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PubMed1995

Stimulated thyrotropin and prolactin secretion in lactating and non-lactating women.

During the postpartum period, lactation is initiated by a massive release of prolactin which, in turn, reflects reduced dopaminergic inhibition of the pituitary lactotrophs. This postpartum prolactin rise can be prevented by administration of dopamine agonists. The release of thyrotropin (TSH) is also controlled by dopaminergic inputs and, therefore, TSH secretion may also be affected by postpartum alterations in dopaminergic activity. To gain further insight into the regulation of TSH and prolactin secretion during the postpartum period, we compared the basal and stimulated TSH and prolactin levels of postpartum lactating (n = 10) and non-lactating women (treated with 5 mg bromocriptine daily, n = 9) with those of normal cycling women (n = 9). Frequent blood samples were obtained on postpartum day 5 or in the early follicular phase before and after administration of thyrotropin-releasing hormone (TRH) for serial determination of TSH and prolactin by immunoradiometric assay (IRMA). Based serum prolactin levels were high (p < 0.001) in lactating women and low in both non-lactating and normal cycling women. When these differences in the basal prolactin concentrations were taken into account, the stimulated prolactin release (relative prolactin increase and area under the prolactin curve) was found to be highest (p < 0.05) in non-lactating women and lowest in lactating women. Basal TSH secretion was not significantly different between the groups of women (p > 0.2). Yet, both the relative TSH increases and the response curves following TRH stimulations were high (p < 0.05) in normal cycling women and low in both lactating and non-lactating postpartum women. These observations confirm a difference in the basal and stimulated prolactin release between lactating and non-lactating women. They also indicate that the TRH-stimulated TSH release is greatly affected by the postpartum state, irrespective of lactation or therapeutic weaning. The observation of a decreased sensitivity of pituitary thyrotrophs in concert with unchanged basal TSH secretion is suggestive of changes in hypothalamic TRH secretion and/or in the TSH metabolic half-life during the postpartum period.

Adult↗
PubMed1981

Serum prolactin in patients with hypothalamus and pituitary disorders.

Serum prolactin concentrations were studied in 115 patients with anatomically defined disorders in the hypothalamo-pituitary region. Fifty of the patients had expansively growing pituitary adenomas; in 17 of them (13 females and four males) the prolactin values were slightly raised (15 to 100 microgram/liter), and in 13 (11 females and two males) they were over 100 microgram/liter. The frequency of elevated prolactin values was higher for females than for males. Fifteen patients with invasively growing pituitary adenomas had very high serum prolactin levels (range 1230 to 31,500 microgram/liter). In a single case of malignant pituitary adenoma, the serum prolactin was at the lower level of detection. Of 49 further patients with suprasellar meningiomas, craniopharyngiomas, or other expansive or destructive lesions of the hypothalamus and sellar region, 15 had slightly raised prolactin values (maximum 114 microgram/liter). Eight of these 49 patients had sellar destruction, with a roentgenological picture similar to that in patients with invasive pituitary adenomas. Among these eight patients, the maximum prolactin value was 67 microgram/liter. It is concluded that moderately raised serum prolactin values (up to 100 microgram/liter) in a patient with a sellar tumor does not prove that the tumor is a prolactinoma. A serum prolactin value of 100 to 1000 microgram/liter strongly indicates a prolactin-producing tumor. In a patient with sellar destruction, a serum prolactin value of over 1000 microgram/liter is proof that the destruction is caused by an invasive pituitary adenoma.

Adenoma↗
PubMed1976

The temporal interaction of corticosterone and prolactin in affecting liver lipid metabolism of the chick.

Experiments were conducted to determine if Brown Leghorn chickens (Gallus domesticus) showed a daily differential responsiveness to the phased injections of corticosterone and prolactin. In experiment 1, 28 day old chicks, maintained on continuous lighting and a standard diet, were treated daily for 6 days with corticosterone (300 mug. in 0.2 cc. saline) and with prolactin (150 mug. in 0.2 cc. saline) for 4 days. The prolactin injections began 2 days after the first corticosterone injection. The interval between daily corticosterone injections at 1800 hours followed by prolactin injections 6, 12 or 18 hours later resulted in a significant increase in the liver lipidcontent in the chicks. However, when corticosterone and prolactin were given at the same time (1800 hours), no increase in liver lipid content was observed. Corticosterone admininstered at 6oo hours and followed by prolactin injections had no effect on liver lipid content regardless of the time of prolactin prolactin injections. Experiment 2 was designed to test the effect of the administration of corticosterone or prolactin alone at either 600 hours or 1800 hours on liver lipid metabolism. Two groups of Brown Leghorn chicks received prolactin alone (for 2 days) at either 600 hours or 1800 hours. None of these treatment groups were significantly different from the uninjected controls. It is concluded that the chick has a diurnal sensitivity to the effects of coritcosterone and that once the liver is affected by corticosterone, a temporal interaction between this steroid and prolactin can affect the liver lipid content of the Brown Leghorn chick.

Animals↗
PubMed2000

Cigarette smoking decreases the prolactin response to serotonergic stimulation in subgroups of alcoholics and controls.

BACKGROUND: The prolactin response to serotonergic stimulation has been used as an index of central nervous system serotonin function. We evaluated the prolactin response to d,l-fenfluramine to determine whether subtypes of alcoholics differed in prolactin responsivity compared with nonalcoholics and whether cigarette smoking affected prolactin response. METHODS: One hundred ten healthy, abstinent men across four groups (controls [23% smokers]; alcoholics [72% smokers]; alcoholics with antisocial personality disorder [94% smokers]; nonalcoholic antisocials [88% smokers]) received d,l-fenfluramine (100 mg orally) in a randomized, double-blind, placebo-controlled study. Plasma prolactin levels were obtained at baseline and at half-hour intervals for 5 hr after fenfluramine/placebo administration. Plasma fenfluramine and norfenfluramine levels were obtained hourly. RESULTS: Smokers had a blunted prolactin response to fenfluramine compared with nonsmokers without any alcoholism or antisocial personality effects. Using a cutoff point of delta peak prolactin < 10 ng/ml, more smokers (41/76, 54%) had a dampened response to fenfluramine than did nonsmokers (7/34, 21%) [chi2(1) = 10.6, p < 0.003]. The percentage of low responders was greatest among smokers regardless of whether they were healthy controls, alcoholics, or antisocial. Multiple regression revealed that three variables--(1) number of pack-years of smoking, (2) actual dosage of fenfluramine received, and (3) plasma norfenfluramine level obtained--explained 43% of the variance (R2 = 0.43) in delta prolactin area under the curve. Variables that included alcoholism diagnostic status, antisocial personality diagnostic status, and impulsive aggressive personality, depressive, and suicidal traits failed to explain any additional unique variance. CONCLUSIONS: Cigarette smoking blunted the prolactin response to a pharmacological challenge with d,l-fenfluramine. Pharmacodynamic and pharmacokinetic factors related to smoking both appear to influence fenfluramine-induced prolactin secretion. Phenotypes of alcoholics did not differ in their prolactin response to this serotonergic probe.

Adolescent↗
PubMed2001

Prolactin directly stimulates transcellular active calcium transport in the duodenum of female rats.

Prolactin has been postulated to be a novel calcium-regulating hormone during pregnancy and lactation. It stimulates both passive and active duodenal calcium transport in several experimental models. Our study was performed on sexually mature female Wistar rats (200-250 g) to study the direct action of prolactin on calcium transport in the duodenum using the Ussing chamber technique. To evaluate the effect of prolactin on total calcium transport in the duodenum, we intraperitoneally injected rats with 0.4, 0.6, and 0.8 mg/kg prolactin. The total calcium transport was divided into voltage-dependent, solvent drag-induced, and transcellular active fluxes by applying short-circuit current and by mucosal glucose replacement with mannitol. The effect of prolactin on each flux was studied separately. Finally, to evaluate the direct action of prolactin on duodenal transcellular active flux, we directly exposed duodenal segments to prolactin that had been added to the serosal solution with or without calcium transport inhibitors. We found that 0.6 and 0.8 mg/kg prolactin ip significantly increased the total mucosa-to-serosa calcium flux from the control value (nmol x hr(-1) x cm(-2)) of 34.53+/-6.81 to 68.07+/-13.53 (P < 0.05) and 84.43+/-19.72 (P < 0.01), respectively. Prolactin also enhanced the solvent drag-induced calcium flux and transcellular active calcium flux, but not the voltage-dependent calcium flux. The duodenal segments directly exposed to 200, 400, and 800 ng/mL prolactin showed a significant increase in the transcellular active calcium absorption in a dose-dependent manner, i.e., from the control value (nmol x hr(-1) x cm(-2)) of 2.94+/-0.47 to 5.45+/-0.97 (P < 0.01), 8.09+/-0.52 (P < 0.001), and 18.42+/-2.92 (P < 0.001), respectively. Its direct action was inhibited by mucosal exposure to 50 microM lanthanum chloride, a calcium transporter protein competitor, and serosal exposure to 0.1 mM trifluoperazine, a Ca2+-ATPase inhibitor. These studies demonstrate that the duodenum is a target organ of prolactin, which enhances transcellular active calcium transport.

Animals↗
PubMed1992

Up-regulation of prolactin gene expression and feedback modulation of lymphocyte proliferation during acute allograft rejection.

BACKGROUND: Although recent evidence suggests that prolactin is important in the immune response, bidirectional communication between prolactin and the immune system has not been demonstrated previously. We examined our hypothesis that this communication exists during mouse skin allograft rejection. METHODS: Serum prolactin levels were measured by bioassay, and pituitary prolactin mRNA was examined by use of Northern blots, in BALB/c mice receiving skin allografts from C57BL mice, on days 2, 4, and 6 after grafting. The feedback effects of prolactin on splenic lymphocytes were assessed in one-way mixed lymphocyte reactions, with or without added interleukin-2 (IL-2) or IL-4. RESULTS: Prolactin mRNA was increased significantly in grafted animals compared with sham animals (2.4-fold by day 4). Serum prolactin bioactivity was also elevated on all days tested. Prolactin treatment resulted in dose-dependent modulation of the mixed lymphocyte reaction with lymphocytes from grafted animals but not from sham animals. These effects depended on the time points and the presence of IL-2 or IL-4; the maximal enhancement occurred with day-4 lymphocytes cultured with IL-4 (80%). CONCLUSIONS: This report is the first to implicate in vivo immune regulation of prolactin gene expression. Our observations indicate that bidirectional interaction exists between prolactin and the immune system and provide a rationale for altering prolactin levels to treat allograft rejection.

Animals↗
PubMedDate not supplied

Prolactin content of the pituitary gland in response to hypertonic saline medium, antithyroid drugs, methallibure and thyroxine in a freshwater teleost Heteropneustes fossilis.

Variations in the prolactin content of the pituitary gland in response to different treatments were studied in a freshwater catfish, H. fossilis. One week of saline (1% NaCl medium) treatment reduced the pituitary prolactin content but enhanced the serum prolactin level showing release of prolactin from the pituitary gland. Two weeks of saline treatment reduced pituitary as well as serum prolactin content presumably a result of reduced prolactin synthesis in the pituitary gland. This reduction of synthetic activity in this species is probably due to a drop in prolactin requirement. All the antithyroid durgs tested as well as L-thyroxine decreased the pituitary prolactin content. Methallibure administration induced the release of prolactin from the pituitary as evidenced by the lowered prolactin level in this gland and a simultaneous increase in the prolactin content of the serum.

Animals↗
PubMed1989

Purification and protein sequence analysis of rat liver prolactin receptor.

Prolactin receptors were purified from rat liver membranes by single-step immunoaffinity chromatography using a specific monoclonal antibody to the rat liver prolactin receptor. Scatchard analysis of 125I-human growth hormone binding to the purified receptor revealed two classes of specific binding sites with Ka = 18.5 x 10(9) and 1.2 x 10(9) M-1. Considering that both classes of binding sites are responsible for high affinity prolactin binding, the partially purified receptor preparation had a binding activity of 1.69 nmol/mg protein, representing 1000-fold purification over microsomal receptors with a recovery of 52%. From three separate purifications, 6 mg of partially purified prolactin receptor were obtained with a purity of approximately 4 to 6.5%. Thus, the use of monoclonal antibody for affinity chromatography resulted in a large improvement of prolactin receptor purification compared to previous hormone affinity chromatography (300-fold purification, 15% recovery). The purified receptor was run on preparative sodium dodecyl sulfate polyacrylamide gel electrophoresis, and a homogeneous preparation of prolactin receptor was obtained by electroelution from gel slices corresponding to Mr 38,000-43,000. Immunoblot analysis using a radiolabeled monoclonal antibody revealed two separate but closely located bands of Mr 42,000 and 40,000 in microsomal, partially purified, and electroeluted preparations. The homogeneous receptor protein was extensively digested with L-1-tosylamido-2-phenylethyl chloromethyl ketone trypsin, and 10 internal amino acid sequences of the rat liver prolactin receptor were determined by gas-phase sequence analysis. Oligonucleotide probes were prepared against two of these internal sequences, and a prolactin receptor cDNA was isolated from a rat liver library using one of these probes (Boutin, J. M., Jolicoeur, C., Okamura, H., Gagnon, J., Edery, M., Shirota, M., Banville, D., Dusanter-Fourt, I., Djiane, J., and Kelly, P. A. (1988) Cell 53, 69-77). The amino acid sequence deduced from the cDNA reveals three potential sites of N-linked glycosylation, two of which were confirmed during protein sequencing. The prolactin receptor was characterized by affinity labeling with 125I-human growth hormone. Cross-linking of microsomes revealed a single band for the hormone-receptor complex with Mr 62,000. On the other hand, cross-linking of Triton X-100-solubilized or partially purified receptor with labeled hormone resulted in the appearance of two bands with Mr 62,000 and 102,000, suggesting the existence of a subunit structure of the prolactin receptor, or alternatively, the existence of two types of prolactin receptor.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1980

Prolactin and fructose in human seminal fluid.

Two hundred thirty-six semen specimens were obtained in the sterility clinic by masturbation after 3 days of abstinence. In a radioimmunoassay for prolactin (NIH, batch no. 5) the dose-response curve obtained with seminal fluid prolactin was parallel to that obtained with serum prolactin. The average seminal fluid prolactin was 780 microunits/ml (35 ng/ml), three times higher than serum prolactin concentration in men. No relationship was found between seminal prolactin concentration and sperm count (per ml or per ejaculate) or sperm motility. There was a significant and positive correlation between seminal prolactin concentration and fructose concentration. The relationship was of an exponential type. Seminal fructose increased progressively with seminal prolactin; however, for prolactin values above 850 microunits/ml, there was no further increase in seminal fructose. A similar relationship was observed between seminal prolactin concentration and volume of the semen specimens. These data support the concept that prolactin may play a key role in male fertility, perhaps by influencing the composition of the milieu where spermatozoa survive rather than by direct effect on spermatogenesis.

Fructose↗
PubMed1980

Prolactin as a regulator of fluid and electrolyte metabolism in mammals.

The evidence that prolactin is a fluid and electrolyte regulator in mammals is reviewed, with particular emphasis on the renal actions of prolactin. Prolactin receptors are found in mammalian kidneys. Prolactin modulates renal formation of cyclic AMP and polyamines and it leads to demonstrable histological changes in the proximal tubules. The renal actions of prolactin primarily involve modulation of the effects of other hormones and are therefore critically dependent on the background physiological situation. Prolactin seems able to cause a prolonged reduction in water, sodium, and potassium excretion, a pattern that is imitated by no other hormone with the possible exception of growth hormone. Prolactin preparations can cause an acute antidiuresis, which may in part be related to contamination of prolactin preparations with vasopressin. However, most of the described effects cannot be explained by vasopressin contamination. This is particularly so with the effects of prolactin on water movements across fetal skin, the amniotic membrane, and in the eye where prolactin and vasopressin have diametrically opposite effects. It is concluded that prolactin is a regulator of fluid and electrolyte metabolism in mammals but that it is a modulator rather than a primary controlling factor.

Aldosterone↗
PubMed1981

Daytime variation in serum prolactin level in patients receiving oral and depot antipsychotic medication.

Serum prolactin levels in psychiatric inpatients were measured at 8:00 AM prior to administration of oral chlorpromazine (CPZ) at 9:00 AM, and at hourly intervals throughout the day until 3:00 PM. Sixteen patients receiving CPZ 400 mg in equally divided doses of 200 mg twice daily at 9:00 AM and 9:00 PM and six patients who had received fluphenazine decanoate (FD) in doses of 25 to 75 mg 2 to 3 weeks prior to study were evaluated. In patients receiving oral CPZ, serum prolactin levels were elevated in the 8:00 AM samples; serum prolactin levels decreased between 8:00 AM and 10:00 AM and then increased sharply, reaching their peak from 11:00 AM to 2:00 PM. Serum prolactin levels were moderately elevated but relatively stable throughout the day in patients who had received im FD. The 8:00 AM serum prolactin levels were correlated with the peak serum prolactin levels during the day in female patients receiving oral CPZ, but not in male patients. The lack of correlation between base line and peak serum prolactin levels in male patients is most likely due to interference from the sleep-induced prolactin increase in 8:00 AM samples. Serum prolactin levels at 9:00 AM were significantly correlated with peak serum prolactin levels in both male and female patients. The importance of determining diurnal variation in serum prolactin levels in psychiatric patients is discussed.

Adult↗
PubMed1981

Calcium specifically stimulates prolactin synthesis and messenger RNA sequences in GH3 cells.

Addition of CaCl2 (0.4 mM) to GH3 cells incubated in a serum-free, Ca2+-free medium increased relative prolactin synthesis (prolactin synthesis/total protein synthesis) 7- to 150-fold by 3-4 days, but had no effect on relative growth hormone synthesis. Half-maximal and maximal stimulation of relative prolactin synthesis occurred at about 0.07 and 0.2 mM CaCl2, respectively. Neither MgCl2 (0.4 mM) nor KCl 0.4 mM) affected relative prolactin synthesis. 32P-labeled rat prolactin and growth hormone cDNA plasmids were employed to measure by RNA gel blot hybridization changes in cytoplasmic levels of the corresponding mRNA sequences. Both prolactin mRNA sequence levels and translatable prolactin mRNA increased in parallel with the CaCl2-induced increase in relative prolactin synthesis. CaCl2 increased prolactin mRNA sequences by 7- to 200-fold, without affecting growth hormone mRNA sequence levels. Dexamethasone (100 nM) decreased prolactin mRNA sequences in cells incubated with CaCl2, antagonized the CaCl2-induced increases in prolactin mRNA sequences independently of the CaCl2 concentration.

Animals↗
PubMed1995

The discovery of human prolactin: a very personal account.

Although prolactin was discovered in the early 1930's in sheep, cows, birds etc., no human form had been because it was thought to be identical to human growth hormone (HGH). In fact, prior to 1970, most endocrinologists doubted human prolactin even existed. Prolactin-like effects could be demonstrated from a homogenate of human pituitary but attempting to purify it identified only growth hormone. Independent histological studies had identified prolactin-secreting "pregnancy cells" fuelling the conviction that prolactin was a distinct and separate pituitary hormone. A search was begun for prolactin through protein synthesis studies using pituitaries from pregnant and postpartum monkeys. Proteins obtained in a radioactive peak were similar to, but not identical with, growth hormone by molecular weight and electrophoretic mobility. The hypothesis that the unknown protein peak represented synthesis of prolactin rather than growth hormone proved correct. Evidence was then obtained confirming that in the human pituitary prolactin and growth hormone synthesis could be distinguished using antibodies to human growth hormone or to sheep prolactin. Human prolactin purified from pituitary glands using immunological tools capable of distinguishing between the two hormones provided ultimate proof of a separate and distinct human prolactin, a hormone which has its major impact today in endocrinology and reproductive medicine. This discovery represented an exciting and truly international collaborative effort.

Animals↗
PubMed1996

Molecular heterogeneity and glycosylation modulation of rat pituitary prolactin isoforms synthesized and secreted in vitro in postnatal ontogeny, gestation, lactation and weaning.

The modulation of both the molecular size heterogeneity and the relative distribution of rat prolactin variants, synthesized and secreted in vitro by rat pituitary cells in the course of postnatal ontogeny and in gestation, lactation and weaning was investigated by SDS-PAGE, immunoblotting, radioimmunological techniques and O-sialoendopeptidase digestion. The outcome of the experiments is as follows: 1) from day 1 of postnatal life 20-, 23-, 26-, 40-44 kDa and oligomeric rat prolactin isoforms were stored and secreted; 2) perinatal life is characterized by a high degree of variability of prolactin size isoforms and their respective repartition in storage and release; in addition to the major variants, transient ones of M, 25-, 28-, 33- and 36 kDa were secreted and/or stored; 3) O-sialoglycoprotease digestion of pituitary cell lysate gave good evidence for 25 kDa prolactin being a glycoform; 4) at 1 month of age 16 kDa rat prolactin appeared and persisted over the whole postnatal span (1 day-->1 year) but only in stored form; 5) the physiology of gestation was essentially characterized by the M(r)-modulation of the glycoform (26 kDa-->26.3 kDa) and the virtual absence of stored 26 kDa rat prolactin at week 1 of pregnancy; 6) in lactation and weaning uncommon multiple banding was observed in secreted oligomeric prolactin; 7) in pregnancy, lactation and weaning the differential distribution of released and stored prolactin isoforms displayed a considerable intra- and intervariability; 8) in the vast array of size isoforms observed in all our experiments monomeric 23 kDa prolactin was always the dominating variant. In conclusion, the molecular size heterogeneity and the differential distribution of secreted and stored rat pituitary prolactin is considerably influenced by age and physiological stimuli. The nature of polymeric prolactin and of the transient variants is presently unclear, and the exact physiological role of molecular heterogeneity modulation is unknown, both in humans and rat, but the patterns of change we observed in definite stages of life, suggest that this phenomenon is important in the maturation of the hypothalamus-pituitary axis and in the metabolic and hormonal changes accompanying gestation.

Animals↗
PubMedDate not supplied

[The formation and regulation of the lactotrophic function of the hypophysis in the prenatal period of rat development. II. Dopamine inhibitory control of prolactin secretion].

Using the technique of radioimmunoassay, we studied the secretion of prolactin and its control by dopaminergic system in 22-day-old rat fetuses under normal conditions and after pharmacological inhibition of dopamine receptors. In order to elucidate the origin of prolactin and dopamine participating in this process, we used decapitation and encephalectomy of fetuses in utero. Decapitation of fetuses did not result in any changes of baseline prolactin secretion into blood in males and insignificantly decreased it in females as compared with nonoperated controls. We conclude that prolactin detected in blood plasma of nonoperated fetuses does not originate in the pituitary, and any prolactin synthesized in the pituitary is not secreted into blood. Inhibition of dopamine receptors in decapitated fetuses did not result in any changes of prolactin level in blood. This provided evidence that in nonoperated fetuses, it is pituitary prolactin which is secreted in response to haloperidol, while the secretion of nonpituitary prolactin is not controlled by dopamine. Encephalectomy increased prolactin level in plasma and resulted in a drastic decrease of its level in the pituitary. The block of dopamine receptors did not affect the level of prolactin in blood plasma or pituitary of encephalectomized fetuses. We conclude that the inhibitory dopaminergic control of prolactin secretion by the pituitary during the prenatal period is accomplished just as in adult animals by dopaminergic neurons of hypothalamus.

Animals↗
PubMedDate not supplied

Prolactin and colorectal cancer: is there a connection?

UNLABELLED: The purpose of this study was to confirm the reported incidence of hyperprolactinemia in colorectal cancer and to find further evidence for an ectopic prolactin production by the tumor. MATERIAL AND METHOD: Thirty two consecutive patients with an adenocarcinoma of the colon (n = 17) or the rectum (n = 15) were included. Preoperative serum prolactin concentrations were determined and correlated with CEA concentrations and tumor stages. To exclude an ectopic production by the colon cancer, prolactin concentrations were determined during the operation, in the peripheral blood and in the efferent venous drainage area of the tumor. After resection, immunohistochemical staining for prolactin was made in all resected tumors. RESULTS: In all except two patients with a rectal cancer, preoperative plasma prolactin concentrations were normal. Peroperative serum concentrations of prolactin were high in all patients. No significant gradient was found between the peripheral venous concentration and the local venous concentration in the drainage area of the tumor. Immunohistochemical staining for prolactin was positive in only one rectal cancer. Finally, no correlation was found between plasma prolactin concentrations and tumor stages or CEA concentrations. CONCLUSION: Our results do not support the hypothesis of an ectopic prolactin production by colon adenocarcinoma. Only in a subgroup of rectal cancers, an ectopic prolactin production remains probable. At present, prolactin cannot be recommended as a tumor marker in colorectal cancer.

Adenocarcinoma↗
PubMed1999

Prolactin controls mammary gland development via direct and indirect mechanisms.

The inactivation of the prolactin receptor gene by homologous recombination has made it possible to investigate the role of prolactin signaling in mammary gland development without resort to ablative surgery of the endocrine glands. In knockout mice lacking the prolactin receptor, mammary development is normal up to puberty. Subsequently, the ducts branch less frequently than those of wild-type animals. While terminal end buds differentiate to alveolar buds in wild-type females by the end of puberty, in knockout females terminal end bud-like structures persist at the ductal ends. To distinguish between the developmental defects that are intrinsic to the epithelium and those that result from systemic endocrine alterations in prolactin receptor knockout mice, mammary epithelium from prolactin receptor knockouts was transplanted into mammary fat pads of wild-type mice. In virgin mice, the knockout epithelial transplants developed normally at puberty, indicating an indirect effect of prolactin on ductal development. Prolactin receptor knockout females are infertile due to multiple reproductive defects, but epithelial transplants allowed us to assess the extent to which the absence of prolactin receptor is limiting, under systemic conditions that allow full mammary gland development. During pregnancy, the prolactin receptor knockout transplants showed normal side branching and the formation of alveolar buds, but no lobuloalveolar development. Thus, prolactin affects mammary morphogenesis in two different ways: it controls ductal side branching and terminal end bud regression in virgin animals via indirect mechanisms, but acts directly on the mammary epithelium to produce lobuloalveolar development during pregnancy.

Animals↗
PubMed1988

In vivo autoradiographic analysis of prolactin binding in brain and choroid plexus of the domestic ring dove.

The binding of intravenously administered prolactin to choroid plexus and brain tissue was determined radioautographically in the ring dove, a species that exhibits prolactin-induced alterations in brain function. An intense autoradiographic reaction was detected over the epithelial cells of the choroid plexus 5 min after the intravenous injection of 125I-ovine prolactin. A significant reaction was also observed over the infundibulum but no significant uptake of prolactin occurred in other brain areas. The binding of radiolabelled prolactin to infundibulum appeared to be non-specific, since excess unlabelled hormone did not reduce silver grain density. In contrast, 125I-ovine prolactin binding in choroid plexus was significantly reduced by excess unlabelled ovine prolactin or human growth hormone, but not by ovine luteinizing hormone. Specific binding to choroid plexus was also detected in vitro. The lack of significant brain uptake of prolactin in vivo is discussed in relation to recent in vitro evidence for specific binding sites for prolactin in several dove brain regions. Similarities between the binding results obtained in this avian species and those reported previously in mammals suggest that the two vertebrate groups exhibit similar patterns of prolactin interaction with neural target tissues.

Animals↗