Cerebral arteriovenous malformation in pregnancy: presentation and neurologic, obstetric, and ethical significance.

Cerebral arteriovenous malformations infrequently complicate pregnancy. We sought to determine the neurologic, obstetric, and ethical significance of such malformations. We present the clinical course of 2 pregnant women with arteriovenous malformations who experienced cerebral hemorrhage and a loss of capacity for decision making. We also review the neurologic and obstetric significance of arteriovenous malformations in pregnancy. Various treatment options with concern for pregnancy and the prognosis for arteriovenous malformations are outlined. The ethical issues involved for pregnant patients whose decisional capacity is compromised as a result of cerebral injury are explored. A review of persistent vegetative state and brain death (death by neurologic criteria) occurring in pregnancy allows us to explore many issues that are applicable to decisionally incapacitated but physiologically functioning pregnant women. We outline a document, the purpose of which is to obtain advance directives from pregnant women regarding end-of-life decisions and to appoint a surrogate decision maker. We believe that evaluation and treatment of the arteriovenous malformation may be undertaken without regard for the pregnancy and that the pregnancy should progress without concern for the arteriovenous malformation.

Muscimol increases acetylcholine release by directly stimulating adult striatal cholinergic interneurons.

Because GabaA ligands increase acetylcholine (ACh) release from adult striatal slices, we hypothesized that activation of GabaA receptors on striatal cholinergic interneurons directly stimulates ACh secretion. Fractional [3H]ACh release was recorded during perifusion of acutely dissociated, [3H]choline-labeled, adult male rat striata. The GabaA agonist, muscimol, immediately stimulated release maximally approximately 300% with EC50 = approximately 1 microM. This action was enhanced by the allosteric GabaA receptor modulators, diazepam and secobarbital, and inhibited by the GabaA antagonist, bicuculline, by ligands for D2 or muscarinic cholinergic receptors or by low calcium buffer, tetrodotoxin or vesamicol. Membrane depolarization inversely regulated muscimol-stimulated secretion. Release of endogenous and newly synthesized ACh was stimulated in parallel by muscimol without changing choline release. Muscimol pretreatment inhibited release evoked by K+ depolarization or by receptor-mediated stimulation with glutamate. Thus, GabaA receptors on adult striatal cholinergic interneurons directly stimulate voltage- and calcium-dependent exocytosis of ACh stored in vesamicol-sensitive synaptic vesicles. The action depends on the state of membrane polarization and apparently depolarizes the membrane in turn. This functional assay demonstrates that excitatory GabaA actions are not limited to neonatal tissues. GabaA-stimulated ACh release may be prevented in situ by normal tonic dopaminergic and muscarinic input to cholinergic neurons.

Pyridostigmine treatment selectively amplifies the mass of GH secreted per burst without altering GH burst frequency, half-life, basal GH secretion or the orderliness of GH release.

Growth hormone (GH) release from the anterior pituitary gland is predominantly regulated by the two antagonistic hypothalamic peptides, growth hormone-releasing hormone (GHRH) and somatostatin. Appraising endogenous GHRH action is thus made difficult by the confounding effects of (variable) hypothalamic somatostatin inhibitory tone. Accordingly, to evaluate endogenous GHRH actions, we used a clinical model of presumptively acute endogenous somatostatin withdrawal with concomitant GHRH release. To this end, we administered in randomized order placebo or the indirect cholinergic agonist, pyridostigmine, for 48 h to 13 healthy men of varying ages (29-77 years) and body mass indices (21-47 kg/m2). We sampled blood at 10-min intervals for 48 h during both placebo and pyridostigmine (60 mg orally every 6 h) administration, and used an ultrasensitive GH chemiluminescence assay (sensitivity 0.0002-0.005 microgram/l) to capture GH pulse profiles. Multiparameter deconvolution analysis was applied to quantitate the number, amplitude, mass, and duration of significant underlying GH secretory bursts, and simultaneously estimate the GH half-life and concurrent basal GH secretion. Approximate entropy was utilized as a novel regularity statistic to quantify the relative orderliness of the hormone release process. All measures of GH secretion/half-life and orderliness were statistically invariant across the two consecutive 24-h placebo sessions. In contrast, pyridostigmine treatment significantly increased the mean serum GH concentration from 0.23 +/- 0.054 microgram/l during placebo to 0.45 +/- 0.072 microgram/l during the first day of treatment (P < 0.01). There was also a significant rise in the calculated 24-h pulsatile GH production rate from 8.9 +/- 1.7 micrograms/l/day on placebo to 27 +/- 5.6 micrograms/l/day during active drug treatment (P < 0.01). Pyridostigmine significantly and selectively amplified GH secretory burst mass to 1.5 +/- 0.35 micrograms/l compared with 0.74 +/- 0.19 microgram/l on placebo (P < 0.01). This was attributable to stimulation of GH secretory burst amplitude (maximal rate of GH secretion attained within the release episode) with no prolongation of estimated burst duration. Basal GH secretion and approximate entropy were not altered by pyridostigmine. However, age was strongly related to more disorderly GH release during both days of pyridostigmine treatment (r = +0.79, P = 0.0013). During the second 24-h of continued pyridostigmine treatment, most GH secretory parameters decreased by 15-50%, but in several instances remained significantly elevated above placebo. Body mass index, but not age, was a significantly negative correlate of the pyridostigmine-stimulated increase in GH secretion (r = -0.65, P = 0.017). In summary, assuming that somatostatin is withdrawn and (rebound) GHRH release is stimulated via pyridostigmine administration, we infer that relatively unopposed GHRH action principally controls GH secretory burst mass and amplitude, rather than apparent GH secretory pulse duration, the basal GH secretion rate, or the serial regularity/orderliness of the GH release process in the human. Moreover, we infer that increasing age is accompanied by greater disorderliness of somatostatin-withdrawn GHRH, and hence rebound GH, release. The strongly negative correlation between pyridostigmine-stimulated GH secretion and body mass index (but not age) further indicates that increased relative adiposity may result in decreased effective (somatostatin-withdrawn) endogenous GHRH stimulus strength.

Carbachol inhibits basal and forskolin-evoked adult rat striatal acetylcholine release.

Acutely dissociated adult rat striatal cholinergic neurons labeled with [3H]choline were used in a perifusion system to study muscarinic regulation of basal and forskolin-stimulated fractional [3H]acetylcholine ([3H]-ACh) efflux in the absence of synaptic modulation. Carbachol inhibited basal (40% maximal inhibition; IC50 approximately 0.7 microM) and forskolin-evoked release (75% inhibition; IC50 approximately 0.05 microM) in a concentration-dependent manner, and both carbachol actions were abolished with atropine. Thus, activation of striatal muscarinic cholinergic autoreceptors potently inhibits basal and adenylate cyclase-stimulated ACh release. Tonic inhibitory control of cholinergic activity by functional striatal circuitry apparently prevents detection of these important physiological interactions in slices or in situ.

D2 dopamine receptor activation inhibits basal and forskolin-evoked acetylcholine release from dissociated striatal cholinergic interneurons.

We tested whether D2 ligands inhibit basal and forskolin-stimulated [3H]ACh release from dissociated striata, as opposed to striatal slices. Quinpirole inhibited both basal (40% maximal inhibition; IC50 approximately 50 nM) and 10 microM forskolin-stimulated release (80% inhibition; IC50 approximately 25 nM quinpirole) and both actions were blocked by a D2 antagonist. Vesamicol prevented the quinpirole and forskolin actions. The ability of D2 agonists to inhibit basal and cyclase-stimulated acetylcholine release emanating from vesamicol-sensitive vesicles appears to be tonically suppressed by inhibitory elements within striatal circuitry.

Adenylate cyclase in striatal cholinergic interneurons regulates acetylcholine release.

Fractional [3H]ACH efflux from dissociated rat striata tested whether tonic inhibition prevents stimulation of acetylcholine (ACH) release by adenylate cyclase. Forskolin stimulated release from the dissociated cells (threshold at 300 nM; EC50 > or = 1 MicroM). Release was also stimulated by 3-isobutyl-1-methylxanthine and was additive with forskolin. The 1,9-dideoxy forskolin analog that lacks cyclase-stimulating activity was ineffective. Thus, stimulation of adenylate cyclase within striatal cholinergic interneurons increases ACH secretion but is tonically inhibited by endogenous striatal transmitters. Disinhibition of the excitatory cyclase by denervation of striatal cholinergic interneurons in situ could contribute to supersensitivity without receptor upregulation.

A D1 dopamine agonist stimulates acetylcholine release from dissociated striatal cholinergic neurons.

We tested the hypothesis that a D1 dopamine agonist could stimulate acetylcholine release directly from striatal cholinergic neurons. A suspension of viable dissociated striatal cells was made enzymatically and mechanically from normal adult male rats. The heterogeneous suspension was incubated in [3H]choline to allow synthesis of [3H]acetylcholine selectively by cholinergic neurons. Fractional [3H]acetylcholine release from the cholinergic cells in the suspension was recorded during continuous dynamic perifusion. The D1 agonist, 50 microM (+/-) SKF 38393, increased the basal rate of release from the cholinergic cells by 50% and the action was inhibited by the D1 antagonist, SKF 83566. Stimulation of [3H]acetylcholine secretion was recorded as low as 500 nM SKF 38393. The (S, -) SKF 38393 stereoisomer was significantly less effective than the (R, +) isomer in stimulating release. The D1-mediated stimulation of acetylcholine secretion was abolished in a low-calcium environment that also inhibited basal release. The data suggest that striatal cholinergic cells express D1 receptors functionally coupled to the regulation of acetylcholine release. These D1 actions in the absence of synaptic circuitry imply that such circuitry is not required in situ. In vivo however, indirectly mediated D1 actions and those of other transmitters may modify the manifestations of this direct cholinergic stimulation.

Acetylcholine release from dissociated striatal cells.

To study the regulation of striatal acetylcholine (ACH) release, adult male rat striata were dissociated and incubated with 3H-choline to synthesize 3H-ACH. Fractional 3H-ACH efflux per min during continuous perifusion was: (1) tightly regulated; (2) dependent on calcium influx; (3) stimulated by 10 mM K+ and 1 mM glutamate; and (4) comparable to ACH release detected by HPLC. Thus, acutely dissociated striata exhibit calcium-sensitive, voltage-dependent secretion of 3H-ACH and direct receptor-mediated stimulation of release through the glutamate receptor family. This new approach toward cholinergic secretory physiology will help clarify complex striatal circuitry.

Acute dopamine depletion potentiates independent stimulatory and inhibitory D1 DA receptor-mediated control of striatal acetylcholine release in vitro.

Fractional release of [3H]ACh was evaluated under basal and evoked conditions in striatal slices from normal and acutely dopamine-depleted adult rats for the influence of D1- and D2-DA receptor agonists. The D1 ligand had no effect on normal slices but DA depletion unmasked two independent but simultaneous supersensitive responses: augmentation of K(+)-evoked and inhibition of glutamate-evoked release. The D2 ligand inhibited evoked release in normal slices and this effect was not potentiated. This is a new cholinergic model of acute D1 receptor supersensitivity.

31P NMR investigation of energy metabolism in perifused MMQ cells.

The MMQ cell line is a unique prolactin-secreting rat pituitary cell line. MMQ cells entrapped in agarose gel threads are metabolically active, as determined by the uptake and phosphorylation of creatine and the maintenance of high energy phosphates for over 15 h. Forskolin activates the catalytic subunit of adenylyl cyclase and, in MMQ cells, elevates the level of cAMP and stimulates prolactin secretion. 31P NMR spectroscopy was used to investigate the energy metabolism of the MMQ cells during stimulation by forskolin. The ability to measure small changes in the energy status of these cells was enhanced by increasing the PCr levels in the cells. Administration of forskolin to the perifused MMQ cells resulted in acute, reversible, and dose-dependent changes in the 31P NMR spectra of the cells within 12 to 24 min of the beginning of forskolin exposure. Several lines of evidence indicate that the changes observed in the MMQ cells are the composite result of the interaction of forskolin with adenylyl cyclase and the plasma membrane glucose transporter. Also, preincubation of the MMQ cells with the dopamine agonist, bromocriptine, attenuates the forskolin-stimulated decrease in the PCr resonance by approximately 50%. This attenuation indicates that the forskolin-stimulated changes in energy metabolism are probably related to the prolactin secretion process.

Role of calcium in dopaminergic regulation of TRH- and angiotensin II-stimulated prolactin release.

The contributions of intracellular and extracellular calcium to thyrotropin-releasing hormone (TRH)- and angiotensin II (ANG II)-stimulated prolactin (PRL) release and the role of calcium in dopaminergic inhibition of these events were examined because of unresolved controversies in these areas. Dispersed normal female rat anterior pituitary cells were used to evaluate radiocalcium fluxes and the intracellular calcium concentration ([Ca]i). Both peptides increased PRL release, fractional 45Ca2+ efflux, and [Ca]i in a spike and plateau pattern, and neither increased 45Ca2+ uptake. In a low-calcium buffer, TRH and ANG II stimulated less than 5% of the normal PRL response, yet efflux was at least 50% of normal and [Ca]i was 20-40% of normal. Dopamine reduced TRH-stimulated PRL release by greater than 90% and abolished the plateau, yet the calcium responses to TRH were at least 50% of normal. Although dopamine prevented the plateau component of peptide-stimulated [Ca]i, the plateau phase of efflux persisted. Thus TRH and ANG II may control at least two cell-associated calcium pools, one readily depleted and the other highly resistant to depletion, without evidence for stimulation of calcium uptake. Dopamine inhibits PRL release stimulated by these peptides, with a relatively greater influence on the plateau component, through mechanisms only minimally related to calcium flux. Dopamine may slightly increase the extrusion of calcium mobilized by these peptides and thus may limit the anticipated increase in [Ca]i.

Interactions of dopamine and neurotensin on calcium fluxes and prolactin release in normal rat pituitary cells.

We studied the role of calcium in dopaminergic control of the neuroendocrine effects of neurotensin. In primary cultures of dispersed normal female rat anterior pituitary cells the interactions of dopamine and neurotensin were examined with reference to the rate of PRL release, the magnitude of 45Ca2+ uptake, the rate of fractional 45Ca2+ efflux, and the dynamic response of the intracellular calcium concentration (Cai) monitored with the fluorescent dye, Indo-1. Neurotensin stimulated calcium uptake and also mobilized a pool of intracellular calcium to increase Cai in a sustained plateau-like pattern. The response of PRL release and fractional efflux to neurotensin, however, each displayed typical spike and plateau profiles. In the presence of dopamine the stimulation of PRL release and calcium uptake due to neurotensin were abolished, and the rise in Cai was barely detectable, but neurotensin-stimulated fractional efflux persisted almost unchanged. These data suggest that dopamine may modulate Cai by inhibiting calcium uptake and possibly also by enhancing cellular calcium extrusion under stimulated conditions. Further, the increased inositol trisphosphate production reportedly stimulated by neurotensin apparently does not generate a spike-like response of intracellular calcium, and stimulated hormone release may display a spike and plateau pattern solely with a plateau Cai profile.

A comparison of the concentration-dependent actions of thyrotropin-releasing hormone, angiotensin II, bradykinin, and Lys-bradykinin on cytosolic free calcium dynamics in rat anterior pituitary cells: selective effects of dopamine.

Using Indo-1 as a fluorescent probe, we studied the dynamics and the underlying mechanisms of the response of cytosolic free calcium ([Ca2+]i) to different concentrations of four prolactin secretagogues, thyrotropin-releasing hormone, angiotensin II, bradykinin, and lys-bradykinin in rat anterior pituitary cells. Low concentrations (1-100 pM) of these peptides caused a sustained increase in [Ca2+]i, whereas high concentrations (up to 100 nM) caused a large transient elevation of [Ca2+]i that was followed by a lower sustained plateau. Experiments with protein kinase C-depleted cells suggested that phorbol diester-sensitive protein kinase C was not involved in the transition of [Ca2+]i from spike to plateau seen with high concentrations of secretagogue. Specific concentrations of secretagogue mobilized different pools of [Ca2+]i, as indicated by experiments with Ca2(+)-depleted medium. Low concentrations of secretagogue induced a Ca2+ response that was abolished by Ca2(+)-depleted medium, whereas high concentrations generated a [Ca2+]i response that was refractory to Ca2(+)-depleted medium. Dopamine (100 nM) abolished the [Ca2+]i plateau response to all four agents at low concentrations and selectively reduced the plateau component of the responses elicited at high concentrations of secretagogue. If the plateau component is represented by utilization of either extracellular Ca2+ or a cell-associated EGTA-accessible pool(s) of Ca2+, then dopamine modulates one or both of these calcium sources.

Physiological and biochemical effects of bradykinin and lys-bradykinin in pituitary cells.

The presence of kallikrein activity, bradykinin (BK) and lys-bradykinin (LBK) in the pituitary gland suggests a possible physiological role of kinins therein. We demonstrated that BK and LBK increased prolactin (PRL), but not growth hormone release, from rat anterior pituitary cells cultured in vitro. Such stimulatory effect on PRL secretion appears to involve B2-type BK receptors, as suggested by the antagonizing effect of B6572 (a B2-type BK receptor antagonist) on PRL release. The BK-induced increase in PRL release is associated with an enhanced [3H]arachidonate (AA) efflux, an elevated cytosolic free calcium concentration [(Ca2+]i), and increased inositol phosphate (InsPx) production. Bradykinin and LBK stimulated [3H]AA liberation, [Ca2+]i elevation and PRL release at lower concentrations than those necessary to stimulate InsPx production. Therefore, AA release and [Ca2+]i elevation may be more important to PRL release than is InsPx production. Dopamine (DA) inhibited BK- or LBK-stimulated PRL release and slightly attenuated the stimulated [Ca2+]i response, but had no effect on stimulated [3H]AA efflux and InsPx generation. This study suggests that BK and LBK may have either an autocrine or a paracrine role in regulating PRL secretion, and are subject to modulation by DA.