Showing papers on "Prolactin published in 1979"

Methods of hormone radioimmunoassay.

Abstract: The best ebooks about Methods Of Hormone Radioimmunoassay that you can get for free here by download this Methods Of Hormone Radioimmunoassay and save to your desktop. This ebooks is under topic such as a radioimmunoassay method for human pituitary luteinizing methods in radioimmunoassay, toxicology, and springer a rapid radioimmunoassay method of (39161) ultrafiltration method for direct radioimmunoassay measurement new solid phases for estimation of hormones by agreement between electrochemiluminescence and raciloimmunoassay: principle and technique jpma parathyroid hormone: radioimmunoassay and clinical radioimmunoassay of plasma hormones: review of plasma examination of the tissue ghrelin expression of rats with 2 radioimmunoassay of gi hormones bprcem erroneous thyroid-stimulating hormone radioimmunoassay prolactin and luteinizing hormone cells of pregnant and a radioimmunoassay for rat ghrelin: evaluation of method luteinizing hormone-releasing hormone levels in human validation of nonradioactive chemiluminescent immunoassay general principles, problems, and interpretation in the radioimmunoassay and related techniques jpma radioimmunoassay for proparathyroid hormone hormone analysis ksu faculty member websites a rapid radioimmunoassay method for serum luteinizing radioimmunoassay of secretin rdspringer a radioimmunoassay for erythropoietin blood journal original article comparative study on determination of measurement of human luteinizing hormone jci comparison of solid-phase radioimmunoassay and competitive standard methods for physiology and biochemistry research radioimmunoassay measurement of secretin half-life in man radioimmunoassay and related procedures in medicine core methods in determining growth hormone concentrations: an serum prolactin levels in humans from birth to adult life efficacy of synthetic gonadotropin releasing hormone radioimmunoassay for the in-vitro determination of methods for assessing the effects of chemicals on the adaptation and analytical validation of a radioimmunoassay radioimmunoassay of human parathyroid hormone in development and validation of a solid-phase radioimmunoassay the embryo project encyclopedia use of in the radioimmunoassay human journal of clinical radioimmunoassay for luteinizing hormone in plasma or

Chronological Changes in Sex Steroid, Gonadotropin and Prolactin Secretion in Aging Female Rats Displaying Different Reproductive States

Abstract: Longitudinal studies were performed in a colony of aging female rats,from 4-33 months of age,to determine the chronologicalchange inreproductive patterns and the changes in sex steroid, prolactin and gonadotropin secretionassociatedwith different reproductive states. The present study demonstrates that the incidence (65%) of irregular estrous cycles in aging rats increased abruptly from 10-12 months of age. Subsequently, female rats became chronically anovulatory with persistentvaginalcornificationsand theirovariescontained developed follicles but no corpora lutea. The highest incidence (65%) of constant estrous (CE) rats occurred at the age of about 19 months. During the anovulatory state, CE rats displayed low to medium levels of serum estradiol, estrone, testosterone and androstenedione, low levels of progesterone and minimal levels of 20nhydroxyprogesterone. Preovulatory increasesin gonadotropin and prolactin release,similar to those seen in young cycling ratson proestrus,were not observed in CE rats.Whereas serum basal LH levels remained unaltered, morning FSH levelswere increased in CE rats.The lattermay account for the persistent follicular development in aging rats during chronic anovulatory state. Serum basal prolactin levels were normal in CE rats during the early phase (11-16 months of age) of the anovulatory state, but were subsequently increased 3 to 4-fold beyond 24 months of age. Moreover, ovariectomy at a young age prevented the increased pituitary prolactin release in old female rats. These results suggest that continuous exposure to medium levels of estrogens, particularly in the presence of sustained low progesterone secretion, may alter pituitary secretion of prolactin in aging rats. With further advance of age and following many months of anovulatory function, aging female rats exhibited ovulatory activity at irregular intervals. After each ovulation, formed corpora lutea were maintained for a prolonged period, presumably due in part to the existing high prolactin levels in the circulation of older female rats. These corpora lutea in old “pseudopregnant (PSP)” rats were functional as indicated by active secretion of progestins, with 20a-hydroxyprogesterone levels greater than those of progesterone in the circulation. These results indicate that the ovaries of aging rats retain their functional capacity to develop follicles and corpora lutea and to secrete steroid hormones. Although the cause(s) responsible for cessation of normal ovulatory cycles in aging female rats is unknown, the present study demonstrates that the chronic anovulatory state in aging female rats is characterized by significantly reduced ovarian secretion and the lack of cyclic increases in pituitary gonadotropin and prolactmn release. The causal relationships between the decreased ovarian steroid production and the absence of preovulatory surges of gonadotropin release in aging CE rats remain to be determined.

Clonal strains of hormone-producing pituitary cells.

Abstract: Publisher Summary This chapter discusses clonal strains of pituitary tumor cells that synthesize and secrete prolactin, growth hormone and adrenocorticotropic hormone (ACTH). The rates of biosynthesis of the specific hormonal peptides by these clonal strains are high and they respond in culture to many of the same regulatory factors as normal pituitary cells do in situ. Strains of homogeneous populations of functional cells serve as useful model systems for determining the mechanisms of action of factors that regulate the release and synthesis of prolactin, growth hormone, and ACTH. Several epithelial cell strains have been cloned, and some have been maintained in continuous culture for as long as 10 years without loss of hormone production. Growth hormone (GH) cells produce large amounts of growth hormone and prolactin. The biosynthesis and release of these two protein hormones are modulated by specific factors that have been found to influence the pituitary gland in the intact animal.

Membrane effects of thyrotropin-releasing hormone and estrogen shown by intracellular recording from pituitary cells

Abstract: The effects of thyrotropin-releasing hormone and 17 beta-estradiol on the electrical membrane properties of a prolactin-secretin pituitary cell line (GH3/B6) were studied with intracellular microelectrode recordings. Of the cells tested, 50 percent were excitable and displayed calcium-dependent action potentials when depolarized. When injected directly on the membrane of an excitable cell, thyrotropin-releasing hormone and 17 beta-estradiol induced action potentials within 1 minute. The spiking activity was preceded by a progressive increase of the input resistance without any detectable change in the resting membrane polarization. The results reveal a rapid effect of both substances on the membrane of GH3/B6 cells. In the case of thyrotropin-releasing hormone, which has both a short-term effect on release of prolactin and a long-term effect on its synthesis, the induced electrical activity may be associated with the stimulation of prolactin production. The physiological implication of 17 beta-estradiol-induced, calcium-dependent spiking activity remains to be elucidated.

Dopamine inhibits adenylate cyclase in human prolactin-secreting pituitary adenomas

Abstract: THERE is evidence for the existence of multiple forms of dopamine (DA) receptors1–3. In particular, some of these receptors are coupled to adenylate cyclase (DA-stimulating enzyme activity), whereas others seem to be independent3–5. These two classes of receptors, which have been designated D-1 and D-2, respectively, would also have different pharmacological properties3. Pituitary mammotroph DA receptors regulating prolactin (PRL) secretion are considered to be typical D-2 receptors. A DA-stimulated adenylate cyclase has not been detected in normal anterior pituitaries3,5,6; furthermore, several studies indicate that cyclic AMP is stimulatory and not inhibitory to PRL secretion7,8. We report here that in homogenates of human PRL adenomas, in which dopaminergic agonists act as inhibitors of PRL secretion, basal adenylate cyclase is inhibited by DA. The DA receptors mediating this inhibition have the same pharmacological properties as those regulating PRL secretion.

Menopausal flushes: a neuroendocrine link with pulsatile luteninizing hormone secreation

Abstract: Menopausal flush episodes were found to be invariably associated with the initiation of pulsatile pituitary release of luteinizing hormone. This was not accompanied by a significant change in circulating catecholamine or prolactin concentrations. Since pulsatile luteinizing hormone release results from episodic secretion of luteinizing hormone releasing factor by the hypothalamus, these findings suggest a link between the neuroendocrine mechanisms that initiate such episodic secretion and those responsible for the onset of flush episodes.

Vasoactive Intestinal Peptide: Evidence for a Hypothalamic Site of Action to Release Growth Hormone, Luteinizing Hormone, and Prolactin in Conscious Ovariectomized Rats*

Abstract: Ovariectomized conscious rats bearing chronically implanted third ventricular cannula were injected with 2 μl 0.9% NaCl or 2 μd saline containing varying doses of vasoactive intestinal peptide (VIP), and plasma LH, PRL, GH, TSH, and FSH levels were measured by RIA in jugular blood samples drawn through an indwelling silastic cannula. Control injections of saline iv or into the third ventricle did not modify plasma hormone levels. Third ventricular injection of 4, 40, and 100 ng VIP produced a significant elevation within 5 min in plasma LH, while PRL levels were elevated only by 40- and 100-ng doses; however, the highest dose of 500 ng had no effect on plasma LH or PRL levels. Plasma GH titers increased significantly after third ventricular injection of each dose of VIP at 15 min and remained elevated for the duration of the experiment. Intravenous injection of VIP at doses of 40 and 1000 ng had no effect on plasma LH, but PRL levels were significantly elevated by the 1000-ng dose. Plasma GH was not odifi...

Ontogenesis of cells producing polypeptide hormones (ACTH, MSH, LPH, GH, Prolactin) in the fetal hypophysis of the rat: Influence of the hypothalamus

Abstract: The ontogenesis of cells containing polypeptide hormones (ACTH, MSH, LPH, GH and Prolactin) was investigated in the fetal rat hypophysis by immunohistochemistry using the peroxidase-antiperoxidase complex. Corticotrophs, melanotrophs and lipotropic cells were revealed earlier in the pars distalis than in the pars intermedia. In the pars distalis, cells producing LPH were found in the morning of day 15 of gestation using anti-γ- or anti-β-LPH sera, and in the afternoon using anti-α- or β-endorphin sera. Cells containing β-MSH were observed from the afternoon of day 15. The cells stainable with the anti-α-MSH, anti-β-(17-39)ACTH and anti-β-(l-24)ACTH sera appeared on day 16. In the pars intermedia, the cells producing α-MSH, β MSH, α- and β-endorphin, γ and β-LPH were observed in the morning of day 17, while cells containing ACTH were only revealed in the afternoon of the same day of gestation. Based on the treatment of serial paraffin sections with various antisera, it was clearly shown that MSH, ACTH, and LPH occur in the same cells located in the pars distalis as in the pars intermedia. The development of the corticotrophs, melanotrophs and lipotropic cells does not require the presence of the fetal hypothalamus or other central nervous structures. The pituitary glands of 21 day-old fetuses encephalectomized on day 16 showed as many reactive cells as those of the littermate controls. The somatotrophs were first revealed in the pars distalis in the afternoon of day 19. The cells producing prolactin were not observed before day 21 of gestation. On some cases GH and prolactin were found together in one cell. The cytodifferentiation of GH and prolactin cells is apparently not under hypothalamic control.

β-Endorphin: Analgesic and hormonal effects in humans

Abstract: The pharmacokinetics and the hormonal, analgesic, and behavioral effects of several doses of human β-endorphin were evaluated after intravenous administration to three patients and intracerebroventricular administration to one patient with pain caused by cancer. These effects were compared to the hormonal effects of intravenously administered morphine sulfate in two patients and an enkephalin analog in two baboons. The mean terminal half-life after intravenous administration of 5 or 10 mg of human β-endorphin to three patients was 37 min; the mean volume of distribution was 178 ml/kg, and the metabolic clearance rate was 3.2 (ml/min)/kg. The half-life of β-endorphin in cerebrospinal fluid after intracerebroventricular administration was 93 min, and the volume of distribution was 0.74 ml/kg. A rapid rise in plasma prolactin followed both intravenous and intracerebroventricular β-endorphin. Intravenous administration did not affect plasma growth hormone, but intracerebroventricular administration suppressed plasma growth hormone. No significant change in plasma growth hormone was noted after intravenous administration of morphine to humans, but plasma growth hormone decreased in one baboon after administration of the enkephalin analog. β-Endorphin-stimulated release of prolactin occurred at doses lower than those required to produce analgesic and other behavioral effects. When both hormonal and analgesic effects were observed (after 7.5 mg were given intracerebroventricularly), the onset of the hormonal response slightly preceded the analgesic and behavioral responses. These studies suggest that the hormonal effects of β-endorphin are species dependent and are similar to those of morphine. Hormonal and analgesic effects of β-endorphin appear to result from the activation of opiate receptors that differ in their locations and characteristics.

Hypothalamic-pituitary-gonadal dysfunction in men using cimetidine.

Abstract: We studied the effect of cimetidine therapy (1200 mg per day by mouth for nine weeks) on the hypothalamic-pituitary-gonadal axis of seven men. There was a 43 per cent mean reduction in sperm count after therapy. The luteinizing hormone response to luteinizing hormone releasing factor was also reduced, and a statistically significant rise in plasma testosterone occurred, although it was less than that before therapy. Gonadotropin responses to provocative clomiphene stimulation were inadequate when compared with those of controls. Cimetidine did not affect the responses of thyroid-stimulating hormone, prolactin, growth hormone and thyroxine to thyrotropin releasing factor. Caution is advisable in administration of cimetidine for prolonged periods to young men. (N Engl J Med 300:1012–1015, 1979)

Reduction in size of a pituitary tumor by bromocriptine therapy.

Abstract: SINCE the development of specific assays for prolactin1 , 2 it has been possible to demonstrate that a large proportion of pituitary tumors secrete prolactin.3 Until the advent of bromocriptine, operation and irradiation had been used as the primary treatments for such tumors.4 The introduction of bromocriptine, an ergot derivative5 and dopamine agonist,6 into therapeutic regimens for pituitary disease is recent and is still being evaluated. It is a potent inhibitor of prolactin secretion. Acting primarily at the level of the pituitary,7 but with a possible hypothalamic effect not yet excluded,8 it lowers prolactin secretion in patients with hyperprolactinemia from any cause, . . .

Effect of Clozapine on Human Serum Prolactin Levels

Abstract: The authors determined serum prolactin levels in 13 patients receiving clozapine, an antipsychotic drug that does not produce extrapyramidal side effects. Morning serum prolactin levels, 11 hours after the last dose, were not elevated during chronic treatment with clozapine in any subject despite its therapeutic effects. Serum prolactin levels were moderately increased between 90 minutes and 4 hours after administration of very high doses of oral clozapine in 4 patients but were smaller than those produced by chlorpromazine in other subjects. The authors suggest that clozapine in other subjects. The authors suggest that clozapine may achieve its antipsychotic effect differently than do classical neuroleptics and that sustained prolactin increases are not essential for antipsychotic action.

Extrapyramidal side effects and increased serum prolactin following fluoxetine, a new antidepressant.

Abstract: Fluoxetine (Lilly 110140) is a potent, specific serotonin (5-HT) uptake blocker which is being tested in man for antidepressant activity. One of 9 depressed patients receiving this drug developed a dystonic reaction, parkinsonian rigidity, and increased serum prolactin levels, all signs of decreased dopaminergic activity. Homovanillic acid levels also decreased in the cerebrospinal fluid of this subject. We postulate that fluoxetine, via the increase in 5-HT activity resulting from 5-HT uptake blockade, inhibited both the nigro-striatal and tubero-infundibular dopaminergic neurons. These results provide additional evidence for a linkage between serotonergic and dopaminergic neurons in man.

A Pregnancy in an Acromegalic Woman during Bromocriptine Treatment: Effects on Growth Hormone and Prolactin in the Maternal, Fetal, and Amniotic Compartments*

Abstract: An unexpected 20-week-old pregnancy was found in a young acromegalic who had been treated with 10 mg bromocriptine/day for 10 months. The drug was continued throughout the period of gestation. No growth of the pituitary adenoma was noticed. The intrauterine development of the fetus was normal. Bromocriptine therapy had no discernible effect on the expected patterns of secretion of placental hormones, but inhibited completely the increase of PRL in the serum of the mother. Maternal plasma GH concentrations were very high in spite of the treatment and progressively declined after delivery. The plasma GH level was normal in the child, but PRL was very low at birth and increased in the following days. The expected high PRL concentration was found in the amniotic fluid. This case study suggests that bromocriptine crosses the human placenta and affects the fetal pituitary, maternal GH does not influence fetal or amniotic GH, and amniotic fluid PRL correlates poorly with either maternal or fetal blood levels and...

Endogenous opiates block dopamine inhibition of prolactin secretion in vitro.

Abstract: OPIATES stimulate prolactin secretion in vivo; plasma prolactin levels are increased by morphine administration in normal1 and steroid-primed male rats2, as well as in immature3 and oestrogen-treated female rats4. Met-enkephalin and β-endorphin were also stimulatory1–6 as were enkephalin analogues3,7,8. Naloxone or naltrexone, specific opiate antagonists, reduce basal prolactin levels when given alone1,3,9, and block, at least partially, the effect of opiate agonists1–4,7,8. None of these drugs is active in vitro when tested alone on anterior pituitaries3 or dispersed pituitary cells2,4. However, as we have previously shown in a preliminary experiment, the inhibitory effect of dopamine on prolactin secretion in vitro was antagonised by the addition of morphine to the incubation medium10. In the present work, we have attempted to clarify further the mode of interaction of opiates with prolactin secretion. We confirmed that morphine, Met-enkephalin and β-endorphin do not affect the spontaneous release of prolactin in vitro, but found that they suppress the inhibitory effect of dopamine on prolactin release. We have also characterised the specificity and the kinetics of this interaction.

Variations in concentrations of prolactin, luteinizing hormone, growth hormone and progesterone in the plasma of broody bantams (Gallus domesticus)

Abstract: The concentrations of prolactin, LH, progesterone and GH were measured in the blood of broody bantam hens. The concentration of prolactin was at its highest when the birds began to incubate their eggs and in six out of nine hens it tended to remain raised until the eggs hatched. The increase in the concentration of prolactin was small: in incubating hens it was only 23% higher than in hens caring for their young and 14% higher than in laying hens (P less than 0.05 for both comparisons). The concentration of GH tended to be depressed in hens caring for young but otherwise was not related to reproductive activity. The concentrations of LH and progesterone decreased at the onset of incubation and remained depressed while the hens sat on their eggs (P less than 0.001) for both comparisons). After the chicks hatched, the level of LH began to increase slowly whereas the level of progesterone remained low. The hens stopped showing broody behaviour between 4 and 10 weeks after the chicks had hatched; this corresponded to the time when the concentration of LH had increased to values found in laying hens. These observations provide some evidence that prolactin secretion increases at the onset of incubation and support the view that the hormone is not secreted at an increased rate while hens are caring for their young.

Morphine and endorphins modulate dopamine turnover in rat median eminence.

Abstract: The is evidence that some of the actions of both endogenous and exogenous opioids (e.g., stimulation of prolactin release) are mediated by interaction with catecholaminergic systems. Morphine (1.67, 5, and 15 mg/kg of body weight, intraperitoneally) altered dopamine turnover as measured by the alpha-methyl-p-tyrosine method in the median eminence, neostriatum, and frontal cortex of male Sprague-Dawley rats. The turnover rate of dopamine was reduced in the median eminence and frontal cortex but accelerated in the neostriatum. In the frontal cortex all doses were effective in decreasing dopamine turnover; however, in the median eminence the lowest dose of morphine did not significantly alter dopamine turnover. All three doses accelerated dopamine turnover in the neostriatum. Naloxone effectively reversed the effects of morphine at all doses in all brain areas, whereas it had no effect on turnover when given alone. In the median eminence, neostriatum, and frontal cortex, intraventricular injection of [D-Ala2,D-Leu5]-enkephalin (25 micrograms) or beta-endorphin (15 micrograms) produced the same effects on dopamine turnover as morphine. The actions of these peptides were blocked by naloxone. It is hypothesized that opiates and opioid peptides increase prolactin release by reducing the activity of the tuberoinfundibular dopaminergic system.

Membrane potential changes caused by thyrotropin-releasing hormone in the clonal GH3 cell and their relationship to secretion of pituitary hormone.

Abstract: Effects of thyrotropin-releasing hormone (TRH; thyroliberin) on membrane electrical properties were studied in the clonal rat anterior pituitary cell (GH3) by continuous recording of the intracellular potential. Application of TRH, which stimulates the release of prolactin and growth hormone from the GH3 cell, elicited a transient hyperpolarization of the cell membrane followed by an enhancement of the generation of action potentials for an extended period in the majority of cells tested. The transient hyperpolarization was due to an increase of the membrane conductance to K+. The enhancement of the spike generation was not due to membrane depolarization. The input resistance of the cell membrane was found to be increased during the facilitation. Thus the mechanism of the facilitatory action of TRH is different from the mechanisms of conventional excitatory neurotransmitters. TRH enhances the spike generation, thus promoting Ca2+ entry from extra- to intracellular space (the action potential of the GH3 cell has a Ca2+ component) and stimulating the release of hormones. This notion is supported by the observation that cobalt ions, which block the calcium spike in these cells, completely abolished the stimulatory effect of TRH on the release of prolactin and growth hormone.

Role of insulin receptors in the changing metabolism of adipose tissue during pregnancy and lactation in the rat.

Abstract: Changes in the volume, the rates of fatty acid synthesis and synthesis of the glycerol moiety of acylglycerols, the activity of lipoprotein lipase, and the number and affinity of insulin receptors of adipocytes, and concentrations of serum insulin, prolactin and progesterone were determined in virgin rats and in rats at various stages of pregnancy and lactation. Changes in the metabolic activities of adipose tissue appeared to be synchronized and primarily comprised a marked decrease in anabolic activity around parturition. In contrast, the number of insulin receptors (Kd 1.5 nM) per adipocyte doubled during pregnancy before returning to normal values around parturition. It is postulated that the increase in the number of insulin receptors is an adaptation to counteract the effects of insulin-antagonistic hormones during pregnancy and that the decrease in the number of receptors is primarily responsible for the loss of anabolic activity around parturition.

The accessory olfactory system and its role in the pheromonally mediated suppression of oestrus in grouped mice.

Abstract: Mice were grouped to induce suppression of oestrus and subjected to removal of the vomeronasal organs or treatment with CB 154 which lowers prolactin levels. Both treatments overcame the suppression of oestrus after 72 h. Oestrus suppression was induced in lesioned mice by haloperidol treatment which raises plasma prolactin, and oestrus returned some 72 h after withdrawal of haloperidol treatment.