Genetic evolution in colon cancer KM12 cells and metastatic derivates

So far, CRC cell lines have contributed to descriptions of 2 patterns of genetic instability, affecting either microsatellite sequences or chromosome number and structure. Often, these patterns are mutually exclusive; while near-diploid karyotypes usually appear with MSI and chromosomal stability, near-triploid or tetraploid cells display a high degree of CIN and are stable at the microsatellite level. In the present study, we describe the genomic instability pattern of KM12 CRC cells. KM12C and derived cell lines with different metastatic properties were analyzed by conventional cytogenetics, CGH and M-FISH. Results were compared to 5 cell lines usually used as model of MSI and CIN. Concordance between our results and previously published SKY data are also reviewed. Interestingly, the poorly metastatic KM12C cell line displayed a near-diploid karyotype with high levels of structural chromosome instability and microsatellite instability. The highly metastatic KM12SM and KM12L4A cell lines showed polyploid karyotypes and maintained CIN and MSI. A comparison between karyotypes of poorly and highly metastatic KM12 cell lines allowed us to delineate a cytogenetic evolution pathway. Our results clearly demonstrated that endoreduplication was the origin of the polyploid dosages in the highly metastatic forms following the monosomic model postulated for CRC. Therefore, we demonstrate that KM12C cells and their metastatic derivates, KM12SM and KM12L4A, are a useful model of chromosomal evolution where MSI may coexist with CIN.

Diversity and species composition of sand flies (Diptera: Psychodidae) in a Venezuelan urban focus of cutaneous leishmaniasis

The present study examined the spatial and temporal abundance and diversity of phlebotomine sand flies in an area of Venezuela that is an ancient focus of leishmaniasis. The study was conducted in 6 stations in urban localities in Trujillo City, located in northwestern Venezuela (9 degrees 22' 24" N, 70 degrees 26' 08" W), which is located in a mountain range in the Andean ecoregion (altitude = 600-1,010 m). During 1995-99, entomological surveys were conducted after and before the rainy season. Shannon light traps were operated from 1800 to 2000 h in peridomestic site trap locations. Twelve species were captured, and Lutzomyia youngi, L. ovallesi, L. scorzai, L. gomezi, L. lichyi, and L. shannoni occurred at all localities in each year. The abundance of these species showed low variation over time but high variation between localities. The Sørensen similarity index, used to compare diversity between years within each locality, ranged from 0.60 at Carmona to 0.84 at La Hacienda. Sand fly communities exhibited annual variation in species richness and diversity. Variations were affected more by changes in species abundance than by changes in species composition. Lutzomyia ovallesi, L. lichyi, and L. scorzai had the highest coefficient of variation between years (63, 38, and 23%, respectively).

Neonatal spinal muscular atrophy with multiple contractures, bone fractures, respiratory insufficiency and 5q13 deletion

We present the case of a floppy neonate with marked and generalized weakness, respiratory insufficiency and fetal akinesia deformation sequence. The infant showed multiple joint contractures, two bone fractures and needed mechanical ventilation from birth to death at 16 days of age. Electrophysiological assessment showed electrically unexcitable motor and sensory nerves. Muscle biopsy showed diffuse atrophy of type I and type II fibers. Necropsy confirmed the diagnosis of infantile spinal muscular atrophy (SMA) with severe loss of motor neurons in anterior horns and motor nuclei of brainstem. There were also neuronal loss, gliosis, chromatolysis, ballooned cells, empty cell beds and neuronophagia figures in other brainstem and brain nuclei. Genetic analysis of the patient revealed homozygous deletions of survival motor neuron gene 1 (SMN1) and a single copy of SMN2 in region 5q13. This case confirms that the loss of spinal motor neurons underlies the muscular atrophy in severe cases of 5q SMA. This case also shows that the presence of multiple joint contractures, bone fractures and respiratory insufficiency in SMA in the neonatal period does not necessarily exclude the occurrence of classical deletions in the SMA 5q13 region. Rather, these atypical clinical findings show the extreme severity and prenatal onset of the disease in these SMA cases, which may be related with the occurrence of a single copy of SMN2 gene. More reports of clinically, pathologically and genetically well-documented cases are essential to define the different types of this disease.

Expression of ghrelin and its functional receptor, the type 1a growth hormone secretagogue receptor, in normal human testis and testicular tumors

Ghrelin, the endogenous ligand for the GH secretagogue receptor (GHS-R), has been primarily linked to the central neuroendocrine regulation of GH secretion and food intake, although additional peripheral actions of ghrelin have also been reported. In this context, the expression of ghrelin and its cognate receptor has been recently demonstrated in rat testis, suggesting a role for this molecule in the direct control of male gonadal function. However, whether this signaling system is present in human testis remains largely unexplored. In this study we report the expression and cellular location of ghrelin and its functional receptor, the type 1a GHS-R, in adult human testis. In addition, evaluation of ghrelin and GHS-R1a immunoreactivity in testicular tumors and dysgenetic tissue is presented. The expression of the mRNAs encoding ghrelin and GHS-R1a was demonstrated in human testis specimens by RT-PCR, followed by direct sequencing. In normal testis, ghrelin immunostaining was demonstrated in interstitial Leydig cells and, at lower intensity, in Sertoli cells within the seminiferous tubules. In contrast, ghrelin was not detected in germ cells at any stage of spermatogenesis. The cognate ghrelin receptor showed a wider pattern of cellular distribution, with detectable GHS-R1a protein in germ cells, mainly in pachytene spermatocytes, as well as in somatic Sertoli and Leydig cells. Ghrelin immunoreactivity was absent in poorly differentiated Leydig cell tumor, which retained the expression of GHS-R1a peptide. In contrast, highly differentiated Leydig cell tumors expressed both the ligand and the receptor. The expression of ghrelin and GHS-R1a was also detected in dysgenetic Sertoli cell-only seminiferous tubules, whereas germ cell tumors (seminoma and embryonal carcinoma) were negative for ghrelin and were weakly positive for GHS-R1a. In conclusion, our results demonstrate that ghrelin and the type 1a GHS-R are expressed in adult human testis and testicular tumors. Overall, the expression of ghrelin and its functional receptor in human and rat testis, with roughly similar patterns of cellular distribution, is highly suggestive of a conserved role for this newly discovered molecule in the regulation of mammalian testicular function.

A reservable antiadhesion barrier gel reduces the perineural adhesions in rats after anastomosis

AIM

The objective of this experimental study was to assess the effectiveness of ADCON T/N in reducing perinerural adhesions when applied around a previously exposed and then anastomosed peripheral nerve in a rat model.

METHODS

Sixteen adult 8-month-old male Wistar rats were used for this study. After the ulnar nerve was exposed bilaterally, the nerves were sectioned and anastomosised. ADCON T/N gel was applied around the nerve suture on 1 limb, while the contralateral limb was left untreated (sham operated control). Treatments were administered according to a randomised schedule revealed to the operator only after the perineural adhesions observed during the 2nd operation had been dissected and complete haemostasis achieved. In other group of 4 Wistar rats, the ulnar nerve was sectioned and the 2 ends connected with a 5 mm silastic tube that was placed bilaterally in each rat but on only one side, chosen randomly, was the nerve treated with ADCON TN and placed within the tube on that side.

RESULTS

Three months after the 1st operation, the same nerves were exposed again in all animals under general anesthesia before microsurgical external neurolysis. The neurolysis sites in 16 rats were evaluated by blinded surgical dissection immediately before death. Parameters examined included: quality of wound healing, possible adverse effects, presence of residual implant material and perineural adhesions. Perineural adhesions around the ulnar nerve were visually scored using a 4-point qualitative scale (Mean 2.81 without gel, and 1.18 with ADCON T/N. p=0.017). There was no evidence of persistence of residual implant material in the ADCON T/N treated sites. No significant difference between the average density of myelinated axons was observed in either group. All ADCON T/N treated rats (4 animals) showed axonal growth through the tube connecting the 2 ends.

CONCLUSION

ADCON-TN decreased fibrosis around the nerve anastomosis sites and did not impede growth between the severed ends of the axons. If reoperation becomes necessary, a reduction of fibrosis would facilitate access to the old site and decrease the risk of nerve lesions.

Antibacterial, antiprotozoal and antioxidant activity of five plants used in Izabal for infectious diseases

Methanol and aqueous extracts from fi ve plant species, used in traditional medicine in Guatemala for the treatment of microbial infections, were tested in vitro for their ability to scavenge DPPH, OH(.) and O(2) (-) radicals and to inhibit lipoperoxidation (LPO) in order to establish a relationship between their antioxidant activities and their effects against infectious agents. Acalypha guatemalensis, Ocimum micranthum and Smilax spinosa possessed a significant activity against both the three free radicals assayed and LPO; Guazuma ulmifolia showed effects against DPPH and OH(.). Piper auritum showed no activity. These extracts were also evaluated for antibacterial and antiprotozoal activities. A. guatemalensis showed activity against Pseudomonas aeruginosa; S. spinosa was active against Salmonella typhi, and A. guatemalensis, and S. spinosa against Trypanosoma cruzi or Leishmania spp.

Immunolocalization of ghrelin and its functional receptor, the type 1a growth hormone secretagogue receptor, in the cyclic human ovary

Ghrelin is a novel 28-amino acid peptide identified as the endogenous ligand for the GH secretagogue receptor (GHS-R). Besides its hallmark central neuroendocrine effects in the control of GH secretion and food intake, an unexpected reproductive facet of ghrelin has recently emerged because expression of this molecule and its cognate receptor has been demonstrated in rat testis. However, whether this signaling system is present in human gonads remains to be evaluated. In this study, we have assessed the presence and cellular location of ghrelin and its functional receptor, namely the type 1a GHS-R, in the cyclic human ovary by means of immunohistochemistry using specific polyclonal antibodies. Strong ghrelin immunostaining was demonstrated in ovarian hilus interstitial cells. In contrast, ghrelin signal was not detected in ovarian follicles at any developmental stage, nor was it present in newly formed corpora lutea (CL) at very early development. However, specific ghrelin immunoreactivity was clearly observed in young and mature CL, whereas expression of the peptide disappeared in regressing luteal tissue. Concerning the cognate receptor, ovarian expression of GHS-R1a protein showed a wider pattern of tissue distribution, with detectable specific signal in oocytes as well as somatic follicular cells; luteal cells from young, mature, old, and regressing CL; and interstitial hilus cells. Of particular note, follicular GHS-R1a peptide expression paralleled follicle development with stronger immunostaining in granulosa and theca layers of healthy antral follicles. In conclusion, our results are the first to demonstrate that ghrelin and its functional type 1a receptor are expressed in the cyclic human ovary with distinct patterns of cellular location. The presence of both components (ligand and receptor) of the ghrelin signaling system within the human ovary opens up the possibility of a potential regulatory role of this novel molecule in ovarian function under physiological and pathophysiological conditions.

Growth-inhibiting effects of intralesional docetaxel and paclitaxel on an experimental model of malignant neuroectodermal tumor

Taxoids are effective agents against a wide variety of tumors, but their effectiveness on neuroectodermal tumors is not well-known. For this reason we have carried out an experimental study on the effect of intratumoral administration of docetaxel (DC) and paclitaxel (PC) on tumor growth, using a murine model of malignant neuroectodermal tumor. The results showed a delay in tumor growth in animals treated with PC compared with controls (dose of 5 mg/kg, three times per week every other day, forming a cycle; three cycles were completed with a break of a week between each cycle). The total dose administered to each animal was 45 mg/kg. When DC was administered, the results showed distinct tumor growth inhibition and tumor regression in 80% of animals (intratumoral administration at a dose of 5 mg/kg, three times per week every other day forming a cycle; three cycles were completed with a break of a week between each cycle). The total dose administered to each animal was 20 mg/kg. These results suggest the utility of taxoids, mainly DC, by intralesional administration, on malignant tumors of the nervous system.

Prognostic significance of tumor-enhancement and angiogenesis in oligodendroglioma

OBJECTIVE

To study the prognostic significance of angiogenesis and enhancement on contrast-enhanced computerized tomography (CT) in oligodendrogliomas.

MATERIAL AND METHODS

CD34 immunostaining was employed in samples of 26 low-grade oligodendrogliomas from patients treated by extensive resection and radiotherapy to determine the tumor angiogenesis index (TAI), calculated by measuring the immunostained endothelial surface area, in microm(2), per 1000 tumor cells. Preoperative CT scan was evaluated in each case, and the absence or presence of tumor enhancement after contrast administration was recorded. Survival was analyzed and statistically compared for subgroups of patients with lesions in which the TAI was less than or greater than 15, and for subgroups of patients having tumors showing presence or absence of enhancement on contrast-enhanced CT.

RESULTS

Survival of patients with tumors showing a TAI of less than 15 was 100% and 71% at 5 and 10 years, respectively, vs a survival of 50% and 0% for patients showing a TAI of more than 15 (P < 0.05). The 14 patients whose tumors showed enhancement in preoperative contrast-enhanced CT had 5- and 10-year survival rates of 57% and 14%, respectively, vs 100% and 83% for the 12 patients whose tumors presented no enhancement (P < 0.05). Moreover, 79% of the tumors showing contrast enhancement had a TAI greater than 15, while 92% of those exhibiting no enhancement had a TAI of less than 15.

CONCLUSION

These findings indicate a relationship between enhancement on preoperative CT scan and endothelial surface area in oligodendrogliomas, and suggest that this enhancement and the TAI may be considered angiogenesis-related factors with similar prognostic significance in terms of survival.

Antitumor effect of TNP-470 is not associated to decrease of angiogenesis in an experimental malignant neuroectodermic tumor

The hypothesis that tumor growth depends on neovascularization has been broadly used in oncology research. TNP-470 is a fumagillin synthetic analog that is isolated from Aspergillus fumigatus, and experimental studies suggested that it shows antitumor effect mediated by its strong antiangiogenic effect. Because limited experience exists about the antitumoral effect of TNP-470 in cerebral tumors, we have carried out a study in order to evaluate the effect of TNP-470 on tumor growth and the vascular area in an experimental malignant neuroectodermic tumor growing in the subcutaneous space of immunocompetent Wistar rats. Our results showed a significant tumor growth inhibition in animals treated with TNP-470 when compared to those in the control group (intratumoral injections were administered in 30 mg/kg dose, three times a week on alternate days during four consecutive weeks). Since the quantitative analysis of tumor vascular parameters--number of microvessels and total intratumor vascular area--in the experimental groups did not show significant statistical differences, we conclude that TNP-470 has a significant antitumor effect on our neuroectodermic tumor, but this effect is mediated by other antineoplastic mechanisms that are independent of its previously described angiostatic capacity.

Vulval squamous cell carcinoma arising in localized Darier's disease

Darier's disease (keratosis follicularis) is a rare vulval lesion and it has been associated with squamous and non-squamous tumors from different origin. A vulval squamous cell carcinoma (SCC) arising in a localized Darier's disease is presented. To our knowledge, this is the first case to report the association of a vulval SCC and a localized Darier's disease. The possibility of delaying or overlooking the diagnosis of a vulval carcinoma is also illustrated. It is suggested to resect the whole lesion of Darier's disease localized to the vulva or take multiple biopsies.

Morphological evidence for uncontrolled proteolytic activity during the ovulatory process in indomethacin-treated rats

The ovulatory process in cyclic rats was studied after prostanoid synthesis was blocked using indomethacin. Animals were injected at 12:00 h in pro-oestrus with 1.0 mg indomethacin or vehicle (olive oil) and killed at 18:30 h in pro-oestrus, at 02:00, 09:00 and 19:00 h in oestrus and at 09:00 h in metoestrus. Additional rats injected with 0.5 or 4.0 mg indomethacin were killed at 09:00 h in oestrus. No differences in either morphology or serum LH concentrations were found between vehicle or indomethacin-treated rats at 18:30 h in pro-oestrus. However, from 02:00 h in oestrus onward, the process of follicle rupture was altered considerably in indomethacin-treated rats, irrespective of the dose. Early vascular changes, observed in control rats at the apex of the follicle, were absent in indomethacin-treated rats. In some follicles, disruption of the theca layers, invasion of the perifollicular tissue by granulosa cells and follicular fluid, and release of the oocyte to the ovarian interstitium were observed at 02:00 h in oestrus. A small number of follicles ruptured at the ovarian surface. Furthermore, invasion of interstitial tissue, rupture of blood vessel walls, production of emboli of granulosa cells and follicular fluid, and inflammatory reactions were observed in oestrus and metoestrus. The results of the present study demonstrate uncontrolled proteolytic activity, and indicate that abnormal follicle rupture (but not inhibition of follicle rupture) is responsible for ovulation failure in indomethacin-treated rats.

[Time course of the myocardial infarction in the rabbit]

The histopathologic evolution of myocardial infarct and of areas distant from infarct in rabbit hearts was studied. The left coronary artery of 55 rabbits was ligated, and rabbits were sacrificed at 2, 4, 6, 8, 12, 14, 16, 18, 26, 35 and 56 days post-ligature (n = 5 per group). Two rabbits were used as control and two were sham operated. The hearts were excised, cut in slices and stained with hematoxilin-eosin, Masson's trichrome and picrosirius red. Histological evaluation was semi-quantitative (scale: 0 to +++). At day 2, presence of neutrophils was +++, disappearing completely at day 6. Fibroblast proliferation increased from day 4 to day 14 post-occlusion. Coagulation necrosis in medial myocardium during the first week was +++. Subendocardic myocytolysis was evident from day 2 up to day 56 post-infarction. During the second week, proliferation of lymphocytes and macrophages (+++), granulation tissue formation (+++), and incipient traces of fibrosis that peaked at day 35 were observed. Cicatrization was complete at day 56 (+++). In areas far from infarction (right ventricle and septum), proliferation of fibroblasts was observed at day 2, and perivascular, interstitial and endocardic fibrosis at day 16. In conclusion, myocardial infarction in rabbits, unlike myocardial infarction in human beings, is characterized by early presence of fibroblasts and subendocardic fibrosis, and quick increase and precocious disappearance of neutrophils. An interesting finding was the early proliferation of fibroblasts in normal areas far from infarct.

Antitumoral effect of irinotecan (CPT-11) on an experimental model of malignant neuroectodermal tumor

Irinotecan (CPT-11) is a topoisomerase I inhibitor with antitumor activity on a wide variety of neoplasms in several preclinical studies, but it showed poor efficacy in patients with nervous system tumors. We have carried out an experimental study in order to evaluate the effect of CPT-11 on the growth of a subcutaneously implanted malignant neuroectodermal tumor, after administration by different routes. The results showed that CPT-11 administration by intraperitoneal injections (at dose 10 mg/kg, 5 days per week, for 2 weeks, followed by 7-days rest period--one course--to a total of two courses) had no significant antitumor effect. Nevertheless, continuous infusion by intraperitoneal osmotic minipump over 28 days (at an infusion rate of 4.4 microg/h) showed a significant delay in tumor growth in 4 weeks of the implantation. The best antitumor effects were observed after CPT-11 intratumoral administration (at dose of 5 mg/kg, 5 days per week, for 2 weeks, followed by 7-days rest period, to a total of three courses) reaching tumor regression in the treated animals. These results suggest the utility of CPT-11, by means of intralesional administration, on malignant tumors of the nervous system.

[The activation of A1 adenosine receptors attenuates myocardial stunning in the rabbit]

Hearts exposed to a prolonged period of ischemia (> or = 30 minutes) present smaller infarct size when reperfused in the presence of adenosine. However, when the period of ischemia is shorter, the infarct areas are not very significant, but a postischemic ventricular dysfunction persists. The objective of this study was to determine the effect of adenosine, (administered only during reperfusion) on systolic and diastolic alterations present in postischemic ventricular dysfunction, as well as to determine whether A1 receptors participate in this effect. Isolated isovolumic rabbit hearts were subjected to 15 minutes of global ischemia followed by 30 minutes of reperfusion. Before ischemia and during reperfusion ventricular function was evaluated. In the control group, the left ventricular developed pressure (LVDP) reached 56 +/- 2% of recovery at 30 minutes of reperfusion. The administration of adenosine improved LVDP 75 +/- 3% (P < 0.05 vs. control). However, when adenosine was given in presence of an A1 receptor selective antagonist (DPCPX), LVDP reached 50 +/- 2% (P < 0.05 vs. control). In the control group, left ventricular end diastolic pressure (LVEDP) (diastolic stiffness), increased 293 +/- 4%, at 30 minutes of reperfusion. Only a 15 +/- 8% (P < 0.05 vs. control) increase in LVEDP was observed with adenosine. Reperfusion with adenosine plus DPCPX did not attenuate an increase of 493 +/- 9% (P < 0.05 vs. control) in diastolic stiffness. Adenosine administered from the beginning of reperfusion attenuated both systolic alterations and diastolic stiffness in postischemic dysfunction. This effect was abolished by DPCPX, suggesting an important role for the A1 receptors in adenosine protection.

Interactions and nuclear import of the N and P proteins of sonchus yellow net virus, a plant nucleorhabdovirus

We have characterized the interaction and nuclear localization of the nucleocapsid (N) protein and phosphoprotein (P) of sonchus yellow net nucleorhabdovirus. Expression studies with plant and yeast cells revealed that both N and P are capable of independent nuclear import. Site-specific mutagenesis and deletion analyses demonstrated that N contains a carboxy-terminal bipartite nuclear localization signal (NLS) located between amino acids 465 and 481 and that P contains a karyophillic region between amino acids 40 and 124. The N NLS was fully capable of functioning outside of the context of the N protein and was able to direct the nuclear import of a synthetic protein fusion consisting of green fluorescent protein fused to glutathione S-transferase (GST). Expression and mapping studies suggested that the karyophillic domain in P is located within the N-binding domain. Coexpression of N and P drastically affected their localization patterns relative to those of individually expressed proteins and resulted in a shift of both proteins to a subnuclear region. Yeast two-hybrid and GST pulldown experiments verified the N-P and P-P interactions, and deletion analyses have identified the N and P interacting domains. N NLS mutants were not transported to the nucleus by import-competent P, presumably because N binding masks the P NLS. Taken together, our results support a model for independent entry of N and P into the nucleus followed by associations that mediate subnuclear localization.

Characterization of antibiotic-resistant bacteria in rendered animal products

Antibiotics are used in food animal production to treat diseases and also to improve performance. Antibiotics are not used on all farms, and antibiotic resistance is occasionally found on farms that do not use antibiotics. Rendered animal protein products are often included in poultry feeds and could potentially serve as a source of antibiotic-resistant bacteria. One hundred sixty-five rendered animal protein products from cattle, poultry, and fish were aseptically collected from poultry feed mills. Fifty-five percent of the poultry meal samples had detectable levels of gram-negative bacteria ranging from 40 to 10,440 colony-forming units/g of sample. Poultry meal and meat and bone meal had the greatest number of samples with bacteria resistant to five or more antibiotics. A high percentage of feed samples (85%) contained bacteria resistant to amoxicillin, ampicillin, clavulanic acid, or cephalothin, whereas few samples contained bacteria resistant to ciprofloxacin, kanamycin, or trimethoprim/sulfamethoxazole. Acinetobacter calcoaceticus, Citrobacter freundii, and Enterobacter cloacae were the most commonly isolated antibiotic-resistant bacteria. Isolation for Salmonella was also performed, with 14% of the meat and bone meal samples containing Salmonella sp. Only one of the meat and bone meal isolates, Salmonella livingstone, was resistant to five or more antibiotics. Many of the antibiotic-resistant bacteria contained integrons, genetic elements that mediate multiple drug resistance.

Cyclic changes in the responsiveness of regressing corpora lutea to the luteolytic effects of prolactin in rats

In cyclic rats, apoptosis of luteal cells during structural luteolysis occurs cyclically at the transition from pro-oestrus to oestrus in response to the preovulatory prolactin surge. This finding indicates that cyclic changes in apoptosis during luteolysis are dependent on prolactin surge cyclicity. In this study, the effects of prolactin on structural luteolysis were studied under different experimental conditions in relation to the phase of the oestrous cycle. In rats treated with prolactin at metoestrus and dioestrus, apoptosis did not occur in regressing corpora lutea, whereas in rats treated with prolactin on the morning of pro-oestrus, a 12.3-fold and 3.4-fold increase were observed in the number of apoptotic cells in regressing corpora lutea of the current and previous oestrous cycles, respectively. However, when the preovulatory prolactin surge and hence the subsequent apoptotic burst were blocked, prolactin treatment at the dioestrus phase induced a 13-fold increase in the number of apoptotic cells and significant changes in the volume of the corpus luteum (38% decrease) and the number of steroidogenic cells per corpus luteum (70% decrease). The results of this study indicate that the responsiveness of the regressing corpus luteum to the pro-apoptotic effects of prolactin are dependent on the phase of the oestrous cycle and on the presence or absence of an apoptotic burst in response to the preovulatory prolactin surge on the evening of pro-oestrus. Steroidogenic cells surviving to the apoptotic burst during the transition from pro-oestrus to oestrus became refractory to the lytic effect of prolactin. Furthermore, these cells also responded to the luteotrophic effects of prolactin, reaching full morphological luteinization, as indicated by the rescue of regressing cyclic corpora lutea during pregnancy.