Spatial distribution and fruiting phenology of Protium heptaphyllum (Burseraceae) determine the design of the underground foraging system of Atta sexdens L. (Hymenoptera: Formicidae)

Leaf-cutting ants have long been recognized to forage via complex trail systems but the nature and the ecological drivers of the different foraging strategies adopted remain a key topic. Here, we described the spatiotemporal use of belowground foraging galleries by Atta sexdens L. in the Brazilian Atlantic forest, and examined the adaptive advantages of this foraging strategy. Protium heptaphyllum adult trees (DBH > 10 cm), seed/seedling clumps and ant gallery entrances were mapped across two 1-ha plots during two consecutive fruiting seasons (2002 and 2004). We recorded 75 ca. 40 cm deep gallery entrances beneath 26 P. heptaphyllum trees at nest distances ranging from 14 to 57 m. Furthermore, gallery abundance and galleries associated with seed/seedling clumps correlated positively with P. heptaphyllum density. Our results indicate that A. sexdens was able to set a permanent system of underground galleries targeting P. heptaphyllum trees and their seeds on the ground. Such network of galleries was spatially arranged according to both the spatial distribution and abundance of P. heptaphyllum trees in a way that most gallery entrances were disposed beneath or in close periphery of P. heptaphyllum crowns. Our findings suggest that underground trail systems shaped by fruit resources represent a foraging strategy clearly more common than existing literature on the subject would suggest. In addition, it reinforces the notion that the spatiotemporal availability of resources combined with predation risk largely influence trail configurations as well as overall foraging strategies adopted by leaf-cutting ants.

Relocation of Croton sonderianus (Euphorbiaceae) seeds by Pheidole fallax Mayr (Formicidae): a case of post-dispersal seed protection by ants?

Although seed dispersal by ants might reduce seed predation near the parent plants, predation on discarded seeds clustered on nest refuse piles may reduce any initial benefit provided by seed removal. Here we examine the fate of Croton sonderianus seeds that were discarded by Pheidole fallax Mayr ants on their nest refuses in caatinga vegetation of northeast Brazil. We collected all seeds discarded in refuse piles of 20 nests and within a radius of 50 cm from their borders, and examined them for evidence of predation. A total of 3,017 seeds were recorded either located in the P. fallax refuse piles (89.1%) or nest vicinity (10.9%). Predation was three fold higher in nest vicinity as compared to refuse piles. By removing seeds from beneath parent plants and relocating then to refuse piles, P. fallax is possibly providing double protection services for C. sonderianus seeds. Our findings represent the first evidence for predator-avoidance as benefit for plants resulting from ant seed-dispersal in the neotropics.

Seed predation by rodents and safe sites for large-seeded trees in a fragment of the Brazilian Atlantic forest

Seed predation by small rodents is an emerging theme in the ecology of modified landscapes. Here we investigate the role played by the small rodent Oryzomys oniscus as a seed predator of large-seeded trees in a large remnant of the Atlantic forest - the Coimbra forest (3,500 ha), Alagoas state, northeastern Brazil. O. oniscus was captured and identified by setting twenty 500 m long transects, each one composed of 25 traps 20 m apart. This procedure resulted in 483 trap-nights set during a 20-mo period. We used 692 seeds (>15 mm length) from ten local large-seeded tree species for the seed predation trials that basically consisted of three treatments: one seed on the ground freely accessed by vertebrates (unprotected seed), one seed totally protected by an exclosure, and one partially-protected seed (exclosure just for medium-sized and large vertebrates). O. oniscus was captured throughout the Coimbra forest including forest edges (76 captures) and interior areas (67), and this small rodent was responsible for all seed predation visually documented inside exclosures. A 24 hours period of seed exposition permitted elevated rates of seed removal and predation. Seeds were much more removed/predated beneath fruiting trees, but rates varied according to the level of seed protection - 26.3% of predation among partially-protected versus 19.2% among unprotected seeds. Seeds suffered higher levels of seed predation/removal at the forest edge as well (up to 90%). In both habitats, most seeds (>84%) remained intact beneath trees without fruits, regardless of the level of seed protection. Our results suggest that O. oniscus may operate as an effective large-seed predator in forest fragments, in which adult trees without fruits constitute low resource spots and thereby provide, at least temporarily, safe sites for large seeds.

Seed shadow, seedling recruitment, and spatial distribution of Buchenavia capitata (Combretaceae) in a fragment of the Brazilian Atlantic Forest

Here we describe the seed shadow, seedling recruitment, ontogenetic structure and spatial distribution of Buchenavia capitata (an emergent canopy tree) in a 380-ha fragment of the Atlantic forest in northeast Brazil. In particular, we examine seed distribution around 10 parental trees and both seedling recruitment and mortality, during an 18 month period beneath and around parental trees. Moreover, we describe: (1) B. capitata occurrence within treefall gaps; (2) population structure in terms of ontogenetic stages for the whole site; and (3) spatial distribution of adults within an area of 51 hectares. 99% of seeds were found beneath parent crowns (n = 4,236) and seed density reached 14.6 ± 29.9 seeds/m² (0-140 seeds/m²). 49% of all seeds germinated but seedling mortality reached 100% after an 18 month period. In addition, saplings of B. capitata were not found in forest understory and within 30 treefall gaps (94-2,350 m²). The adults showed an average DBH of 69.3 ± 22.1 cm, were 19.2 ± 2.9 m tall and presented a clumped spatial distribution. B. capitata matched some of the features presented by shade intolerant trees or large-gap specialists, and we hypothesize that low rates or even lack of long distance seed dispersal events may be reducing the probability of B. capitata seeds reaching suitable habitats for successful seedling recruitment and growth. Because of that (1) seedlings face high levels of early mortality; (2) there is no sapling recruitment at the study site; and (3) local population faces senility and it is threatened by local extinction.

Distance from roads and cities as a predictor of habitat loss and fragmentation in the caatinga vegetation of Brazil

Roads and cities represent huge sources of degradation for adjacent ecosystems regarding nutrient cycling, energy, water flow and species composition. In this study we test the hypothesis that distance from roads and cities is associated with habitat loss and fragmentation in the caatinga vegetation--a dry forest to scrub vegetation that covers ca. 736,000 km2 of northeast Brazil. The study site comprised a 2,828.8 km2 piece (64 km x 44.2 km) of Xingó region (09 degrees 36'S, 37 degrees 50'W), which is located between the States of Alagoas and Sergipe. Based on satellite imagery we mapped the remaining vegetation, 145 km of paved roads and the seven small-sized cities set in the study site. A positive correlation was found between the combined distance from roads and cities and the percentage of remaining vegetation as it dropped from 18% at 12 km distant to 5.9% at 1 km distant from cities and roads. Thus, remaining vegetation was reduced by one third near cities and roads. A positive correlation was also found between distance from cities and roads and the percentage of fragments larger than 200 ha, which ranged from 3.6% (within 3 km distance class) to 23.3% (15 km distance class) of all fragments. Our results suggest a road/city-effect zone of 12 to 15 km width, over which habitat loss and fragmentation extend throughout the caatinga vegetation. These findings should be considered in the regional polices for biodiversity conservation and economic development of the caatinga region.

The soil seed bank during Atlantic Forest regeneration in Southeast Brazil

A survey was conducted to determine the density and species composition of viable seeds buried in four stands of a tropical montane forest at Parque Estadual Intervales, Brazil. The objective was to understand: (1) how numbers and composition of the soil seed bank change as the forest regrows, and (2) how such changes affect the species available for regeneration if forests of different ages are cut down. In each forest stand (5, 18, 27-yr-old and a mature forest), 57 soil samples were collected (0-2.5 and 2.5-5 cm deep). Viable seed density of herbaceous species ranged between 11,003 seeds. m-2 (5-yr-old vegetation) and 482 (mature forest), and between 25 (5-yr-old vegetation) and 389 seeds. m-2 (mature forest) for woody plant species in the 0-5 cm soil layer, suggesting a decrease in seed stocks in the course of forest regeneration. Seeds buried in the 0-2.5 cm soil layer represented between 56.9% and 67.4% of all viable seeds. Most of the viable seeds belonged to weeds of Asteraceae, Poaceae, Malvaceae and Solanaceae. The results provide evidence that, in forests of different ages, the soil does not store seeds of the same key ecological groups involved in the regeneration of Atlantic forest. Allochthonous seeds from remaining patches of forest, as well as their vertebrate dispersers, are needed for forest regeneration since the soil seed bank does not store large seeds of shade-tolerant species.

Tree species impoverishment and the future flora of the Atlantic forest of northeast Brazil

Estimates of species extinction due to human impact on tropical forests have previously been based on the relationship between species number and area. Here we use a different approach to estimate loss of tree species in the Atlantic forest of northeast Brazil. We evaluate the characteristics of plant species, their avian dispersers and the distribution of the forest remnants on the landscape to estimate that about 33.9% of tree species in this region will become extinct on a regional scale. Because northeast Brazil is the most threatened sector of South American Atlantic forest, our results highlight the need to change the current conservation paradigm for this region. Rather than focus on the creation of isolated reserves in any medium-to-large forest remnant, a bioregional planning approach is urgently required to rescue this unique biota from extinction.

Precocious puberty due to a lipid-cell tumour of the ovary

A 4-year-old girl with a lipid cell tumour of the ovary showed isosexual precocious pseudopuberty. The endocrine activity of the tumour led to elevated plasma levels of dehydroepiandrosterone sulphate, oestradiol, testosterone and androstenedione. After tumour resection the clinical signs of abnormal hormonal stimulation disappeared within 10 months. The girl developed precocious puberty again 2 years later without any sign of relapse. Therapy with luteinizing hormone releasing hormone agonist was effective although premature activation of the hypothalamic-pituitary-gonadal axis could not clearly be demonstrated by hormonal investigations.

R339H and P453S: CYP21 mutations associated with nonclassic steroid 21-hydroxylase deficiency that are not apparent gene conversions

Steroid 21-hydroxylase deficiency is the most common enzymatic defect causing congenital adrenal hyperplasia, an inherited disorder of cortisol biosynthesis. All mutations thus far characterized that cause this disorder appear to result from recombinations between the gene encoding the enzyme, CYP21B (CYP21), and the adjacent pseudogene, CYP21A (CYP21P). These are either deletions caused by unequal crossing-over during meiosis or apparent transfers of deleterious sequences from CYP21A to CYP21B, a phenomenon termed gene conversion. However, a small percentage of alleles do not carry such a mutation. We analyzed DNA from a patient with the mild, nonclassic form of 21-hydroxylase deficiency, who carried one allele that had no gene conversions detectable by hybridization with oligonucleotide probes. Sequence analysis revealed that this allele carried two missense mutations, R339H and P453S, neither of which has been previously observed in CYP21A or CYP21B. Each of these mutations was introduced into CYP21 cDNA which was then expressed in COS1 cells using a vaccinia virus system. Each mutation reduced the ability of the enzyme to 21-hydroxylate 17-hydroxyprogesterone to 50% of normal and the ability to metabolize progesterone to 20% of normal. Thus, each of these mutations represents a potential nonclassic 21-hydroxylase deficiency allele that is not the result of an apparent gene conversion.

Identification of molecular defects causing congenital adrenal hyperplasia by cloning and differential hybridization of polymerase chain reaction-amplified 21-hydroxylase (CYP21) genes

Congenital adrenal hyperplasia (CAH), one of the most common autosomal recessive disorders, is caused primarily by defects in the gene encoding steroid 21-hydroxylase, CYP21B. The molecular diagnosis of CAH, important for prenatal diagnosis, carrier detection, and a better understanding of the various clinical CAH forms, is complicated by the close proximity of a highly similar pseudogene, CYP21A, containing (and probably donating, by gene conversion-like events) most of the defects underlying CAH. In this study, we describe an efficient strategy to identify molecular defects causing CAH: polymerase chain reaction-amplified CYP21 loci are cloned and hybridized to a set of oligonucleotides, allowing rapid and allele-specific identification of all known CYP21B mutations relevant to 21-hydroxylase function. Possible new mutations can be identified by subsequent nucleic acid sequencing provided they reside within the cloned CYP21B fragment (from the TATA box to the 8th of the 10 CYP21B gene exons). Using this method, the CYP21B gene mutations of a heterozygous carrier and 25 CAH patients have been identified by oligonucleotide hybridization. All disease haplotypes seem to have been generated by recombinational events involving the CYP21A pseudogene. In 5 individuals, these data were subsequently verified by nucleic acid sequencing. The procedure can be used for diagnostic applications and may facilitate identification of new CYP21B defects.

Free α-Subunit, Free β-Subunit of Human Chorionic Gonadotropin (hCG), and Intact hCG in Sera of Healthy Individuals and Testicular Cancer Patients

To determine the serum concentrations of human chorionic gonadotropin (hCG), its free beta-subunit (hCG beta), and the free alpha-subunit (free alpha) common to all human glycoprotein hormones under physiological and pathological conditions, we developed monoclonal antibody-based immunoenzymometric assays. Free alpha-subunit was detected in the sera of all healthy individuals of both sexes; hCG was measurable in sera of 54% of the men, and 46% were positive for free hCG beta; in nonpregnant women, 69.5% were positive for hCG, 68.4% for the free beta-subunit. Pathological conditions, i.e., hCG-producing tumors, were studied in vitro and in vivo. In vitro, the concentrations of hCG, free hCG beta, and free alpha in tissue-culture supernates of a choriocarcinoma cell-line ("JAR") showed a parallel pattern during time-course analysis. In vivo, in long-term follow-up studies of 13 patients with testicular cancer, serum concentrations of the three analytes paralleled each other, whether the disease was in remission or not. Because of a selective increase of free hCG beta and free alpha in 27% of seminomatous tumor patients and in 13% of the nonseminomatous patients, the percentage of tumor-marker-positive sera was increased from 15% to 42% and 57% to 70%, respectively, by the additional measurement of free hCG beta and free alpha. Thus hCG, free hCG beta, and free alpha are physiologically present in a high percentage of the sera from healthy men, and the determination of free hCG beta and free alpha, although not of prognostic value, improves the diagnostic possibilities in patients with testicular cancer.

Free alpha-subunit, free beta-subunit of human chorionic gonadotropin (hCG), and intact hCG in sera of healthy individuals and testicular cancer patients

To determine the serum concentrations of human chorionic gonadotropin (hCG), its free beta-subunit (hCG beta), and the free alpha-subunit (free alpha) common to all human glycoprotein hormones under physiological and pathological conditions, we developed monoclonal antibody-based immunoenzymometric assays. Free alpha-subunit was detected in the sera of all healthy individuals of both sexes; hCG was measurable in sera of 54% of the men, and 46% were positive for free hCG beta; in nonpregnant women, 69.5% were positive for hCG, 68.4% for the free beta-subunit. Pathological conditions, i.e., hCG-producing tumors, were studied in vitro and in vivo. In vitro, the concentrations of hCG, free hCG beta, and free alpha in tissue-culture supernates of a choriocarcinoma cell-line ("JAR") showed a parallel pattern during time-course analysis. In vivo, in long-term follow-up studies of 13 patients with testicular cancer, serum concentrations of the three analytes paralleled each other, whether the disease was in remission or not. Because of a selective increase of free hCG beta and free alpha in 27% of seminomatous tumor patients and in 13% of the nonseminomatous patients, the percentage of tumor-marker-positive sera was increased from 15% to 42% and 57% to 70%, respectively, by the additional measurement of free hCG beta and free alpha. Thus hCG, free hCG beta, and free alpha are physiologically present in a high percentage of the sera from healthy men, and the determination of free hCG beta and free alpha, although not of prognostic value, improves the diagnostic possibilities in patients with testicular cancer.

Influence of oral contraceptives on coagulation tests in native blood and plasma

Routine coagulation laboratory tests, clotting times in native (not anticoagulated) whole blood, platelet-rich and platelet-poor plasma, and recalcification times in citrated whole blood, platelet-rich and platelet-poor plasma were performed in 14 healthy premenopausal women. Blood was taken before and after one or two cycles of low-dose oral contraceptives. After oral contraceptives a reduction in clotting time in native platelet-rich plasma and activated partial thromboplastin time were observed. Recalcification times in whole blood and platelet-rich plasma were shorter than clotting times in their native counterparts. The observed changes are compatible with a procoagulant effect seen soon after the start of oral contraceptive use. The absence of these changes in the recalcification times in citrate systems suggests a masking effect of citrate. The reduction in clotting times in native platelet-rich but not in platelet-poor plasma indicates that the hypercoagulability in oral contraceptives users is mainly related to platelets.

Bilateral breast tumours in acute lymphatic leukemia

We report on a patient with acute lymphatic leukemia, who developed bilateral mammary deposits.

[Morphologic changes in cervix smears by intrauterine pessary]

656 cervical smears and 74 endocervical biopsies were studied for morphological alterations associated with the presence of an intrauterine device. 12,085 cervical smears served as a control for inflammatory and metaplastic cellular changes. Slight to moderate cellular alterations were found in 202 (31%) out of 656 cases. Metaplastic and inflammatory lesions were identified in 26 (35%) out of 74 endocervical biopsies. We found no increased incidence of dysplastic lesions in women wearing an intrauterine device. Inflammatory and metaplastic cellular alterations have been seen more frequently in women with IUD than in the controls. The duration of time the IUD were in situ, did not have an effect on the cellular alterations. "Actinomyces-like" organisms were described in 38 (6%) out of 656 cases. The cytopathologist may be able to identify an "IUD-related" specimen in about one third of PAP-smears from women with an IUD, when he is aware that cervical smears from women having IUD may present with cellular alterations.

Placental hormones: II. Immunofluorescence studies of the localization of prolactin/placental lactogen- and human chorionic gonadotrophin-receptors in human and rat placenta

Human term placentae and rat placentae of gestation day 15 and 17 were examined for the localization of prolactin (PRL)/placental lactogen (PL) and human chorionic gonadotrophin (hCG) receptors by means of an immunofluorescence technique in order to determine possible target cells for PRL/PL and hCG and to obtain indirect evidence for the localization of steroid producing cells. In the human placenta, PRL/PL- and hCG-receptors were observed in the syncytiotrophoblast of the chorionic villi and in the giant cells of placental septa and cytotrophoblastic islands in the intervillous space. In the rat placenta, PRL/PL- and hCG-binding was localized mainly to the giant cells and vacuolated glycogen cells of the basal zone.

Placental hormones: I. Immunofluorescence studies of the localization of chorionic gonadotrophin, placental lactogen and prolactin in human and rat placenta and in the endometrium of pregnant rats

Chorionic gonadotrophin (CG), placental lactogen (PL) and prolactin (PRL) were localized in sections of human and rat placenta using the indirect immunofluorescence technique. Antisera were absorbed with homologous and unrelated antigens by affinity chromatography or complexed with their respective antigens. To exclude binding of IgG and immune complexes to Fc-receptor in chorionic tissue, thus leading to erroneous results, sections were preincubated with an excess of rat IgG. The results indicate that, in the human placenta, human CG (hCG) and human PL (hPL) can be identified in the syncytiotrophoblast. Using antibodies to hPRL fluorescence was found in giant cells within the cytotrophoblastic islands in the intervillous space and in cytotrophoblastic cells within placental septa. In the rat placenta rat PL (rPL) and rat PRL (rPRL) could be identified in the giant cells of the basal zone. Furthermore rPRL/rPL was localized in the endometrium and adjacent decidial cells of rat pregnancy. No staining of chorionic cells was detected using antibodies against hCG and bLH, which cross-reacted with rLH. These experiments provide further evidence that the rat placenta is unlikely to produce a CG/LH-like hormone.

Antiserum to LH reverses the abortifacient effect of Bromergocryptine treatment in early rat pregnancy

In vivo experiments showed that anti-bovine luteinizing hormone rabbit serum (a-LH) reversed the abortifacient effect of Bromergocryptine (BEC) on day 6 of pregnancy in 13 of 19 rats when injected 5-15 h after the initial BEC administration. Radioreceptor assay studies revealed that BEC treatment entailed an 85% drop of ovarian LH-receptor (LH-rec) concentration and a drastic decrease in progesterone serum levels. a-LH restored both the ovarian LH-rec content and progesterone serum levels in those rats that were found to have macroscopically intact implantations. A time course study of LH serum levels after BEC treatment showed a trend for BEC to stimulate LH secretion with a maximum 12-18 h after the initial BEC injection. These experiments indicate that (i) BEC terminates early rat pregnancy primarily by inducing a process of desensitization of ovarian LH-rec by blocking prolactin (PRL) secretion and possibly also by additionally stimulating LH secretion, which in the absence of endogenous PRL causes HL-rec and serum progesterone levels to drop; (ii) a-LH administration without simultaneous PRL substitution may rescue LH-rec of BEC treated rats from being desensitized as well as prevent fetuses from being resorbed. It is suggested that the contribution of PRL in the luteotropic complex is permissive for the luteotropic action of LH and/or for keeping the corpus luteum in a functional state rather than being luteotropic by itself.

Rat placental hormones: attempts for identification of rat chorionic gonadotrophin and rat placental lactogen by in vivo experiments

Rat placental extracts (rPE) were investigated in bioassays for their possible content of rat placental lactogen (rPL) and rat chorionic gonadotrophin (rCG). Luteotrophic and lactogenic activity of rPL was assessed by substitution of rats depleted of endogenous prolactin (Prl) by means of bromoergocryptine (BEC) in early pregnancy and the period of lactation, respectively. The abortifacient effect of a single dose of BEC on day 6 of pregnancy was abolished by rPE equivalent to 1 g rat placenta corresponding to 5 IU bovine Prl (NIH-P-B 2). Substitution was necessary until the evening of day 7 indicating that rPL does not take over the function of Prl before day 8. During lactation rPE reversed the lactation inhibiting effect of daily BEC treatment. In this assay rPL activity corresponded to 1.25–2.5 IU bPrl/g placenta.

In order to test for the possible existence of rCG the gonadotrophic activity of rPE was assessed in immature female mice. No gonadotrophic activity was found when rPE equivalent to 1 g rat placenta was administered, whereas equivalents of 3 mg human placenta and 12 mg rat pituitary entailed a dose-dependent response. In this system 0.12 IU human chorionic gonadotrophin (hCG), which served as standard, was the minimal dose (MD) resulting in increased uterine weight.

In addition rPE was tested in the immature female rat, where the limit of detection was found to be 0.5 IU hCG. Again no gonadotrophic activity was found in rPE. As the effects of rCG might have been restricted to its presumed target, the corpus luteum of pregnancy, rPE was also tested in pregnant rats depleted of endogenous luteinizing hormone (LH) by a single injection of anti-LH antibodies on day 10 of pregnancy. A MDof 0.5 IU hCG, which served as standard, prevented resorption of foetuses in all animals tested. rPE equivalent to 3.5 g rat placenta, rat pregnancy serum of day 18 and placental transplants could not substitute for endogenous LH.

In vivo studies on prolactin function in the female rat: divergent effects of treatment with bromergocryptine and antisera to rat prolactin

The effect of suppression of prolactin (PRL) serum levels on early pregnancy and lactation in the rat by means of either bromergocryptine (BEC) or rabbit antiserum to rat PRL has been examined. BEC terminated early pregnancy when given on any day from 1 to 6 and significantly impaired lactation performance when injected during the lactation period. Antibodies against rat PRI, however, showed no effect on either early pregnancy or lactation, although the sera of the treated rats contained free PRL antibodies as evidence for sufficient dosage of antiserum. This finding can be explained in two ways: either the antibodies are not able to neutralize the biological activity of the bound PRL, or the effect of BEC is not mediated by PRL-suppression alone but requires a second component not provided by the specific antiserum.

Effect of bromocryptine on 20 alpha-hydroxysteroiddehydrogenase regulation in the corpus luteum of the pregnant rat

Pregnant Sprague Dawley rats were passively immunized with antiserum to bovine luteinizing hormone (anti-LH) on day 10 of pregnancy, and treated with 1 mg/day or 1.5 mg/day of the prolactin (Prl) inhibitor bromocryptine (BEC) between days 10 to 12 or 9 to 12, respectively. On day 12 a laparotomy was performed to assess the state of pregnancy and to remove the ovaries for histochemical detection of 20 alpha-hydroxysteroiddehydrogenase (20 alpha-OHSD) in the corpora lutea of pregnancy. In a second experiment pregnant rats were treated with 1.5 mg BEC/day from days 17 to 22, checked for foetal state and ovariectomized on day 22 before giving birth. Treatment with BEC in effective doses did not interfere with anti-LH-induced termination of pregnancy and consequent reappearance of 20 alpha-OHSD activity on day 12, or with spontaneous recurrence of enzyme activity at the end of gestation. It is concluded that Prl has no direct and immediate role in 20 alpha-OHSD regulation, at least on day 12, although substitution by endogenous rat placental lactogen at the end of pregnancy cannot be excluded.

Characterization of antisera against bovine prolactin for in vivo studies on prolactin function in the rat

The IgG fraction of rabbit antisera to bovine prolactin (PRL), intended for in vivo studies on the role of PRL in the rat, was prepared and characterized in vitro and in vivo. The antibodies showed a strong reaction with bovine PRL in double diffusion, immunoelectrophoresis, radioimmunoassay and passive haemagglutination using bovine PRL-coated erythrocytes. In indirect immunofluorescence on paraffin sections of bovine pituitary glands the antibodies could be used for the detection of PRL-producing cells. Cross-reaction with rat PRL was observed in passive haemagglutination with rat PRL-coated erythrocytes and in indirect immunofluorescence on rat pituitary gland, but not in any of the other test systems. The ability of the antibodies to neutralize homologous, i.e. bovine, PRL was tested in lactating rats depleted of endogenous PRL by bromergocriptin treatment. The impaired lactation performance of such animals can be restored by substitution with bovine PRL. If the bovine PRL used for substitution was complexed with anti-bovine PRL-IgG, it lost its biological activity. On the other hand, injections of even high amounts of the antibodies into lactating rats failed to reveal any effect on lactation. It is concluded that either the antibodies do not cross-react with circulating rat PRL in contrast to pituitary PRL (preprolactin?) or that the cross-reacting antibody-populations(s) lack(s) the ability to neutralize the biological function of rat PRL.