroid treatment.
p-Chlorophenylalanine (pCPA; 250 mg/kg)+ l-dihydroxyphenylalanine (l-DOPA; 200 mg/kg), which depress serotonin and enhance catecholamine synthesis respectively, failed to reinstate LH surges, but these were restored in 22% of the rats receiving l-DOPA alone. pCPA, followed 2 days later by 5-hydroxytryptophan (5-HTP) at 11.00 h, reinstated LH surges in 88% of rats, and a dose–response curve showed that as little as 4 mg 5-HTP/kg stimulated repetitive LH surges when given with pCPA according to this schedule. However, the administration of α-methyl-p-tyrosine + l-DOPA, an analogous treatment involving catecholamines, was only marginally effective (15%).
These findings suggest that perturbations of monoamine metabolism occurring in ovariectomized rats exposed to oestrogen for several weeks contribute to loss of daily LH surges. Since pCPA + 5-HTP restored LH surges most effectively, then positive feedback may disappear as the facilitatory effect of serotonin is lost after chronic oestrogen administration.
An investigation of diurnal and cyclic changes in the secretion of luteinizing hormone in the domestic hen
Authors: Wilson S. C. , Jennings R. C. , Cunningham F. J. 
Published: December 2008

The characteristics of the diurnal rhythm in the concentration of LH in plasma of the domestic hen varied according to age and duration of photoperiod. A pronounced increase in LH was observed at the onset of darkness in immature hens whether maintained on schedules of 16 h light:8 h darkness (16L:8D) or 8L:16D. During weeks 4·5–15 or −17·5 raised concentrations of LH were maintained until 6 and 12 h after the onset of darkness in hens held on 16L:8D and 8L:16D respectively. By 19 weeks of age the diurnal rhythm of LH secretion had changed to resemble more closely that observed in the laying hen. An increase in the concentration of LH in plasma at the onset of darkness was of comparatively short duration and gave way, within 2–3 h, to a steep decline before a further slight increase in LH, which tended to occur at 11–14 h after the onset of darkness.
Superimposed on this diurnal rhythm of LH secretion in the laying hen were a one- to threefold increase in the concentration of LH during 8–4 h before ovulation and a much less pronounced increase in LH during 0–8 h after ovulation. The pattern of changes in the concentration of LH in plasma during the ovulatory cycle was not modified by the repeated withdrawal of blood at intervals of 2 h.
Effect of human pituitary luteinizing hormone administration on plasma levels of dehydroepiandrosterone, androstenediol and their sulphates and testosterone in women with secondary amenorrhoea
Authors: Sirinathsinghji D. J. S. , Mills I. H. 
Published: December 2008

Human pituitary LH (1200 i.u.) was infused for 4 h (from 10.00 to 14.00 h) into six women with anorexia nervosa and into five women with polycystic ovarian disease (PCO). Plasma dehydroepiandrosterone sulphate (DHAS), androstenediol sulphate, dehydroepiandrosterone (DHA), androstenediol and testosterone were estimated by gas–liquid chromatography in blood samples taken every 2 h from 10.00 to 20.00 h. The values were compared with those obtained at the same times on the previous control day. There were no significant changes in the plasma levels of DHAS and androstenediol sulphate in response to LH at any of the sampling times in either the anorexia nervosa or the PCO patients. In the anorexia nervosa women, plasma DHA levels were significantly increased at 16.00 (P<0·001), 18.00 (P<0·001) and 20.00 h (P<0·05) after LH infusion. In the PCO women, DHA levels increased significantly at 14.00 (P<0·01), 16.00 (P<0·001), 18.00 (P<0·001) and 20.00 h (P<0·001) in response to LH infusion. Plasma androstenediol levels increased significantly in the anorexia nervosa patients at 12.00 (P<0·001), 14.00 (P<0·01) and 16.00 h (P<0·01) in response to LH. Similar increases were also found in the PCO patients at 12.00 (P<0·01), 14.00 (P<0·001) and 16.00 h (P<0·01). Plasma testosterone decreased progressively in the anorexic women in response to LH, becoming significant at 16.00 (P<0·05), 18.00 (P<0·05) and 20.00 h (P<0·01). A similar progressive decrease in plasma testosterone was seen in the PCO women, the levels being significantly lower than controls at 16.00 (P<0·05), 18.00 (P<0·05) and 20.00 h (P<0·05).
The results represent the first experimental evidence for a direct regulatory role for LH on androgen secretion in women. In addition, the data have a significant bearing on the pathogenesis of the PCO syndrome and the development of hirsutism which may be directly related to the high androgen levels in PCO women in whom the levels of LH are normally raised. The data may also offer an explanation for the mechanisms responsible for the low androgen levels in anorexia nervosa patients in whom there is a gonadotrophin deficiency.
Modulation of luteinizing hormone receptors: effect of an inhibitor of prolactin secretion, p-coumaric acid
Authors: Chowdhury Mridula , Kabir S. N. , Pal A. K. , Pakrashi Anita 
Published: December 2008

Daily oral administration of p-coumaric acid (PCA) at a dose of 50 mg/kg body wt for 21 days to adult male mice caused a dramatic reduction in serum prolactin concentrations. A significant fall in testicular LH binding was also observed after PCA treatment. Complete recovery of testicular LH binding was obtained by daily administration of prolactin (500 μg/mouse) when given simultaneously from day 9 of PCA treatment. A lower daily dose of prolactin (250 μg) was found to be ineffective.
Scatchard analysis of binding data suggested a decrease in the number of testicular LH binding sites after PCA treatment whereas the affinity constant was unchanged.
These results provide direct evidence for an inhibitory effect of PCA on prolactin secretion and also provide additional evidence in favour of a role of prolactin in the modulation of LH receptors.