Expression of Periostin in Normal, Atopic, and Nonatopic Chronically Inflamed Canine Skin.

In humans, periostin plays a critical role in the enhancement and chronicity of allergic skin inflammation; however, whether it is involved in the pathogenesis of canine dermatitis remains unknown. The aim of this study was to examine the expression patterns of periostin in healthy, atopic, and nonatopic chronically inflamed canine skin. Biopsy specimens from 47 dogs with skin disease and normal skin tissue from 5 adult beagles were examined by light microscopy, immunohistochemistry, and in situ hybridization. In normal skin, periostin was localized just beneath the epidermis and around the hair follicles. In chronically inflamed skin, periostin expression was most intense in the dermis with inflammatory cell infiltrates. In contrast, low levels of periostin were detected in acutely inflamed and noninflamed skin. Conversely, all canine atopic dermatitis tissues characteristically showed the most intense expression of periostin in the superficial dermis, particularly at the epidermal-dermal junction. In situ hybridization showed that periostin mRNA was broadly expressed in the basal epidermal keratinocytes, outer root sheath cells, and dermal fibroblasts in normal dog skin. High expression of periostin mRNA was observed in fibroblasts in dog skin with chronically inflamed dermatitis. Moreover, in some chronically inflamed skin specimens, periostin mRNA expression was increased in basal keratinocytes. The severity score of chronic pathologic changes and CD3+ cell number in the dermis were correlated with distribution pattern of periostin in the atopic skin. These data suggest that periostin could play a role in the pathophysiology of chronic dermatitis, including atopic dermatitis, in dogs.

Endocrinological responses during suckling in Hatano high- and low-avoidance rats.

Hatano high-avoidance (HAA) and low-avoidance (LAA) animals were originally selected from Sprague-Dawley rats for good and poor active avoidance learning in a shuttle box. We studied the endocrinological profile in lactating rats to determine the effect of suckling during mid-lactation in HAA and LAA rats. The pups were separated from their mother rats 6 h before the onset of suckling and blood samples were drawn from unanaesthetized mother rats via a jugular cannula at 0, 5 and 15 min after the suckling stimulus and then 15, 45 and 105 min after pups were removed. Plasma concentrations of oxytocin in HAA rats were significantly higher than in LAA rats during the suckling period. Plasma concentrations of prolactin and ACTH in HAA rats were significantly higher than in LAA rats during the suckling period, and at 15 min and 45 min after the pups were removed. However, there were no strain differences in circulating corticosterone between the two lines, indicating that the response of the hypothalamo-pituitary axis to the suckling stimulus was greater in HAA rats than in LAA rats, whereas the ACTH-induced adrenal response of corticosterone release was higher in LAA rats than in HAA rats. Since dopamine from the median eminence inhibits prolactin secretion from the lactotrophs of the anterior pituitary, and tuberoinfundibular dopaminergic neurones are partially regulated by the level of circulating prolactin, we evaluated the activity of tyrosine hydroxylase (TH), the rate-limiting enzyme in dopamine biosynthesis. TH, measured by the accumulation of 3,4-dihydroxyphenylalanine, was significantly higher in HAA rats than in LAA rats before the suckling stimulus. After the suckling stimulus, TH activity in HAA rats was significantly lower than before suckling, whereas TH activity in LAA rats was not changed. These findings clearly demonstrated that apparent differences between the two Hatano lines exist in endocrinological profiles during suckling. These strain differences probably originate from neurotransmitter changes, such as dopamine.

Differential responses of the hypothalamo-pituitary-adrenocortical axis to acute restraint stress in Hatano high- and low-avoidance rats.

The high- and low-avoidance animal (HAA and LAA respectively) strains of Hatano rats were originally selected and bred from Sprague-Dawley rats for their performance in the shuttle-box task. The present study focused on the activity of the hypothalamo-pituitary-adrenocortical (HPA) axis of HAA and LAA rats in response to restraint stress. The restraint stress induced an elevation in plasma concentrations of ACTH, prolactin, corticosterone and progesterone. Peak levels of plasma ACTH during stress conditions were significantly higher in HAA rats than in LAA rats, while peak levels of prolactin were significantly lower in HAA rats than in LAA rats. Under stress conditions, ACTH and prolactin synthesis in the anterior pituitary glands was significantly higher in HAA rats compared with LAA rats. The peak plasma concentrations of corticosterone, during restraint stress, were significantly higher in LAA rats compared with HAA rats. These results indicate that the response of the hypothalamo-pituitary axis to acute restraint stress is greater in HAA rats than in LAA rats, whereas the ACTH-induced adrenal response of corticosterone release is higher in LAA rats than in HAA rats. On the other hand, prolactin secretory activity is higher in LAA rats compared with HAA rats. These differences in endocrine responses to stress may be involved in the regulation of the avoidance responses in the shuttle-box task.

Minor involvement of somatic growth in the onset of puberty of Hatano high- and low-avoidance rats.

The present study was planned to examine the effects of somatic growth on the determination of timing of puberty using Hatano high- and low-avoidance rats (HAAs and LAAs); the rats were genetically selected from Sprague-Dawley (SD) rats for good or poor performance in a two-way active avoidance-learning test. Since these two lines were found to have different characteristics, such as body weight at birth, maternal care and timing of male puberty, the present study characterized female puberty in Hatano rats and then compared postnatal growth and timing of puberty between the two lines of rats when they were nursed by foster SD dams. When nursed under biological dams, HAAs became heavier, exhibited vaginal opening at a younger age and first ovulation was accompanied by more oocytes than LAAs. In all of the HAAs, but none of the LAAs, ovulation was induced by a single s.c. injection of 5 IU equine chorionic gonadotropin (eCG) on day 22 after birth. An additional treatment with 10 IU human CG revealed that, in the ovaries of LAAs, a small number of follicles had developed to an ovulable stage as a result of the treatment. The fostering improved somatic growth, and weights of LAAs were sustained at a heavier level than those of fostered HAAs. The fostering, however, did not eliminate the line difference in the timing of puberty of both sexes; it did accelerate the vaginal opening of LAAs but not the balanopreputial separation. Thus, there is a phenotypic difference in the timing of female puberty in Hatano rats exhibiting a different timing of ovarian development in response to gonadotropin. The present study indicates that postnatal somatic growth is not the predominant determinant in the onset of puberty in Hatano rats.

Effects of reduction of the number of primordial follicles on follicular development to achieve puberty in female rats.

Effects of reduction of the number of primordial follicles on follicular development and concentrations of circulating hormones were examined in immature female rat offspring of dams given busulfan intraperitoneally on day 14 of gestation. The offspring of dams treated with 5 mg busulfan kg(-1) showed vaginal opening at an age comparable with the offspring of dams treated with 2.5 mg busulfan kg(-1) or with corn oil as a control, although they exhibited an irregular oestrous cycle until week 14 after birth. The serum concentrations of immunoreactive inhibin and FSH on day 26 after birth of the offspring treated with 5 mg busulfan kg(-1) were similar to those of age-matched controls. On day 15 after birth, however, the concentration of their immunoreactive inhibin was markedly lower than that of controls, whereas the concentration of their FSH was increased inversely. Comparison of the numbers of ovarian follicles in the controls and groups treated with 2.5 mg busulfan kg(-1) and 5 mg busulfan kg(-1) revealed that prenatal treatment with busulfan reduced the number of follicles in the primordial or primary phase and in the preantral phase on day 7 after birth. Although the increase of the ratio of the number of preantral follicles during days 7-13 after birth tended to vary with the prenatal dose of busulfan, the number of preantral follicles in the group treated with 5 mg busulfan kg(-1) was still smaller than in the controls. The concentration of serum immunoreactive inhibin of the offspring treated with busulfan was reduced on day 7 after birth without alteration of the concentration of gonadotrophin. On day 13 after birth, the concentration of serum immunoreactive inhibin was reduced only in the offspring treated with 5 mg busulfan kg(-1), and the concentration of serum FSH of the offspring was increased inversely as found on day 15 after birth. These results indicate that a reduction in the number of primordial follicles decreases the number of follicles that enter the growing phase, a major source of circulating inhibin in the neonatal and infantile ovary, and that consequently increased circulating FSH may accelerate follicular development to achieve puberty.

Postnatal behavior in hatano high- and low-avoidance rats following prenatal exposure to low-dose methylazoxymethanol.

The hypothesis that genetic factors influence behavioral effects was tested in rats exposed prenatally to methylazoxymethanol (MAM). We examined whether baseline behavior is an important factor influencing behavioral effects, and whether a behaviorally selected strain was useful for study of neurobehavioral teratology. Pregnant high- and low-avoidance animals (HAAs and LAAs) of the Hatano strain, selectively bred for high and low shuttlebox avoidance responses, respectively, were given an IP injection of a low dose of MAM (15 mg/kg) on day 14 of gestation. The offspring of these animals were subjected to behavioral tests for locomotor activity (running-wheel and open-field tests) and learning ability (Biel maze and shuttlebox avoidance tests). There were no significant effects of MAM on running-wheel activity or shuttlebox avoidance learning, whereas the number of errors in the Biel maze was increased in the MAM offspring of both strains. Interestingly, open-field activity of the MAM offspring was markedly decreased in LAAs but not in HAAs. Therefore, an additional experiment was performed to determine plasma levels of ACTH and corticosterone following open-field exposure. When compared to control offspring of the respective strains, plasma levels of ACTH and corticosterone were not altered by prenatal MAM treatment in LAAs. Instead, the MAM offspring in HAAs exhibited decreased ACTH levels in absence of behavioral alterations. These results demonstrated that prenatal exposure to low doses of MAM may alter postnatal behavior and endocrine response of the offspring, although to a differing degree in HAAs and LAAs. Our observations suggested that behaviorally selected strains are sensitive to neurobehavioral teratogens such as MAM.

Plasma ACTH levels during early, two-way avoidance acquisition in high- and low-avoidance rats (Hatano strains).

Having successfully bred for high- and low-avoidance rats (HAA and LAA, respectively) on a shuttlebox task, we performed three experiments designed to identify factors which might be related to the phenotypic differences seen in avoidance behavior. In experiment 1, shuttlebox behavior was measured to determine whether the phenotypic difference was activity related. In terms of intertrial responses, there was no difference between HAA and LAA rats in locomotor activity during the conditioning process. Experiment 2 compared adrenal weights of HAA and LAA rats at 11 weeks of age. The observation that the adrenal glands were heavier in HAA than in LAA rats suggested that these strains might differ in aspects of endocrine response. In experiment 3, plasma levels of ACTH and corticosterone were determined during early escape/avoidance acquisition in the shuttlebox. Plasma levels of ACTH after the shuttlebox testing were higher in HAA than in LAA rats. There was no difference between the two strains in plasma levels of corticosterone after testing, possibly due to a ceiling effect. These results suggest that the phenotypic differences in the acquisition of avoidance behavior of HAA and LAA rats may be related to different endocrine responses, rather than to locomotor activity.

Effects of indomethacin on the selective release of follicle-stimulating hormone during the period of ovulation in the rat.

To determine whether indomethacin, a potent inhibitor of prostaglandins endoperoxide synthetase, affects the selective follicle-stimulating hormone (FSH) surge during the period of ovulation, the compound was administered intravenously (i.v.), concurrent with 10 IU human chorionic gonadotropin (hCG), to diestrous female rats at 16:00 hr. Indomethacin inhibited the number of ovulations in a dose-dependent manner, and treatment with 500 micrograms indomethacin reduced number of oocytes in the ampullae most effectively without enteric lesions. In the histological observation, oocytes that had began to mature were found not only in unruptured luteinized follicles but also in ovarian interstitium beneath ruptured luteinized follicle. Despite the inhibitory effects of indomethacin on ovulation, peri-ovulatory FSH and progesterone surges occurred in comparable levels and duration to vehicle-treated animals. These results indicate that indomethacin-induced inhibition of prostaglandin synthesis does not affect the selective release of FSH during the peri-ovulatory period.

Inhibition by hop bract polyphenols of cellular adherence and water-insoluble glucan synthesis of mutans streptococci.

The inhibitory effect of hop bract polyphenols (HBP) on cariogenic streptococci was investigated. It was found that the high molecular weight polyphenol (estimated about 36,000-40,000) inhibited the cellular adherence of Streptococcus mutans MT8148 (serotype C) and Streptococcus sobrinus ATCC 33478 (serotype g) at much small concentrations than the polyphenols extracted from oolong tea or green tea leaves. Furthermore, HBP also inhibited the action of glucosyltransferase, which was involved in the water-insoluble glucan synthesis, but did not suppress the growth and the acid production of the bacteria. These results suggest that HBP would be a candidate to act against dental caries caused by Mutans Streptococci.

In-vitro model of uterine leiomyomas: formation of ball-like aggregates.

To clarify the biological characteristics of uterine leiomyomas, cells explanted and cultured from uterine leiomyomas and from normal myometrial tissue were observed by time-lapse cinemicrography and phase-contrast microscopy. The histological characteristics were evaluated by electron microscopy and immunofluorescence microscopy, and these observations revealed significant differences. By time-lapse cinemicrography, the cells cultured from leiomyomas and myometrium differed in their behaviour. Cells from the myometrium started to grow in parallel with the cell's major axis and formed topographically uniform hills and valleys by day 21 of culture. In contrast, the cells from leiomyomas started to grow irregularly, as if having no contact inhibition, and formed ball-like aggregates of cells by day 21 of culture. The aggregates resembled the nodules of leiomyoma in vivo. Ultrastructurally, cells from both leiomyomas and myometrium had typical features of smooth muscle. Immunofluorescently, a different distribution of alpha-smooth muscle actin-positive filaments and different staining of cellular fibronectin and N-cadherin between the cells from leiomyomas and myometrium were observed, which may contribute in part of the different behaviour of the cells. Given that the explant cell culture system resembles the features of uterine leiomyomas in vivo, this suggests that it can be used as an in-vitro model.

Pantothenic acid decreases valproic acid-induced neural tube defects in mice (I).

The effect of the administration of pantothenic acid (PTA) on valproic acid (VPA)-induced teratogenesis was examined in ICR mice. VPA (300, 400, and 500 mg/kg, s.c.) or PTA (3 x 10, 3 x 100, and 3 x 300 mg/kg, i.p.) was injected on day 8.5 of gestation (plug day = day 0.5). Exencephaly was induced dose dependently by single injections of VPA. Three administrations of PTA alone at any dose levels showed neither embryocidal nor teratogenic effects. In combined treatment experiments, PTA (3 x 300 mg/kg) was injected 1 hr before, immediately before, and 1 hr after VPA administration. PTA significantly reduced VPA-induced exencephaly, while none of the other external malformations such as open eyelid or skeletal malformations such as fused, absent, or bifurcated ribs and fused thoracic vertebrae and fused sternebrae were reduced. The results suggest that PTA reduces the incidence of neural tube defect induced by VPA in mice.

Detection of in situ localization of long form prolactin receptor messenger RNA in lactating rats by biotin-labeled riboprobe.

Biotinylated riboprobe that specifically hybridized with messenger RNAs (mRNAs) encoding the long form of prolactin receptor (PRLRL) was transcribed from 269 bp Hind III and Xho I fragment of the cytoplasmic domain of PRLRL complementary DNA (cDNA). The probe was used for in situ hybridization to identify tissue localization of PRLRL mRNA in the mammary gland, liver, ovaries and kidneys from lactating rats at 24-36 h after delivery. Histochemical detection of signals by means of horseradish peroxidase (HRP)-labeled streptavidin revealed that the PRLRL gene was expressed on the alveolar epithelial cells and mammary ductal epithelium in the mammary gland, and hepatocytes in the liver. In the ovary, the PRLRL gene was expressed on the luteal cells in the newly formed corpus luteum, granulosa cells and theca cells of follicles at various stages of development, hypertrophied theca cells in the atretic follicle, and secondary interstitial cells, but no signal was observed in the kidney. Biotinylated sense RNA probe did not detect any signals in any of the tissues examined. In situ hybridization with non-radiolabeled probe provided the identification of PRLRL mRNA in the fine tissues, such as follicular epithelium in the ovary, and showed the morphology of individual cells expressing the PRLRL gene. In particular, the diversity of signal intensity in the same mammary gland with different appearances suggested the existence of a local mechanism controlling PRLRL gene expression.

Changes in various tissues in the arterial wall of spontaneously hypertensive rats.

1. Using stroke-prone spontaneously hypertensive rats (SHRSP), stroke-resistant spontaneously hypertensive rats (SHRSR) and Wistar-Kyoto rats (WKY), vascular complications and the longevity of rats were investigated. 2. SHRSP aged more than 9.5 months tended to suffer from severe vascular complications such as periarteritis nodosa (PN) of mesenteric artery, while SHRSR very rarely showed severe vascular complications and WKY did not show any complications, because of the different level of systolic blood pressure. 3. Among some tissues PN tended to occur early in the small arteries of the testes and then in mesenteric artery, when these tissues of SHRSP were investigated microscopically. 4. Concerning the influence of systolic blood pressure on arterial smooth muscle layer, the deviation force of this layer was larger in SHRSR compared to WKY (44.7 times in Y axis), which was calculated mathematically and physically using computer analysis. 5. The arterial wall area of PN was enlarged, resulting in the low ratio of lumen/wall. The ratio of arterial lumen/wall was lower in SHRSP when compared to the age-matched WKY. 6. In search for myocardial ischaemia, ECG was recorded. There were positive correlations between PQ interval or SV1 + RV5 and age in the three strains of rats. ST depression more than 1 mm on ECG was most prevalent in old SHRSP, indicating probably the presence of myocardial ischaemia.

Inhibition of carbon tetrachloride-induced hepatotoxicity by neopterins.

We investigated the inhibitory effects of neopterin (NP) and its reduced form, 5,6,7,8-tetrahydroneopterin (NPH4), on carbon tetrachloride (CCl4)-induced hepatotoxicity. In in vivo experiments, intraperitoneal administration of NP or NPH4 significantly inhibited the elevation of plasma alanine aminotransferase activity induced by CCl4 in mice. In in vitro experiments using cultured rat hepatocytes, CCl4 induced in a manner which was both time- and dose-dependent lactate dehydrogenase release, and the addition of NP or NPH4 to the culture-medium significantly inhibited its release from cells. NPH4, but not NP, reacted directly with a stable radical, 1,1-diphenyl-2-picrylhydrazyl. These results suggest that NP and NPH4 inhibit CCl4-induced hepatotoxicity through different mechanisms.

General pharmacology of the non-sulfhydryl angiotensin converting enzyme inhibitor N-[8-amino-1(S)-carboxyoctyl]-L-alanyl-L-proline.

The effects of N-[8-amino-1(S)-carboxyoctyl]-L-alanyl-L-proline (AB-47, CAS 120008-53-9), an orally active angiotensin converting enzyme inhibitor, on the central nervous, respiratory and cardiovascular, autonomic systems, isolated smooth muscles and other functions were investigated in various experimental animals. AB-47 had no effect on central nervous, autonomic systems and isolated smooth muscles. AB-47 (10 and 30 micrograms/kg i.v.) significantly lowered femoral blood pressure without affecting respiration and heart rate in anesthetized rats. However, AB-47 had no effect on the contractile tension of mammalian isolated atrium and aorta. AB-47 had no effect on gastrointestinal transit in mice. Very slight injury of gastric mucosa was observed 4 h after the oral administration of AB-47 in rats but AB-47 did not damage the small intestinal mucosa. AB-47 had no effect on the contraction of rat phrenic nerve-diaphragm preparation induced by electrical stimulation. AB-47 did not affect the incidence of acetic acid-induces writhings. AB-47 potentiated carrageenan-induced hind paw edema in rats. The potentiation of edema may be due to an accumulation of bradykinin induced by the inhibition of angiotensin converting enzyme (ACE), because ACE is the identical enzyme with kinase II. The pretreatment of AB-47 for 7 days (1, 3, 10 mg/kg/d p.o.) inhibited the cardiac hypertrophy induced by isoproterenol (isoprenaline). This result suggests that the renin-angiotensin-aldosterone system directly or indirectly participates in the cardiac hypertrophy induced by isoproterenol.(ABSTRACT TRUNCATED AT 250 WORDS)

Toxicity studies of the non-sulfhydryl angiotensin converting enzyme inhibitor N-[8-amino-1(S)-carboxyoctyl]-L-alanyl-L-proline in rats.

The acute and subacute toxicities of N-[8-amino-1(S)-carboxyoctyl]-L- alanyl-L-proline (AB-47, CAS 120008-53-9), which is a non-sulfhydryl angiotensin converting enzyme inhibitor, were studied in male and female Fischer 344 rats. In the acute study, male and female rats were orally given 5000 mg/kg of AB-47. No rats were dead during the observation period (14 days) after the administration. The LD50 values of AB-47 were more than 5000 mg/kg in both male and female rats. Although only diarrhoea as toxic sign was observed 2 to 7 h after the administration, this sign disappeared within 24 h after the administration. Necropsy at the termination of observations revealed no macroscopic lesions in any rats. In the subacute study, male and female Fischer 344 rats were orally given 40, 200 or 1000 mg/kg/d of AB-47 for 4 weeks. Neither toxic signs nor death due to drug effects were observed at any dosage levels of AB-47. Furthermore, AB-47 did not influence body weight, food consumption, food efficiency, urinalytical and hematological parameters in both male and female rats. The minor changes of serum parameters, which consisted of very slight increases in serum potassium and decreases in serum albumin/globulin ratio, occurred in male rats given 200 and 1000 mg/kg/d of AB-47. Serum urea nitrogen values were elevated in both male and female rats given 1000 mg/kg/d of AB-47. Slight decreases of heart weight and heart weight/body weight ratios were observed at all dosage levels of AB-47.(ABSTRACT TRUNCATED AT 250 WORDS)

Hypotensive and hemodynamic effects of the new non-sulfhydryl angiotensin converting enzyme inhibitor N-[8-amino-1(S)-carboxyoctyl]-L-alanyl-L-proline.

The hypotensive effects of N-[8-amino-1(S)-carboxyoctyl] -L-alanyl-L-proline (AB-47, CAS 120008-53-9) were examined in normotensive rats and various hypertensive rat models. The hemodynamic effect of AB-47 was also examined in anesthetized spontaneously hypertensive rats (SHR). In 2-kidney, 1-clip renal hypertensive rats (2K, 1C-RHR) and SHR, the single administration of AB-47 (10 mg/kg, p.o.) induced potent and long-lasting hypotensive effects. The repeated administration of AB-47 (1 to 10 mg/kg, p.o.) to SHR for 29 days produced a dose-dependently and sustained hypotensive effect of 20 to 70 mmHg. AB-47 (10 mg/kg, p.o.) had a weak hypotensive effect in DOCA-salt hypertensive rats but no effects in normotensive and 1-kidney, 1-clip renal hypertensive rats (1K, 1C-RHR). AB-47 (3 mg/kg, p.o.) reduced blood pressure in intact SHR but not in bilateral nephrectomized SHR. The single intravenous injection of AB-47 (10 to 100 micrograms/kg) dose-dependently lowered systemic blood pressure, left ventricular systolic pressure (LVSP) and dp/dtmax without affecting heart rate (HR) and these effects of AB-47 were more potent than those of captopril and enalaprilat. These results suggest that AB-47 is a potent and long-lasting hypotensive agent and may be useful for the therapy of both hypertension and congestive heart failure.

Inhibitory activity and protein binding of L-lysine derivatives as angiotensin converting enzyme inhibitors.

Four compounds 1a-4a containing one L-lysine residue in the molecule including a diastereomer mixture of lisinopril (N-(1-carboxy-3-phenylpropyl)-L-lysyl-L-proline) and N epsilon-carbobenzoxy-L-lysine derivatives 1b-4b of each of the four compounds were synthesized to compare the angiotensin converting enzyme (ACE) inhibitory activities in vitro and in vivo. They all showed high ACE inhibitory activity in vitro (IC50 = 0.14-42 nmol/l). A marked difference, however, was observed in inhibition of the pressor response to angiotensin I between 1a-4a (high activity) and 1b-4b (low activity). The binding of these compounds to human serum proteins in vitro was investigated by means of equilibrium dialysis and ultracentrifugation. Compounds 1b-4b showed higher levels of binding to serum albumin than that of the corresponding compounds 1a-4a, and the percentage of binding ranged from 20.1 to 89.1%. Furthermore, the inhibitory activity of compounds 1b-4b in vitro was decreased by the addition of albumin in a concentration-dependent manner. These results suggested that the difference in the protein binding rate of compounds is one of the important factors influencing the inhibitory activity in vivo.

Expression of two forms of prolactin receptor in rat ovary and liver.

The screening of a size-selected cDNA library from the ovary revealed the existence of a second form of PRL receptor in the rat. The polypeptide sequence deduced from cDNAs has a much longer cytoplasmic domain (357 amino acids) than the form previously identified in the liver (57 amino acids). Nucleotide sequence analysis and comparison with rabbit, mouse, and human PRL receptor cDNAs suggests that the two forms of rat PRL receptor result from alternative splicing of a primary transcript. Complementary DNAs encoding the long form of the receptor were also found in a library prepared from estradiol-treated rat liver, although they represent a minor fraction of total PRL receptor cDNAs obtained from this tissue. DNA polymerase chain reaction amplification of cDNA confirmed the presence of the two receptor forms in both the ovary and liver. Northern analysis, using probes that specifically hybridize with either form of mRNA, indicates a major transcript of 1.8 kilobases (kb) in estradiol-treated liver, which encodes the receptor with a short cytoplasmic domain, while the long form of the receptor is encoded by mRNAs of 2.5 and 3 kb. In the ovary, a complex pattern of hybridization to multiple mRNAs (1.8-5.5 kb) is obtained with the probe specific to the long form, and essentially only a 5.5-kb mRNA is obtained with the probe specific to the short form. The predicted size of the mature form of the long PRL receptor (PRL-R2) is 591 amino acid residues.(ABSTRACT TRUNCATED AT 250 WORDS)