Endogenous Prolactin Research Articles

Role of prolactin in the development of mammary gland tumors induced by dimethylbenzanthracene

The action of high prolactin content on dimethylbenzanthracene-induced mammary carcinoma was studied in rats with varying bodily content of estrogens. It was found that the high content of endogenous prolactin in rats provoked by ligation of the hypophyseal peduncle or aminazin injection stimulates the development of dimethylbenzanthracene-induced carcinoma even in the presence of the lowered estrogenic content. Ovarectomy dramatically reduced the effect of hypophyseal peduncle ligation. Combined action of estrogens and prolactin is conducive to the development of hormone dependent mammary carcinoma. The role of hormones in the pathogenesis of mammary carcinoma and approaches to its prevention and choice of an adequate treatment are discussed.

Effects of bromocriptine and PRL on luteal and adrenal cholesterol ester hydrolase and serum progesterone concentrations in mature pseudopregnant rats.

Experiments were conducted to investigate regulation by prolactin (PRL) of luteal, and possibly of adrenal, cholesterol ester hydrolase (CEH) in mature, pseudopregnant rats, and to correlate changes in CEH activity and serum PRL, luteinizing hormone (LH) and progesterone (P) concentrations. 2-Br-α-ergocryptine (EC), EC plus ovine PRL (oPRL), or EC + P were administered to mature rats on pseudopregnancy Day 5 (PP5) and/or PP6. Injection of EC at 1100 and 2300 h PP5 drastically reduced serum PRL concentrations at 1800 h PP5 and 0600 h PP6, indicating that both the diurnal surge of PRL on PP5 and the nocturnal surge of PRL on PP6 had been successfully blocked. Luteal CEH and serum P measured at these time periods were not affected. However, by 1200 h PP6, both were significantly decreased. Injection of oPRL with EC significantly increased luteal CEH at 0600 h and 1200 h PP6, and significantly increased serum P by 1200 h PP6. However, injection of oPRL at 1600 h PP5 and 0300 h PP6 after EC at 1100 and 2300 h PP5, had no effect on luteal CEH at 0600 h, even though serum P at that time was significantly increased. Blocking only the nocturnal PP6 PRL surge by injection of EC at 2300 h PP5 caused significant reductions in both luteal CEH and serum P by 1200 h PP6, but these decreases were not as great as those observed after elimination of both PRL surges. Injection of oPRL at 0300 h PP6, 4 h after EC (2300 h PP5), significantly increased both luteal CEH and serum P by 1200 h PP6. Injection of 2 mg P with EC at either 1100 h and 2300 h PP5, or only at 2300 h PP5, had no effect on luteal CEH activity at 1200 h PP6. None of the treatments had any effect on adrenal CEH activity or on serum LH concentrations, except for one treatment (injection of EC plus oPRL at 1100 and 2300 h PP5 followed by sacrifice at 0600 h) which significantly decreased serum LH. These data indicate that in mature pseudopregnant rats, PRL stimulates luteal CEH activity and concomitantly increases serum P concentrations. A time interval of 6-9 h after exogenous or endogenous PRL is both necessary and optimal for stimulation of luteal CEH. Both PRL surges are necessary for complete luteal function, but the nocturnal surge appears to exert the greater influence on the parameters studied. The action of PRL on luteal CEH does not seem to be mediated by P at concentrations of P injected, and under conditions of these experiments PRL had no effect on adrenal CEH.

Effects of Human Chorionic Gonadotropin, Prolactin, and Bromocriptine on Photoperiodinduced Testicular Regression and Recrudescence in Golden Hmsters

Exposure of adult male hamsters to short day‐length (short photoperiod) causes atrophy of their reproductive systems. Hamsters were transferred from long to short photoperiod and, starting two months later, injected three times a week for three weeks with saline, 1.25, 5, or 20 IU of human chorionic gonadotropin (hCG). Treatment with 5 or 20 IU hCG resulted in significant increases in the weights of the testes and the seminal vesicles. In another group of animals, identical doses of hCG were injected starting at the time of transfer from long to short photoperiod. After 14 weeks of treatment, testicular weight was significantly greater in animals given 20 IU hCG than In animals injected with saline, although it approximated only 50% of testicular weight In adult males kept in long photoperiod. Since we have previously obtained very similar results using prolactin (PRL) producing ectopic pituitary homografts, it was of interest to examine the interaction of pituitary grafts and hCG. Male hamsters were transferred to a short photoperiod and treated with a transplant of one pituitary from an adult female hamster plus 5 IU hCG three times a week or with hCG alone. After 15 weeks, the weights of the testes and the seminal vesides were significantly greater In grafted hCG‐treated hamsters than in those animals treated with hCG only. Testicular weight in animals given both grafts and hCG corresponded to approximately 75% of testicular weight in long photoperiod controls, while seminal vesicle weights in these two groups did not differ.To examine the role of endogenous PRL in long photoperiod‐induced testicular recrudescence, hamsters which had been exposed to a short photoperiod for two months were returned to a long photoperiod and treated daily with bromocriptlne (Sandoz CB‐154, an inhibitor of PRL release) or with vehicle. After three weeks, the weights of the testes and the seminal vesicles were significantly lower in bromocriptine‐treated than in control hamsters, but after five and a half weeks these differences were no longer evident.We conclude that (1) suppression of the release of both PRL and gonadotropins is responsible for gonadal regression in short photoperiod, and (2) stimulation of PRL secretion contributes to recrudescence of the male reproductive system in long photoperiod.

Prolactin in cerebrospinal fluid: A probable site of prolactin autoregulation

The purpose of this study was to examine the thesis that increasing concentrations of prolactin within the cerebrospinal fluid (CSF) increase the activity of dopaminergic terminals within the median eminence and that this increased dopaminergic activity is temporally associated with a suppression of endogenous prolactin secretion. To avoid difficulties encountered in performing catecholamine turnovers in the undisturbed rat, the measurement of tyrosine hydroxylase was validated as an index of dopaminergic activity within the median eminence. In the median eminence, but not the medial preoptic area, parallel increases in the activity of tyrosine hydroxylase and the turnover of dopamine (but not norepinephrine) occurred following hyperprolactinemia. Twenty-six hours but not 2.5 h after the subcutaneous administration of ovine prolactin, the activity of tyrosine hydroxylase was increased in the median eminence, and endogenous prolactin secretion was inhibited. During a 26 h continuous intracerebroventricular (icv) infusion (88 ng/h) of rat prolactin, there was a complete suppression of endogenous prolactin secretion. Twenty-six but not 2.5 h after the initiation of the icv infusion of prolactin, there was an increase in tyrosine hydroxylase activity in the median eminence. The results of these studies suggest that: (1) measurement of tyrosine hydroxylase activity within the median eminence is a useful index of the activity of dopaminergic terminals; (2) increasing concentrations of prolactin within the CSF suppressed prolactin secretion by the anterior pituitary; (3) this suppression of prolactin is accompanied by an increased activity of dopaminergic terminals within the median eminence; (4) those neural structures concerned with the regulation of prolactin secretion respond directly to prolactin itself; (5) the autoregulation by prolactin of its own secretion manifests a certain latency more characteristic of a tonic rather than a phasic inhibitory control; and finally, (6) dopaminergic terminals in the median eminence but not the preoptic area appear uniquely sensitive to prolactin.

Modulation of testicular lutropin receptors in the developing male rat

In the developing male rat around 40 days of age, the testis appears to contain the maximum amount of lutropin receptors per unit weight. During this period, circulating levels of testosterone markedly increase without the concomitant major surges in lutropin levels. The increased sensitivity and responsiveness of tests to basal levels of circulating lutropin during this period is accompanied by enhanced serum prolactin levels suggesting that this hormone may be involved in this process. The finding that prolactin treatment of pubertal rats for 3 days induced the formation of more testicular lutropin receptors supports the above premise. However, shortterm immunoneutralisation of endogenous prolactin did not significantly alter the specific binding of [ 125 I ]-labelled lutropin to testicular membranes. Interestingly, during development, a close correction exists between receptor occupancy and capacity of the tissue to bind labelled lutropin. The apparent dissociation between serum lutropin levels, on the one hand and tissue occupancy and free receptor contents on the other, suggests that factors other than lutropin (presumably prolactin) are involved in the modulation of the sensitivity and the responsiveness of the testis to lutropin during early development.

Incorporation of endogenous prolactin by granulosa cells and dictyate oocytes in the postpartum rat: effects of estrogen.

Ovarian follicles were examined for the presence and distribution of endogenous PRL in nor mally lactating control rats and comparable rats which had been subjected no a variety of annilacta tional, luteonropic estrogen treatments. Control ovaries contained both preantral follicles and annral follicles up to 500 @m in diameter. In healthy antral follicles, PRL was present in the cyno plasm and nuclei of granulosa cells (GC), in follicular fluid (FF) and also in the cytoplasm of the manuring dicnyane oocynes (OC), where ins lattice-like distribution resembled that of, and sug gesned an association with, yolk material. PRL was distributed similarly in OC of healthy preannral follicles, but in was absent from the surrounding GC. In anresia, both GC and OC showed disturb ances of PRL distribution (absence from GC nuclei, irregular staining of yolk lattice) or complete absence of staining for PRL. The changes in OC were seen in rats given only 4 @g estradiol benzo ate/day. Stronger estrogen treatments produced anrenicchanges in GC as well. These findings suggest at least two periods of PRL incorporation by healthy dicnyane OC: one prior no, or early in, the stage of meionic arrest, the other during preovulanory manuranional en largement. During the later period, when PRL is transported no the OC through GC cytoplasm and FF, in also enters GC nuclei. The prolonged retention of PRL within the OC and ins renewed in corporation as this cell approaches innerphase, together with recent evidence that PRL may play a role in the inhibition of meiosis in mammalian oocynes, suggest that the specific local resistance no ovulation -inducing stimuli, which is needed for both selective maintenance of the dicnyane state and fine control of preovulatory maturation, might be a function of the PRL snored within the OC itself.

Effect of ergocristine on prolactin secretion in the male rat with pituitaries grafted beneath the kidney capsule.

Male rats in which three pituitaries were grafted beneath the kidney capsule showed approximately a fourfold increase in circulating plasma prolactin concentration. The elevated plasma prolactin concentration did not remain at a constant level but fluctuated with time. The elevated prolactin concentration declined immediately after a single bolus injection of ergocristine (30 micrograms/kg). The slope of the prolactin decay curve, determined by sequential blood sampling, was parallel to a theoretical slope having a 7-min half-life. This result indicates that ergocristine blocked prolactin secretion immediately and completely as the decay curve (T 1/2 = 6.5 min, confidence interval 4.5--11.3) resulting from the administration of ergocristine is the same as the endogenous prolactin decay curve (T 1/2 = 7 min).

Synergistic effects of prolactin and estradiol in the luteotropic process in the pregnant rat: regulation of estradiol receptor by prolactin.

Our findings that the direct luteotropic effect of estrogen was dependent on the presence of prolactin or rat placental lactogen have suggested to us that prolactin may control estrogen receptor content in the corpora lutea of pregnant rats. To test this hypothesis, the cytosolic and nuclear contents of estrogen receptor were measured in the corpora lutea of pregnant rats in which endogenous prolactin was removed by 1) hypophysectomy and hysterectomy on Day 9, or 2) treatment with ergocryptine (1 mg/rat) on Day 6. Within 24 h, nuclear content of estrogen receptor in lutea cells dropped by 70% in hypophysectomized-hysterectomized rats and 75% in ergocryptine treated rats, while cytosol content dropped by 40% and 38%, respectively. Estradiol treatment (100 �g/ day) did not prevent the decrease in cytosolic or nuclear receptor, whereas prolactin (250 �gI day) or serum containing rat placental lactogen did maintain luteal cell cytoplasmic receptor content. Nuclear content of estradiol receptor was maintained in ergocryptine treated rats by administration of prolactin alone. However, estradiol had to be administered with prolactin in hypophysectomized-hysterectomized rats to achieve the same effect, suggesting that after ergocryptine treatment intraluteal concentrations of estrogen were sufficient to affect the translocation of cyrosolic receptor to the nucleus. These studies indicate that the synergistic action of prolactin with estradiol in the luteotropic process in the pregnant rat may involve, in part, prolactin stimulation of luteal receptor for estradiol, a prolactin dependent response not previously reported.

Circadian phase-dependent prolactin mechanisms in hepatic lipogenesis of a teleost.

In the teleost, Fundulus grandis, injections of prolactin early in the light phase cause an immediate 50% depression in the rate of hepatic lipogenesis ([14C]acetate incorporation); 10 h later, that rate has returned to levels not different from controls. Injections of prolactin late in the light phase cause an even more dramatic immediate depression of lipogenesis (79%) followed by a gradual increase in lipogenic rate which is 2.6 times higher than the control rate after 24 h. The stimulation of lipogenesis by prolactin is blocked by simultaneous treatment with indomethacin, an inhibitor of prostaglandin synthesis. These circadian phase-dependent effects of prolactin on hepatic lipogenesis are discussed with reference to possible mechanisms of action exerted by endogenous prolactin rhythms.

Metabolism of prolactin in mice with a high incidence of mammary tumours: evidence for greater conversion into a non-immunoassayable form.

Monomeric mouse prolactin containing small amounts of 125I-labelled prolactin was administered to adult female mice of a high (C3H/St) and low (C57BL/St) mammary tumour strain. Their endogenous prolactin had been suppressed with 2-bromo-alpha-ergocryptine. The chromatographic profile, on Sephadex G-100, of prolactin in the serum of mice injected with mouse prolactin was compared by direct measurement (radioactivity count) and by radioimmunoassay (RIA) at several intervals after injection. With both methods, the injected hormone was found in the serum in predominantly two molecular sizes, the so-called 'big' and 'little' forms. Although 'little' prolactin in both strains constituted a constant 80% of the total hormone at most intervals by direct measurement, it comprised a comparatively smaller proportion by RIA. In addition, the RIA-determined 'little' prolactin, after reaching maximum levels at 15 min, progressively decreased with time, the decrease being greater in the C3H/St than in the C57BL/St strain. Similar experiments with mouse growth hormone revealed no such discrepancies between the radioactivity counts and the RIA measurements. A fraction of both 'big' and 'little' forms in the C3H/St strain failed to precipitate completely after the material had been incubated with an antiserum to mouse prolactin. These results demonstrate that the prolactin injected into mice is metabolized in serum into two non-immunoreactive forms, one that elutes with the same elution volume on Sephadex G-100 column as the monomer and the other that elutes as the 'big' form. Furthermore, the loss of immunoreactivity of monomeric mouse prolactin is greater in the high-tumour C3H/St strain than in the low-tumour C57BL/St strain. Endogenous immunoreactive prolactin, on the other hand, was found mainly in the 'big' form in the serum of female mice of the C3H/St strain under basal conditions, whereas it was present only in the 'little' form in comparable mice of the C57BL/St strain, even though pituitary extracts of both strains contained mainly the 'little' form. These results support the concept that monomeric prolactin in the systemic circulation of the tumour-prone C3H/St strain is largely in a non-immunoreactive form.

Prolactin action on extracellular fluid volume in tails of stage XII bullfrog tadpoles

The effect of prolactin (PRL) on electrolyte and water content of total tail and tail muscle tissues of stage XII bullfrog tadpoles was studied after injection of ovine PRL or removal of endogenous PRL by injection of a specific antiserum to ovine PRL (PRL A S ). PRL treatment (5 μg per tadpole daily for 5 days) caused a significant increase in sodium and water content while potassium content of total tail tissues decreased, when compared to saline-treated controls. No differences were observed in electrolyte and water content in tail muscle tissues, and plasma electrolyte concentrations were unchanged. These data indicate that the increased tail sodium and water represent an expansion of extracellular fluid volume in the tail fin. Injection of PRL A S (every 5 days for 15 days) caused a decreased sodium and water content of total tail tissues as compared to control animals injected with normal rabbit serum. Again, no differences were found in tail muscle electrolytes, water content, and plasma electrolyte concentrations in the PRL A S group. Thus, removal of endogenous PRL caused a decreased extracellular fluid volume in the tail. These results indicate that a prolactin-like substance is present in stage XII bullfrog tadpoles and may be involved in chronic regulation of extracellular fluid volume in the tail fin.

Immunocytochemical technique for detection of prolactin (PRL) and growth hormone (GH) in hyperplastic and neoplastic lesions of dog prostate and mammary gland.

An immunocytochemical technique was described to test for immunoreactive prolactin (PRL) and growth hormone (GH) in spontaneous and experimentally induced hyperplastic and neoplastic lesions of the prostate and mammary gland. The dog was used as an animal model. The specificity and validity of the immunocytochemical staining procedure and of the antisera to canine PRL and canine GH can be regarded as established for the demonstration of PRL- and GH-dependent staining respectively. In mammary and prostatic tissues, both endogenous PRL and GH as well as intracellular free binding sites (for exogenous PRL and GH) were detected immunocytochemically. The technique presented seems to be an important tool to localize putative target sites for pituitary hormones in hormone-dependent hyperplasia and neoplasia.

Prolactin and Leydig Cell Responsiveness to LH/hCG in the Rat

The effects of prolactin and 2-bromo-alpha-ergocryptine (CB-154) on Leydig cell function in intact and hypophysectomized male rats were studied. The conclusions can be summarized as follows: prolactin (1) has a direct stimulatory effect on the number of LH receptors on rat Leydig cells, (2) has no effect on the characteristics of the dose-response curve of isolated Leydig cells (hCG stimulated androgen production) in vitro even after treatment with pharmacological doses in vivo, and (3) acts synergistically with LH to stimulate the quantity of androgen produced by the Leydig cells in response to hCG in vitro and to increase the sensitivity of the hCG-dose-response curve. Treatment of intact rats with CB-154 reduced the quantity of androgen produced by the Leydig cells in vitro after exposure to hCG and decreased LH binding to the same cells by 50%. These results suggest that under normal conditions, endogenous prolactin plays a key role in maintaining the functional integrity of rat Leydig cells.

Effect of prolactin on glomerular filtration rate.

1. The effect of infusion of ovine prolactin was studied in anaesthetized dogs pretreated with bromocryptine to reduce the release of endogenous prolactin. 2. Prolactin, injected intravenously and also directly into one kidney, resulted in a 12--18% increase in glomerular filtration rate (GFR) by both kidneys. 3. This increased GFR was not associated with any demonstrable changes in whole-kidney blood flow, distribution of intrarenal blood flow, fractional excretion of sodium or osmolar or free-water clearance. 4. We conclude that ovine prolactin produced an increase in GFR not dependent on an increase in whole-kidney plasma flow.

Osmoregulatory activity of prolactin in the skin of the crested newt

Changes in short-circuit current (SCC) in isolated skin from the crested newt ( Triturus cristatus carnifex Laur.) subjected to several experimental treatments have been measured. In “winter” animals, when prolactin release is at its highest, both hypophysectomy and radiothyroidectomy produce a pronounced enhancement of active sodium transport, which is restored to normal values by administration of ovine prolactin. Injection of bromocryptine (a prolactin-inhibiting drug) likewise elevates the skin SCC, thus showing indirectly that depression of sodium transport across the skin is promoted by endogenous prolactin. Additional evidence for the control of SCC by prolactin comes from the observation that the striking rise in skin SCC induced by ovariectomy is corrected by replacement therapy with estradiol-17β, reported to be a prolactin-stimulatory hormone. Thyroxine tends to counteract endogenous prolactin action in the “winter” animal, but not in the aestivating animal. Correlation of the above experimental results with the seasonal pattern of pituitary prolactin release and the annual life cycle of the crested newt seems to lend support to the assumption that this hormone is involved in the control of the osmoregulatory processes exerted by the skin.

Stabilization of casein mRNA by prolactin and glucocorticoids

Prolactin injected into pseudopregnant rabbits led to a parallel enhancement of casein synthesis and casein mRNA concentration. When this stimulation was followed by a withdrawal of prolactin obtained by injections of bromocriptine, the rate of casein synthesis progressively diminished. In the presence of endogenous prolactin after the initial stimulation, the decline of casein synthesis was delayed. Hydrocortisone acetate injected with bromocriptine after the initial stimulation by prolactin was able to maintain a high rate of casein synthesis. Measurements of casein mRNA concentration by hybridization with casein cDNA indicated that in all cases the amount of casein mRNA was correlated with the magnitude of casein synthesis. This suggests that the lactogenic hormones, prolactin and glucocorticoids, which were previously demonstrated to be responsible for the enhancement of casein mRNA concentration are involved in their stabilization.

Effects of prolactin and methallibure on second metamorphosis and plasma androgens in male newts, Taricha granulosa

1. 1.Male rough-skinned newts, Taricha granulosa, were injected during late spring with ovine prolactin and/or methallibure (ICI 33,828), a known inhibitor of gonadotropin release. 2. 2. Methallibure injections, either alone or with prolactin, reduced androgen concentrations in the plasma, as measured by radioimmunoassay. 3. 3. Exogenous prolactin injections failed to affect plasma androgen titers in intact newts at this season. 4. 4. Saline-injected controls exhibited a diminution in tail fin height and water drive, preference for total submergence in water. 5. 5. The decrease in tail fin height and water drive was inhibited by prolactin treatment and, to a lesser degree, by methallibure treatment, suggesting that methallibure stimulated an increase in endogenous prolactin.

The Effect of Exposure to Ether on Prolactin Secretion and the Half-Life of Endogenous Prolactin in Normal and Castrated Male Rats

Normal and castrated male rats implanted with permanent right atrial cannulae were used, and sequential blood samples were taken every 2 min through the cannula. When the rats, both normal and castrated, were exposed to ether for 2 min, the prolactin (Prl) concentration in plasma was immediately and dramatically elevated. During 40 min of continuous ether anesthesia, plasma Prl concentration was not sustained. After the initial 'surge' of Prl secretion, which lasted about 15 min, the concentration returned to normal levels. Following the peak of the Prl 'surge', Prl disappeared from the circulation with a calculated half-life of 7 min (mean value: 6.9 min; confidence interval: 6.3-7.7).

Evidence for androgen-dependent intracellular binding of prolactin in rat ventral prostate gland.

In an attempt to localize endogenous prolactin (PRL) in rat ventral prostate gland at the light microscope level, the following 4-step immunohistochemical reaction sequence was applied to fixed tissue sections: I) goat anti-monkey γ-globulin (AMγG), II) NIAMDD rabbit anti-rat PRL (APRL), III) goat anti-rabbit γ-globulin: peroxidase conjugate (AR-γG-per), and IV) chromogenic substrate. AMγG was required to block the nonspecific staining pattern produced by direct binding of AR-γG-per to the tissue and unmask that produced by APRL. APRL-dependent staining occurred in the Golgi region of ventral prostate epithelial cells. Golgi region staining was attenuated and eventually disappeared with increased APRL dilution and was not reproduced when normal rabbit serum or rabbit antisera to rat LH or rat TSH replaced APRL. However, absorption of APRL with highly purified NIAMDD rat PRL (1-1) neither attenuated nor eliminated Golgi region staining. This suggested tliat the APRL-dependent staining of rat ventral prosta...

CHANGES IN NEUROMAST CHEMOSENSITIVITY IN XENOPUS LAEVIS KEPT UNDER VARIOUS ENVIRONMENTAL CONDITIONS

Istituti di Fisiologia generale e di Istologia ed Embriologia della Facoltà di Scienze Matematiche, Fisiche e Naturali, Università di Torino, Italy (Received 18 February 1977) In Xenopus laevis, chemosensitivity declines after subtotal hypophysectomy, but is restored to a normal level by injections of ovine prolactin (Blanchi, Camino & Guardabassi, 1976). Changes in the level of endogenous prolactin should, therefore, also give this effect. This might be shown experimentally in progressively desiccated toads, which would mimic the conditions prevailing in their natural habitat. The possibility was examined with animals housed in a thermostatic cupboard at 24–28 °C in containers lined in the bottom with a layer of drying mud. After 7days, to simulate a heavy shower, some toads were abruptly thrown into tap water. The neuromast chemosensitivity of six animals kept under dry conditions was compared with that of neuromasts from 'dry' animals returned to water for 12(1 animal), 24 (5)