Kallikrein- and prolactin-producing cells in the rat anterior pituitary are the same

Kallikrein-positive cells in the anterior pituitary of female rats were identified to be the same as prolactin-producing cells by using an immunoelectron microscopic method. The kallikrein immunoreactivity was localized at the Golgi apparatus, the rough endoplasmic reticulum, and secretory granules, suggesting that kallikrein is synthesized in the prolactin-producing cells and also may be secreted into the blood vessels.

Comparison of norethindrone and medroxyprogesterone acetate with natural progesterone and estradiol in stimulating prolactin production from cultured endometrial stromal cells

Progestins stimulate prolactin production from endometrial stromal cells in culture. We compared the potencies of the synthetic progestins norethindrone and medroxyprogesterone acetate to natural progesterone in inducing stromal prolactin production. Modifications of the culture system provided an increase in stromal cell yield, thus permitting multiple comparisons from the treatment of cells from a common endometrial sample. The effects of high-dose estradiol also were evaluated in this system. The findings suggest relative potencies of 50:1 for medroxyprogesterone acetate and progesterone. Norethindrone gave intermediate and more variable responses. Estradiol potentiated prolactin production from only submaximal progestins doses. The differences between the progestin effects, in large measure, were due to differential culture growth as reflected by culture mass. Compared to controls and estradiol alone, all the progestins induced much greater prolactin production. Thus during decidualization, progestins probably promote both stromal growth and intracellular prolactin production. High-dose estradiol may not interfere with these events.

Molecular cloning and nucleotide sequence analysis of complementary DNA for bullfrog prolactin

A prolactin cDNA was cloned from a cDNA expression library constructed from total RNA of bullfrog (Rana catesbeiana) adenohypophyses by immunoscreening with antiserum against bullfrog prolactin. The cDNA clone thus obtained contained a 249 bp insert. Using this clone as a probe, plaque hybridizations were performed and two additional clones obtained. These clones had a polyadenylation site different from that of the first obtained clone, suggesting that the 3'-untranslated sequence was heterogeneous in length. The longest clone contained 830 bp, which encoded part of the signal peptide and the entire sequence of mature prolactin. The deduced amino acid sequence was in good accord with that determined by direct protein sequencing of purified bullfrog prolactin. The length of the bullfrog prolactin mRNA was estimated by Northern blot analysis to be about 1.0 kb. Homologies of prolactin nucleotide and amino acid sequences between bullfrog and other vertebrates were 64 and 65% for man, 66 and 68% for pig, 61 and 52% for rat, 69 and 74% for chicken, and 50 and 35% for salmon respectively. Highly conserved regions reported for mammalian prolactins also existed in bullfrog prolactin. Homologies of nucleotide and amino acid sequences between prolactin and GH of bullfrog origin were 49 and 25% respectively. Using the cDNA, the content of prolactin mRNA in the pituitary glands of metamorphosing tadpoles was measured. Prolactin mRNA levels rose at the mid-climax stage, suggesting that the increase in plasma and pituitary prolactin levels known to occur at the climax stage accompanies the increase in prolactin synthesis.

[Inhibitory effect of arachidonic acid on the synthesis of prolactin in human decidual tissues]

Much evidence indicates that human tissues produce prolactin. However, little is known as to which agents regulate its production in decidual tissues. Therefore, it is of interest to examine the effect of arachidonic acid on the production of prolactin, since it is present in considerably large amounts in decidual tissues. The addition of arachidonic acid to culture media resulted in a significant reduction in the amount of prolactin secreted from incubated decidual tissues in a dose-related fashion. Other poly-unsaturated fatty acids, i.e. linoleic and gamma-linolenic acid also inhibited its secretion, whereas saturated fatty acid and mono-unsaturated fatty acids, such as oleic acid, were without effect. The addition of phospholipase A2 and phospholipase C, enzymes to liberate arachidonic acid from phospholipids, also suppressed the secretion of prolactin. Indomethacin and BW-755C, inhibitors of cyclooxygenase and lipoxygenase, respectively, had essentially no effect on the secretion of prolactin. Translatable mRNA for prolactin was detected in decidual tissues. Arachidonic did not alter either the amount of mRNA in prolactin of the amount of its mRNA as a percentage of total mRNA. Thus, it appears that arachidonic acid possibly plays a role as a physiological regulator of prolactin secretion in human decidual tissues. The action of arachidonic acid is not mediated by cyclooxygenase or lipoxygenase products, suggesting that arachidonic acid itself, or its metabolites other than prostaglandin and leukotriene, may be involved in the regulation of prolactin secretion.

Identification of prolactin-like proteins synthesized by normal murine lymphocytes

Cultured murine lymphoid cells release a PRL-like immunoreactive (IR) protein which may be important in immunity, as anti-PRL antisera inhibit lymphocyte proliferation in vitro. We examined culture supernatants (SNs) and cell lysates from concanavalin A (Con A) activated murine thymocytes to identify these proteins. Western blot analysis of cell lysates revealed three specifically-stained PRL-IRs. A doublet of bands at 35.6 and 33.6 kDa was associated with the particulate fraction of the cell. These PRL-IRs were present in lymphocytes independently of mitogen stimulation. In contrast, a 22 kDa PRL-IR was only produced in mitogen stimulated cells, and was specifically immunoprecipitated with anti-PRL antiserum. In addition, all three PRL-like IRs incorporated 35S-methionine in vitro, indicating that they are synthesized by these cells. Only the 22 kDa PRL-like protein was present in culture medium from stimulated cells, suggesting that this may be the PRL bioactivity previously demonstrated in SNs from murine lymphocytes.

[Clinical study of hypogonadotropic hypogonadism]

Clinical study of eight cases of hypogonadotropic hypogonadism was performed. These cases consisted of five prepubertal cases and three postpubertal cases induced by prolactin-producing hypophyseal tumor. The former five cases had the chief complaints of incomplete development of their external genitalia. The chief complaints in three postpubertal cases were decreased libido in two and infertility in one. The average testicular volumes were 7.8 ml and 20 ml in prepubertal and postpubertal cases, respectively. The basal levels of luteinizing hormone (LH) were within the normal limit in most cases and follicle stimulating hormone (FSH) were low in most cases. There were no differences between the levels of these hormones in prepubertal cases and those in postpubertal cases. The range of basal level of prolactin in blood was 92 mg/ml to 1,070 ng/ml in the postpubertal cases. The basal level of testosterone in blood was low in all cases. Most cases had rather good responses of LH and FSH after the administration of luteinizing hormone releasing hormone. The plasma level of testosterone was elevated after the administration of human chorionic gonadotropin (hCG) in most cases. The appearance of sperm in the semen was observed after the hCG therapy in only one of the prepubertal cases. On the other hand, all the postpubertal cases showed almost normal findings in semen analysis after hormone therapy.

Immunohistochemical localization of kallikrein within the prolactin-producing cells of the rat anterior pituitary gland

The localization of tissue kallikrein in the pituitary gland of rats was investigated by an immunohistochemical technique using antiserum against rat urinary kallikrein. Kallikrein-positive cells were detected in the anterior lobe of the pituitary of both male and female rats, but were not observed in the posterior lobe of the pituitary in either sex. The kallikrein-positive cells in the anterior pituitary of female rats in oestrus were found to correspond to the prolactin-producing cells, whereas the cells producing GH, LH and ACTH were negative for kallikrein. It is possible, therefore, that the tissue kallikrein may be involved in the production of prolactin and not that of the other anterior pituitary hormones, such as GH, LH, FSH, ACTH and TSH.

Production of prolactin by cultures of isolated cells from human first-trimester decidua

An enriched fraction of first-trimester decidual cells that synthesize and release prolactin (PRL) was obtained by discontinuous Percoll gradient (20-50%) centrifugation of collagenase type I- and deoxyribonuclease I-dispersed cells (3 mg/mL and 50 micrograms/mL, respectively). Centrifugation of the cell suspension yielded three major bands aggregating at the density interfaces. The fraction of the 30-40% Percoll interface contained enlarged decidual cells and constantly secreted significant amounts of PRL into the medium for at least 10 days. The fraction of the 40-50% Percoll interface contained fibroblastic cells and secreted a small amount of PRL into the medium. Cells in the other fractions did not attach to the plastic dishes in 48 hours. Under the influence of progesterone (100 ng/mL), the cultured decidual cells retained their capability of PRL production for at least 10 days because no decline of the secretion rate was observed. The culture system established by the present study is satisfactory for investigating decidual cell functions, including the regulatory mechanisms of PRL production.

Differential effects of progestin and relaxin on the synthesis and secretion of immunoreactive prolactin in long term culture of human endometrial stromal cells

PRL secretion from human endometrium is a continuous process extending from the luteal phase of the menstrual cycle throughout the entire gestational stage. We have developed a long term primary cell culture system to elucidate the hormonal requirements for this sustained production of PRL. The effects of medroxyprogesterone acetate (MPA), progesterone, and relaxin (RLX) on the production of immunoreactive PRL were investigated. MPA stimulated cell growth and PRL production rate during days 5-20 of culture. Progesterone was 20-40% less effective in stimulating PRL than MPA. Stimulation of PRL was continued 1-2 weeks after MPA withdrawal. Relaxin did not promote cell growth. However, it induced the PRL production which fluctuated during the long term culture. The maximal response to RLX was 2- to 3-fold higher or similar to that of MPA. Only five of nine endometrial specimens examined responded to RLX alone. The effect of MPA plus RLX was significantly greater than that of MPA or RLX alone. The highest production rate was shown in cells treated with MPA and then RLX in sequence. After a month of culture, the production rates (micrograms of PRL per 0.1 mg cell DNA/day) under various culture conditions (A, control; B, MPA; C, MPA for 10-15 days and no hormone afterward; D, both MPA and RLX; and E, MPA and RLX in sequence) were: A, about 0-0.01 (n = 12); B, 2.5 +/- 0.9 (n = 8); C, 4.8 +/- 2.5 (n = 8); D, 5.7 +/- 3.0 (n = 5); and E, 11 +/- 3.7 (n = 7); mean +/- SD; n, number of specimens). Endometrial stromal cells were incubated with [35S]methionine, and [35S]immunoreactive PRL and other secretory proteins were analyzed on sodium dodecyl sulfate-polyacrylamide gel electrophoresis to characterize the size and isoforms of immunoreactive PRL. PRL was one of the five major secretory proteins (23-25K, 32K, 42K, 78K, and 150K daltons, sodium dodecyl sulfate-polyacrylamide gel electrophoresis under reducing condition) induced by MPA and RLX in endometrial stromal cells. More than 90% of immunoreactive PRL was secreted into the medium. The apparent mol wt of immunoreactive PRL were 21K, 23K (the predominant size), and 25K daltons. Results obtained from the incorporation of [14C]glucosamine into immunoreactive PRL indicated that both 23K and 25K PRL contained glycosylated PRL. A 45K-dalton glycosylated immunoreactive PRL was also present in the culture medium.(ABSTRACT TRUNCATED AT 400 WORDS)

Electroporation of rat pituitary (GH) cell lines: optimal parameters and effects on endogenous hormone production

An efficient electroporation procedure was established for the genetic transformation of two clonal strains of hormone producing rat pituitary cells (GH12C1 and GH3). We used the bacterial chloramphenicol acetyltransferase (CAT) gene as reporter gene to determine optimal conditions for electroporation. The conditions found to be optimal, measured as expression of the highest CAT activity, were 240-300 V and a DNA concentration of 30-60 micrograms/ml in sucrose buffer. Cell viability was then about 50 per cent. Maximum CAT activity was seen 24 hours after electroporation. The electroporation procedure, in the presence or absence of DNA, caused a transient decrease in endogenous growth hormone (GH) and prolactin (PRL) production.

Blockade of low and high threshold Ca2+ channels by diphenylbutylpiperidine antipsychotics linked to inhibition of prolactin gene expression

The effects of diphenylbutylpiperidine (DPBP) antipsychotics on Ca2+ currents and prolactin (PRL) synthesis were studied in rat pituitary growth hormone (GH) cell lines (GH3 and GH4C1). In whole-cell patch-clamp experiments, DPBPs including fluspirilene, penfluridol, and pimozide at concentrations ranging from 0.25 to 5 microM each blocked current through low threshold T-type as well as high threshold L-type channels. Each of the drugs preferentially blocked T-type current, and complete inhibition was observed at concentrations as low as 1 microM. Inhibition of L-type channels by DPBPS was enhanced at depolarized holding potentials and promoted by prolonged channel activation. At concentrations similar to those which blocked Ca2+ currents, each of the three DPBPs markedly reduced basal PRL production by GH cells. PRL synthesis stimulated by the dihydropyridine Ca2+ agonist R5417 or thyrotropin releasing hormone (TRH) was also inhibited. The inhibitory effects of the DPBPs were observed at the level of gene transcription. Penfluridol and fluspirilene inhibited basal, Ca2(+)- and TRH-stimulated expression of a fusion gene construct containing the 5'-flanking sequence of the rat PRL gene linked to the luciferase gene. The effect was concentration-dependent with the IC50 values for both drugs of less than 1 microM. Nimodipine also reduced basal, R5417, and TRH-stimulated expression of the reporter gene construct. Similar results were obtained with a reporter gene construct containing the 5'-flanking sequence of the rat GH gene. The GH luciferase construct was only slightly responsive to R5417 and TRH; however, these responses were reduced by fluspirilene and nimodipine at concentrations of less than 1 microM. These studies demonstrate that the DPBP antipsychotics block T- as well as L-type Ca2+ channels in GH cells and inhibit PRL production at the level of transcription. They also indicate that functioning Ca2+ channels are necessary for TRH-stimulated PRL gene transcription.

Changes in content of prolactin mRNA during the rat estrous cycle

An attempt was made to clarify the relationship between the synthesis of prolactin (PRL) and its secretion during the rat estrous cycle by examining the changes in PRL messenger RNA (mRNA); PRL secretion and anterior pituitary PRL content. At various stages of the estrous cycle, pituitary and serum levels of PRL and growth hormone (GH) were measured by radioimmunoassay, while their respective mRNA contents were determined by the hybridization method. The content of pituitary PRL mRNA did not increase in parallel with the increment of the serum level of the hormone. Significant increase in PRL mRNA were observed as three peaks; 1st peak at 14:00 on the proestrus (PE) day, 2nd peak at 4:00 and 3rd peak at 22:00 on the estrus (E) day. The GH levels in the pituitary and serum, or the change in PRL mRNA appeared to be unrelated to the rat estrous cycle. From the present results, we speculate that the three peaks of PRL mRNA content might be ascribable to the direct effect of estrogen on transcription, indirect activation of transcription followed by rapid and massive secretion of PRL, and mammotrope proliferation, respectively.

Immunocytochemical and biochemical evidence of renin in human lactotrophic cell cultures

Primary cell cultures from human prolactin (PRL)-secreting adenomas were used to test the ability of human lactotrophs to synthesize renin in vitro. The renin content of the culture medium and of cellular extracts was measured by enzyme-linked immunosorbent assay. The level of PRL release in the culture medium and the amount of PRL in a cellular extract were determined by radioimmunoassay. Morphologic studies included indirect immunofluorescence, pre-embedding immunoelectron microscopy using a three-layer peroxidase-antiperoxidase method and postembedding immunoelectron microscopy using protein A-gold complexes. Renin was detected in cellular extracts and was found to be absent in the culture medium, whereas PRL was extracellularly secreted. PRL and renin immunoreactivity was observed in all the cultures studied by immunofluorescence. The subcellular localization of renin was found to be similar to that of PRL and was observed in the rough endoplasmic reticulum, the Golgi apparatus, and cytoplasmic secretory granules. The results suggest that, in vitro, renin may be synthesized and intracellularly metabolized in human adenomatous lactotrophic cells rather than secreted. Cell cultures may be a useful model to further the understanding of the role of a local renin-angiotensin system in PRL secretion.

Fetal pituitary graft is capable of initiating hormone synthesis in median eminence removed adult rat

Rathke's pouches of 12- and 13-day-old rat embryos were implanted beneath the kidney capsule of adult male rats subjected to the removal of median eminence or to sham-operation. Host animals were sacrificed 28 days after grafting and the implanted pituitaries were processed for immunohistological examination. ACTH, LH-beta, FSH-beta, TSH-beta, GH and PRL immunopositive cells could be observed in fetal grafts of all experimental groups. However, the number and staining intensity of different hormone containing cells largely varied and presumably depended on the hormonal state of host animals. The results indicate that undifferentiated fetal pituitary does not require hypothalamic hypophysiotrophic neurohormones for proliferation and cytodifferentiation and that its development might be modulated by circulating trophic hormones of host animals.

Bacterial production and purification of recombinant human prolactin

Escherichia coli cells transformed with a recombinant plasmid (pT7L) containing the coding sequence of human prolactin (hPrl) expressed a new protein. This protein, comigrating with human Prl on sodium dodecyl sulfate (SDS)-polyacrylamide gels, represented 50% of the total bacterial extract. Immunoprecipitation of [35S]methionine-labeled bacterial lysate with a rabbit antiserum to hPrl followed by SDS-polyacrylamide gel electrophoresis (PAGE) analysis showed that the major component had a Mr identical to that of standard hPrl. The majority of the recombinant hPrl (r-hPrl) accumulated in inclusion bodies. Analysis of these inclusion bodies by SDS-PAGE under nonreducing conditions showed that they are composed mostly of fully reduced monomers. Solubilization of the inclusion bodies and protein denaturation were performed in 8 M urea. Refolding during the renaturation procedure was confirmed by SDS-PAGE under nonreducing conditions. r-hPrl was further purified by gel permeation chromatography on a fast protein liquid chromatography column. More than 95% of the molecules were recovered as oxidized monomeric forms. The refolded molecule was tested for its bioactivity in the Nb2 lymphoma mitogenic assay. The dose-response curves obtained with either r-hPrl or pituitary-derived hPrl showed a complete parallelism. Furthermore, Nb2 cell proliferation was completely blocked by addition of hPrl antiserum to both preparations. Recombinant hPrl is identical to natural hPrl except for an additional methionine group at the amino terminal end.

The effects of ions and hypothalamic factors on the in vitro activity of rainbow trout prolactin cells

The influence of various ions and of dopamine and somatostatin on the in vitro activity of rainbow trout prolactin (PRL) cells was investigated. There was a positive correlation between medium Ca2+ concentration and both PRL synthesis and release up to 1.8 mM Ca2+, above which no further increase occurred. Even with no Ca2+ in the medium, there was still PRL secretion during the incubation. Replacement of Ca2+ with Ba2+ in the medium did not elevate either total PRL levels or PRL release above that in Ca2 +)-free medium. Neither elevated Mg2+ nor increased medium K+ had any effect on PRL synthesis or release. Dopamine inhibited PRL release but not synthesis, as did the D2 receptor agonist, apomorphine. However, the D2 receptor antagonist, (+)-butaclamol was unable to prevent the action of dopamine on PRL release. Somatostatin inhibited both PRL synthesis and release in normal Ca2+ medium, but release only in reduced Ca2+ medium. Thus, Ca2+, dopamine, and somatostatin may all have roles in regulating prolactin secretion in this fish. In addition, oPRL reduced trout PRL release, indicating a possible negative feedback mechanism for trout PRL secretion.

Influence of calcitriol on prolactin and prostaglandin production by human decidua

Receptors for calcitriol are described in human decidua. They exhibit a dissociation constant of 35 +/- 6 pM and they are at concentrations similar to those found in other tissues (0.45 +/- 0.04 fmol/micrograms DNA). They are highly specific for calcitriol since neither of the other vitamin D3 derivatives nor the steroid hormone tested displaced labeled calcitriol from the receptor. Also, calcitriol at concentrations of 10(-13) to 10(-11) M stimulates prolactin secretion by dispersed decidual cells. At these concentrations, however, the hormone has no effect on prostaglandin production. The specificity of calcitriol action was further examined by studying the effect of estrogen, progesterone, testosterone, dexamethasone and cortisol, all at 10(-7) M, on the secretion of prolactin and prostaglandins. Under the conditions used in this study, the steroids have no effect on prolactin secretion; but dexamethasone significantly inhibits prostaglandin F2 alpha output by the cells. Taken together with previous studies from our laboratory demonstrating that decidua can synthesize calcitriol the present study indicates that this hormone has an autocrine effect on human decidual cells.

The effects of the antiprogestin mifepristone, in vivo, and progesterone in vitro on prolactin production by the human decidua in early pregnancy

This study investigated the regulatory effect of progesterone on decidual prolactin (dPRL) production during early human pregnancy (6-7 weeks). Patients (n = 7) were treated with the antiprogestin-mifepristone (RU 486; 600 mg single oral dose) for 24-36 h before termination of pregnancy by curettage. Tissue was also obtained from patients without pretreatment in vivo (n = 8) and acted as controls. Decidual tissue was incubated in vitro with and without progesterone and mifepristone for 5 days and the medium changed daily. Prolactin production by decidua parietalis decreased over the period of incubation and was unaffected by addition of progesterone or mifepristone. However, in the group pretreated in vivo with mifepristone, the production of dPRL was markedly lower than in the control group. In contrast, the production of dPRL by decidua capsularis to which trophoblast was attached, was maintained at a constant level over 5 days of culture and was unaffected by pretreatment with mifepristone in vivo or its addition in vitro, or by progesterone. Prolactin was immunolocalized using avidin-biotin immunoperoxidase staining to decidualized cells within the decidua and the intensity of staining was reduced or absent in the decidua parietalis from the mifepristone group compared to controls, but was similar in decidua capsularis in both control and mifepristone groups, in good agreement with the in-vitro production of dPRL. Our findings suggest that the effect of progesterone may be only facilitative, maintaining decidual differentiation, and dPRL production might only be associated with the presence of progesterone-dependent differentiated decidual cells. Apart from progesterone, factors from trophoblast cells can maintain dPRL production during pregnancy.

Cell-type specific posttranslational processing of peptides by different pituitary cell lines

In order to compare prohormone processing in two distinct pituitary cell types, somatomammotrope cells (GH3) and corticotrope cells (AtT-20) were stably transfected with vectors encoding preproneuropeptide Y (preproNPY) containing four different pairs of basic amino acids at the single endoproteolytic cleavage site: wildtype or KR (lysine-arginine), RR, RK, and KK. The GH-NPY cell lines cleaved proNPY to a similar extent, regardless of the sequence of the basic amino acids at the cleavage site (KR = RR = RK = KK). AtT-20-NPY cells are known to exhibit a strong hierarchy of cleavage site preference when processing wildtype and mutated proNPY forms (KR = RR greater than RK much greater than KK). All four types of GH-NPY and AtT-NPY cells faithfully produced NPY (1-36) NH2 from proNPY (1-69), regardless of the amino acid sequence at the cleavage site. All four types of GH-NPY cells produced some of the expected proNPY-COOH-terminal peptide with Ser40 at its NH2-terminal [proNPY (40-69)]. GH3 cells expressing the RR, RK, and KK forms of proNPY yielded in addition some proNPY-COOH-terminal peptide retaining the amino terminals Lys39 or Arg39 residue. In contrast, AtT-NPY-RK cells produced only the Lys39 form of proNPY-COOH-terminal peptide while the other three AtT-NPY lines (KR, RR, and KK) produced only the Ser40 form of proNPY-COOH-terminal peptide. The residence time of proNPY and NPY in GH3 cells was dramatically increased by treatment with insulin, estradiol, and epidermal growth factor, in concert with the expected increase in PRL synthesis and decrease in GH synthesis; increased residence time in the cells did not result in an increase in the extent of cleavage of proNPY to NPY. AtT-20 cells did not respond to the somatomammotrope-specific set of hormones. Thus, there are several important differences in the posttranslational processing and storage of peptide hormones in corticotropes and somatomammotropes.

Recombinant methionyl bovine prolactin: loss of bioactivity after single amino acid deletions from putative helical regions

We have previously described a method for producing recombinant methionyl bovine PRL (Met-bPRL), which is as bioactive as the authentic hormone in the Nb2 cell lactogen bioassay; in contrast, a Met-bPRL variant lacking tyrosine 28 was essentially devoid of bioactivity. In the present study we have investigated this loss of bioactivity at the molecular level by determining the bioactivities of a number of Met-bPRL variants engineered to contain specific changes in their primary structures. It was found that the presence of tyrosine per se at the 28 position in Met-bPRL was not essential for high bioactivity, since Met-bPRL variants prepared by replacing tyrosine 28 with other amino acids (arginine, phenylalanine, alanine, and histidine) still had substantial bioactivity (40-74% that of Met-bPRL). Neither was the loss of bioactivity related to a shift in the relative positions of conserved histidines 27 and 30; in fact, histidine 27 was found not to be essential for the bioactivity of the hormone. The loss of bioactivity after deletion of tyrosine 28 from Met-bPRL appears to be related to the removal of an amino acid from the middle of a putative helix (no. 1) rather than to the loss of a residue specific to lactogen function. This suggestion is supported by the finding that Met-bPRL variants obtained by deletion of selected single amino acids from center domains of putative helix 2, 3, or 4 were also essentially devoid of bioactivity. It is speculated that this lack of bioactivity reflects an inability of the proteins to assume a native conformation.

Prolactin and related peptides in pregnancy

This brief review has attempted to portray the complex involvement of prolactin in pregnancy. Pituitary prolactin production and lactotroph proliferation are markedly affected by oestrogens and pregnancy. Enlargement of pre-existing prolactinomas may occur during pregnancy induced with dopamine agonist drugs, and this can be a major clinical problem with larger tumours. Prolactin is produced by late luteal and decidualized endometrium as well as by the pituitary gland, but much less is known about its secretory regulation or its function. The family of prolactin-related protein hormones is rapidly expanding with the recognition of placental lactogens, variant growth hormone, proliferin, decidual luteotropin, and at least two further prolactin-related peptides in rodents. This complex system of related but distinct protein hormones, with different temporal patterns of production during gestation, suggests an important physiological role, but it remains to be seen to what extent they are involved in placental function itself, maternal metabolism or fetal growth.

Opposing actions of Bay K 8644 enantiomers on calcium current, prolactin secretion, and synthesis in pituitary cells

Dihydropyridine (DHP) Ca2+ channel modulators were used to explore the relationship between voltage-gated Ca2+ channels and PRL secretion, synthesis, and mRNA in PRL-secreting pituitary cells. Optical isomers of the Ca2+ channel agonist Bay K 8644 produced stereospecific and opposing effects on L-type Ca2+ current, PRL release, and synthesis in GH3 and GH4C1 cells. (-)-Bay K 8644 (R5417) behaved as a pure agonist, enhancing Ca2+ current several-fold while shifting the current-voltage curve 10-15 mV in the hyperpolarizing direction. The agonist effect was independent of holding potential, but decreased during prolonged Ba2+ or Ca2+ entry. R5417 produced a concentration-dependent increase in acute PRL release and enhanced PRL production by GH cells several-fold during a 72-h period. (+)-Bay K 8644 (R4407) behaved as a weak Ca2+ channel antagonist, inhibiting L-type Ca2+ current, KCl-stimulated PRL secretion, and PRL production at concentrations of 0.5-5 microM. These two isomers produced similar effects on PRL production by normal rat pituitary cells in dispersed culture. R5417 (500 nM) increased PRL produced in 72 h to 233 +/- 8% of the control value. R4407 reduced this quantity by 36 +/- 9%. The effects of the DHPs on PRL mRNA levels were consistent with the effects observed for acute secretion and hormone production. The agonist R5417 increased PRL mRNA 147 +/- 5% over a 30-h period, and the potent DHP Ca2+ channel blocker nimodipine inhibited PRL mRNA production 2-fold. These results demonstrate that racemic Bay K 8644 interacts with L-type Ca2+ channels in normal and transformed pituitary cells as a mixed agonist-antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Progesterone and human chorionic gonadotropin do not stimulate placental proteins 12 and 14 or prolactin production by human decidual tissue in vitro

To investigate the regulation of the synthesis and secretion of placental proteins-12 (PP12) and -14 (PP14) and PRL, explants and enriched preparations of stromal cells and gland cells obtained from 10 human early pregnancy decidua were preincubated in medium for 24 h (baseline), followed by incubation in medium with or without progesterone (0.02-32 mumol/L), hCG (10 and 100 ng/ml), or cAMP (0.25-1 mmol/L) in an atmosphere of 5% CO2-95% air at 37 C for another 96-120 h. Media were changed each 24 h, and PP12, PP14, and PRL levels were determined by RIA. Decidual explants, as well as their isolated cells produced detectable levels of PP12, PP14, and PRL in vitro. The gland cells synthesized and secreted about 30 times more PP14 than did stromal cells. After 96-120 h of incubation, the production of each protein by control cultures was increased 81-167% compared to the baseline (not significant). The secretion of these proteins in medium supplemented with progesterone or hCG was not significantly different from that in the control groups. 8-Bromo-cAMP significantly increased the secretion of PRL and PP12, but not PP14, by stromal cells compared to control values. We conclude that 1) PP14 is mainly produced by decidual gland cells; 2) progesterone at the concentrations used in our study does not stimulate production of PP12, PP14, and PRL in decidualized endometrium in vitro; 3) hCG does not stimulate the production of PP12 and PP14 in decidualized endometrium; and 4) 8-bromo-cAMP stimulates decidual stromal cell secretion of PRL and PP12.