Expression of retinaldehyde dehydrogenase 1 in the anterior pituitary glands of adult rats

Retinoic acid (RA) plays a critical role in cell growth and tissue development and is also a regulatory factor of pituitary function. However, whether RA is generated in the pituitary gland and plays a role as a paracrine and/or autocrine factor is generally unknown. RA is synthesized from retinoids through oxidation processes. Dehydrogenases that catalyze the oxidation of retinal to RA are members of the retinaldehyde dehydrogenase (RALDH) family. Recently, we demonstrated that RALDH2 and RALDH3, but not RALDH1, were expressed in the developing anterior pituitary gland of rats, but the expression of RALDHs in the adult pituitary gland was not determined. Therefore, we have now examined the expression of RALDH1, RALDH2, and RALDH3 mRNAs in the pituitary gland of adult rats. Analysis by quantitative real-time polymerase chain reaction of adult pituitary glands has revealed a high level of RALDH1 mRNA but not of RALDH2 mRNA or RALDH3 mRNA. We have also detected mRNA expression for RALDH1 in the anterior pituitary gland by in situ hybridization with digoxigenin-labeled cRNA probes. Double-staining for RALDH1 mRNA and pituitary hormones or S-100 protein, a marker of folliculo-stellate cells (FS-cells), has revealed RALDH1 mRNA expression in a portion of prolactin-producing cells, marginal layer cells, and FS-cells. Our results suggest that RA is generated in the adult anterior pituitary gland, and that it may act locally on pituitary cells. This work was supported by a Grant-in-Aid for Young Scientists (B) from the Japanese Ministry of Education, Culture, Sports, Science, and Technology (18790149) and by the Foundation of Growth Science.     

Association of annexin V with prolactin in the rat anterior pituitary gland.

When pituitary extracts were subjected to non denaturing polyacrylamide gel electrophoresis, an unknown protein was found to associate with a proportion of the prolactin. This protein was dissociated from prolactin by sodium dodecyl sulfate. The protein was purified and sequenced. As the amino terminus was blocked, the amino acid sequences of three peptide fragments were determined. The obtained sequences of 41 amino acids were identical to partial sequences of a known protein, rat Annexin V. The molecular mass, 36 kDa, was also the same as the molecular weight of Annexin V. The existence of Annexin V mRNA in rat pituitary glands was also confirmed by polymerase chain reaction. These results show that Annexin V, a member of the calcium-dependent phospholipid binding proteins, is synthesized in the rat pituitary gland, and suggest its association with prolatin in the gland.     

Gastrin releasing peptide (GRP) is present in a GRP(1-27) form in anterior pituitary cells of the guinea pig

Immunohistochemical and chromatographic studies were performed on the guinea pig anterior pituitary gland with an antiserum recognizing an epitope within the gastrin releasing peptide (GRP) carboxyterminal amino acid sequence Val-Gly-His-Leu-Met-NH2. Within the anterior pituitary gland GRP-like immunoreactive cells were identified. The GRP-like immunoreactive cells were distributed heterogenously in the gland, predominantly located in ventral aspects of the anterior pituitary. Intracellularly, the immunoreactivity elements were identified as granula-like structures in the cytoplasma. To further characterize the peptide displaying GRP-like immunoreactivity within the pituitary cells, the GRP-like substances were analyzed by radioimmunoassay and gel filtration chromatography. Using this analytical approach it was determined that the guinea pig pituitary extract contained a peptide with characteristics similar to that of authentic porcine GRP(1-27). Only trace amounts of smaller C-terminal fragments were identified. These results indicate, in contrast to findings in other tissues, the GRP(1-27) is not further degraded into smaller peptide fragments.     

Characteristics and significance of albumin-positive hepatocytes in analbuminemic rats

Analbuminemic rats (NAR) are a mutant strain in which splicing of the albumin mRNA is blocked due to a seven-base-pair deletion in an intron of the albumin gene. NAR liver contains a few hepatocytes that react with anti-rat albumin antibody (Alb+ hepatocytes), and these cells increase in number during aging and on treatment with hepatocarcinogens. To characterize these Alb+ hepatocytes, we examine their albumin mRNA, the biochemical specificity of their albumin, and its intracellular distribution. Signals of albumin mRNA were observed in a few hepatocytes by in situ hybridization. Moreover, a small amount of cytoplasmic albumin mRNA was detected by RNA blot analysis in the liver of aged NAR and NAR treated with 3'-methyl-4-diaminoazobenzene (DAB). Immunoelectron microscopic examination revealed the cisternae of the rough and smooth endoplasmic reticula, Golgi complexes, and secretory vesicles of the Alb+ hepatocyte of NAR being filled with material that reacted with anti-rat albumin antibody. These facts suggested that albumin was gradually synthesized in Alb+ hepatocytes but that its secretion was disturbed. The albumin-like proteins of NAR were shown by Western blot analysis to consist of three species of 68 kDa, 50 kDa, and 25 kDa proteins. The 50 kDa albumin was thought to be formed by exon-skipping splicing of the albumin mRNA precursor, which was recently reported by Shalaby and Shafritz (Proc. Natl. Acad. Sci. USA 87, 2652-2656 (1990)). The 25 kDa protein was suspected to be formed by fragmentation of the 50 kDa protein.(ABSTRACT TRUNCATED AT 250 WORDS)     

Trafficking and postsecretory events responsible for the formation of secreted human salivary peptides: a proteomics approach

To elucidate the localization of post-translational modifications of different classes of human salivary proteins and peptides (acidic and basic proline-rich proteins (PRPs), Histatins, Statherin, P-B peptide, and "S type" Cystatins) a comparative reversed phase HPLC-ESI-MS analysis on intact proteins of enriched granule preparations from parotid and submandibular glands as well as parotid, submandibular/sublingual (Sm/Sl), and whole saliva was performed. The main results of this study indicate the following. (i) Phosphorylation of all salivary peptides, sulfation of Histatin 1, proteolytic cleavages of acidic and precursor basic PRPs occur before granule storage. (ii) In agreement with previous studies, basic PRPs are secreted by the parotid gland only, whereas all isoforms of acidic PRPs (aPRPs) are secreted by both parotid and Sm/Sl glands. (iii) Phosphorylation levels of aPRPs, Histatin 1, and Statherin are higher in the parotid gland, whereas the extent of cleavage of aPRP is higher in Sm/Sl glands. (iv) O-Sulfation of tyrosines of Histatin 1 is a post-translational modification specific for the submandibular gland. (v) The concentration of Histatin 3, Histatin 5, and Histatin 6, but not Histatin 1, is higher in parotid saliva. (vi) Histatin 3 is submitted to the first proteolytic cleavage (generating Histatins 6 and 5) during granule maturation, and it occurs to the same relative extent in both glands. (vii) The proteolytic cleavages of Histatin 5 and 6, generating a cascade of Histatin 3 fragments, take place after granule secretion and are more extensive in parotid secretion. (viii) Basic PRPs are cleaved in the oral cavity by unknown peptidases, generating various small proline-rich peptides. (ix) C-terminal removal from Statherin is more extensive in parotid saliva. (x) P-B peptide is secreted by both glands, and its relative quantity is higher in submandibular/sublingual secretion. (xi) In agreement with previous studies, S type Cystatins are mainly the product of Sm/Sl glands.     

Dopamine-induced apoptosis of lactotropes is mediated by the short isoform of D2 receptor

Dopamine, through D2 receptor (D2R), is the major regulator of lactotrope function in the anterior pituitary gland. Both D2R isoforms, long (D2L) and short (D2S), are expressed in lactotropes. Although both isoforms can transduce dopamine signal, they differ in the mechanism that leads to cell response. The administration of D2R agonists, such as cabergoline, is the main pharmacological treatment for prolactinomas, but resistance to these drugs exists, which has been associated with alterations in D2R expression. We previously reported that dopamine and cabergoline induce apoptosis of lactotropes in primary culture in an estrogen-dependent manner. In this study we used an in vivo model to confirm the permissive action of estradiol in the apoptosis of anterior pituitary cells induced by D2R agonists. Administration of cabergoline to female rats induced apoptosis, measured by Annexin-V staining, in anterior pituitary gland from estradiol-treated rats but not from ovariectomized rats. To evaluate the participation of D2R isoforms in the apoptosis induced by dopamine we used lactotrope-derived PR1 cells stably transfected with expression vectors encoding D2L or D2S receptors. In the presence of estradiol, dopamine induced apoptosis, determined by ELISA and TUNEL assay, only in PR1-D2S cells. To study the role of p38 MAPK in apoptosis induced by D2R activation, anterior pituitary cells from primary culture or PR1-D2S were incubated with an inhibitor of the p38 MAPK pathway (SB203850). SB203580 blocked the apoptotic effect of D2R activation in lactotropes from primary cultures and PR1-D2S cells. Dopamine also induced p38 MAPK phosphorylation, determined by western blot, in PR1-D2S cells and estradiol enhanced this effect. These data suggest that, in the presence of estradiol, D2R agonists induce apoptosis of lactotropes by their interaction with D2S receptors and that p38 MAPK is involved in this process.     

Physical properties of some snake plasma albumins

The albumin-like proteins were purified from the plasma of three terrestrial elapids and two sea snakes. The albumin-like fraction averaged 25% (range: 21-30%) in concentration of the total plasma proteins as determined by densitometer. The physical properties of the albumin-like proteins purified from these snakes were compared. These properties, e.g. electrophoretic mobility, isoelectric point, extinction coefficient, and molecular weight, were shown to be strikingly similar to those of human plasma albumin. The physical properties of the plasma albumins of the snakes studied are similar to one another. This similarity does not explain our previous observation that Naja albumin is considerably remote immunologically from those of other elapids (Mao et al., 1983).     

Charles River Sprague Dawley rats lack early age-dependent susceptibility to DMBA-induced mammary carcinogenesis

Developmental stages of mammary glands influence their susceptibility to initiating events related to carcinogenesis. The "window of susceptibility" to mammary carcinogenesis is classically defined as the time in early puberty when the mammary gland morphology is most sensitive to initiation events. Administration of the polyaromatic hydrocarbon, 7,12-dimethylbenz(a)anthracene (DMBA), in a single oral dose yields maximal mammary tumor formation when administered in this "window". We examined the DMBA treated mammary glands, precursor lesions, and morphology of the uninvolved mammary epithelium for the first 100 days of life for Charles River Sprague Dawley CD(R) IGS. Our goal was to determine the DMBA dose at which 50% of the rats (IC50) developed carcinoma in situ (CIS) within three months of dosing. Here we demonstrate, rather than the classical U-shaped dose curve in which there is maximum sensitivity for DMBA at 50 days, there is an increasing degree of sensitivity with age in the CD(R) IGS rat. Additionally, we report that vehicle-treated animals developed mammary CIS without any known initiator, and 100 day virgin animals demonstrated lactational changes, independent of DMBA exposure or dose. Lastly, we demonstrate this strain of virgin female rats has elevated pituitary prolactin immunoreactivity independent of the level of mammary differentiation. We conclude this strain of Charles River Sprague Dawley rats has prolactin-induced pituitary stimulation, and therefore, the window of susceptibility for mammary tumorigenesis is absent.     

Biological evidence for a precursor protein of serum albumin.

Radioactive leucine was injected into the portal vein of rats followed after 15 seconds by a 180 fold excess of nonradioactive leucine. An albumin-like protein in the liver became highly labelled within 15 minutes after injection. After 150 minutes, the radioactivity in the albumin-like protein had decreased to one tenth. In the serum, radioactively labelled albumin started to appear after 15 minutes and increased there-after up to 150 minutes after injection. Radioactivity in albumin within the liver remained constant at a low level. These results suggest that the albumin-like protein is a biological precursor protein of serum albumin, i.e. a proalbumin.     

D－半乳糖致衰老小鼠与幼龄小鼠的垂体差异蛋白质分析

脑垂体是控制动物生长发育衰老死亡非常重要的一个器官.随着机体的衰老,垂体功能退化是必然趋势.D 半乳糖致衰老模型已被广泛用于研究衰老机制和筛选药物靶标,然而其分子机制尚未清楚.本研究采用差异蛋白质组学方法,以寻找D 半乳糖致衰老小鼠和幼龄小鼠垂体的差异蛋白质,为弄清其功能障碍的分子机制提供新的研究方法和线索.基于双相电泳和质谱结合的方法,本研究发现了46个大于2倍的差异蛋白质,其中32个得到可靠的鉴定（P <005）. 对差异蛋白质功能分析发现, 这些显著差异蛋白质主要分布于糖代谢通路,可能与线粒体功能紊乱有关.我们的研究数据为更好地理解D 半乳糖致衰老小鼠垂体功能障碍的内在机制提供了线索.     

Biosynthesis of serum albumin in rat liver. Evidence for the existence of `proalbumin''

1. A protein(s) of rat liver (precipitated from soluble extracts of the microsomal fraction by anti-albumin) yields albumin after limited hydrolysis by trypsin. 2. Evidence that the product of limited tryptic hydrolysis is albumin, is based upon ion-exchange chromatography, electrofocusing and peptide `mapping'. 3. The albumin `precursor' is recognized by anti-albumin and is apparently not distinguished from albumin by anti-albumin. 4. A small peptide is liberated from the presumptive albumin precursor during limited tryptic hydrolysis. This peptide is labelled by arginine, but not by leucine, lysine or methionine. 5. These results support our previous suggestion based on kinetic evidence that the albumin-like protein(s), in the anti-albumin precipitate from rat liver, is an albumin precursor.     

Increases in the basal secretion rate of follicle-stimulating hormone (FSH) accompany age-associated changes in serum FSH levels on estrus

This laboratory has recently reported that by 5-6 months of age, alterations in the secretion and production of follicle-stimulating hormone (FSH) occur in virgin female rats which precedes the age-related disruption of estrous cycles and attenuation of preovulatory gonadotropin surges. Specifically, circulating immunoreactive FSH levels are higher on estrus in rats 5 months and older compared to levels measured in 2- to 3-month-old rats. Therefore, the present study was conducted to explore a possible mechanism for this age-related increase in FSH levels. At 1400 hr on proestrus, estrus and diestrus-1, groups (n = 6-12 rats/group) of 3- and 7-month-old, cyclic rats were decapitated, trunk blood was collected, and anterior pituitary glands were bisected and placed in incubation flasks containing 1 ml media (medium 199). Following a 30-min preincubation period, hemipituitary fragments were incubated for an additional 2 hr. Media and serum FSH levels were quantified by RIA. Levels of FSH were twofold higher in the serum of 7-month-old rats than 3-month-old rats on estrus. Similarly, the basal secretion rate (BSR) of FSH (expressed as ng FSH/ml/2 hr) was significantly (P less than 0.05) higher from incubated hemipituitary fragments of 7-month-old estrous rats than from fragments obtained from younger estrous rats (7 month: 1637 ng/ml/2 hr vs 3 months: 1253 ng/ml/2 hr). Neither the serum FSH levels nor the BSR of FSH differed between age groups on proestrus or diestrus-1. These results show that age-associated increases in circulating FSH levels on estrus may be attributed to an enhanced basal secretion of FSH from the pituitary gland.     

Immunolocalization of a gonadotropin-releasing hormone receptor site in murine endometrium that mediates apoptosis

Circumstantial evidence from a previous study indicated that antibodies generated against a synthetic N-terminal extracellular domain mouse pituitary gonadotropin-releasing hormone (GnRH) receptor peptide acted directly on the murine uterus affecting endometrial regression. Affinity-purified polyclonal sheep antibodies were used to assess tissue-specificity of antibody reactions in diestrous mice. Antibody binding was localized by immunofluorescence staining to anterior pituitary gland and endometrium. Ovary, brain, liver, kidneys, heart, lungs, spleen, gastrointestinal tract, adrenal glands, thymus, thyroid gland, muscle, and adipose were unreactive. Fragmented deoxyribonucleic acid, a marker of programmed cell death/apoptosis, was detected by digoxigenin labeling-immunoperoxidase in endometrial (but not pituitary) glands of animals injected with antipeptide antibodies or native ligand. It appears that luteal phase endometrium of mice expresses a GnRH receptor moiety that is coupled to a cell death (endonuclease) transduction pathway.     

Chronic ethanol consumption depresses hypothalamic-pituitary-adrenal function in aged rats.

In separate experiments, nine (n = 20) and fifteen (n = 12) month old rats were treated with either 6% ethanol or 12% sucrose (to balance caloric intake) in the drinking water to examine the effect of chronic ethanol consumption on the hypothalamic-pituitary-adrenal axis of aged rats. Rats were maintained on these treatment regimens for thirty days and were killed by decapitation. Blood was collected and plasma concentrations of adrenocorticotropin (ACTH) and corticosterone were determined by radioimmunoassay. Adrenal glands were cleaned, quartered and used to test in vitro responsiveness to ACTH. Anterior pituitary glands from all 15 month old rats and one half of the nine month old rats were collected, frozen and extracted for measurement of tissue ACTH concentration. The remaining anterior pituitary glands from the nine month old rats were challenged with corticotropin releasing hormone (CRH) to test in vitro responsiveness. In nine month old rats, chronic ethanol consumption decreased plasma ACTH and corticosterone (P less than 0.05). Pituitary ACTH concentrations were unchanged in treated nine month old rats, but the amount of pituitary ACTH released in response to CRH was decreased (P less than 0.05) in rats consuming ethanol. In vitro responsiveness of the adrenal gland to ACTH in nine month old rats consuming ethanol was unchanged (P greater than 0.05). Plasma ACTH and corticosterone concentrations were also decreased in 15 month old rats chronically consuming ethanol (P less than 0.05). No differences were noted in responsiveness of the adrenal gland or in the amount of pituitary ACTH due to ethanol consumption in 15 month old rats (P greater than 0.05). The results of these experiments indicate that chronic ethanol consumption decreases hypothalamic-pituitary-adrenal function in aged rats.     

Evidence for the spontaneous formation of interspecies hybrid molecules of human, rat and bovine serum albumins

Utilizing electrophoretic and gel filtration techniques it was shown that a bovine C-terminal peptic fragment [residues 307-582] spontaneously forms interspecies hybrid molecules with three complementary N-terminal fragments derived from human [residues 1-308; 49-308] and rat [residues 1-308] albumins. The fragments associate with 1:1 stoichiometry to produce an albumin-like complex which has a molecular weight and electrophoretic mobility similar to intact albumin. These data demonstrate, for the first time, that albumin fragments derived from different species associate in a complementary fashion and provide direct evidence that the tertiary structure may be highly conserved.     

Detection of the pro-opiomelanocortin peptide fragments--beta-endorphin and ACTH--in the adrenals of rats and mice by immunohistochemistry

Independent peptide fragments of pro-opiomelanocortin molecule, beta-endorphin and ACTH, have been detected immunohistochemically in the adrenal glands of rats and mice. Immunoreactive beta-endorphin and ACTH have been revealed in the adrenal medulla and reticular zone of the adrenal cortex. beta-endorphin and ACTH distribution patterns in adrenal sections were identical, which is indicative of the linked synthesis of these peptides in the adrenal gland. The data obtained suggest the existence of pituitary-independent mechanisms regulating corticosteroidogenesis in the adrenal gland, involving adrenal pro-opiomelanocortin fragments.     

Antiapoptotic Factor Humanin Is Expressed in Normal and Tumoral Pituitary Cells and Protects Them from TNF-α-Induced Apoptosis

Humanin (HN) is a 24-amino acid peptide with cytoprotective action in several cell types such as neurons and testicular germ cells. Rattin (HNr), a homologous peptide of HN expressed in several adult rat tissues, also has antiapoptotic action. In the present work, we demonstrated by immunocytochemical analysis and flow cytometry the expression of HNr in the anterior pituitary of female and male adult rats as well as in pituitary tumor GH3 cells. HNr was localized in lactotropes and somatotropes. The expression of HNr was lower in females than in males, and was inhibited by estrogens in pituitary cells from both ovariectomized female and orquidectomized male rats. However, the expression of HNr in pituitary tumor cells was not regulated by estrogens. We also evaluated HN action on the proapoptotic effect of TNF-α in anterior pituitary cells assessed by the TUNEL method. HN (5 µM) per se did not modify basal apoptosis of anterior pituitary cells but completely blocked the proapoptotic effect of TNF-α in total anterior pituitary cells, lactotropes and somatotropes from both female and male rats. Also, HN inhibited the apoptotic effect of TNF-α on pituitary tumor cells. In summary, our results demonstrate that HNr is present in the anterior pituitary gland, its expression showing sexual dimorphism, which suggests that gonadal steroids may be involved in the regulation of HNr expression in this gland. Antiapoptotic action of HN in anterior pituitary cells suggests that this peptide could be involved in the homeostasis of this gland. HNr is present and functional in GH3 cells, but it lacks regulation by estrogens, suggesting that HN could participate in the pathogenesis of pituitary tumors.     

Iodine-Induced Thyroid Blockade: Role of Selenium and Iodine in the Thyroid and Pituitary Glands

The purpose of this study was to determine the content of iodine and selenium in the thyroid and pituitary glands of rats under iodine-induced blockade of the thyroid gland. Electron probe microanalysis, wavelength-dispersive spectrometry, and point analysis were used in this investigation. We also determined the expression of sodium iodide symporter and caspase 32 in the thyroid and pituitary glands and the expression of thyroid-stimulating hormone in the pituitary. The samples for iodine analysis must be thoroughly dehydrated, and for this purpose, we developed a method that produced samples of constant mass with minimal loss of substrate (human thyroid gland was used for the investigation). Normal levels of iodine and selenium were found in the thyroid, pituitary, ovaries, testes hypothalamus, and pancreas of healthy rats. The levels of iodine and selenium in I- or Se-positive points and the percentage of positive points in most of these organs were similar to those of controls (basal level), except for the level of iodine in the thyroid gland and testes. Blockade of the thyroid gland changed the iodine level in iodine-positive points of the thyroid and the pituitary glands. On the sixth day of blockage, the iodine level in iodine-positive points of the thyroid gradually decreased to the basal level followed by an abrupt increase on the seventh day, implying a rebound effect. The opposite was found in the pituitary, in which the level of iodine in iodine-positive points increased during the first 6 days and then abruptly decreased on the seventh day. Expression of the thyroid-stimulating hormone in the pituitary decreased during the first 5 days but sharply increased on the sixth day, with a minimum level of iodine in the thyroid and maximum in the pituitary, before normalization of the iodine level in both glands preceding the rebound effect. The expression of sodium iodide symporter increased during the first 4 days of blockage and then decreased in both glands. The fluctuations of the thyroid-stimulating hormone in the pituitary gland reflected the changes of iodine in the thyroid gland more precisely than the changes of sodium iodide symporter. The selenium level in the selenium-positive points changed only in the pituitary, dropping to zero on the second and fifth day of the blockade. Simultaneously, the maximum induction of caspase 32 was observed in the pituitary gland. We believe that these results may help to clarify a role of the pituitary gland in the thyroid blockade.     

Binding of intravenously injected antibodies against laminin to developing and mature endocrine glands

Summary To determine whether circulating antibodies against laminin can bind in vivo to basement membranes within endocrine glands, affinity-purified sheep or rabbit anti-laminin IgG was intravenously injected into rats. One to five hours after injection, anti-laminin IgG was bound to all basement membranes of adrenal and anterior pituitary glands of mature as well as 2-day-old newborn rats as shown by immunofluorescence microscopy. After the injection of anti-laminin conjugated directly to horseradish peroxidase (HRP), HRP reaction product was also present throughout adrenal and pituitary basement membranes in mature and immature glands 1–5 h post-injection. Ultrathin Lowicryl sections from rats that received unconjugated rabbit anti-laminin IgG 1 h prior to fixation with paraformaldehyde were labeled directly with anti-rabbit IgG-colloidal gold. In these cases, gold also bound specifically over the lamina densa and lamina rara. When adrenal or pituitary glands from mature rats were examined by immunofluorescence 1 week after the injection of sheep anti-laminin IgG, the patterns and amounts of bound sheep IgG were indistinguishable from those observed 1 h after injection. In contrast, significantly less fluorescence was present in glands from 7-day-old rat pups that had received anti-laminin IgG 5 days earlier. In addition, when anti-laminin IgG-HRP was injected into newborns and glands were fixed 5 days later, lengths of labeled endothelial and epithelial basement membranes were often interspersed with unlabeled lengths in zones of cellular proliferation in the outer adrenal cortex and throughout the pituitary gland. These results indicated that unlabeled basement membranes in these regions were probably assembled after the injection of anti-laminin IgG, which would also explain diminished labeling of basement membranes in these animals. Despite the continued presence of heterologous anti-laminin IgG within endocrine basement membranes, however, rat IgG, rat C3, inflammatory cells, or histologic abnormalities were observed in neither newborn nor adult glands under the conditions examined here. Sections from rats injected with control IgG or control IgG-HRP were entirely negative by immunofluorescence, immunoperoxidase, and immunogold techniques. We therefore conclude that (1) apparently large amounts of circulating anti-laminin IgG can bind to adrenal and pituitary basement membranes, and (2) at least some of these basement membranes are assembled during development by progressive splicing of newly synthesized matrix into that already present.     

Stimulatory action of prolactin on gonadotropin secretion in vitro

The action of prolactin (PRL) on the secretion of gonadotropin was investigated by means of a cell culture system of rat anterior pituitary gland. Anterior pituitary glands were removed from Wistar male rats, enzymatically digested and cultured. Luteinizing hormone (LH) release into medium was increased by adding PRL dose-dependently in the range between 10 ng/ml and 1 microgram/ml. This effect of PRL was further augmented by the presence of either gonadotropin-releasing hormone or estradiol. The intracellular LH concentration was also increased by PRL. PRL also caused an increase in follicle-stimulating hormone release into medium dose-dependently. In conclusion, PRL was shown to stimulate the secretion of gonadotropin at the pituitary level, thus suggesting a paracrine mode of PRL action in the anterior pituitary gland.