Merging Transport Data for Choroid Plexus with Blood-Brain Barrier to Model CNS Homeostasis and Disease More Effectively

Robust modeling of CNS transport integrates molecular fluxes at the microvascular blood-brain barrier and epithelial choroid plexus blood-cerebrospinal fluid (CSF) barrier. Normal activity of solute transporters, channels and aquaporins, in the cerebral endothelium and choroidal epithelium, sets the microenvironment composition for neurons and glia. Conversely, perturbed transport/permeability at the barrier interfaces causes interstitial fluid dyshomeostasis (e.g. edema) arising in neural disorders. Critically-important transependymal solute/water distribution between brain and CSF needs more attention. This treatise encourages procuring transport data simultaneously for blood-brain barrier, blood-CSF barrier and CSF. In situ perfusion and multicompartmental analyses (tracers, microdialysis) provide dynamic assessments of molecular transfer among various CNS regions. Diffusion, active transport and convection are distorted by disease- and age-associated alterations in barrier permeability and CSF turnover (sink action). Clinical complications result from suboptimal conveyance of micronutrients (folate), catabolites (β-amyloid) and therapeutic agents (antibiotics) within the CNS. Neurorestorative therapies for stroke, traumatic brain injury, multiple sclerosis and brain tumors are facilitated by insight on molecular and cellular trafficking through the choroid plexus-CSF nexus. Knowledge is needed about fluxes of growth factors, neurotrophins, hormones and leukocytes from ventricular CSF into the hippocampus, subventricular zone and hypothalamus. CSF and brain removal of potentially toxic catabolites and neuropeptides merits further investigation to manage the degeneration of Alzheimer's disease and normal pressure hydrocephalus. Novel therapies will rely on delineating peptide and drug distributions across the blood-brain barrier and choroid plexus-CSF, and how they modulate the intervening neural-glial networks and neurogenic sites. Multicompartmental transport modeling is key to devising specific pharmacologic targeting and thus impactful CSF translational research for CNS disorders.

Alzheimer's therapeutics targeting amyloid beta 1-42 oligomers I: Abeta 42 oligomer binding to specific neuronal receptors is displaced by drug candidates that improve cognitive deficits

Synaptic dysfunction and loss caused by age-dependent accumulation of synaptotoxic beta amyloid (Abeta) 1-42 oligomers is proposed to underlie cognitive decline in Alzheimer's disease (AD). Alterations in membrane trafficking induced by Abeta oligomers mediates reduction in neuronal surface receptor expression that is the basis for inhibition of electrophysiological measures of synaptic plasticity and thus learning and memory. We have utilized phenotypic screens in mature, in vitro cultures of rat brain cells to identify small molecules which block or prevent the binding and effects of Abeta oligomers. Synthetic Abeta oligomers bind saturably to a single site on neuronal synapses and induce deficits in membrane trafficking in neuronal cultures with an EC50 that corresponds to its binding affinity. The therapeutic lead compounds we have found are pharmacological antagonists of Abeta oligomers, reducing the binding of Abeta oligomers to neurons in vitro, preventing spine loss in neurons and preventing and treating oligomer-induced deficits in membrane trafficking. These molecules are highly brain penetrant and prevent and restore cognitive deficits in mouse models of Alzheimer's disease. Counter-screening these compounds against a broad panel of potential CNS targets revealed they are highly potent and specific ligands of the sigma-2/PGRMC1 receptor. Brain concentrations of the compounds corresponding to greater than 80% receptor occupancy at the sigma-2/PGRMC1 receptor restore cognitive function in transgenic hAPP Swe/Ldn mice. These studies demonstrate that synthetic and human-derived Abeta oligomers act as pharmacologically-behaved ligands at neuronal receptors--i.e. they exhibit saturable binding to a target, they exert a functional effect related to their binding and their displacement by small molecule antagonists blocks their functional effect. The first-in-class small molecule receptor antagonists described here restore memory to normal in multiple AD models and sustain improvement long-term, representing a novel mechanism of action for disease-modifying Alzheimer's therapeutics.

A cell junction pathology of neural stem cells leads to abnormal neurogenesis and hydrocephalus

Most cells of the developing mammalian brain derive from the ventricular (VZ) and the subventricular (SVZ) zones. The VZ is formed by the multipotent radial glia/neural stem cells (NSCs) while the SVZ harbors the rapidly proliferative neural precursor cells (NPCs). Evidence from human and animal models indicates that the common history of hydrocephalus and brain maldevelopment starts early in embryonic life with disruption of the VZ and SVZ. We propose that a "cell junction pathology" involving adherent and gap junctions is a final common outcome of a wide range of gene mutations resulting in proteins abnormally expressed by the VZ cells undergoing disruption. Disruption of the VZ during fetal development implies the loss of NSCs whereas VZ disruption during the perinatal period implies the loss of ependyma. The process of disruption occurs in specific regions of the ventricular system and at specific stages of brain development. This explains why only certain brain structures have an abnormal development, which in turn results in a specific neurological impairment of the newborn. Disruption of the VZ of the Sylvian aqueduct (SA) leads to aqueductal stenosis and hydrocephalus, while disruption of the VZ of telencephalon impairs neurogenesis. We are currently investigating whether grafting of NSCs/neurospheres from normal rats into the CSF of hydrocephalic mutants helps to diminish/repair the outcomes of VZ disruption.

Traumatic brain injury and recovery mechanisms: peptide modulation of periventricular neurogenic regions by the choroid plexus-CSF nexus

In traumatic brain injury (TBI), severe disruptions occur in the choroid plexus (CP)-cerebrospinal fluid (CSF) nexus that destabilize the nearby hippocampal and subventricular neurogenic regions. Following invasive and non-invasive injuries to cortex, several adverse sequelae harm the brain interior: (i) structural damage to CP epithelium that opens the blood-CSF barrier (BCSFB) to protein, (ii) altered CSF dynamics and intracranial pressure (ICP), (iii) augmentation of leukocyte traffic across CP into the CSF-brain, (iv) reduction in CSF sink action and clearance of debris from ventricles, and (v) less efficient provision of micronutritional and hormonal support for the CNS. However, gradual post-TBI restitution of the injured CP epithelium and ependyma, and CSF homeostatic mechanisms, help to restore subventricular/subgranular neurogenesis and the cognitive abilities diminished by CNS damage. Recovery from TBI is facilitated by upregulated choroidal/ependymal growth factors and neurotrophins, and their secretion into ventricular CSF. There, by an endocrine-like mechanism, CSF bulk flow convects the neuropeptides to target cells in injured cortex for aiding repair processes; and to neurogenic niches for enhancing conversion of stem cells to new neurons. In the recovery from TBI and associated ischemia, the modulating neuropeptides include FGF2, EGF, VEGF, NGF, IGF, GDNF, BDNF, and PACAP. Homeostatic correction of TBI-induced neuropathology can be accelerated or amplified by exogenously boosting the CSF concentration of these growth factors and neurotrophins. Such intraventricular supplementation via the CSF route promotes neural restoration through enhanced neurogenesis, angiogenesis, and neuroprotective effects. CSF translational research presents opportunities that involve CP and ependymal manipulations to expedite recovery from TBI.

The distributional nexus of choroid plexus to cerebrospinal fluid, ependyma and brain: toxicologic/pathologic phenomena, periventricular destabilization, and lesion spread

Bordering the ventricular cerebrospinal fluid (CSF) are epithelial cells of choroid plexus (CP), ependyma and circumventricular organs (CVOs) that contain homeostatic transporters for mediating secretion/reabsorption. The distributional pathway ("nexus") of CP-CSF-ependyma-brain furnishes peptides, hormones, and micronutrients to periventricular regions. In disease/toxicity, this nexus becomes a conduit for infectious and xenobiotic agents. The sleeping sickness trypanosome (a protozoan) disrupts CP and downstream CSF-brain. Piperamide is anti-trypanosomic but distorts CP epithelial ultrastructure by engendering hydropic vacuoles; this reflects phospholipidosis and altered lysosomal metabolism. CP swelling by vacuolation may occlude CSF flow. Toxic drug tools delineate injuries to choroidal compartments: cyclophosphamide (vasculature), methylcellulose (interstitium), and piperazine (epithelium). Structurally perturbed CP allows solutes to penetrate the ventricles. There, CSF-borne pathogens and xenobiotics may permeate the ependyma to harm neurogenic stem cell niches. Amoscanate, an anti-helmintic, potently injures rodent ependyma. Ependymal/brain regions near CP are vulnerable to CSF-borne toxicants; this proximity factor links regional barrier breakdown to nearby periventricular pathology. Diverse diseases (e.g., African sleeping sickness, multiple sclerosis) take early root in choroidal, circumventricular, or perivascular loci. Toxicokinetics informs on pathogen, anti-parasitic agent, and auto-antibody distribution along the CSF nexus. CVOs are susceptible to plasma-borne toxicants/pathogens. Countering the physico-chemical and pathogenic insults to the homeostasis-mediating ventricle-bordering cells sustains brain health and fluid balance.

Report on a conference analyzing the role of cerebrospinal fluid prophylaxis for brain tumors

This is a report of a meeting sponsored by MundiPharma International to identify ways to exploit the cerebrospinal fluid system pharmacologically, for more effective management and prevention of primary and metastatic CNS tumors.

Report on BrainChild hydrocephalus conference

A report of a meeting sponsored by the BrainChild Foundation on the challenges for hydrocephalus researchers to provide the information required for better management of cerebrospinal fluid disorders.

Chemotherapy delivery issues in central nervous system malignancy: a reality check

PURPOSE

This review assesses the current state of knowledge regarding preclinical and clinical pharmacology for brain tumor chemotherapy and evaluates relevant brain tumor pharmacology studies before October 2006.

RESULTS

Chemotherapeutic regimens in brain tumor therapy have often emerged from empirical clinical studies with retrospective pharmacologic explanations, rather than prospective trials of rational chemotherapeutic approaches. Brain tumors are largely composed of CNS metastases of systemic cancers. Primary brain tumors, such as glioblastoma multiforme or primary CNS lymphomas, are less common. Few of these tumors have well-defined optimal treatment. Brain tumors are protected from systemic chemotherapy by the blood-brain barrier (BBB) and by intrinsic properties of the tumors. Pharmacologic studies of delivery of conventional chemotherapeutics and novel therapeutics showing actual tumor concentrations and biologic effect are lacking.

CONCLUSION

In this article, we review drug delivery across the BBB, as well as blood-tumor and -cerebrospinal fluid (CSF) barriers, and mechanisms to increase drug delivery to CNS and CSF tumors. Because of the difficulty in treating CNS tumors, innovative treatments and alternative delivery techniques involving brain/cord capillaries, choroid plexus, and CSF are needed.

Micronutrient and urate transport in choroid plexus and kidney: implications for drug therapy

With application of molecular biology techniques, there has been rapid progress in understanding how many drugs and micronutrients (e.g., vitamins) are transferred across the choroid plexus (CP), the main transport locus of the blood-cerebrospinal fluid (CSF) barrier, and the renal tubular epithelial cells. In many cases, these molecules are transported by separate, specific carriers or receptors on the apical and/or basal side of the CP or renal epithelial cells. This commentary focuses on four micronutrient transport systems in CP (ascorbic acid, folate, inositol, and riboflavin), all of which have been recently cloned, expressed and for which knockout mice models were developed and transporter localization studies performed. Also reviewed is the recently cloned uric acid transport system in human kidney in which there exists a human "knockout" model. The implications of these transport systems for drug therapy of central nervous system and renal disorders are discussed, especially with regard to methods to circumvent the blood-brain and blood-CSF barriers to deliver drugs to the brain.

Amiodarone inhibits thyroidal iodide transport in vitro by a cyclic adenosine 5'-monophosphate- and iodine-independent mechanism

Thyroid side effects are common in patients treated for cardiac arrhythmias with amiodarone (AM). A major disturbance is inhibited thyroidal radioiodine uptake in AM-induced thyrotoxicosis, which makes 131I therapy ineffective. On the other hand, failure to escape from the Wolff-Chaikoff effect by down-regulation of the sodium/iodide symporter (NIS) is proposed to explain AM-induced hypothyroidism. However, previously no experimental studies on the possible mechanisms have been conducted. We therefore investigated the early effects of AM on thyroidal iodide transport using bicameral chamber cultures of primary pig thyrocytes that reproduce the three tissue compartments (epithelium, lumen, and extrafollicular space) of the gland. AM dose-dependently (1-50 microm) inhibited the TSH-stimulated transepithelial (basal to apical) transport of 125I- by up to 90%. The inhibitory effect was noticed already after 8 h and was further pronounced after 1-4 d, depending on the AM concentration. The intracellularly accumulated 125I- was reduced by perchlorate but not AM, and quantitative real-time RT-PCR revealed no change in the NIS expression in AM-treated cells. Blocking of cAMP degradation with 3-isobutyl-1-methylxanthine or withdrawal of AM reversed AM-induced changes in electrolyte transport but were unable to recover the suppressed 125I- transport. The iodine-free AM analog dronedarone also inhibited 125I- transport to the same extent as AM. The findings indicate that AM blocks thyroidal iodide uptake by reducing the iodide permeability of the apical plasma membrane of the thyroid epithelial cells. The effect is iodine independent and long-lasting and does not involve impaired function of NIS or the TSH receptor/cAMP signaling pathway.

Homeostatic capabilities of the choroid plexus epithelium in Alzheimer's disease

As the secretory source of vitamins, peptides and hormones for neurons, the choroid plexus (CP) epithelium critically provides substances for brain homeostasis. This distributive process of cerebrospinal fluid (CSF) volume transmission reaches many cellular targets in the CNS. In ageing and ageing-related dementias, the CP-CSF system is less able to regulate brain interstitial fluid. CP primarily generates CSF bulk flow, and so its malfunctioning exacerbates Alzheimers disease (AD). Considerable attention has been devoted to the blood-brain barrier in AD, but more insight is needed on regulatory systems at the human blood-CSF barrier in order to improve epithelial function in severe disease. Using autopsied CP specimens from AD patients, we immunocytochemically examined expression of heat shock proteins (HSP90 and GRP94), fibroblast growth factor receptors (FGFr) and a fluid-regulatory protein (NaK2Cl cotransporter isoform 1 or NKCC1). CP upregulated HSP90, FGFr and NKCC1, even in end-stage AD. These CP adjustments involve growth factors and neuropeptides that help to buffer perturbations in CNS water balance and metabolism. They shed light on CP-CSF system responses to ventriculomegaly and the altered intracranial pressure that occurs in AD and normal pressure hydrocephalus. The ability of injured CP to express key regulatory proteins even at Braak stage V/VI, points to plasticity and function that may be boosted by drug treatment to expedite CSF dynamics. The enhanced expression of human CP 'homeostatic proteins' in AD dementia is discussed in relation to brain deficits and pharmacology.

Choroid plexus electrolytes and ultrastructure following transient forebrain ischemia

A temporal profile of lateral and fourth ventricle rat choroid plexus (LVCP and 4VCP, respectively) tissue injury and recovery was determined using alterations in K, Na, and H2O content and ultrastructure after 10 min of transient forebrain ischemia (TFI). At 0.5 h postischemia the LVCP displayed a maximum reduction in K content by 32% and a significant increase in Na content by 85% and H2O content by 22%. LVCP tissue K, Na, and H2O content returned to sham values by 24 h postischemia. Ultrastructural changes appeared more severe between 0.5 and 12 h postischemia, whereas by 24 h, normal ultrastructure was restored. Elevations in 4VCP tissue Na (P < 0.05) and H2O content, which were less than those in LVCP, gradually reached a maximum by 24 h compared with sham. No change in 4VCP tissue ultrastructure was observed. These results indicate that the LVCP tissue is more vulnerable than 4VCP in the bilateral carotid artery occlusion model but that it recovers in a timely manner after TFI. Furthermore, the ability of the LVCP tissue to rapidly recover suggests its functional importance in helping to restore brain homeostasis.

Hydrocephalus decreases chloride efflux from the choroid plexus epithelium

To explore the novel concept of intrinsic brain regulation of the choroid plexus (CP), we studied the function of the CP exposed to increased intracranial pressure (ICP). The function of the CP was evaluated by in vitro chloride (Cl-) efflux from isolated CP 21 days after kaolin induced hydrocephalus. The Cl- efflux was significantly decreased in animals with elevated intracranial pressure (rate constant, K = 0.024 +/- 0.001 s-1) and enlarged ventricles (K = 0.023 +/- 0.001 s-1) compared to sham animals (K = 0.031 +/- 0.001 s-1). In contrast, the Cl- efflux of CP from animals with normal ICP and ventricular size did not differ from sham animals. These results illustrate the first demonstration of regulation of the CP epithelial function with elevated ICP; they also suggest a brain-CP regulatory mechanism that alters CP function.

Adenosine as substrate and receptor agonist in the ovary

In the present study the possible dual effects of adenosine as substrate and adenosine receptor agonist in rat granulosa cells, cumulus-oocyte complexes, luteal cells and ovarian membranes are discussed. Adenosine is an indispensable compound in cell energy metabolism, as precursor to cofactors, second messenger and nucleic acids. Adenosine is also an agonist to adenosine receptors. The adenosine receptor can either inhibit (A1) or stimulate (A2) adenylate cyclase. Alternatively, in some cells adenosine receptor activation is linked to other cellular events like inhibition of Ca2+ fluxes. Adenosine is taken up by isolated preovulatory granulosa and luteal cells from pregnant mare serum gonadotropin-treated immature rats, but follicle stimulating hormone (FSH) decreases the uptake by granulosa cells. Adenosine, but not the non-metabolizable adenosine analogs 5'-(N-ethyl)carboxamide-adenosine (NECA), 2-chloro-adenosine (2-Clado), N6-(R-phenyl-isopropyl)-adenosine (R-PLA) and N6-(S-phenyl-isopropyl)-adenosine (S-PLA), increase granulosa cell ATP levels. FSH and luteinizing hormone (LH) decrease granulosa cell ATP levels in the presence or absence of adenosine. It has previously been shown that FSH and LH decrease oxygen consumption by cumulus-oocyte complexes and increase their lactate production. These effects have been suggested to be due to a competition of cofactors (e.g. ADP) common to glycolysis and the respiratory chain. The fact that adenosine reverse the gonadotropin-induced effects on oxygen consumption and lactate production support this theory. Adenosine and its analogs increase cAMP accumulation in luteal and granulosa cells only in the presence of gonadotropins, and this effect is antagonized by the adenosine receptor antagonist 8-phenyl-theophylline (8-PHT). Furthermore, adenylate cyclase is stimulated by adenosine analogs in membranes from non-luteinized and luteinized ovarian membranes and in luteal cell homogenates. The effect of NECA is antagonized by 8-PHT. In the membranes, the rank order of potency was NECA greater than 2-Clado greater than R-PLA greater than S-PLA, suggesting adenosine A2 receptors. In summary, it is suggested that adenosine can act both as a substrate to intracellular metabolism and as an adenosine A2 receptor agonist in granulosa and luteal cells. A paracrine short loop positive feedback model is proposed where extracellular adenosine, derived from a gonadotropin-induced extracellular increase in cAMP and a decrease in cellular ATP, enhances gonadotropin stimulation in granulosa and luteal cells.

Refractoriness to follicle-stimulating hormone in rat ovarian granulosa cells--a concentration- and time-dependent phenomenon

Granulosa cells from pre-ovulatory ovarian follicles of rats were exposed, in vitro, to one or two pulses of follicle-stimulating hormone (FSH) in a superfusion apparatus. The superfusate was analysed for cyclic adenosine-3',5' monophosphate (cAMP) and steroids. In experiments with two consecutive FSH pulses, the response to the second pulse (100 ng/ml) was inversely related to the concentration of the first FSH pulse (2.5-100 ng/ml). Within certain limits, a lower total amount of cAMP and progesterone was accordingly released in response to the two FSH pulses when the concentration of the first pulse was increased. This refractoriness declined within a few hours as shown in experiments with extended pulse intervals. Two short and separate FSH pulses also evoked a higher combined response than did a single long FSH pulse lasting the whole time period. In these cases the cells thus responded with a lower total cAMP and progesterone release when exposed to a higher amount of FSH. Clinical trials on i.m. versus pulsatile i.v. FSH administration to anovulatory women have shown a similar relationship between FSH dose and effect, though other parameters were measured than those in the present study.

Methotrexate/fluorouracil scheduling influences normal tissue toxicity but not antitumor effects in patients with squamous cell head and neck cancer: results from a randomized trial

To test the hypothesis that sequential scheduling of methotrexate (MTX) and fluorouracil (FU) produces a synergistic antitumor effect, we randomized 113 patients with recurrent or locally advanced squamous cell carcinoma of the head and neck to receive MTX-FU either 18 hours apart or simultaneously, with leucovorin rescue. There were 100 patients with locally advanced newly presenting disease and 13 patients with recurrence. Excessive toxicity was observed in the first 11 patients who received MTX 250 mg/m2 administered intravenously (IV) and leucovorin at 36 hours, therefore all subsequent patients received MTX 200 mg/m2 administered IV and leucovorin at 24 hours. FU 600 mg/m2 IV was administered to all patients, and treatment was given on days 1 and 8 of 21-day cycles. The treatment groups were well balanced for known prognostic variables. The response rate was 47.3% (26 of 55) for simultaneous v 44.8% (26 of 58) for sequential therapy. These results exclude a 20% difference in response rate favoring sequential therapy at P = .04. There was no observed difference in survival between the two treatment arms (P = .55) with a minimum follow-up of 8 months. Toxicity was greater in patients who received sequential therapy, and the difference was confined to the gastrointestinal (GI) tract. A comparison of the distribution in maximum Eastern Cooperative Oncology Group (ECOG) toxicity scores during chemotherapy for the two treatment groups showed greater stomatitis (P = .001), diarrhea (P = .04), and overall toxicity (P = .02) for sequential treatment without an observed difference in bone marrow toxicity. The results of this trial indicate that sequential MTX-FU is not superior to simultaneous therapy for the treatment of patients with head and neck cancer. Biochemical modulation of MTX-FU by drug scheduling may occur in vivo and may be organ specific.

Luteotropic effects of prostaglandin E2 on the human corpus luteum of the menstrual cycle and early pregnancy

Human corpora lutea (CL) of the menstrual cycle and early pregnancy were excised at operation, cut into pieces, and incubated or superfused in the presence of hCG or prostaglandin (PG) E2. After incubation, the tissue levels of cAMP and the medium concentrations of progesterone (P) were determined, while the concentration of P was analyzed after superfusion. PGE2 stimulated cAMP formation in CL from all phases of the menstrual cycle as well as from early pregnancy and caused an increase in P formation in CL from the early and midluteal phases of the menstrual cycle as well as from early pregnancy. A difference was found in the latency, the lag phase until maximal response, and the duration of response between the effects of PGE2 and hCG on both cAMP and P formation. Thus, the effect of PGE2 started more rapidly and was of shorter duration than that of hCG. The stimulatory effect of PGE2 on CL from early pregnancy was of the same magnitude as that of CL from the menstrual cycle. On the other hand, hCG had less stimulatory effect on cAMP and P formation in CL from early pregnancy compared to CL from the menstrual cycle. We conclude that PGE2 stimulates P and cAMP formation in isolated human CL from all phases of the menstrual cycle as well as in early pregnancy, indicating a luteotropic effect of this PG.

A technique for superfusion of isolated granulosa cells. Dynamics of cAMP production and steroidogenesis in response to gonadotropins

A superfusion model for isolated ovarian cells was developed and characterized in detail. Granulosa cells isolated from pre-ovulatory rat ovarian follicles were placed in superfusion (perifusion) chambers with a volume of 125 microliters. Culture medium was pumped through the chambers, collected in 20-min fractions of 600 microliters and analysed for cAMP and steroids. Viability was confirmed by morphological examination. The use of polycarbonate membranes to retain the cells in the chambers was abandoned since the membranes caused severe cell damage. The temporal relationships between gonadotropic stimuli and the release of cyclic 3':5'-adenosine monophosphate (cAMP) and steroids was investigated. Within 10 min FSH elicited transient increase in the release of cAMP and progesterone but had no effect on testosterone or estradiol-17 beta release. Amplitude and duration of the response in cAMP and progesterone release were correlated to concentration and length of the FSH pulse when these parameters were varied within the ranges 1-100 micrograms/l and 30-270 min, respectively. Compared with the cAMP response, the progesterone response peaked up to 30 min later and lasted 1 to 2 h longer but could not be extended to more than approximately 6 h, not even with longer FSH pulses. These results could indicate a development of desensitization.

Steroidogenesis in isolated rat granulosa cells--changes during follicular maturation

Steroid release was investigated in granulosa cells isolated from rat ovarian follicles at different maturation stages. Immature rats were treated with 10 IU of pregnant mare's serum gonadotrophin (PMSG) to induce follicular growth and maturation. Granulosa cells were isolated and subsequently incubated for 4 h in the absence or presence of follicle stimulating hormone (FSH), luteinizing hormone (LH) or forskolin. The concentrations of progesterone (P), 20 alpha-dihydroprogesterone (20 alpha DHP), testosterone (T) and oestradiol (E2) in the media were determined by radioimmunoassay. During maturation, basal release of T increased markedly at late dioestrus. At pro-oestrus, concomitant with a sharp rise in E2 and P release, T release returned to previously low levels. Addition of FSH or LH stimulated P release at late dioestrus and pro-oestrus but had no effect on E2 or T levels. Basal 20 alpha DHP levels remained low until a sharp rise at mid pro-oestrus. A stimulatory effect of gonadotrophins on 20 alpha DHP was first seen at this stage. The adenylate cyclase stimulator forskolin resembled FSH in all its effects. In summary, the present study demonstrates that maturing, but not preovulatory, granulosa cells have an increased capacity to release T during a relatively short period. It is suggested that this T peak could be of great importance for the further progress of follicular maturation.