bluuebunny/crossref_metadata_2025 huggingface dataset:
PATTERNS OF PLASMA CONCENTRATIONS OF INSULIN AND GLUCAGON AFTER INTRAVASCULAR AND INTRARUMINAL ADMINISTRATION OF VOLATILE FATTY ACIDS IN THE GOAT
Authors: DE JONG A.
Published: December 2008

To determine whether volatile fatty acids (VFA) are involved in the regulation of plasma concentrations of insulin or glucagon in the goat, VFA, separately or in combination, were administered into the jugular vein, the portal vein or the rumen, and their effects on pancreatic hormones as well as on VFA measured in venous blood. Propionate, n-butyrate and n-valerate, but not acetate, injected in pharmacological doses, were potent stimuli not only of the secretion into the plasma of insulin but also of glucagon. As regards insulin, the response to VFA was probably not mediated to an appreciable extent by glucose or glucagon. β-Hydroxybutyrate did not mediate the effect of n-butyrate on insulin and glucagon. The effects of VFA appear to be peculiar to the ruminant since in the rat injection of similar doses resulted in either no changes or very small changes of plasma insulin and glucagon.

Intraportal infusions over 4 h of mixtures of VFA, resulting in less extreme, more physiological blood concentrations of VFA, elicited sudden transient increases in insulin and to a lesser extent in glucagon. After these peaks insulin and glucagon declined to preinfusion levels and remained virtually unaltered during the remainder of the infusion in spite of sustained, raised concentrations of VFA in the peripheral circulation. These results suggest that under these conditions the rate of increase of VFA is a signal for the secretion of pancreatic hormones. Intraruminal infusions, representing a more physiological route of administration, of single VFA at high rates resulted in a small increase in insulin for propionate infusion only, whereas a mixture of VFA at a physiological rate induced barely any change in insulin or glucagon. It is concluded that under physiological conditions the rate of increase of VFA may contribute to the insulin secretion in the free-feeding goat, but it is unlikely that VFA are the sole controlling agents of insulin release. It is even less probable that the release of glucagon is governed by VFA in the free-feeding goat.
CORRELATION OF IODIDE TRANSPORT WITH Na+, K+ -ATPase, HCO−3-ATPase AND CARBONIC ANHYDRASE ACTIVITIES IN DIFFERENT FUNCTIONAL STATES OF THE RAT THYROID GLAND
Authors: CHOW S.-Y. , KEMP J. W. , WOODBURY D. M.
Published: December 2008

The effects of thyrotrophin, hypophysectomy, and chronic treatment with thyroxine and methimazole on radioiodide uptake (thyroid/plasma (T/P) 125I− ratio), protein and DNA contents and activities of Na+,K+ -ATPase, HCO−3-ATPase, and carbonic anhydrase (CA) of rat thyroid gland were evaluated. Thyrotrophin given to intact rats slightly increased thyroid iodide uptake, did not affect protein or DNA content, and slightly inhibited CA activity (units/g cell water). Hypophysectomy markedly decreased T/P 125I− ratio, increased protein content, decreased activity of Na+,K+-ATPase, and slightly increased HCO−3-ATPase (nmol/mg DNA per min) and CA (units/g cell water) activities. Thyro-trophin given to hypophysectomized rats (as compared with untreated hypophysectomized control animals) markedly increased T/P 125I− ratio, slightly decreased protein content and decreased Na+,K+-ATPase and CA activities. Chronic treatment with methimazole increased T/P 125I− ratio, decreased protein content, markedly increased Na+,K+-ATPase and HCO−3-ATPase activities, and decreased CA activity. Chronic treatment with thyroxine, in contrast, decreased T/P 125I− ratio, decreased Na+,K+-ATPase activity, and increased CA activity. There was a significant inverse correlation between T/P 125I− ratio and CA activity in follicular cells for the various induced functional states of the thyroid.
FEEDBACK EFFECT OF OESTROGEN ON LUTEINIZING HORMONE SECRETION BY THE RAT PITUITARY GLAND
Authors: HIGUCHI TAKASHI , KAWAKAMI MASAZUMI
Published: December 2008

Ovariectomized rats with neural deafferentation at the level of the posterior border of the anterior hypothalamic area (AC rats) were used to re-evaluate the direct feedback effect of oestrogen on the regulation of LH secretion by the pituitary gland. Synthetic LH releasing hormone (LH-RH; 300 ng/kg), injected at 30-min intervals into AC rats with undetectable basal LH, induced pulsatile increase of serum LH concentrations. Oestradiol-17β (5 μg), administered i.v. just before the first LH-RH injection, significantly decreased the LH response to a second injection of LH-RH given 30 min later and to subsequent injections. Maximal inhibition was 58%. Oestradiol-17β (5 μg) given i.v. to control ovariectomized rats decreased serum LH concentrations 40 min after administration; the maximum reduction being 52%. An s.c. injection of oestradiol benzoate (5 μg) increased pituitary responsiveness to LH-RH by the next day in AC rats but decreased serum LH levels in control ovariectomized rats. These results indicate that acute inhibitory and chronic facilitatory effects of oestrogen on LH secretion are exerted at the pituitary gland, without a change in LH-RH secretion. The prolonged inhibitory effect of oestrogen is at the level of the hypothalamus and causes a reduction in LH-RH secretion.
Modulation by catecholamines and thyrotrophin of cyclic AMP response to β-adrenergic stimulation by cultured porcine thyroid cells
Authors: Dumas D. , Charrier B. , Margotat A. , Mauchamp J.
Published: December 2008

Thyroid cell cyclic AMP synthesis is stimulated by β-adrenergic agonists. We have characterized this sensitivity on cultured porcine thyroid cells and have studied its modulation by chronic treatment with thyrotrophin.

The synthesis of cyclic AMP in intact porcine thyroid cells in primary culture was stimulated by the β-adrenergic agonist, isoproterenol. This stimulation was dose-dependent and was inhibited by the β-adrenergic antagonists propranolol and alprenolol. The cell responsiveness (i.e. the response elicited by 5 μm-isoproterenol after 5-min stimulation) was increased when the cells were cultured in the absence of thyrotrophin. Thyrotrophin, when present in the culture medium at the onset of culturing, inhibited this increase. A concentration of 100 μu. thyrotrophin/ml was sufficient to reduce the cyclic AMP response to 15% of its control value. Prostaglandin E2 or dibutyryl cyclic AMP did not mimic the effect of thyrotrophin. The low sensitivity of thyrotrophin-treated cells to β-adrenergic agonists could be explained by a decreased number of β-adrenergic receptors. [125I]Iodohydroxybenzyl pindolol specific binding was ten times greater in membrane preparations of control cells than in membranes derived from thyrotrophin-treated cells. The β-adrenergic sensitivity of cultured thyroid cells was also decreased after long-term treatment by terbutaline. A time- and dose-dependent desensitization was observed.
Effect of high-dose oestrogen administration on the growth and prolactin receptor content of N-nitrosomethylurea-induced mammary tumours in the rat
Authors: Manni Andrea , Rainieri John , Arafah B. M. , Pearson O. H.
Published: December 2008

The effect of chronic administration of a high dose of oestradiol benzoate (OB) on growth and prolactin receptor content of the N-nitrosomethylurea (NMU)-induced rat mammary tumour was investigated. Daily i.m. administration of 50 μg OB for 8 days to tumour-bearing rats induced marked reduction in tumour size which was already significant after only three injections. Simultaneous daily administration of 1 mg perphenazine to stimulate endogenous prolactin release counteracted the inhibitory effect on tumour growth of OB but only partially since the tumours grew significantly more when perphenazine was injected alone. No treatment significantly affected prolactin receptor content in the tumours. We concluded that administration of pharmacological doses of OB has a potent antitumour action on the NMU-induced rat mammary tumour. This effect can only partially be explained by inhibition of the peripheral action of prolactin.
Characterization and properties of a progesterone receptor in the uterus of the quokka (Setonix brachyurus)
Authors: Owen F. J. , Cake M. H. , Bradshaw S. D.
Published: December 2008

A progesterone receptor system, with a high specificity for progestins, was detected in the uterine tissue of the marsupial, Setonix brachyurus (quokka), using the synthetic progestin 17α,21-dimethyl-19-nor-4,9-pregnadiene-3,20-dione (R5020). The apparent equilibrium dissociation constant of the ligand binding to the cytosolic component was 2·2 nmol/l, and to the nuclear component 4·8 nmol/l. Significant loss of binding ability of the receptor occurred when cytosol was pretreated with dextran-coated charcoal. All binding studies were performed, therefore, in the presence of endogenous steroid which was demonstrated to affect the dissociation constant but have no effect on the estimation of the concentration of binding sites. Cytosolic binding was increased sixfold by oestradiol-17β treatment in vivo, and the translocation of the bound complex into the nucleus was effected by progesterone. It is suggested that the binding component described plays a role in the action of progesterone on the uterine tissue of the quokka.
Effects of metoclopramide and bromocriptine on prolactin secretion in the pregnant ewe
Authors: Fitzgerald B. P. , Cunningham F. J.
Published: December 2008

Metoclopramide and bromocriptine, drugs which are respectively antagonistic and agonistic to dopamine receptor activity, were used to investigate the control of prolactin secretion in the ewe during pregnancy. Normal concentrations of prolactin were found during pregnancy, i.e. values were low and stable during the first 100 days but thereafter increased progressively to reach maximum values at day 140. Treatment with bromocriptine suppressed levels to undetectable values (< 1·4 μg/l plasma) between days 40 and 100 of pregnancy. Later in gestation, however, bromocriptine administered between days 120 and 140 was less effective, indicating that the pituitary gland was less responsive to the same degree of inhibition. Treatment with metoclopramide alone provoked a progressively greater release of prolactin as pregnancy advanced whereas in bromocriptine-treated animals an associated release of prolactin in response to metoclopramide was seen only between days 120 and 140 of pregnancy.

These results are interpreted as evidence that the raised concentrations of prolactin characteristic of late pregnancy in the ewe are due to a reduced responsiveness of the pituitary gland to inhibitory stimuli, or to a decreased secretion of endogenous dopamine into the hypophysial portal blood system or to both.
Photoperiodism in quail: testicular growth and maintenance under skeleton photoperiods
Authors: Follett B. K. , Milette J. J.
Published: December 2008

Testicular growth was induced in quail which were exposed to a skeleton photoperiod that included a pulse of light given during the dark period (night-interruption). The minimum duration of the pulse inducing testicular growth was 3·75 min per day. Longer pulses induced greater rates of growth, and of LH and FSH secretion; maximum rates occurred with a night-interruption of 60 min. Pulses even shorter than 3·75 min maintained testicular function in previously photostimulated quail. A night-interruption of 14 s maintained full testicular size and hormone secretion in four out of six quail, and with 56 s no regression whatsoever occurred. The rate of testicular growth was largely independent of the duration of the main light period used in the skeleton treatment. The light intensity within the nightinterruption also affected the degree of testicular development and gonadotrophin secretion.
Androgen levels in the liquid of the canine vas deferens and peripheral plasma
Authors: Boulanger P. , Desaulniers M. , Dupuy G. M. , Bleau G. , Roberts K. D. , Chapdelaine A.
Published: December 2008

Radioimmunoassays were used for the measurement of several androgens in canine plasma and in the liquid of the vas deferens. Large variations in the plasma concentrations of androstenedione, testosterone and 5α-dihydrotestosterone occurred during a period of 24 h, but there was no evidence of a circadian rhythm. The ratios of the androgen concentration in the liquid of the vas deferens compared with that in the peripheral plasma were: androstenedione, 4·6; testosterone, 1·9; 5α-dihydrotestosterone, 13·6; 5α-androstane-3α,17β-diol, 17·0; 5α-androstane-3β,17β-diol, 22·4. These high levels of androgens in the liquid of the vas deferens could play a role in the development of prostatic hypertrophy.
Role of the ovary in the sexual differentiation of prolactin and growth hormone cells in the mouse adenohypophysis: a stereological morphometric study by electron microscopy
Authors: Sasaki Fumihiko , Sano Masao
Published: December 2008

The number of prolactin and growth hormone cells was estimated in the mouse anterior pituitary gland. During postnatal development in females, the number of prolactin cells showed a rectilinear increase from about 0·3 × 104 at 20 days of age to about 21 × 104 in adult female mice, while growth hormone cells gradually increased from about 7 × 104 on day 20 to about 20 × 104 on days 60–70, with a plateau level of about 14 × 104 cells around puberty. Prolactin cells were more abundant in adult female (about 21 × 104) than in male (about 5 × 104) mice, while there were fewer growth hormone cells in adult females (about 20 × 104) than in males (about 25 × 104). Ovariectomy before puberty induced the male pattern of pituitary development by inhibition of the increase in the number of prolactin cells and stimulation of that of growth hormone cells. In animals ovariectomized just before puberty (30–35 days of age) or 5 days after vaginal opening (40–45 days of age) the number of prolactin cells showed no further increase after the day of operation. On the other hand, when animals were ovariectomized at 10 days of age, the number of prolactin cells increased to the level found in 30-day-old normal control females. This implies that the increase in prolactin cells between 10 and 30 days of age is not dependent on the ovary, although after puberty the increase does depend on the presence of the ovary.
Influence of age and sex on the concentrations of thyroid hormone in serum in the rat
Authors: Segal Joseph , Troen B. R. , Ingbar S. H.
Published: December 2008

Studies of the influence of age and sex on the concentrations of total thyroxine (T4) and 3,5,3′-tri-iodothyronine (T3) in serum and on the free T4 and free T3 indices, were conducted in Sprague–Dawley rats of the CD strain varying in age between 10 days and 12 months. Both sex- and age-related differences were found. In all age-groups studied, serum T4 concentrations were higher in the male than in the female, whereas serum T3 concentrations were higher in the female. In both sexes, concentrations of T4 and T3 in serum reached a peak early in life, between the first and second month of age, and declined thereafter. In addition, in both sexes the intensity of thyroid hormone binding, as judged from values of the in-vitro uptake of T3, did not change with age, suggesting that free T4 and T3 concentrations in the serum display the same sex differences and age-related changes as do the concentrations of total T4 and T3. It remains to be determined whether these sex-and age-related alterations in serum thyroid hormone concentration are expressed in differences in the activity of various thyroid hormone-dependent processes.
Fate of human corticotrophin immediately after intravenous administration to the rat
Authors: Ambler Linda , Bennett H. P. J. , Hudson Anne M. , McMartin Colin
Published: December 2008

The distribution and degradation of tritium-labelled human 1–39 corticotrophin have been studied after intravenous administration to the rat. Within 5 min of injection a single major metabolite, 3–39 corticotrophin, appears in the circulation. This metabolite, however, has only 3·6% of the steroidogenic potency of 1–39 corticotrophin and the evidence suggests that it is formed in muscle and skin. By 5 min, extensive degradation had occurred in all the major tissues in the body (muscle, skin, liver, kidney, gut).
Oestrogen induction of progestin receptors in the rat brain and pituitary gland: quantitative and kinetic aspects
Authors: Clark C. R. , MacLusky N. J. , Naftolin F.
Published: December 2008

The processes of oestrogen-receptor binding, translocation and nuclear processing in the pituitary gland, preoptic area (POA), mediobasal hypothalamus (MBH) and amygdala were explored in relation to the induction of cytosol progestin receptors (PRc). Ovariectomized rats were injected i.v. with a single saturating dose (3·6 μg/kg body wt) of oestradiol-17β (OE2). At various times thereafter cytosol (ERc) and salt-extractable nuclear (ERn) oestrogen-receptor concentrations were determined by exchange assay. In all four tissues at 1 h after injection ERc fell and ERn increased, suggesting translocation of ERc into the nucleus. The extent of ERc depletion, however, was not identical in all tissues: substantially less depletion was observed in the amygdala (34%) and POA–MBH (56%) than in the pituitary gland (74%). Depletion of ERc was followed by a phase of replenishment, restoring ERc to preinjection values by 24 h. Concentrations of ERn in all tissues declined between 1 and 24 h, concomitant with the replenishment of ERc.

Concentrations of PRc in the pituitary gland and POA–MBH increased during the first 12 h after injection of OE2 to a plateau value between 12 and 24 h, then declined to control values by 72 h. No induction of PRc was seen in the amygdala. A second injection of OE2 2 h after the first injection refilled the nuclear binding sites, restoring ERn to levels indistinguishable from those seen 1 h after a single OE2 treatment. The extent of ERc depletion after two injections with OE2 was, however, proportionately less than that seen after a single treatment with OE2. The second OE2 injection raised PRc concentrations above those seen after a single injection in the POA–MBH but not in the pituitary gland. When the two OE2 injections were more widely spaced (14 h apart) the PRc response in both the pituitary gland and POA–MBH was greater than after a single OE2 injection, and was comparable to that seen in animals given a very large dose (360 μg/kg body wt) of OE2. These results confirm the existence of differences between the pituitary gland, POA–MBH and amygdala in the ERc and PRc responses to oestrogen treatment. In addition, they suggest that the PRc response of the pituitary gland and POA–MBH to OE2 is influenced by previous exposure to OE2.
Human skin androgen metabolism and preliminary evidence for its control by two forms of 17β-hydroxysteroid oxidoreductase
Authors: Hodgins M. B. , Hay J. B. , Donnelly J. B.
Published: December 2008

Human forehead skin incubated in vitro is known to metabolize testosterone to 17-oxosteroids faster than the reverse reaction, while axillary skin rapidly metabolizes androstenedione to 17β-hydroxysteroids, such as testosterone and 5α-dihydrotestosterone, While this has been confirmed using a larger number of patients, some indication has been found that 17β-hydroxysteroid oxidoreductase activity declines with age in the axilla. The relative rates of 17β-oxidation and reduction (direction of operation of skin 17β-hydroxysteroid oxidoreductase activity) were not altered by a variety of incubation conditions. Large amounts of a membrane-bound 17β-hydroxysteroid oxidoreductase, showing preference for NAD as coenzyme and testosterone (rather than androstenedione) as steroid substrate, were found in forehead skin from one patient. On the other hand, the main axillary skin enzyme in skin from another patient was soluble and showed preference for NADP and androstenedione. It is postulated that 17β-oxidation and reduction in skin is controlled by the relative amount, the coenzyme preferences and the kinetic properties of these two enzymes.
Comparative pharmacology of oestrogens and catechol oestrogens: actions on the immature rat uterus in vivo and in vitro
Authors: Franks S. , MacLusky N. J. , Naftolin F.
Published: December 2008

The effects of primary and catechol oestrogens on the uterus of the immature rat were compared. Because differences between the in-vivo and in-vitro oestrogenic actions of catechol oestrogens on the secretion of LH had been observed, their effects on a peripheral target organ, the uterus, were examined under similar conditions. In-vivo effects were assessed by measurement of uterine weight, induction of uterine cytoplasmic progestogen receptors, and by histological examination. In-vitro actions were determined by measurement of oestrogen-specific induced protein. It was found that the uterotrophic effects in vivo of 4-hydroxyoestradiol were indistinguishable from those of oestradiol whereas 2-hydroxyoestradiol was only weakly oestrogenic and 2-hydroxyoestrone had no effect. However, in vitro, 2-hydroxyoestradiol was as effective as 4-hydroxyoestradiol or oestradiol in stimulating synthesis of uterine induced protein, and 2-hydroxyoestrone, although less potent than oestradiol, had a significant effect. These results were consistent with the observed effects on the secretion of LH. The differences between in-vivo and in-vitro uterotrophic properties of catechol oestrogens can be explained on the basis of known pharmacokinetic factors.
Identification of β-cell-trophin, a peptide of the pituitary pars intermedia which stimulates insulin secretion in plasma from genetically obese (ob/ob) mice
Authors: Billingham N. , Beloff-Chain Anne , Cawthorne M. A.
Published: December 2008

The influence of plasma from genetically obese (ob/ob) and lean (+/+) mice on insulin secretion has been studied by perifusion of collagenase-prepared pancreatic islets maintained for 48 h in culture. Insulin secretion was measured at 2-min intervals and plasma from the ob/ob mice not from the +/+ mice rapidly stimulated insulin release, reaching a maximum in 2–4 min and falling to basal levels in about 10 min. Experimental evidence is given indicating that the plasma insulin secretagogue is identical to β-cell-trophin, a peptide of the pituitary pars intermedia which stimulates insulin secretion. The evidence is based on (1) the antigenic properties of the peptides (both cross-react with a -COOH terminal ACTH antiserum raised to the 17–39 moiety of ACTH), (2) identical chromatographic separation on Biogel columns and on reverse-phase high pressure liquid chromatography and (3) the similarity of their insulin releasing action from perifused islets.
Increased steroidogenesis by rat zona glomerulosa cells with increased cell concentration in vitro: evidence for a novel aldosterone-stimulating factor and implications regarding aldosterone biosynthesis
Authors: Campbell D. J.
Published: December 2008

A fourfold increase in the concentration of rat zona glomerulosa cells incubated in Krebs–Ringer bicarbonate buffer (KRBGA) increased aldosterone production per cell twofold. This cell concentration associated (CCA) increase in aldosterone production showed a dose–response relationship with the number of cells per incubation and was further increased in modified Medium 199, compared with KRBGA.

The combination of a fourfold increase in cell concentration with each of maximally steroidogenic concentrations of K+, angiotensin II, ACTH, 5-hydroxytryptamine or cyclic AMP produced an increase in aldosterone production greater than that predicted from the algebraic sum of the steroidogenic effects of the factors acting separately.

The CCA increase in basal aldosterone production was maximal during the first 30 min of incubation, could not be accounted for by accumulation of corticosterone in the incubation medium and was largely or completely abolished by the addition of pregnenolone, progesterone, deoxycorticosterone or corticosterone to the incubation medium. Together, these data support the proposal that the CCA effect was due to a novel aldosterone-stimulating factor which increased aldosterone production by stimulating pregnenolone formation.

The aldosterone and corticosterone responses to exogenous pregnenolone, progesterone, deoxycorticosterone and corticosterone demonstrated that aldosterone and corticosterone production by zona glomerulosa cells in vitro may represent separate biosynthetic pathways. Furthermore, these studies provided evidence for a mechanism by which increased levels of exogenous pregnenolone, progesterone and deoxycorticosterone were able to increase their per cent conversion to aldosterone, but not to corticosterone.
Role of dopamine in the angiotensin II-induced vasopressin release in the conscious dehydrated dog
Authors: Brooks D. P. , Claybaugh J. R.
Published: December 2008

The effect of the dopamine antagonist, haloperidol, on arginine-vasopressin (AVP) release induced by angiotensin II was studied in six dehydrated conscious dogs. Angiotensin II (10 ng/kg per min) alone caused a twofold increase (P<0·05) in plasma AVP concentration, a 25 mmHg increase (P<0·01) in mean arterial blood pressure (ABP) and a 70% decrease (P<0·01) in plasma renin activity (PRA). In the presence of haloperidol (3 μg/kg per min), angiotensin II caused similar changes in mean ABP (+25 mmHg; P<0·01) and PRA (−65%, P<0·01), but a small insignificant decrease in plasma AVP (−22%). The AVP response to angiotensin II in the presence of haloperidol was significantly (P<0·05) different from its response to angiotensin II alone. Neither haloperidol alone nor the two vehicles had any effect on plasma AVP or mean ABP but PRA dropped slightly. The results suggest that a dopaminergic mechanism may be involved in angiotensin II-induced AVP release.
Effect of hypothalamic implantation of perphenazine on milk yield in goats
Authors: Messom G. Vandeputte-Van , Peeters G.
Published: December 2008

The effects of perphenazine on galactopoiesis were studied in 52 goats in the phase of declining lactation (September–December). At the beginning of September, perphenazine (1 mg) was stereotaxically implanted into the hypothalamus, sham-implantations being performed on control animals. After the operation milk yield decreased and stabilized at a new starting level in most animals of both groups. The average weekly milk yield of the sham-implanted goats gradually fell during the experimental period. This progressive decline in yield was greatly reduced if perphenazine had been implanted in the median eminence (ME). No galactopoietic effects were observed when the implantation was localized outside the ME.
Priming effect of luteinizing hormone releasing hormone in the hypogonadal mouse
Authors: Fink G. , Sheward W. J. , Charlton H. M.
Published: December 2008

We have investigated the LH response to LH releasing hormone (LH-RH) in female hypogonadal (hpg) mice in which the hypothalamus contains no LH-RH and the pituitary gland contains significantly less LH than in normal mice. Both the releasing action and the priming effect of LH-RH were not significantly different in hpg compared with normal mice. Raised plasma concentrations of oestradiol-17β reduced pituitary responsiveness to LH-RH in normal but not in hpg mice. These results show that in the mouse neither longterm exposure to normal levels of LH-RH nor a normal pituitary content of LH are necessary for either the releasing or the priming action of LH-RH.
Effect of oestradiol benzoate or luteinizing hormone on levels of progesterone in the pseudopregnant rat
Authors: de Greef W. J. , Uilenbroek J. Th. J. , de Jong F. H.
Published: December 2008

The present study was concerned with a possible involvement of LH in the process of functional luteolysis in the pseudopregnant rat.

Daily injections with 2 μg ovine LH during pseudopregnancy reduced peripheral and ovarian levels of progesterone in intact and hysterectomized rats and in hypophysectomized rats with a pituitary transplant under the kidney capsule. However, a daily dose of 10 μg LH did not alter the levels of progesterone. A short-lasting decrease in plasma progesterone occurred when endogenous levels of LH were temporarily raised in pseudopregnant rats by a single injection of LH releasing hormone (LH-RH). Treatment with LH or LH-RH, however, did not shorten the duration of pseudopregnancy.

Daily treatment of pseudopregnant rats with 5 or 20 ng oestradiol benzoate, but not with 1000 ng, decreased plasma levels of progesterone. On the other hand, daily treatment with oestradiol benzoate did not affect plasma progesterone in pseudopregnant rats which were hypophysectomized and had an ectopic pituitary gland. Plasma levels of LH were not increased in the animals receiving 5 or 20 ng oestradiol benzoate daily, suggesting that the effect of oestradiol benzoate on plasma progesterone is not through an enhanced secretion of LH. Treatment with oestradiol benzoate did not affect the duration of pseudopregnancy.

In conclusion, low doses of LH can reduce peripheral levels of progesterone during pseudopregnancy, but it seems improbable that LH is involved in the process of functional luteolysis. Furthermore, low doses of oestradiol benzoate can also decrease plasma progesterone, but the mechanisms involved are still not understood.
Distribution and number of gonadotrophic cells in the pituitary gland of prepubertal female rats
Authors: Jansen H. G.
Published: December 2008

The localization and number of LH- and FSH-containing cells (LH cells and FSH cells) in the pituitary gland of prepubertal female rats aged 5, 10, 15, 20, 25 and 30 days were determined by means of immunocytochemical light microscopy of 5 μm horizontal sections. Anti-rat LHβ and anti-rat FSHβ were used in combination with the unlabelled peroxidase–antiperoxidase method.

The gonadotrophic cells were regularly distributed throughout the pars distalis but at 5 and 10 days of age fewer LH and FSH cells were found in lateral regions. The numbers of LH and FSH cells per pituitary gland increased with age. The number of LH cells per unit volume of pituitary tissue reached a maximum at 20 days; the number of FSH cells reached a maximum at 15 days and then decreased with increasing age. At all ages except 5 days more LH than FSH cells were counted per unit volume. Some cells reacting with both anti-rat LHβ and anti-rat FSHβ were detected.

Comparison of the data obtained on the dynamics of cell number with data previously obtained on pituitary gonadotrophin content suggests that at successive prepubertal ages LH and FSH cells contain increasing amounts of their respective hormones.
Latency and duration of the effects of bromocriptine and prolactin on milk secretion in lactating rabbits
Authors: Mena F. , Martínez-Escalera G. , Aguayo D. , Clapp C. , Grosvenor C. E.
Published: December 2008

Milk yields were measured at 8-h intervals in rabbits during early (days 11–14) and late (days 31–34) lactation. A single injection of 1 mg bromocriptine given to rabbits 30 min before suckling on days 11 or 31 caused a significant reduction in milk yield after approximately 8 h. The depressant effect of the drug was then maintained over the next 24–36 h. Recovery of milk yield occurred in bromocriptine-treated rabbits during both early and late lactation 8-16 h after a single injection of 3 mg prolactin. The recovery accelerated more in the rabbits in the early lactating group. Attainment of the maximal stimulatory effect occurred by 24 h after prolactin injection during both early and late lactation although the improvement in milk yield lasted for a shorter period (8 h compared with 24 h) during late lactation compared with early lactation. These differences in response of the rabbit to prolactin during late lactation may contribute substantially to the declining milk yields characteristic of late lactation in this species.
Evidence of a photoinducible phase for the release of luteinizing hormone in the domestic hen
Authors: Wilson Susan C.
Published: December 2008

Hens raised on a schedule of 8 h light: 16 h darkness (8L : 16D) were exposed to changes in photoperiod at 17 or 18 weeks of age. These involved exposure to either an abrupt increase in photoperiod to 16 h per day or to skeleton photoperiods comprising a main period of 7·75 or 4 h light together with a pulse of 15 min or 4 h light provided at different times during the period of darkness.

An increase in photoperiod to 16 h per day stimulated a two- to threefold increase in the plasma concentration of LH within 1–3 days. Interruption of a 7·75L : 16D schedule by 15 min light between 13·75 and 19·75 h after the beginning of the main photoperiod stimulated LH secretion in the immature and adult hen and a higher rate of lay than that of the 8L : 16D control group. There was a significant (P < 0·01) correlation between the concentration of LH in the plasma and the rate of lay. The photostimulated rise in the plasma concentration of LH in the immature hen was not associated with any increase in the responsiveness of the pituitary gland to LH releasing hormone. Of the treatments in which a 15-min pulse of light was provided, the schedules of 7·75L : 10D : 0·25L : 6D and 7·75L : 12D : 0·25L : 4D, which were most effective in stimulating LH release, appeared to be interpreted as 0·25L : 6D : 7·75L : 10D and 0·25L : 4D : 7·75L : 12D respectively. In hens given a 7·75-h main photoperiod, in which phase-reversal did not occur, 15 min light was most stimulatory when given 14–16 h after the begining of the main photoperiod, although not to the same extent as an increase in photoperiod to 16 h per day. In hens for which an 8-h complete photoperiod was changed to a 4-h main photoperiod, together with a further 4-h pulse of light provided at different times during the period of darkness, the period of maximum sensitivity to light occurred 11 h after the onset of the main photoperiod and at this time light stimulated LH release to the same extent as an increase in complete photoperiod from 8 to 16 h per day. Results of this study suggest that the period of maximum photosensitivity shifts its phase after a change in the form of photoperiod and is primarily entrained to dusk.
Binding of androgens in 5α-reductase-deficient human genital skin fibroblasts: inhibition by progesterone and its metabolites
Authors: Hodgins M. B.
Published: December 2008

Binding of [3H]testosterone and 5α-dihydro[3H]testosterone ([3H]DHT) to specific androgen-receptor sites of 5α-reductase-deficient human genital skin fibroblasts (five cell-lines) was studied in the intact cultured cells at 37 °C. Under the conditions of the experiments, conversion of [3H]testosterone into [3H]DHT was negligible. Both steroids bound to the same set of high-affinity saturable sites in cytoplasmic and nuclear fractions of the cells. Unlabelled testosterone, DHT and methyltrienolone competed effectively with the labelled steroids. Progesterone and oestradiol were weaker competitors; cortisol did not compete. The dissociation constant (Kd) for high-affinity complexes with [3H]testosterone (0·44 ± 0·035 nmol/l) was higher than that for [3H]DHT complexes (0·20 ± 0·090 nmol/l). Unlabelled DHT was more effective than unlabelled testosterone in competing with either radioactive steroid. Complexes of [3H]DHT and receptor dissociated more slowly than [3H]testosterone-receptor complexes and [3H]DHT bound more extensively to low-affinity non-saturable sites in fibroblasts. As judged by competition with the radioactive androgens, progesterone bound to the androgen receptor with a Kd of about 7 nmol/l. 5α-Pregnane-3,20-dione had an approximately fivefold lower affinity than progesterone for androgen receptors; 3α/β- or 20α-reduction lowered its affinity further. It is suggested that in 5α-reductase deficiency in man, progesterone in amniotic fluid and blood could effectively inhibit testosterone binding to androgen receptors in the male embryonic external genitalia. One function of the high levels of 5α-reductase activity normally found in embryonic external genitalia and urogenital sinus may be to protect these tissues from the potentially antiandrogenic action of progesterone.
Gestational effects on placental and serum androgen, progesterone and prolactin-like activity in the mouse
Authors: Soares M. J. , Talamantes F.
Published: December 2008

The concentrations of androgen, progesterone and prolactin-like activity in serum, placentae and media from placental incubations during the second half of pregnancy in the C3H mouse were evaluated. Serum concentrations, placental content and in-vitro placental release of androgen were raised on day 10 of pregnancy. Serum progesterone levels showed minor fluctuations during the second half of gestation, whereas placental content and in-vitro release of progesterone were increased on day 10 of gestation. The serum profile of prolactin-like activity showed a significant mid-pregnancy increase on day 10 which did not correlate with placental content or in-vitro placental release of prolactin-like activity. The placental content and in-vitro release of prolactin-like activity were low during midpregnancy and increased during the latter days of gestation when serum prolactin-like activity was reduced.
Repeated convulsions induce pseudopregnancy in the intact rat and inhibit steroid-mediated gonadotrophin secretion in the ovariectomized rat
Authors: Bhanot R. , Wilkinson M.
Published: December 2008

We have investigated the effects of repeated flurothyl-induced seizures on reproductive function in the female rat. This treatment rapidly induced a state of pseudopregnancy in intact cyclic rats. Prolactin is clearly implicated in this response since treatment with bromocriptine readily counteracted the influence of the convulsions. The mechanism of action of repeated seizures was further characterized in experiments on ovariectomized rats. Thus, 11 daily convulsions, but not a single acute seizure, were able to inhibit the positive feedback effect of progesterone on LH and FSH release in oestrogen-primed animals. In this model also the pituitary gland response to gonadotrophin releasing hormone in vitro was significantly reduced. However, the convulsions had no effect on basal serum or basal in-vitro secretion of LH and FSH in ovariectomized or oestrogen-treated ovariectomized rats. Thus, repeated seizures modified the hypothalamo-pituitary axis in such a way as to prevent it from responding to stimulation.

Our results indicate that normal reproductive function in the female rat is very sensitive to repeated seizures and suggest that similar effects may be evident in women subjected to electroconvulsive shock therapy. The successful use of bromocriptine in reversing the influence of seizures in the rat suggests its use in man also.
Influence of protein deficiency in rats on hormonal status and cytoplasmic glucocorticoid receptors in maternal and fetal tissues
Authors: Mulay S. , Varma D. R. , Solomon S.
Published: December 2008

The influence of dietary protein deficiency on maternal plasma corticosterone and progesterone levels as well as on maternal and fetal liver and lung cytoplasmic glucocorti-coid receptors has been studied in Sprague–Dawley rats during the last 3 days of gestation. Plasma corticosterone levels of control but not protein-deficient rats increased on days 20 and 21 of gestation; corticosterone levels of protein-deficient rats decreased on day 21 of gestation. Maternal adrenalectomy caused only a moderate decrease in corticosterone levels in both groups of pregnant rats. Fetal corticosterone levels of the two groups of rats were similar. Progesterone levels were consistently lower in protein-deficient than in control animals from day 20 of gestation until 2–12 h after parturition. There were no differences in the binding of [3H]dexamethasone to liver cytosol of non-pregnant control and protein-deficient rats. However, receptor levels were lower in pregnant controls than in pregnant protein-deficient rats. Maternal protein deficiency led to an increase in fetal liver glucocorticoid receptor levels but exerted no significant effect on receptor levels in fetal lung. It is suggested that lower levels of plasma corticosterone and progesterone and high levels of liver glucocorticoid receptors in protein-deficient rats might be related to some of the adverse consequences of maternal malnutrition on fetal development.
A new bioassay for human growth hormone based on incorporation of labelled proline into skin
Authors: Rudman C. G. , Gaines Das Rose E. , Parsons J. A.
Published: December 2008

An in-vivo bioassay for human growth hormone (hGH) has been developed, based on the dose-related enhancement of radioactivity in skin of hypophysectomized rats given daily s.c. injections of hGH and a single i.p. injection of labelled proline. The measured radioactivity, taken as the response, was shown to be independent of the site at which the skin was sampled. Valid dose–response relationships were obtained after as little as 3 days of treatment with GH.

The assays by this method are shown to be more precise than the widely used weight-gain and tibial-width bioassays. Assays carried out gave an average index of precision of 0·036.
Estimation of insulin secretion using extracts of plasma from mice injected with anti-insulin serum: effects of arginine, glucose and anti-insulin serum
Authors: Beck L. V. , Basu Ilora , Hegeman Sally L.
Published: December 2008

Anti-insulin serum (AIS) injected intravenously into adult male mice was allowed to complex endogenous plasma insulin for a fixed time before blood samples were taken. In each plasma sample, insulin was separated from antibody using acid alcohol and the free insulin was estimated by radioimmunoassay. We consider AIS to be most useful for the estimations of in-vivo insulin secretion rates over the period 0·5–5 min after its injection. The lower limit is governed by the time required for mixing and complexing of endogenous insulin. The use of a short upper limit is because antibody complexed with antigen leaves plasma more rapidly than does free antibody, carrying antigen with it. Increases in insulin per ml plasma were appreciably greater in mice injected with glucose or l-arginine plus AIS than in mice injected with glucose or l-arginine only. Hence more realistic values for in-vivo insulin secretion rates may be obtained by the use of AIS to retain most insulin in plasma than by estimations of plasma insulin levels.
Characterization of the pituitary gonadotroph cells of hypogonadal (hpg) male mice: comparison with normal mice
Authors: McDowell I. F. W. , Morris J. F. , Charlton H. M.
Published: December 2008

Hypogonadal (hpg) mice lack hypothalamic luteinizing hormone releasing hormone (LH-RH). Gonadotrophs from male hpg mice have been identified by immunocytochemistry for LH and quantitative electron microscopy allied with radioimmunoassay of the gonadotrophins. In comparison with those of normal mice, gonadotrophs in male hpg animals are less numerous and smaller, with less cytoplasm and rough endoplasmic reticulum and a smaller Golgi apparatus. They have fewer granules, especially those of larger (> 210 nm) diameter. Thus, in the absence of LH-RH, gonadotrophs can differentiate but remain relatively inactive.
Incidence, growth and oestradiol-receptor levels of 7,12-dimethylbenz(a)anthracene-induced mammary tumours in rats: effects of neonatal sex steroids and oestradiol implants
Authors: Verhoeven G. , Vandoren G. , Heyns W. , Kühn E. R. , Janssens J. P. , Teuwen D. , Goddeeris P. , Lesaffre E. , De Moor P.
Published: December 2008

The effects of neonatally administered steroids on the sensitivity of the mammary gland to tumour induction by 7,12-dimethylbenz(a)anthracene was studied as a model for delayed (de)differentiating effects of steroid hormones. Immediately after birth male and female rats were gonadectomized and treated with testosterone, oestradiol or oil. Control animals were left intact. On day 45 all the gonadectomized animals and some of the control animals received an implant which delivered continuous low levels of oestradiol. The carcinogen was administered on day 55. The administration of an oestradiol implant, which increased prolactin levels in all animals, markedly reduced tumour incidence in intact female rats and increased tumour incidence in intact male rats. Neonatal administration of testosterone or oestradiol did not significantly influence tumour incidence, histopathology or oestradiol responsiveness in neonatally gonadectomized rats but tended to decrease tumour oestradiol-receptor levels. This lack of effect of neonatal steroids in gonadectomized animals suggests that the effects observed by other authors in intact rats are mediated by changes in gonadal secretions. It is concluded that the hormonal environment during and after tumour induction plays a major role in the development of 7,12-dimethylbenz(a)anthracene-induced mammary carcinomas.
Electrophysiological effects of testosterone on the medial preoptic–anterior hypothalamus of the rat
Authors: Kendrick K. M.
Published: December 2008

Castration in the rat significantly lengthened the refractory period of medial preoptic–anterior hypothalamic neurones with outputs into the medial forebrain bundle but not of those with outputs to the lateral septum. Treatment with testosterone propionate reduced the neuronal refractory period to its lowest level at the same time as it restored mounts and intromissions (after 5 days). Equally, when treatment was ended at 15 days, mounts and intromissions were no longer shown when the refractory period lengthened again 14 days later. The sub-population of neurones which also received inputs from the contralateral fimbria (through the corticomedial amygdala) showed the same results as the overall population. Castration also significantly increased the baseline firing rates of medial preoptic–anterior hypothalamic neurones receiving inputs from the medial forebrain bundle. The same effect was observed for the sub-population of neurones which also had inputs from the contralateral fimbria, but castration significantly reduced the percentage of neurones responding to this additional input. The neurones having inputs with the fastest conduction velocity were responsible for these changes in firing rate and the input neurones were therefore probably non-dopaminergic.
Differences in the seasonal rhythmicity of plasma prolactin in elderly human subjects: detection in women but not in men
Authors: Touitou Yvan , Carayon Alain , Reinberg Alain , Bogdan André , Beck Hervé
Published: December 2008

Effects of age, sex and mental condition on the circadian and circannual rhythmicity of plasma prolactin in human subjects were investigated. Circannual changes were recorded on a circadian basis in January, March, June and October in four groups of subjects: seven young men, six elderly men, six elderly women and six senile demented patients (two men and four women). Blood samples were drawn every 4 h over a 24-h period at the four sampling sessions. Circadian rhythms of the hormone were validated in all groups and at all sampling sessions except twice in elderly demented subjects. The 24-h mean levels of prolactin in plasma were approximately the same in young and elderly subjects. The circadian acrophases were most often located in the vicinity of 02.00–04.00 h. The circannual rhythmicity of the hormone showed a sex difference; the rhythm was not validated in either young or elderly men but was detected in the groups of elderly women and elderly demented patients (mainly women). The acrophases were located in May. This paper strongly suggests a sex difference in the circannual rhythmicity of plasma prolactin levels in elderly subjects.