Long-term outcomes of SARS-CoV-2 variants and other respiratory infections: evidence from the Virus Watch prospective cohort in England.

This study compared the likelihood of long-term sequelae following infection with SARS-CoV-2 variants, other acute respiratory infections (ARIs) and non-infected individuals. Participants (n=5,630) were drawn from Virus Watch, a prospective community cohort investigating SARS-CoV-2 epidemiology in England. Using logistic regression, we compared predicted probabilities of developing long-term symptoms (>2 months) during different variant dominance periods according to infection status (SARS-CoV-2, other ARI, or no infection), adjusting for confounding by demographic and clinical factors and vaccination status. SARS-CoV-2 infection during early variant periods up to Omicron BA.1 was associated with greater probability of long-term sequalae (adjusted predicted probability (PP) range 0.27, 95% CI = 0.22-0.33 to 0.34, 95% CI = 0.25-0.43) compared with later Omicron sub-variants (PP range 0.11, 95% CI 0.08-0.15 to 0.14, 95% CI 0.10-0.18). While differences between SARS-CoV-2 and other ARIs (PP range 0.08, 95% CI 0.04-0.11 to 0.23, 95% CI 0.18-0.28) varied by period, all post-infection estimates substantially exceeded those for non-infected participants (PP range 0.01, 95% CI 0.00, 0.02 to 0.03, 95% CI 0.01-0.06). Variant was an important predictor of SARS-CoV-2 post-infection sequalae, with recent Omicron sub-variants demonstrating similar probabilities to other contemporaneous ARIs. Further aetiological investigation including between-pathogen comparison is recommended.

Behaviour of simple thymic cysts over time; is surveillance required?

AIM: Anterior mediastinal lesions can be a source of uncertainty on imaging, and thymic cysts present a unique diagnostic challenge. Differentiation of non-simple fluid-containing benign simple thymic cysts from small thymic neoplasms is challenging with computed tomography (CT) alone. Additionally, the malignant potential of simple thymic cysts is unclear and guidelines for imaging surveillance are not established. MATERIALS AND METHODS: All imaging studies containing the phrase "thymic cyst" were identified at our institution between October 2012 and October 2022. Studies were excluded if the main radiological diagnosis was anything other than a thymic cyst. This yielded 107 individual patient records, of which 11 did not meet inclusion criteria, leaving 96 unique patients. RESULTS: While most cysts evaluated remained stable throughout the period of surveillance (53%; n=51), some increased in size (13%), some decreased in size (6%), and some fluctuated (5%). Some cysts changed in internal attenuation/signal characteristics in keeping with interval haemorrhage (6%). 34% of cysts (n=31) demonstrate internal average attenuation values of more than 20HU. Of the entire cohort of patients studied over 10 years, none developed malignancy within the period of surveillance. CONCLUSION: Unilocular thymic cysts are most often discovered incidentally but their imaging characteristics can be difficult to interpret on CT, as they are commonly hyperdense and may change in size and internal content. Once simple thymic cysts are adequately characterised with magnetic resonance imaging (MRI) then extended radiological surveillance may not be required.

Chest CT screening for COVID-19 in elective and emergency surgical patients: experience from a UK tertiary centre.

AIM: To determine the incidence of possible COVID-19-related lung changes on preoperative screening computed tomography (CT) for COVID-19 and how their findings influenced decision-making. To also to determine whether the patients were managed as COVID-19 patients after their imaging findings, and the proportion who had SARS-CoV2 reverse transcriptionpolymerase chain reaction (RT-PCR) testing. MATERIALS AND METHODS: A retrospective study was undertaken of consecutive patients having imaging prior to urgent elective surgery (n=156) or acute abdominal imaging (n=283). Lung findings were categorised according to the British Society of Thoracic Imaging (BSTI) guidelines. RT-PCR testing, management, and outcomes were determined from the electronic patient records. RESULTS: 3% (13/439) of CT examinations demonstrated findings of classic/probable COVID-19 pneumonia, whilst 4% (19/439) had findings indeterminate for COVID-19. Of the total cohort, 1.6% (7/439) subsequently had confirmed RT-PCR-positive COVID-19. Importantly, all the patients with a normal chest or alternative diagnoses on CT who had PCR testing within the next 7 days, had a negative RT-PCR (92/407). There was a change in surgical outcome in 6% (10/156) of the elective surgical cohort with no change to surgical management was demonstrated in the acute abdominal emergency cohort requiring surgery (2/283). CONCLUSION: There was a 7% (32/439) incidence of potential COVID-19-related lung changes in patients having preoperative CT. Although this altered surgical management in the elective surgical cohort, no change to surgical management was demonstrated in the acute abdominal emergency cohort requiring surgery.

Prospective study on a novel treatment for leaking cystic bleb: Efficacy and safety of collagen crosslinking.

IMPORTANCE: Management of cystic bleb leak is difficult. It would be essential to look for a method to strengthen the original pathological conjunctiva and reverse bleb leak. BACKGROUND: To evaluate the long-term efficacy and safety of collagen crosslinking in patients with leaking cystic bleb. DESIGN: Prospective interventional case series at a university-based hospital. PARTICIPANTS: Twelve eyes in 12 subjects with late-onset bleb leak from cystic bleb, without indications for prompt surgical interventions were included. METHODS: The subjects underwent crosslinking with 0.1% riboflavin application to bleb surface, followed by ultraviolet irradiation for 30 minutes. The subjects were followed up at baseline and at 1 week, 1 month, 3 months, 6 months post-treatment and then every 6 months afterwards. MAIN OUTCOME MEASURES: Interval from treatment to cessation of bleb leak, recurrence rate of bleb leak and side effects of treatment. RESULTS: The mean follow-up after crosslinking was 29.33 ± 12.45 months. Bleb leak subsided in 11 (92%) of 12 patients after a single session of crosslinking, after 1 to 8 weeks (median 3 weeks). Time to leak cessation was significantly correlated with the number of prior glaucoma interventions (R = .71, P = .014). Bleb wall at 3 months was significantly thicker than at baseline (0.70 ± 0.67 vs 0.81 ± 0.62 mm, P = .008). None of the patients experienced any complications. CONCLUSIONS AND RELEVANCE: Crosslinking achieves resolution of cystic bleb leak which lasts for at least 12 months, without the need of subsequent surgical interventions. Crosslinking is a simple, non-invasive treatment for bleb leak. It aims to restore the integrity of conjunctiva.

Peripheral nerves are pathologically small in cerebellar ataxia neuropathy vestibular areflexia syndrome: a controlled ultrasound study.

BACKGROUND AND PURPOSE: Sensory neuronopathy is a cardinal feature of cerebellar ataxia neuropathy vestibular areflexia syndrome (CANVAS). Having observed that two patients with CANVAS had small median and ulnar nerves on ultrasound, we set out to examine this finding systematically in a cohort of patients with CANVAS, and compare them with both healthy controls and a cohort of patients with axonal neuropathy. We have previously reported preliminary findings in seven of these patients with CANVAS and seven healthy controls. METHODS: We compared the ultrasound cross-sectional area of median, ulnar, sural and tibial nerves of 14 patients with CANVAS with 14 healthy controls and 14 age- and gender-matched patients with acquired primarily axonal neuropathy. We also compared the individual nerve cross-sectional areas of patients with CANVAS and neuropathy with the reference values of our laboratory control population. RESULTS: The nerve cross-sectional area of patients with CANVAS was smaller than that of both the healthy controls and the neuropathy controls, with highly significant differences at most sites (P < 0.001). Conversely, the nerve cross-sectional areas in the upper limb were larger in neuropathy controls than healthy controls (P < 0.05). On individual analysis, the ultrasound abnormality was sufficiently characteristic to be detected in all but one patient with CANVAS. DISCUSSION: Small nerves in CANVAS probably reflect nerve thinning from loss of axons due to ganglion cell loss. This is distinct from the ultrasound findings in axonal neuropathy, in which nerve size was either normal or enlarged. Our findings indicate a diagnostic role for ultrasound in CANVAS sensory neuronopathy and in differentiating neuronopathy from neuropathy.

Suspected iatrogenic ureteric injury: an approach to diagnostic imaging.

Iatrogenic ureteric injury (IUI) is the leading cause of ureteric trauma and a complication of major abdominal and pelvic surgery. IUI carries significant morbidity and mortality, which can be further compounded by delayed diagnosis due to its non-specific clinical presentation. We review ureteric anatomy, types of IUI, and imaging strategies available for diagnosis. We propose an imaging protocol for prompt diagnosis and follow-up.

Hijacking of N-fixing legume albumin-1 genes enables the cyclization and stabilization of defense peptides.

The legume albumin-1 gene family, arising after nodulation, encodes linear a- and b-chain peptides for nutrient storage and defense. Intriguingly, in one prominent legume, Clitoria ternatea, the b-chains are replaced by domains producing ultra-stable cyclic peptides called cyclotides. The mechanism of this gene hijacking is until now unknown. Cyclotides require recruitment of ligase-type asparaginyl endopeptidases (AEPs) for maturation (cyclization), necessitating co-evolution of two gene families. Here we compare a chromosome-level C. ternatea genome with grain legumes to reveal an 8 to 40-fold expansion of the albumin-1 gene family, enabling the additional loci to undergo diversification. Iterative rounds of albumin-1 duplication and diversification create four albumin-1 enriched genomic islands encoding cyclotides, where they are physically grouped by similar pI and net charge values. We identify an ancestral hydrolytic AEP that exhibits neofunctionalization and multiple duplication events to yield two ligase-type AEPs. We propose cyclotides arise by convergence in C. ternatea where their presence enhances defense from biotic attack, thus increasing fitness compared to lineages with linear b-chains and ultimately driving the replacement of b-chains with cyclotides.

Bovine ephemeral fever virus uses a clathrin-mediated and dynamin 2-dependent endocytosis pathway that requires Rab5 and Rab7 as well as microtubules.

The specific cell pathways involved in bovine ephemeral fever virus (BEFV) cell entry have not been determined. In this work, colocalization of the M protein of BEFV with clathrin or dynamin 2 was observed under a fluorescence microscope. To better understand BEFV entry, we carried out internalization studies with a fluorescently labeled BEFV by using a lipophilic dye, 3,30-dilinoleyloxacarbocyanine perchlorate (DiO), further suggesting that BEFV uses a clathrin-mediated endocytosis pathway. Our results suggest that clathrin-mediated and dynamin 2-dependent endocytosis is an important avenue of BEFV entry. Suppression of Rab5 or Rab7a through the use of a Rab5 dominant negative mutant and Rab7a short hairpin RNA (shRNA) demonstrated that BEFV requires both early and late endosomes for endocytosis and subsequent infection in MDBK and Vero cells. Treatment of BEFV-infected cells with nocodazole significantly decreased the M protein synthesis and viral yield, indicating that microtubules play an important role in BEFV productive infection, likely by mediating trafficking of BEFV-containing endosomes. Furthermore, BEFV infection was strongly blocked by different inhibitors of endosomal acidification, suggesting that virus enters host cells by clathrin-mediated and dynamin 2-dependent endocytosis in a pH-dependent manner.

The N-terminal ß-sheet of the hyperthermophilic endoglucanase from Pyrococcus horikoshii is critical for thermostability.

The ß-1,4-endoglucanase (EC 3.2.1.4) from the hyperthermophilic archaeon Pyrococcus horikoshii (EGPh) has strong hydrolyzing activity toward crystalline cellulose. When EGPh is used in combination with ß-glucosidase (EC 3.2.1.21), cellulose is completely hydrolyzed to glucose at high temperature, suggesting great potential for EGPh in bioethanol industrial applications. The crystal structure of EGPh shows a triosephosphate isomerase (TIM) (ß/α)(8)-barrel fold with an N-terminal antiparallel ß-sheet at the opposite side of the active site and a very short C-terminal sequence outside of the barrel structure. We describe here the function of the peripheral sequences outside of the TIM barrel core structure. Sequential deletions were performed from both N and C termini. The activity, thermostability, and pH stability of the expressed mutants were assessed and compared to the wild-type EGPh enzyme. Our results demonstrate that the TIM barrel core is essential for enzyme activity and that the N-terminal ß-sheet is critical for enzyme thermostability. Bioinformatics analyses identified potential key residues which may contribute to enzyme hyperthermostability.

Age-specific progression of nigrostriatal dysfunction in Parkinson's disease.

OBJECTIVE: To investigate in vivo the impact of age on nigrostriatal dopamine dysfunction in Parkinson's disease (PD). METHODS: PD patients (n = 78) and healthy control subjects (n = 35) underwent longitudinal positron emission tomography assessments using 3 presynaptic dopamine markers: (1) [¹¹C](±)dihydrotetrabenazine (DTBZ), to estimate the density of the vesicular monoamine transporter type 2; (2) [¹¹C]d-threo-methylphenidate, to estimate the density of the plasma membrane dopamine transporter; and (3) 6-[¹8F]-fluoro-L-dopa, to estimate the activity of the enzyme dopa-decarboxylase. RESULTS: The study comprised 438 PD scans and 241 control scans (679 scans in total). At symptom onset, the loss of putamen DTBZ binding was substantially greater in younger compared to older PD patients (p = 0.015). Remarkably, however, the rate of progression of DTBZ binding loss was significantly slower in younger patients (p < 0.05). The estimated presymptomatic phase of the disease spanned more than 2 decades in younger patients, compared to 1 decade in older patients. INTERPRETATION: Our results suggest that, compared to older patients, younger PD patients progress more slowly and are able to endure more damage to the dopaminergic system before the first motor symptoms appear. These observations suggest that younger PD patients have more efficient compensatory mechanisms.

Uptake and internalisation of copper by three marine microalgae: comparison of copper-sensitive and copper-tolerant species.

Although it has been well established that different species of marine algae have different sensitivities to metals, our understanding of the physiological and biochemical basis for these differences is limited. This study investigated copper adsorption and internalisation in three algal species with differing sensitivities to copper. The diatom Phaeodactylum tricornutum was particularly sensitive to copper, with a 72-h IC50 (concentration of copper to inhibit growth rate by 50%) of 8.0 microg Cu L(-1), compared to the green algae Tetraselmis sp. (72-h IC50 47 microg Cu L(-1)) and Dunaliella tertiolecta (72-h IC50 530 microg Cu L(-1)). At these IC50 concentrations, Tetraselmis sp. had much higher intracellular copper (1.97+/-0.01 x 10(-13)g Cu cell(-1)) than P. tricornutum (0.23+/-0.19 x 10(-13)g Cu cell(-1)) and D. tertiolecta (0.59+/-0.05 x 10(-13)g Cu cell(-1)), suggesting that Tetraselmis sp. effectively detoxifies copper within the cell. By contrast, at the same external copper concentration (50 microg L(-1)), D. tertiolecta appears to better exclude copper than Tetraselmis sp. by having a slower copper internalisation rate and lower internal copper concentrations at equivalent extracellular concentrations. The results suggest that the use of internal copper concentrations and net uptake rates alone cannot explain differences in species-sensitivity for different algal species. Model prediction of copper toxicity to marine biota and understanding fundamental differences in species-sensitivity will require, not just an understanding of water quality parameters and copper-cell binding, but also further knowledge of cellular detoxification mechanisms.

Multiple Sclerosis in the Asia Pacific Region: A Systematic Review of a Neglected Neurological Disease.

Background: Multiple sclerosis is thought to be relatively uncommon in the Asia Pacific region with prevalence estimated between 0 and 20 per 100,000. There is reason to doubt these estimates due to the lack of data from many countries and the growing evidence of variability in prevalence across small geographic areas. This study was conducted to systematically review the population prevalence, incidence, mortality and disability progression estimates of MS within the Asia Pacific region. Methods: The systematic review was conducted on articles from 1985 till 31st July 2017 within the PubMed/MEDLINE, EMBASE, SCOPUS, and The Cochrane Library databases. The review included articles that were population-based studies conducted on patients with MS in the Asia Pacific region that reported either incidence, prevalence, mortality, or disease progression. Hospital-based studies and non-research articles were excluded to ensure that only information representative of the population was included for analysis. Data appraisal and extraction was done by independent reviewers. This review was registered with PROSPERO (ID: CRD42017082760). Findings: Of the 2,757 articles found, 16 studies were included. Information on 6 (18.75%) of 32 Asia Pacific countries was found, with data representing 8% of the total population. Prevalence estimates were available for 6 countries while estimates for incidence (3 countries), mortality (4 countries), and disease progression (2 countries) were limited. Interpretation: The lack of epidemiological data available in the Asia Pacific region creates a blind spot in the surveillance of MS which obscures the true burden of MS, causing patients to struggle to receive the resources and funding that they need.

Acupuncture in the treatment of fatigue in Parkinson's disease: A pilot, randomized, controlled, study.

Introduction: Fatigue is a common and disabling problem in patients with Parkinson's disease (PD), and there is currently no satisfactory treatment. As acupuncture has been reported to be effective in fatigue related to other conditions, we sought to evaluate its efficacy in PD. Methods: This was a single center, randomized, sham-controlled study. Forty PD patients with moderately severe fatigue were randomized to receive 5 weeks of biweekly real or sham acupuncture. The primary outcome was change on the General Fatigue score of the Multidimensional Fatigue Inventory (MFI-GF) at 5 weeks. Secondary outcomes included MFI-Total score, Unified Parkinson's Disease Rating Scale Motor score (UPDRS Motor), Parkinson's Disease Questionnaire-39 (PDQ 39), Geriatrics Depression Scale (GDS), and Epworth Sleepiness Scale ESS). All outcome measures were evaluated at baseline, 5 and 9 weeks. Results: Both groups showed significant improvements in MFI-GF and MFI-Total scores at 5 and 9 weeks, but there were no significant between-group differences. There were no improvements from baseline for PDQ 39, GDS, and ESS. Although improvements were noted for the UPDRS Motor score in the real acupuncture group, no between-group difference could be demonstrated. Conclusions: Both real and sham acupuncture are equally effective in improving PD-related fatigue, and it is likely that this is due to nonspecific or placebo effects.

Silica@layered double hydroxide core-shell hybrid materials.

A series of silica@layered double hydroxides (SiO2@Mg2Al-CO3-AMO-LDHs) have been synthesised by in situ precipitation of Mg2Al-CO3-LDH at room temperature in the presence of amorphous spherical silica particles (∼500 nm). We have systematically investigated a number of synthetic parameters in order to evaluate their effects on the composition, morphological and physical properties of the isolated materials. Syntheses carried out at moderate stirring speeds (e.g. 500 rpm) were found to promote the formation of vertically aligned LDH platelets with respect to the silica surface. Addition rates of the metal solutions slower than 0.43 mmol h-1 were found to create a thicker LDH shell consisting of vertically aligned LDH platelets. When the metal solutions were added rapidly (0.86 mmol h-1), we observed that for both slow and fast stirring speeds the synthesised core-shell materials had thin LDH shells and the majority of the LDH precipitated independent of the silica, forming unbound "free" LDH.

Effects of aromatase inhibitors, aminoglutethimide, and 4-hydroxyandrostenedione on cyclic rats and rats with 7,12-dimethylbenz(a)anthracene-induced mammary tumors.

4-Hydroxyandrostenedione (4-OHA) is a more potent and specific inhibitor of aromatase (estrogen synthetase) than aminoglutethimide (AG). The two inhibitors were compared in rats with 7,12-dimethylbenz(a)anthracene-induced, hormone-dependent tumors and in normal cyclic rats treated for 4 and 2 weeks, respectively. Ovarian estradiol levels and aromatase activities were not consistently reduced, and tumors regressed in only two of eight rats treated with AG. In animals treated with 4-OHA or 4-OHA:AG, the total tumor volume, estradiol levels, and aromatase activity decreased by greater than 70%. Ovarian weights and plasma luteinizing hormone (LH) levels were also reduced by 4-OHA but increased by AG. Uterine weights were not altered by AG treatment but were increased by 4-OHA. Similar but more consistent results were obtained with these treatments in normal, cyclic rats. In ovariectomized rats, AG had no effect, whereas 4-OHA decreased LH levels and increased uterine weights. The results suggest that, although AG reduces ovarian estrogen secretion by aromatase inhibition, this may lead to an increase in LH secretion. Increased LH may promote ovarian growth and aromatase synthesis, counteracting the inhibitory action of AG to some extent. 4-OHA which inactivates aromatase may also prevent new enzyme synthesis by directly inhibiting gonadotropins. This would result in more effective reduction in ovarian estrogen production by 4-OHA than AG during long-term treatment.

Effects of cyclic nucleotides on ornithine decarboxylase activity in mammary gland explants from mid-pregnant mice.

Dibutyryl cAMP and prolactin stimulated ornithine decarboxylase activity in mouse mammary gland explants which had been preincubated with insulin and cortisol for 1 day; maximally stimulatory concentrations of dibutyryl cAMP and prolactin produced a response which was greater than the sum of the responses of prolactin and dibutyryl cAMP when tested alone. 8-Bromo-cGMP inhibited ornithine decarboxylase activity whereas other derivatives of cyclic nucleotides were without effect. Cortisol concentrations were found to be important for optimizing the dibutyryl cAMP and prolactin responses. Optimal prolactin responses were obtained with cortisol concentrations greater than 10(-7) M, whereas optimal dibutyryl cAMP responses were observed with cortisol concentrations less than 10(-7) M. Despite the differing optimal cortisol concentrations for the prolactin and dibutyryl cAMP responses, it is concluded that prolactin and dibutyryl cAMP probably stimulate ornithine decarboxylase activity in the mammary gland via the same mechanism.

A clinical inflammatory syndrome attributable to aerosolized lipid-DNA administration in cystic fibrosis.

Immunologic reactivity to lipid-DNA conjugates has traditionally been viewed as less of an issue than with viral vectors. We performed a dose escalation safety trial of aerosolized cystic fibrosis transmembrane conductance regulator (CFTR) cDNA to the lower airways of eight adult cystic fibrosis patients, and monitored expression by RT-PCR. The cDNA was complexed to a cationic lipid amphiphile (GL-67) consisting of a cholesterol anchor linked to a spermine head group. CFTR transgene was detected in three patients at 2-7 days after gene administration. Four of the eight patients developed a pronounced clinical syndrome of fever (maximum of 103.3EF), myalgias, and arthralgia beginning within 6 hr of gene administration. Serum IL-6 but not levels of IL-8, IL-1, TNF-alpha, or IFN-gamma became elevated within 1-3 hr of gene administration. No antibodies to the cationic liposome or plasmid DNA were detected. We found that plasmid DNA by itself elicited minimal proliferation of peripheral blood mononuclear cells taken from study patients, but led to brisk immune cell proliferation when complexed to a cationic lipid. Lipid and DNA were synergistic in causing this response. Cellular proliferation was also seen with eukaryotic DNA, suggesting that at least part of the immunologic response to lipid-DNA conjugates is independent of unmethylated (E. coli-derived) CpG sequences that have previously been associated with innate inflammatory changes in the lung.

Differential responses of sex steroid target tissues of rats treated with 4-hydroxyandrostenedione.

4-Hydroxyandrostene-3,17-dione (4-OHA) inhibits ovarian aromatase activity and causes regression of carcinogen-induced hormone-dependent mammary tumors in rats. Although estrogen levels were reduced, LH levels did not increase nor did uterine weight decline in 4-OHA-treated animals. These findings are in contrast to those in animals deprived of estrogen by ovariectomy. The possible direct action of 4-OHA on gonadotropin secretion and uterine growth was, therefore, investigated in ovariectomized rats not treated with the carcinogen. Treatment with 4-OHA for 2 weeks prevented regression of the uterus and the increase in gonadotropin secretion in ovariectomized rats in a dose-dependent manner. The effect on gonadotropin secretion of 4-OHA at 50 mg/kg.day was similar to that of dihydrotestosterone at 0.5 mg/kg.day and could be completely antagonized by administration of the antiandrogen flutamide. The stimulation of uterine growth by 4-OHA was also blocked by flutamide, but not by the antiestrogen enclomiphene. The trophic action of 4-OHA at 50 mg/kg.day was equivalent to that of 1.8 mg/kg.day dihydrotestosterone. Furthermore, treatment with 4-OHA caused a reduction in uterine estrogen receptor and progesterone receptor levels. The reduction in uterine estrogen and progesterone receptor levels was also counteracted by the concomitant injection of flutamide, but not by enclomiphene. The results suggest that in the rat 4-OHA has multiple actions on sex steroid target tissues in addition to inhibition of aromatase. The effects appear to be related to the androgenic rather than estrogenic activity of the compound. Inhibition of gonadotropins may help maintain reduced ovarian estrogen secretion and contribute to the antitumor activity of this compound.

Effects of phospholipases on ornithine decarboxylase activity in mammary gland explants from midpregnant mice.

Phospholipases A2 (PLA2) and C (PLC) stimulate ornithine decarboxylase (ODC) activity in mouse mammary gland explants preincubated with insulin and cortisol. PLC concentrations of 0.1 micrograms/ml produced responses that were close in magnitude to that of PRL, whereas PLA2 at concentrations of 5-50 micrograms/ml was 35-40% as efficacious as 1 microgram/ml PRL in stimulating ODC activity. The time courses of PLC, PLA2, and PRL actions on ODC activity were not different from one another. When PRL and PLC were tested together, a response greater than the sum of the responses of each of these agents alone was observed; PLA2 (25 micrograms/ml) when tested with PRL produced a nonadditive response. The action of PRL on ODC activity was significantly attenuated by quinacrine, an inhibitor of PLC and PLA2 activities. These results suggest that PRL, PLA2, and PLC stimulate ODC activity via similar mechanisms in the mammary gland and make tenable the idea that the action of PRL on ODC activity may be carried out via an action of PRL on PL activity.