Acetylcholine dramatically increases prostanoid synthesis in piglet parietal cortex

Regulation of the Cerebral Circulation During Development

The cerebral microcirculation undergoes dynamic changes in parallel with the development of neurons, glia, and their energy metabolism throughout gestation and postnatally. Cerebral blood flow (CBF), oxygen consumption, and glucose consumption are as low as 20% of adult levels in humans born prematurely but eventually exceed adult levels at ages 3 to 11 years, which coincide with the period of continued brain growth, synapse formation, synapse pruning, and myelination. Neurovascular coupling to sensory activation is present but attenuated at birth. By 2 postnatal months, the increase in CBF often is disproportionately smaller than the increase in oxygen consumption, in contrast to the relative hyperemia seen in adults. Vascular smooth muscle myogenic tone increases in parallel with developmental increases in arterial pressure. CBF autoregulatory response to increased arterial pressure is intact at birth but has a more limited range with arterial hypotension. Hypoxia-induced vasodilation in preterm fetal sheep with low oxygen consumption does not sustain cerebral oxygen transport, but the response becomes better developed for sustaining oxygen transport by term. Nitric oxide tonically inhibits vasomotor tone, and glutamate receptor activation can evoke its release in lambs and piglets. In piglets, astrocyte-derived carbon monoxide plays a central role in vasodilation evoked by glutamate, ADP, and seizures, and prostanoids play a large role in endothelial-dependent and hypercapnic vasodilation. Overall, homeostatic mechanisms of CBF regulation in response to arterial pressure, neuronal activity, carbon dioxide, and oxygenation are present at birth but continue to develop postnatally as neurovascular signaling pathways are dynamically altered and integrated. © 2021 American Physiological Society. Compr Physiol 11:1-62, 2021.

Centrally administered CDP-choline induced cardiovascular responses are mediated by activation of the central phospholipase-prostaglandin signaling cascade

The present study was designed to determine the involvement of central prostaglandin synthesis on the pressor and bradycardic effect of cytidine 5'-diphosphocholine (CDP-choline). Intracerebroventricular (i.c.v.) administration of CDP-choline was made and blood pressure and heart rate were recorded in male Sprague Dawley rats throughout this study. Microdialysis and immunohistochemical studies were performed to measure extracellular total prostaglandin concentration and to show cyclooxygenase-1 and -2 (COX-1 and -2) immunoreactivities, respectively, in the posterior hypothalamic area. Moreover, rats were pretreated (i.c.v) with mepacrine [a phospholipase A2 (PLA2) inhibitor], ibuprofen [a nonselective COX inhibitor], neomycine [a phospholipase C (PLC) inhibitor] or furegrelate [a thromboxane A2 (TXA2) synthesis inhibitor] 5 min prior to the injection of CDP-choline to determine the effects of these inhibitors on cardiovascular responses to CDP-choline. Control rats were pretreated (i.c.v) with saline. CDP-choline caused a dose- and time-dependent increase in blood pressure and decrease in heart rate. Immunohistochemical studies showed that CDP-choline increased COX-1 and -2 immunoreactivities in the posterior hypothalamic area. CDP-choline also elevated hypothalamic extracellular total prostaglandin concentration by 62%, as shown in microdialysis studies. Mepacrine or ibuprofen pretreatments almost completely blocked the pressor and bradycardic responses to CDP-choline while neomycine or furegrelate partially attenuated the drug-induced cardiovascular effects. The results suggest that CDP-choline may stimulate prostaglandin synthesis through the activation of PLA2, cyclooxygenases (COX-1 and -2) and prostaglandins and at least TXA2, may mediate the drug׳s cardiovascular effects.

The effect of centrally injected CDP-choline on respiratory system; involvement of phospholipase to thromboxane signaling pathway

CDP-choline is an endogenous metabolite in phosphatidylcholine biosynthesis. Exogenous administration of CDP-choline has been shown to affect brain metabolism and to exhibit cardiovascular, neuroendocrine neuroprotective actions. On the other hand, little is known regarding its respiratory actions and/or central mechanism of its respiratory effect. Therefore the current study was designed to investigate the possible effects of centrally injected CDP-choline on respiratory system and the mediation of the central cholinergic receptors and phospholipase to thromboxane signaling pathway on CDP-choline-induced respiratory effects in anaesthetized rats. Intracerebroventricularly (i.c.v.) administration of CDP-choline induced dose- and time-dependent increased respiratory rates, tidal volume and minute ventilation of male anaesthetized Spraque Dawley rats. İ.c.v. pretreatment with atropine failed to alter the hyperventilation responses to CDP-choline whereas mecamylamine, cholinergic nicotinic receptor antagonist, mepacrine, phospholipase A2 inhibitor, and neomycin phospholipase C inhibitor, blocked completely the hyperventilation induced by CDP-choline. In addition, central pretreatment with furegrelate, thromboxane A2 synthesis inhibitor, also partially blocked CDP-choline-evoked hyperventilation effects. These data show that centrally administered CDP-choline induces hyperventilation which is mediated by activation of central nicotinic receptors and phospholipase to thromboxane signaling pathway.

Involvement of arachidonic acid cascade in working memory impairment induced by interleukin-1 beta

The aim of the present study is to clarify the possible relevance of the arachidonic acid cascade to working memory in rats, by using a three-panel runway apparatus. Interleukin-1 beta, injected bilaterally into the dorsal hippocampus at a dose of 100 ng/side, significantly impaired working memory, and this impairment was attenuated by pretreatment with 10 mg/kg (s.c.) of diclofenac, a cyclooxygenase inhibitor. Working memory was also impaired in rats administered a bilateral intrahippocampal injection of prostaglandin E2, in a dose-dependent manner at 0.01-1 microg/side. Furthermore, an injection of 100 ng/side of interleukin-1 beta significantly increased production of prostaglandin E2 (580 +/- 32 pg to 1142 +/- 101 pg/100 mg wet tissue) in the hippocampus. Taken together, these findings suggest that the activation of the arachidonic acid cascade was causative of the working memory impairment induced by interleukin-1 beta.

Prostaglandins may participate in opioidergic and cholinergic control of the diurnal changes of tuberoinfundibular dopaminergic neuronal activity and serum prolactin level in ovariectomized, estrogen-treated rats

The roles of prostaglandins (PGs) involved in opioidergic, cholinergic, and serotonergic regulation of the diurnal changes of tuberoinfundibular dopaminergic (TIDA) neuronal activities were investigated in ovariectomized, estrogen-treated rats. Treatment with naloxone [10 mg/kg, intraperitoneal (i.p.)], atropine (5 mg/kg, i.p.), or ketanserin (10 mg/kg, i.p.) at either 1200 or 1400 h prevented the afternoon decrease of TIDA neuronal activity and the prolactin (PRL) surge. Intracerebroventricular (i.c.v.) injection of PGE(1) (5 microg/3 microl/rat) at 1500 h significantly reversed the effects of naloxone and atropine, but not that of ketanserin. In ovariectomized, estrogen-primed rats pretreated with indomethacin, i.c.v. injection of either nicotine (10 ng/rat) or fentanyl (10 ng/rat) failed to suppress the TIDA neuronal activity and to stimulate the PRL secretion. These data suggest that PG may be involved in opioidergic and cholinergic control of the diurnal changes of TIDA neuronal activity and the PRL secretion in ovariectomized (OVX) + E(2) rats.

Angiotensin II stimulates PGF(2 alpha)release in cultured neonatal rat ventricular myocytes via L-type calcium channels

Angiotensin II (Ang II) has been shown to cause Prostaglandin F(2 alpha)(PGF(2 alpha)) release in neonatal rat ventricular myocytes and smooth muscle cells. In these cells, Ang II has also been shown to regulate growth. We used neonatal rat ventricular myocytes to investigate the role of calcium in maintenance of Ang II-induced PGF(2 alpha)release. The amount of PGF(2 alpha)produced was determined by radioimmunoassay. Ang II-induced PGF(2 alpha)release. Pretreatment of neonatal rat ventricular myocytes with different doses (10(-8)M, 10(-7)M, 10(-6)M and 10(-5)M) of diltiazm (voltage-sensitive L-type calcium channel blocker) produced significant inhibition in Ang II-induced PGF(2 alpha)release. Inhibition was first noted at 10(-8)M and was complete at 10(-6)M. Conversely, pretreatment of neonatal rat ventricular myocytes with different doses (10(-8)M, 10(-7)M, 10(-6)M and 10(-5)M) of calcium channel blockers (conotoxin; voltage-sensitive N-type calcium channel blocker or thapsigargin; intracellular calcium channel blocker) produced no changes in Ang II-induced PGF(2 alpha)release. These results strongly suggest that Ang II-induced PGF(2 alpha)release in neonatal rat ventricular myocytes is maintained, at least in part, via increase in extracellular calcium influx.

Angiotensin II stimulates hypertrophic growth of cultured neonatal rat ventricular myocytes: roles of PKC and PGF2alpha

Angiotensin II (Ang II) has been shown to regulate growth in smooth muscle cells. Protein kinase C (PKC), which mediates Ang II action, has been implicated in myocardial cell hypertrophy. Acute pressure overload in the left ventricles has been demonstrated to produce prostaglandin F2 alpha (PGF2alpha) release. Therefore, we used cultured neonatal rat ventricular myocytes to study Ang II, PKC and PGF2alpha and their relationship to hypertrophy. The amount of PGF2alpha produced was determined by radioimmunoassay, Ang II-induced hypertrophy and PGF2alpha release. Pretreatment with 10(-6) M of PKC inhibitor, 1-(5-isoquinolinesulfonyl-methyl) piperazine (H7), blocked Ang II-induced hypertrophy and PGF2alpha release. In neonatal rat ventricular myocytes that were treated with either Ang II or PKC activator (Phorbol 12, 13, dibutyrate; PDBu), PKC enzyme assay showed PKC was translocated from the cytosol to the membrane which indicates activation. This suggests that PKC mediates, in part, Ang II-induced PGF2alpha release and hypertrophy. In summary, Ang II activates PKC, which causes PGF2alpha release and hypertrophy, and this PGF2alpha release and hypertrophy can be overcome by pretreatment with PKC inhibitor.

Angiotensin II-induced ET and PGI2 release in rat aortic endothelial cells is mediated by PKC

Angiotensin II (Ang II) has been shown to stimulate the release of immunoreactive endothelin (ET) from cultured bovine ECs. Also, Ang II activates phospholipase A2 (PLA2) in various tissues, resulting in the release of arachidonic acid and formation of prostaglandins. We used rat aortic endothelial cells to investigate the role of protein kinase C (PKC) in Ang II-induced release of both ET and prostacyclin (PGI2). The amount of ET and PGI2 produced were determined by radioimmunoassay. Ang II-induced the release of both ET and PGI2. Pretreatment with 10(-6) M of any one of the PKC inhibitors: 1-(5-isoquinolinesulfonyl) piperazine(CL), staurosporine, 1-(5-isoquinolinesulfonylmethyl)piperazine(H7), and calphostin C blocked AII-induced release of both ET and PGI2. In rat aortic endothelial cells that were treated with either AII or PDBu, PKC enzyme assay showed PKC was translocated from the cytosol to the membrane which indicates activation. This suggests that PKC mediates AII-induced ET and PGI2 release. In summary, AII activates PKC which inhibits rat aortic endothelial cells ET and PGI2 formation, and this inhibition can be overcome by pretreatment with PKC inhibitors.

Endothelin-induced prostacyclin production in rat aortic endothelial cells is mediated by protein kinase C

Endothelin (ET) is a vasoconstrictor peptide released from endothelial cells that is known to cause prostaglandin (PG) release. The mechanism remains unclear. To determine whether the protein kinase C (PKC) signaling pathway is stimulated by endothelin, we pretreated rat aortic endothelial cells with either PKC activator or inhibitors and measured the release of prostacyclin (PGI2) by radioimmunoassay. ET (10(-9) M) produced a 10-fold increase in PGI2 release. Pretreatment with 10(-9) M of three different PKC inhibitors: 1-(5-isoquinolinesulfonyl) piperazine (CL), staurosporine, and 1-(5-isoquinolinesulfonyl-methyl) piperazine (H7) blocked ET induced PGI2 release. ET induced prostacyclin release was also blocked by pretreatment with inhibitors of either phospholipase A2 (7,7,dimethyleicosadienoic acid or trifluoromethyl ketone analogue) (10(-9) M) or cyclooxygenase (indomethacin) (10(-9) M). We conclude that ET activates PKC which activates phospholipase A2 which liberates arachidonic acid which increases PGI2 production and release.

Behavioral thermoregulatory response to chlorpyrifos in the rat

Chlorpyrifos (CHP) is a heavily used organophosphorous-based insecticide that elicits thermoregulatory dysfunction in the rat characterized by an initial period of hypothermia followed by a delayed hyperthermia lasting 24-72 h after exposure. The purpose of the present study was to determine (1) if the delayed hyperthermia is linked to CHP-induced hypothermia and (2) if the hypothermia and delayed hyperthermia are regulated by the CNS thermoregulatory centers. Core temperature (Tc) and motor activity (MA) of female Long-Evans rats were monitored via radiotelemetry. Rats housed in a temperature gradient were administered the control vehicle or CHP (25 mg/kg (p.o.)) while Tc, MA and ambient temperature (Ta) preferred by rats in the gradient (i.e. selected Ta) were recorded. There was an initial reduction in Tc concomitant with a decrease in selected Taa A gradual recovery in Tc occurred during the first night along with a preference for warmer Ta's and depressed MA. The day after CHP there was an elevation in Tc but no change in selected Ta, suggesting that the delayed rise in Tc was regulated. In another experiment, the hypothermic effects of CHP (25 mg/kg (p.o.)) were blocked by raising Ta from 22 to 31 degrees C immediately after CHP administration. Non-heated rats administered CHP underwent a marked period of hypothermia followed by an elevation in diurnal Tc for 2 days. Heated rats showed no hypothermic response but did undergo a hyperthermic response 48 h after CHP. MA was reduced during the first night after CHP in both non-heated and heated groups. Overall, the CHP-induced hyperthermia is not dependent on the development of hypothermia. Behavioral thermoregulatory observations suggest that both hypothermia and hyperthermia are regulated by CNS thermoregulatory centers.

Protein kinase C mediates angiotensin II-induced contractions and the release of endothelin and prostacyclin in rat aortic rings

Angiotensin II (Ang II) stimulation of vascular smooth muscle results in a myriad of intracellular signals that interact to produce the final physiologic response of the cell. We used rat aortic rings to investigate the role of protein kinase C (PKC) in Ang II-induced contractions and in the concomitant release of endothelin (ET) and prostacyclin (PGI2). Ang II (10(-9) M) produced a rapid contraction which was sustained for 10 min. When aortic rings were pretreated with graded concentrations of each of the four different inhibitors of PKC, that is, (i) 1-(5-isoquinolinesulfonylmethyl) piperazine (H7); (ii) 1-(5-isoquinolinesulfonyl) piperazine(CL); (iii) staurosporine; or (iv) calphostin C, inhibition of Ang II-induced contractions began at 10(-9) M, and was nearly complete at 10(-6) M. Ang II-induced contractions were associated with a 10-fold increase in the release of both ET and PGI2. Pretreatment with 10(-6) M of any one of the same four PKC inhibitors blocked Ang II-induced release of both ET and PGI2. Pretreatment with a blocker of the endothelin-A receptor, BQ123 (10(-6) M), inhibited, by approximately 50%, Ang II-induced contractions, and the release of both ET and PGI2. In aortic rings denuded of endothelium, Ang II-induced contractions, and the release of both ET and PGI2 were significantly reduced, compared to intact rings. We conclude that PKC mediates Ang II-induced contractions in rat aortic rings and that the secondary release of both ET and PGI2 during Ang II-induced contractions is mediated, at least in part, by PKC. In addition, approximately half of Ang II-induced contractile force and of PGI2 release is dependent upon the ET released from endothelial cells.

Cyclosporine A-induced contractions and prostacyclin release are maintained by extracellular calcium in rat aortic rings: role of protein kinase C

Chronic treatment with the immunosuppressive drug, Cyclosporine A (CsA), is associated with increased intracellular calcium in vascular smooth muscle cells, which may cause vasoconstriction and/or activate phospholipase A2. We used rat aortic rings to investigate the role of protein kinase C (PKC) in CsA-induced contractions and secondary prostacyclin (PGI2) release. CsA (10(-9) M) produced a sustained contraction in rat aortic rings. Both CsA-induced contractions and PGI2 release were inhibited 84 to 89% by 10(-9) M, and 99 to 100% by 10(-6) M pretreatment doses of any of three different PKC inhibitors, i.e. 1-(5-isoquinolinesulfonylmethyl) piperazine (H7), staurosporine or 1-(5-isoquinolinesulfonyl) piperazine. Pretreatment with (10(-9) M) of diltiazem (a voltage-sensitive L-type calcium channel blocker) completely inhibited both CsA-induced contractions and PGI2 release. Conversely, pretreatment with (10(-9) M) of thapsigargin (an intracellular calcium channel blocker) did not alter the action of CsA. These results strongly suggest that PKC, in association with an influx of extracellular calcium mediates CsA-induced contractions and secondary PGI2 release in rat aortic rings.

Endothelin-induced prostacyclin production in rat aortic rings is mediated by protein kinase C

Endothelin (ET) is a vasoconstrictor peptide released from endothelial cells that is known to cause prostaglandin release. The mechanism remains unclear. To determine whether the protein kinase C (PKC) signaling pathway is stimulated by endothelin, we pretreated rat aortic rings with either PKC activator or inhibitors and measured the release of prostacyclin (PGI2) by radioimmunoassay. ET (10(-9) M) produced a 10-fold increase in PGI2 release. Pretreatment with 10(-9) M of three different PKC inhibitors, 1-(5-isoquinolinesulfonyl)piperazine(CL), staurosporine, and 1-(5-isoquinolinesulfonyltmethyl)piperazine (H7), blocked ET-induced PGI2 release. ET-induced PGI2 release was also blocked by pretreatment with inhibitors of either phospholipase A2 7,7-dimethyleicosadienoic acid or trifluoromethyl ketone analogue) (10(-9) M) or cyclooxygenase (indomethacin) (10(-9) M). We conclude that ET activates PKC, which activates phospholipase A2, which liberates arachidonic acid, which increases PGI2 production and release.

Pharmacological analysis of diisopropyl fluorophosphate: effects on core temperature, heart rate, and motor activity in the unrestrained rat

Humans acutely exposed to anticholinesterase (anti-ChE) pesticides often become febrile, whereas rats and other rodents become markedly hypothermic. The rat may nonetheless be a useful model for anti-ChE toxicity because recent work using radiotelemetry demonstrated an elevation in core temperature of unrestrained rats for several days following acute exposure to the anti-ChE, diisopropyl fluorophosphate (DFP). To discern the mechanisms of DFP-induced hypothermia and hyperthermia, various pharmacological agents were administered acutely or chronically to rats injected with 1.5 mg/kg DFP (SC). Core temperature, heart rate, and motor activity were monitored continuously via radiotelemetry. Methylscopolamine, a peripheral muscarinic antagonist, attenuated the DFP-induced hypothermia by 1.0 degree C and reversed the DFP-induced bradycardia. Chronic scopolamine, a central and peripheral muscarinic antagonist, delivered via a subcutaneously implanted minipump (9.5 mg/kg/day) blocked DFP-induced hypothermia and hyperthermia. Propranolol (10 mg/kg; SC), a general beta blocker, augmented the bradycardic effects of DFP but had no effect on body temperature. Sodium salicylate (200 and 300 mg/kg; IP), an antipyretic that inhibits prostaglandin synthesis, administered during the period of DFP-induced hyperthermia produced a transient recovery in body temperature. Overall, DFP-induced hypothermia and hyperthermia in the rat appear to be mediated via cholinergic activation in the CNS because both are blocked by scopolamine. The decrease in core temperature following sodium salicylate suggests that prostaglandin release is involved in the manifestation of DFP-induced hyperthermia. The elevation in core temperature after DFP appears to involve neurochemical pathways similar to that of fever.

Action of protein kinase C in endothelin-induced contractions in rat aortic rings

Endothelin (ET) is a potent vasoconstrictor peptide that induces characteristically long-lasting contractions. We used both intact and endothelium-denuded rat aortic rings to investigate the role of protein kinase C (PKC) in ET-induced contractions. ET (10(-9) M) and phorbol 12,13-dibutyrate (PDBu), a PKC activator, produced a gradual and sustained contraction of greater magnitude in denuded aortic rings than in intact rings. When aortic rings were pretreated with graded concentrations of different PKC inhibitors, inhibition of ET-induced contractions began at 10(-9)M and was nearly complete at 10(-3)M, and the reduction was greater in intact than in denuded rings. Pretreatment of aortic rings with PDBu or NG-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthase, potentiated ET-induced contractions. PKC enzyme assay showed activation of PKC in aortic rings that were treated with either ET or PDBu, inhibition after pretreatment with PKC inhibitors, and no change with 4 alpha-phorbol 12,13-didecanoate (PDD), an inactive phorbol ester. ET significantly increased nitrate and nitrite production, which was further increased by pretreatment with PKC inhibitors. PDBu prevented ET-induced nitrate/nitrite production, and PDD had no effect. These results strongly suggest that PKC mediates, in part, ET-induced contractions in rat aortic rings and that an intact endothelium is required for maximum inhibition by PKC inhibitors because PKC stimulated by ET inhibits nitric oxide release.

Thermoregulatory aspects of environmental exposure to anticholinesterase agents

Anticholinesterase (antiChE) agents can be highly toxic to birds and mammals and constitute a major proportion of the pesticides used throughout the world. AntiChEs consist of the organophosphates (OP), which irreversibly inhibit the enzyme acetylcholinesterase (AChE), and the carbamates (CB), which reversibly inhibit AChE. AChE inhibition elicits cholinergic stimulation in the central nervous system and in peripheral tissues and organs, which can lead to marked dysfunction of homeostatic systems, including temperature regulation. The control of body temperature uses cholinergic pathways in the integration and central processing of thermal information, as well as in the control of thermoeffector responses. Hence, the cholinergic stimulation elicited from exposure to antiChEs has profound effects on body temperature at rest as well as during exercise. Ambient heat and cold stress can also modulate the animal's sensitivity to antiChE exposure. After exposure to most OPs, rodents and other small species undergo a marked hypothermic response lasting up to 24 hours. On the other hand, humans exposed to OP pesticides rarely become hypothermic but rather experience a fever that may last many days. Recent studies monitoring body temperature in OP-exposed, telemetered rats demonstrated that the initial hypothermic response is followed by a period of hyperthermia lasting several days. That the hyperthermia can be blocked with administration of sodium salicylate suggests that the hyperthermia is a fever. Thus, the antiChE-induced effects on body temperature and other physiological systems cannot be explained solely by the immediate consequences of AChE inhibition and stimulation of cholinergic systems. Research into the mechanisms of action of antiChE toxicity will be improved with a better understanding of their effects on temperature regulation.

Prostacyclin receptor in the brain and central terminals of the primary sensory neurons: an autoradiographic study using a stable prostacyclin analogue [3H]iloprost

Presence and localization of the prostacyclin receptor in the rat brain and spinal cord were examined by in vitro autoradiography using [3H]iloprost, a highly specific and stable agonist for this receptor. Density of specific binding sites for iloprost was generally high in four regions of the lower brain stem, that is, the medial and commissural subnuclei of the nucleus tractus solitarius, the area postrema, superficial layers of the spinal trigeminal nucleus caudalis and dorsal horn. Moderate density was found in the thalamus, cerebral cortex, hippocampus, striatum and dorsal cochlear nucleus. The distribution pattern was distinct from those of other prostanoid binding sites previously studied except that prostaglandin E2 binding sites were also abundant in the nucleus tractus solitarius, spinal trigeminal nucleus caudalis and dorsal horn. Even in these regions, binding sites for iloprost had several features clearly different from those for prostaglandin E2. First, within the medial and commissural subnuclei of the nucleus tractus solitarius, iloprost binding sites were distributed preferentially in the dorsal part, while those for prostaglandin E2 were located more ventrolaterally. Second, on postnatal day 0, iloprost binding sites have already been expressed in large amounts in the nucleus tractus solitarius, spinal trigeminal nucleus caudalis and dorsal horn of rats, while prostaglandin E2 binding sites are negligible at this stage. Thirdly, the binding of 10 nM [3H]iloprost in these three regions was almost completely displaced by 10 microM unlabelled iloprost but only slightly by 10 microM unlabelled prostaglandin E2. Unilateral nodose ganglionectomy or dorsal rhizotomy decreased the density of iloprost binding sites in the nucleus tractus solitarius or dorsal horn, respectively, with a greater decrease in the operated side. Ligation of the vagus either central or peripheral to the nodose ganglion resulted in an accumulation of iloprost binding sites proximal to the ligation. These results suggest that specific binding sites for iloprost, presumably prostacyclin receptor, are present in the nervous system and, in particular, that the iloprost binding sites in the nucleus tractus solitarius, dorsal horn and possibly in the superficial layers of the spinal trigeminal nucleus caudalis are produced in their sensory ganglia and transported to central terminals of the primary sensory afferents as well as to their peripheral terminals.

Rapid induction of prostaglandin synthesis in piglet astroglial cells by interleukin 1 alpha

We examined effects of interleukin 1 alpha (IL-1 alpha) on prostaglandin production in piglet cultured astroglia. Immuno- and morphologically identified polymorphic and process-bearing astrocytes were collected from cerebral cortex and white matter from piglets (1-3 days of age). Levels of prostaglandins were determined using enzyme immunoassay. Baseline levels for prostaglandin (PG) F2 alpha were 631 +/- 332 pg/ml and increased to 1417 +/- 353 pg/ml 20 min after addition of 11 micrograms/ml IL-1 alpha (p < 0.05) and to 2280 +/- 391 pg/ml 20 min after addition of 22 micrograms/ml IL-1 alpha (p < 0.05) (n = 7). Only small amounts of 6-keto-PGF 1 alpha or PGE2 were detected in medium under baseline conditions or in the presence of IL-1 alpha. Medium alone did not change PGF2 alpha levels (n = 3). Coapplication of cycloheximide (10(-3) M) blocked the increase in PGF2 alpha (n = 3). We conclude that IL-1 alpha causes a rapid increase in prostaglandin production by astroglia, and this process involves a step requiring continued or increased protein synthesis.

In vivo effect of visible light on feline cortical microcirculation

The present study was designed to test the hypothesis that prolonged illumination of the cerebral cortex, for instance during neurosurgical interventions, may affect the pial microcirculation. Experiments were performed with the closed window technique in cats. The cortical surface below the window was exposed to visible, cold light of 61,000 lumens/m2 (lux) over a period of 1 to 5 hours. Pial arterioles reacted with a slight initial dilatation to 106.8 +/- 2.6% of their resting diameter after switching to the high intensity light. Measurements of the cortical surface temperature showed an average temperature increase of 1.5 +/- 0.34 degrees C within the first 10 minutes of illumination. For assessment of pial vascular function, the responses to topical application of acetylcholine (ACh) were tested before and during the illumination period. The effect of sustained illumination on the cortical microcirculation consisted of abolition of the endothelium dependent relaxation due to ACh, and of intravascular thrombus formation, the latter, however, only in the presence of topically applied ACh. The suspected mechanism responsible for these functional alterations is light-induced generation of free oxygen radicals which are known to inactivate or destroy the endothelium-derived relaxing factor (EDRF). Further studies are recommended to elucidate the practical and clinical relevance of these findings to neurosurgical procedures.

Effects of phorbol esters on pial arteriolar diameter and brain production of prostanoids in piglets

We determined the effects of phorbol 12,13-dibutyrate (PDB), which activates protein kinase C, on pial arteriolar diameter and cerebrospinal fluid (CSF) prostanoid levels in newborn pigs. A closed cranial window was implanted, and the diameter of one pial arteriole was determined by intravital microscopy. In addition, CSF was sampled from under the window, and prostanoid levels (prostaglandin [PG] E2, 6-keto-PGF1 alpha, PGF2 alpha, and thromboxane B2) were determined by radioimmunoassay. Diameter and CSF prostanoid levels were determined during application of artificial CSF containing no drugs and during application of 10(-8), 10(-7), and 10(-6) M PDB. We also determined effects of 4 alpha-phorbol 12,13-didecanoate (4 alpha-PDD), a phorbol ester that does not activate protein kinase C, and dimethyl sulfoxide, the vehicle for the phorbol esters, on pial arteriolar diameter and CSF prostanoid levels. Initial diameters were 100-200 microns. At 10(-8)-10(-6) M, PDB progressively constricted pial arterioles and increased CSF levels of prostanoids; the other phorbol ester and dimethyl sulfoxide had no such effects. Baseline arteriolar diameter was 147 +/- 17 microns (mean +/- SEM), and diameter was 140 +/- 17 microns at 10(-8) M PDB, 120 +/- 18 microns at 10(-7) M PDB (p less than 0.05), and 108 +/- 14 microns at 10(-6) M PDB (p less than 0.05) (n = 5).(ABSTRACT TRUNCATED AT 250 WORDS)

Mono-L-arginine-containing compounds dilate piglet pial arterioles via an endothelium-derived relaxing factor-like substance

We determined the effects of mono-L-arginine-containing compounds on pial arterioles of anesthetized piglets. A closed cranial window was implanted, and the diameter of one pial arteriole was determined by intravital microscopy. Diameter was determined during application of artificial cerebrospinal fluid containing no drugs and during application of 10(-5), 10(-4), 10(-3), and 10(-2) M L-arginine (ARG), L-arginine ethyl ester (AEE), N alpha-benzoyl-L-arginine (NBA), N alpha-benzoyl-L-arginine ester ethyl (BAEE), and L-citrulline (CIT). Initial diameters were 100-200 microns. All of these compounds dilated arterioles, but the threshold concentration needed to elicit dilation varied: 10(-5) M for NBA (n = 5), 10(-3) M for AEE (n = 9) and BAEE (n = 6), and 10(-2) M for ARG (n = 6) and CIT (n = 4). Maximal responses were 15 +/- 8% for CIT, 17 +/- 4% for ARG, 19 +/- 8% for BAEE, 28 +/- 5% for NBA, and 27 +/- 6% for AEE. Indomethacin pretreatment (5 mg/kg i.v.) did not change arteriolar responses to AEE, NBA, and BAEE. However, coadministration of methylene blue (0.5 x 10(-4) M or 0.5 x 10(-3) M) abolished dilation to 10(-3) M AEE or BAEE and attenuated dilation to 10(-5) M NBA. In addition, coadministration of hemoglobin (0.4 x 10(-4) M) abolished dilation to AEE, BAEE, or NBA. Last, intravenous (5 mg/kg) and coadministration (10(-3) M) of NG-methyl-L-arginine blocked dilation to NBA or AEE. We conclude that mono-L-arginine-containing compounds produce pial arteriolar dilation in piglets, possibly involving an endothelium-derived relaxing factor.

Changes in cerebrovascular prostaglandins and thromboxane as a function of systemic blood pressure. Cerebral blood flow autoregulation of the newborn

Cerebrovascular concentrations of prostaglandin E (PGE), prostaglandin F2 alpha (PGF2 alpha), 6-ketoprostaglandin F1 alpha (6-keto-PGF1 alpha), and thromboxane B2 (TXB2) were determined over a blood pressure range of 17-117 mm Hg (induced by inflation of balloon-tipped catheters placed in the thoracic descending aorta and at the aortic root) in eight newborn piglets to access the role of prostanoids in cerebral blood flow (CBF; measured using radioactive microspheres) autoregulation. Basal systemic blood pressure, heart rate, blood gases, total CBF, and prostanoid concentrations were stable. CBF was constant between 50 and 90 mm Hg, but beyond this range CBF varied directly with blood pressure (tau = 0.48; p less than 0.05). Sagittal sinus concentrations of PGE, PGF2 alpha, and 6-keto-PGF1 alpha varied with blood pressure according to a quadratic function (R2 = 0.92 to 0.96; p less than 0.0001), exhibiting lowest values between mean blood pressures of 60 and 90 mm Hg. During hypotension (17-49 mm Hg), there was a greater relative increase in sagittal sinus concentrations of TXB2 than of PGE, PGF2 alpha, and 6-keto-PGF1 alpha; at the lowest blood pressures, TXB2 increased by 658 +/- 44%, and prostaglandins increased on the average by 331 +/- 49% (p less than 0.01) from their values during normotension (50-90 mm Hg). During hypertension (91-117 mm Hg), cerebrovascular production and concentrations of prostaglandins increased by 142 +/- 31% and 45 +/- 10%, respectively, but did not change for TXB2.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of thromboxane A2/endoperoxide antagonist SQ29548 on the contractile response to acetylcholine in newborn piglet cerebral arteries

Previous studies have shown that cholinergic stimulation results in a prostanoid-dependent cerebral vasoconstriction in piglets. The present study specifically investigated the contribution of thromboxane A2 (TXA2)/prostaglandin endoperoxide and prostaglandin F2 alpha (PGF2 alpha) to the cerebral vascular response to exogenous acetylcholine (ACh). Effects of TXA2/prostaglandin endoperoxide-receptor antagonist SQ29548 on responsiveness of pial arterioles to ACh (10(-7) and 10(-4) M), PGF2 alpha (10(-7)-10(-5) M), TXA2 mimetic 9,11-methanoepoxy prostaglandin H2 (U46619, 5 and 10 ng/ml), and norepinephrine (10(-6)-10(-4) M) were studied by use of a closed cranial window in 37 anesthetized mechanically ventilated newborn piglets. Pial arteriolar diameter was measured by intravital microscopy. Topical application of exogenous PGF2 alpha and U46619 resulted in dose-dependent cerebral vasoconstriction, and the dose-response curve for each agonist was shifted to the right by the increasing concentrations of SQ29548 (10(-6)-10(-8) M). Topical application of high concentration of ACh (10(-4) M) caused a transient 34 +/- 4% decrease in pial arteriolar diameter from 98 +/- 6 to 65 +/- 5 microns (p less than 0.05). This constriction was attenuated (16 +/- 3%) in the presence of 10(-8) M SQ29548 and abolished with 10(-6) or 10(-4) M SQ29548. SQ29548 (10(-6) M) was without effect on the vasoconstrictor response to exogenous norepinephrine. Low concentration of ACh (10(-7) M) had no consistent effect on pial arterioles in the absence or presence of TXA2/prostaglandin endoperoxide-receptor blockade. The data suggest that vascular prostaglandin/endoperoxide receptors mediate cerebral vasoconstriction upon muscarinic-receptor stimulation.

Perivascular blood attenuates noradrenergic but not cholinergic effects on piglet pial arterioles

We examined the chronic and acute effects of perivascular blood on cerebrovascular responses to norepinephrine and acetylcholine in 35 piglets. In the chronic experiment, fresh autologous blood (n = 15) or cerebrospinal fluid (n = 14, control) was placed under the dura mater over the parietal cortex, and the piglets were allowed to recover from anesthesia. One to 4 days later, a closed cranial window was placed over the parietal cortex and baseline pial arteriolar responses and responses to topical application of the neurotransmitters norepinephrine (10(-6) and 10(-4) M) and acetylcholine (10(-4) M) were determined. We also sampled cerebrospinal fluid from under the window during baseline conditions and during application of the neurotransmitters, and we measured the concentrations of prostanoids (6-ketoprostaglandin F1 alpha, thromboxane B2, prostaglandin F2 alpha, and prostaglandin E2) via radioimmunoassay. Pial arterioles in the chronic control group (n = 13) constricted by 20 +/- 2% (mean +/- SEM) in response to 10(-4) M norepinephrine and by 28 +/- 2% in response to 10(-4) M acetylcholine. In the chronic blood group (n = 14), pial arterioles did not constrict significantly in response to 10(-4) M norepinephrine but constricted normally (23 +/- 4%) in response to 10(-4) M acetylcholine. In the acute experiment, six other piglets had blood placed on the brain surface for 30 minutes and then removed; pial arterioles constricted by 21 +/- 1% in response to 10(-4) M norepinephrine (n = 5) and by 28 +/- 4% in response to 10(-4) M acetylcholine (n = 3).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of dopamine on pial arteriolar diameter and CSF prostanoid levels in piglets

We examined effects of topically applied dopamine on pial arteriolar diameter and CSF prostanoid levels in newborn pigs. Vascular responses were determined using the closed cranial window technique and intravital microscopy, and prostanoids were determined by radioimmunoassay. Topical application of dopamine did not change arteriolar diameter at 10(-7)-10(-5) M, but constricted arterioles at 10(-4) (16%) and 10(-3) M (30%). Intravenous administration of indomethacin (5 mg/kg) did not alter this constriction. In addition, CSF prostanoid levels did not increase in response to application of dopamine except for a modest increase of prostaglandin E2 at 10(-3) M. We conclude that dopamine is a constrictor at high doses of piglet pial arterioles and that this response is not modified by endogenous prostanoids.

Cholinergic mechanisms in the cerebral circulation of the newborn piglet: effect of inhibitors of arachidonic acid metabolism

The cerebrovascular response to cholinergic stimulation and the effect of inhibition of the lipoxygenase and cyclooxygenase pathways on the response to acetylcholine (ACh) was investigated in newborn piglets. Responsiveness of pial arterioles to ACh, methacholine, and nicotine was studied using a closed cranial window. Pial arteriolar diameter was measured using intravital microscopy. Pial arteriolar responses to ACh, 10(-8)-10(-4)M, applied to the cortical surface, were variable and dose-dependent. At low concentration, 10(-7)M, 45% of the arterioles increased diameter by 9 +/- 1%, 19% responded by decreasing diameter by 9 +/- 1%, and 35% did not respond. The response to high concentration, 10(-4)M, was a profound decrease in diameter, 28 +/- 3%, in 78% of the arterioles studied. These effects were abolished by atropine (0.5 mg/kg i.v.). Muscarinic agonist, methacholine, 10(-5)-10(-3)M, also resulted in a decrease in cerebral vascular diameter, while nicotine, 10(-6)-10(-4)M, had no effect. In six animals, administration of cyclooxygenase inhibitor, indomethacin (5 mg/kg i.v.), blocked the response to 10(-4)M ACh but did not affect the response to 10(-7)M ACh. In five animals, administration of lipoxygenase inhibitor, nordihydroguaiaretic acid (2 mg/kg i.v.) augmented the vasoconstrictor response at both ACh concentrations. The data suggest that, in the newborn piglet, vasoactive prostanoids released following cholinergic activation of a muscarinic-type receptor mediate vasoconstriction in cerebral arterioles.

Cerebral superoxide anion generation during seizures in newborn pigs

Cerebral superoxide anion generation during bicuculline-induced seizures was measured in newborn pigs. Using two closed cranial windows inserted over the parietal cortices, superoxide dismutase (SOD)-inhibitable nitroblue tetrazolium (NBT) reduction was determined during 20 min of seizure activity induced by bicuculline, 5 mg/kg i.v. A modest increase in SOD-inhibitable NBT reduction was observed in piglets subjected to bicuculline-induced seizure activity (2.4 +/- 0.6 pmol/mm2 in 20 min) when compared to control piglets (0.4 +/- 0.3 pmol/mm2 in 20 min). Pretreatment with indomethacin (5 mg/kg i.v.) reduced SOD-inhibitable NBT reduction during seizures to the control level (0.5 +/- 0.4 pmol/mm2 in 20 min). We conclude that small quantities of superoxide anion radical are produced by newborn pig brain during bicuculline-induced seizures and that cyclooxygenase metabolism of arachidonic acid appears to be a major source.

Molecular pharmacology of muscarinic receptor heterogeneity

Muscarinic receptors can be pharmacologically classified into 3 types at the present time, however, five genes for the receptor have been identified. The muscarinic receptor types have unique antagonist selectivity, distribution and are linked to specific second messenger systems. The interaction between the muscarinic receptor types and G proteins may depend on the systems in which the receptors are integrated. Expression of the cloned gene in mammalian cells will be useful in delineating the relationships between the pharmacological types of muscarinic receptors and their genes and studying the interactions between the receptor, G proteins, and second messenger coupling.

Vascular responses to vasopressin are tone-dependent in the cerebral circulation of the newborn pig

The effects of lysine vasopressin (LVP) on pial arteriolar diameter and cortical periarachnoid fluid prostanoid concentrations were investigated in newborn pigs. Chloralose-anesthetized piglets were equipped with closed cranial windows over the parietal cortex for observation of pial arterioles and collection of cerebrospinal fluid (CSF) passing over the cerebral surface. Prostanoids in the CSF were determined by radioimmunoassay. LVP (10-1,000 microU/ml) elicited concentration-dependent increases in pial arteriolar diameter associated with increased levels of 6-keto-prostaglandin (PG)F1 alpha, PGE2, thromboxane B2, and PGF2 alpha. LVP-induced pial arteriolar dilation was unchanged after intravenous indomethacin (5 mg/kg). Conversely, LVP constricts pial arterioles previously dilated by physiological (hemorrhagic hypotension) and pharmacological (topically applied PGE2 or isoproterenol) intervention. This constriction is potentiated by indomethacin. Vascular and biochemical changes elicited by LVP were blocked by intravenous [1-(beta-mercapto-beta beta-cyclopentamethylene propionic acid),2,(O-methyl)-Tyr-AVP] (5 micrograms/kg), a putative V1 receptor antagonist, whereas vascular effects of norepinephrine and U46619, a thromboxane A2 mimic, were unchanged. Therefore, the degree of vascular tone appears to influence responses of the newborn pig cerebral circulation to LVP.

Stimulation of arachidonic acid release and inhibition of mitogenesis by cloned genes for muscarinic receptor subtypes stably expressed in A9 L cells

A family of genes encoding four distinct muscarinic receptors (designated m1-m4) has been cloned and stably expressed in A9 L cells. When the m1 and m3 receptors were stimulated with carbachol, there was a rapid rise of liberated arachidonic acid, inositol phosphates, and cAMP, while m2 and m4 receptor stimulation had no detectable stimulation of these second messengers. Pretreatment with phorbol 12-myristate 13-acetate (PMA) caused a marked acceleration and amplification of m1 and m3 receptor-mediated arachidonic acid release. In contrast, m1- and m3-mediated inositol phosphate formation was inhibited by the same PMA pretreatment. Arachidonic acid release was unaffected by manipulations of cAMP levels. Arachidonic acid production was inhibited by calcium-free medium and 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester (TMB-8; an inhibitor of cytosolic calcium mobilization) yet was unaffected by verapamil, a calcium-channel blocker. These experiments show that arachidonic acid release induced by the m1 and m3 receptors is regulated independently of phospholipase C and cAMP accumulation. Carbachol stimulation of the m1 and m3 cAMP accumulation. Carbachol stimulation of the m1 and m3 receptors also markedly decreased mitogenesis as measured by thymidine incorporation. The m1 receptor-mediated inhibition of mitogenesis could be partially blocked by indomethacin, a cyclooxygenase inhibitor. The inhibition of mitogenesis could be mimicked by cAMP elevation.