Desipramine modulates 3H-ouabain binding in rat hypothalamus.

We have previously shown that Na+, K(+)-ATPase activity in hypothalamus is increased after administration of an acute dose of desipramine, a noradrenaline uptake inhibitor (Viola et al., Cell Molec Neurobiol 9:263-271, 1989). In this report the same treatment (10 mg per kg) was applied to evaluate 3H-ouabain binding in rat brain sections by quantitative autoradiography. Results disclosed an increase in the number of ouabain binding sites in hypothalamus but not in cerebral cortex. Concomitantly, such acute DMI treatment enhanced K(+)-stimulated-p-nitrophenylphosphatase activity in hypothalamus membranes whereas it failed to modify cerebral cortex membranes. A direct interaction of DMI with the enzyme was ruled out since in vitro DMI is known to inhibit the enzyme. It may be speculated that DMI indirectly stimulates Na+, K(+)-ATPase through the increase in noradrenaline which acts in turn on the external phosphorylated site of the enzyme.

Hypotensive and hypertensive effects of catecholamines intrathecally injected in anesthetized rats.

The cardiovascular effects of catecholamines intrathecally (i.t.) injected at the T12-L1 level were analyzed in pentobarbital anesthetized rats. Volumes of injection were not greater than 3 microliters. Noradrenaline in doses ranging from 0.03 to 0.3 micrograms (i.t.) did not alter the mean blood pressure (MBP) while higher doses (1, 3 and 10 micrograms, i.t.) caused a dose-dependent increase in MBP. Adrenaline induced hypotensive effects at low doses (0.03-0.3 micrograms i.t.) and pressor effects at high doses (3 and 10 micrograms, i.t.). Neither adrenaline nor noradrenaline modified the heart rate. The pressor responses to both catecholamines were antagonized by the alpha 1-adrenoceptor blocker prazosin (0.05-1 microgram, i.t.) and by the selective alpha 1A-adrenoceptor antagonist 5-methyl urapidil (10 and 15 micrograms, i.t.). In contrast, these pressor effects were not modified by the alpha 1B-adrenoceptor antagonist chloroethylclonidine (90 micrograms i.t.). In animals pretreated with 1 microgram prazosin (i.t.), low doses of noradrenaline (0.03 and 0.1 microgram, i.t.) caused a hypotensive effect. Prazosin (1 microgram i.t.) failed to alter the hypotension caused by 0.1 microgram adrenaline. The hypotensive response induced by either 0.1 microgram noradrenaline (in the presence of prazosin) or 0.1 microgram adrenaline was blocked by the alpha 2-adrenoceptor antagonist yohimbine (1 mg/kg, i.v.), by the GABA-A antagonists bicuculline (3.2 micrograms, i.t.) and picrotoxin (2.7 micrograms, i.t.), and by the GABA-B antagonist 2-hydroxy saclofen (30 micrograms, i.t.). The glycine-receptor antagonist strychnine (25 micrograms, i.t.) did not modify the hypotension induced by either noradrenaline (in the presence of prazosin) or adrenaline. These findings suggest that in the low thoracolumbar spinal cord of pentobarbital-anesthetized rats, noradrenaline and adrenaline have excitatory as well as inhibitory effects on the control of the BP. The pressor responses of high doses of i.t. injected catecholamines could be mediated by the activation of spinal alpha 1A-adrenoceptors, although the participation of alpha 1B-adrenoceptors cannot be rule out entirely. The hypotensive responses induced by low doses of i.t. injected catecholamines seem to involve the activation of spinal alpha 2A-adrenoceptors and the stimulation of an inhibitory GABAergic neuron in the spinal cord.

Central alpha 1- and alpha 2-adrenoceptors and brain cholinergic stimulation in sinoaortic denervated rats.

The central alpha-adrenoceptor role in cardiovascular responses to intracerebroventricular (i.c.v.) injection of neostigmine, a tertiary anticholinesterase, was studied in conscious sham-operated and sinoaortic-denervated rats. Neostigmine (0.1-1 micrograms i.c.v.) showed dose-dependent pressor and bradycardiac effects in vehicle-pretreated sham-operated rats but only an increased pressor effect in sinoaortic-denervated animals. The pretreatment with the catecholaminergic neurotoxin, 6-hydroxydopamine (250 micrograms i.c.v.), given 72 h previous to the corresponding operation, blunted the cardiovascular effects of neostigmine in both groups of rats. Prazosin (10 and 30 micrograms i.c.v.), an alpha 1-adrenoceptor antagonist, prevented the pressor response to neostigmine (0.3 micrograms i.c.v.) in sham-operated and sinoaortic-denervated rats. Yohimbine, a alpha 2-adrenoceptor antagonist (10 and 30 micrograms i.c.v.), only prevented the bradycardia induced by neostigmine (0.3 micrograms i.c.v.) in the sham-operated rats. 6-Hydroxydopamine pretreatment lowered the norepinephrine content in hypothalamus, midbrain, medulla oblongata and spinal cord, but did not modify it in the pons, in sham-operated rats and sinoaortic-denervated animals. The present results suggested that brain alpha 1-adrenoceptors would mediate the pressor response to neostigmine (i.c.v.) in sham-operated and sinoaortic-denervated rats and central alpha 2-adrenoceptors mediate the bradycardia in sham-operated rats. This work lends support to the view that cardiovascular responses to brain cholinergic stimulation in sham-operated and sinoaortic-denervated rats could be mediated by a central catecholaminergic activation.

Effects of angiotensin II and angiotensin-(1-7) on the release of [3H]norepinephrine from rat atria.

We examined the effects of angiotensin II (Ang II) and Ang-(1-7) on the release of [3H]norepinephrine elicited by nerve stimulation (2 Hz, 0.5 millisecond, for 2 minutes) in rat atria isolated with their cardioaccelerans nerves. The stimulation-induced release of [3H]norepinephrine was increased 50% by 3 x 10(-8) mol/L of either peptide. No further increase in [3H]norepinephrine release was observed with peptide concentrations up to 3 x 10(-7) mol/L. This effect was completely blocked by the nonselective angiotensin receptor antagonist saralasin (1 x 10(-7) mol/L). The type 1 angiotensin receptor antagonist DuP 753 (1 x 10(-6) mol/L) entirely prevented the increases in [3H]norepinephrine caused by Ang II and Ang-(1-7). On the other hand, the type 2 angiotensin receptor antagonist PD 123319 (1 x 10(-6) mol/L) prevented the increase in [3H]norepinephrine release elicited by Ang-(1-7) but not by Ang II. These results suggest that Ang-(1-7), like Ang II, could have a neuromodulatory function in rat atria via activation of specific angiotensin receptor subtypes, which could be the subtype 1 angiotensin receptor for Ang II and subtypes 1 and 2 for Ang-(1-7).

Cardiovascular responses to cholinergic agonists in sinoaortic denervated rats.

1. The cardiovascular effect of systemic nicotinic and muscarinic cholinergic stimulation were studied in conscious sham operated and sinoaortic denervated (SAD) rats, 7 days after the corresponding operation. 2. The administration of the nicotinic ganglionic agent, 1,1-dimethyl-4-phenylpiperazinium (DMPP, 50-100 micrograms.kg-1, i.v.) induced a fall of heart rate that was significantly higher in SAD rats than in sham rats. DMPP induced in sham rats an increase of arterial pressure but in SAD animals a biphasic response: an initial hypotension followed by an increase of arterial pressure. 3. Under muscarinic blockade, DMPP only showed a pressor and tachycardic action in both groups of rats without differences between them. 4. The muscarinic agonist, carbachol (0.1-10 micrograms.kg-1, i.v.) showed the same hypotensive and bradycardic action in both groups of rats. 5. Our results suggest that after 7 days of SAD, differences in the response to DMPP between sham and denervated animals could be due to the loss of baroreflex mechanisms. The increased bradycardic effect of DMPP in SAD rats could be mediated by a supersensitivity of parasympathetic ganglionic nicotinic receptors, whilst the sympathetic ganglionic nicotinic receptors remained unaltered. On the other side, the cardiovascular muscarinic responses to carbachol remain unaffected in SAD rats.

Na+,K(+)-ATPase activity in CNS and noradrenergic neurotransmission: time course of differential desipramine (DMI) effects.

ATPase activities in CNS membranes were studied after administration of desipramine (DMI), a noradrenaline (NA) uptake inhibitor. In a previous paper we reported that Na+,K(+)-ATPase activity significantly increased 3 h after DMI administration (10 mg/kg) in hypothalamus and mesencephalus but not in cerebral cortex and pons-medulla oblongata membranes (Viola et al., Cell. molec. Neurobiol. 1989, 9, 263-271). Here it was observed that Na+,K(+)-ATPase increase induced by acute DMI disappeared at 24 h in hypothalamus but remained during 21 days in mesencephalus. Na+,K(+)-ATPase increase by acute DMI was inhibited when endogenous NA was depleted by the noradrenergic neurotoxin DSP-4 or the NA synthesis inhibitor alpha-methyl-p-tyrosine. On the whole, Mg(2+)-ATPase activity was not modified by treatment. 5'-nucleotidase, another membrane-bound enzyme, was unchanged by acute DMI. The addition of DMI in vitro (50 ng/mg tissue) during Na+,K(+)-ATPase assay failed to affect ATPase activities. Acute DMI effects on Na+,K(+)-ATPase are thus attributable to noradrenergic neurotransmission rather than to non-specific drug-CNS membrane interaction. Furthermore, DMI produces differential effects on membrane Na+,K(+)-ATPase, depending on treatment conditions and CNS area studied.

Beta-adrenoceptor desensitization by/clenbuterol in rat uterus.

1. The relaxant response and cAMP production mediated by stimulation of isoproterenol is reduced in uterine rings from clenbuterol treated rats (0.25 mg kg-1 s.c. 24 hr before experiments) precontracted with 50 mM KCl. 2. Forskolin, in contrast, showed similar relaxant responses in untreated or clenbuterol treated rats. 3. Isoproterenol produces a biphasic response that is composed of a rapid relaxation followed by a slower regaining of tension, which is considered as desensitization. 4. The kinetic study demonstrates marked changes in the desensitization process of beta-adrenoceptors after clenbuterol administration.

Effect of endothelium removal on basal and muscarinic cholinergic stimulated rat mesenteric vascular bed prostanoid synthesis.

The ability of the rat mesenteric vascular bed to synthesize prostanoids with and without endothelium in basal conditions and in response to acetylcholine (ACh) stimulation was investigated. Isolated and perfused mesenteric vascular bed released 6-keto-prostaglandin F1 alpha and thromboxane B2 (TXB2) (stable metabolites of prostacyclin (PGI2) and TXA2, respectively), and also prostaglandin E2 (PGE2) and PGF2 alpha. PGI2 was the major prostanoid formed by the mesenteric vascular bed. ACh 10(-5) M markedly increased PGI2 release without any effect on the other prostanoids. Atropine 10(-6) M added to the perfusion medium previous to ACh reduced the release of PGI2. Atropine alone did not modify the basal prostanoid pattern. Removal of endothelium with 96% ethanol produced a 50% reduction in the production of PGI2 and TXA2 with respect to basal values, without modifying PGE2 or PGF2 alpha. Cholinergic stimulation by ACh of the de-endothelialized mesenteric vascular bed significantly increased only TXA2 production. Atropine prevents this response to ACh. Our results indicate that in mesenteric vascular bed, endothelium mainly produces a potent vasodilator prostanoid, PGI2, but also a lesser proportion of TXA2. ACh, in stimulating muscarinic receptors, induces the production and release of PGI2 from endothelium and TXA2 from vascular smooth muscle when the endothelium is absent.

Noradrenergic-GABAergic interaction in anterior hypothalamus from normotensive and sinoaortic denervated rats.

1. GABA content is decreased in anterior hypothalamus and medulla oblongata of hypertensive rats by sinoaortic denervation (SAD) when compared to control animals which underwent a sham-operation (sham). 2. Lesion of noradrenergic pathways by 6-hydroxydopamine (6-OHDA), intracerebroventricularly administered, induced depletion of noradrenergic content in frontal cortex, anterior and posterior hypothalamus in both SAD and sham-operated rats. 3. As a consequence of this noradrenergic depletion there was an increase of GABA content in anterior hypothalamus only, from sham- and SAD-operated animals, without changes in other areas. 4. There is a noradrenergic-GABAergic interaction in the anterior hypothalamus of normotensive rats which is not impaired in hypertensive rats by sinoaortic denervation.

Involvement of renal dopamine synthesis in the diuretic effect of furosemide in normohydrated rats.

The present study was designed to investigate whether the modification of dopamine synthesis affects furosemide responses. Experiments were performed on pentobarbital-anesthetized rats. Basal urine flow was approximately 3 microliters/min-1/g-1 of kidney weight (k.w.); furosemide (0.2 mg/kg-1 i.v.) induced a rapid diuretic effect (19.3 +/- 1.4 microliters/min-1/g-1 of k.w.). The dopadecarboxilase inhibitor, benserazide (25 mg/kg-1 i.v.), reduced furosemide-induced diuresis to 8.3 +/- 2.1 microliters/min-1/g-1 of k.w., whereas levo-dihydroxyphenylalanine (L-dopa; 1 micrograms/kg-1/min-1 infused for 60 min) increased it to 41.4 +/- 6.1 microliters/min-1/g-1 of k.w. Natriuretic response and fractional Na+ excretion induced by furosemide were significantly lower in benserazide-treated and higher in L-dopa-treated animals. Urine dopamine (DA) excretion was enhanced by furosemide from 0.44 +/- 0.05 to 0.98 +/- 0.22 ng/min-1/g-1 of k.w. and was markedly reduced in benserazide-pretreated animals, whereas both basal DA excretion and that induced by furosemide were increased significantly during L-dopa infusion. However, in benserazide- or L-dopa-treated animals, basal urine flow was not different from the control group. Urine furosemide excretion was reduced by 60% by benserazide treatment and increased by 62% during L-dopa infusion. The results are consistent with the suggestion that although endogenous DA is apparently unimportant in the maintenance of basal urine output, it is involved in furosemide-induced diuresis. The diuretic response can be altered by acute administration of substances that affect dopamine synthesis.

Activation of 5-HT2 receptors inhibits the evoked release of [3H]noradrenaline in the rat spinal cord.

1. The participation of 5-HT2 receptors in the modulation of the evoked release of [3H]noradrenaline from rat spinal cord slices has been examined. 2. In rat spinal cord slices preincubated with [3H]noradrenaline, the alpha 2-receptor agonist clonidine (10(-6) mol/l) decreased the release of tritium evoked by field stimulation (600 pulses at 5 Hz, 20 mA, 2 msec), while the alpha 2-antagonist yohimbine (10(-6) mol/l) increased it. 3. The 5-HT2/5-HT1c agonist DOI (3 x 10(-7) mol/l) decreased the evoked release of tritium, an effect which was prevented by ketanserin (10(-7) mol/l). 4. It is suggested that in addition to presynaptic alpha 2-adrenoceptors, there are 5-HT2 receptors which modulate the release of noradrenaline in the rat spinal cord.

Role of cyclic AMP in the release of noradrenaline from isolated rat atria. Effect of pretreatment with clenbuterol.

The possible role of cyclic AMP (cAMP) on tritium overflow evoked by stimulation of the cardio-accelerant nerves was studied in rat atria preincubated with [3H]-noradrenaline. Addition of the activator of adenylate cyclase forskolin (1 mumol/l), or of the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX, 100 mumol/l), did not affect both basal and evoked overflow. However, in the presence of the alpha 2-adrenoceptor antagonist yohimbine (0.03 mumol/l) both forskolin and IBMX increased the stimulation-induced transmitter overflow by 49% and 141%, respectively (compared to yohimbine 0.03 mumol/l). Thus, in rat atria the cAMP-dependent facilitation of noradrenaline release is only present when the autoinhibition exerted by activation of prejunctional alpha 2-adrenoceptors is blocked. Propranolol (0.1 mumol/l) that did not produce any effect on noradrenaline release markedly reduced the facilitatory response induced by forskolin in the presence of yohimbine. When rats were pretreated with the beta 2-adrenoceptor agonist clenbuterol (0.3 mg.kg-1, s.c., twice daily, 14 days), a treatment which desensitizes beta-adrenoceptor-mediated facilitation of noradrenaline release (Kazanietz and Enero 1989), the facilitatory effect of forskolin and IBMX in the presence of yohimbine was abolished. The results indicate that in rat atria the effect of forskolin and IBMX on noradrenaline release are only to be observed after blockade of presynaptic alpha 2-adrenoceptor autoinhibition. beta-adrenoceptor blockade or clenbuterol pretreatment decreases the facilitatory response to forskolin and hence prejunctional beta-adrenoceptor-mediated enhancement of noradrenaline release is linked to the stimulation of adenylate cyclase.

Cardiovascular responses of sinoaortic-denervated rats to intracerebroventricular injection of alpha 1- and alpha 2-adrenoceptor agonists.

The aim of the present work was to analyse the cardiovascular responses induced by i.c.v. administration of the alpha 1- and alpha 2-adrenoceptor agonists, phenylephrine and clonidine, respectively, in conscious normal and sinoaortic-denervated rats. Sinoaortic denervation involves changes in central and peripheral catecholaminergic pathways. Clonidine (1-10 micrograms) produced a dose-dependent rise in blood pressure and a bradycardiac response in sham-operated animals, whereas in sinoaortic-denervated rats it provoked a brief rise in blood pressure followed by a marked fall as well as bradycardia. The responses involved mostly activation of central alpha 2-adrenoceptors, but the blood pressure responses induced by clonidine in sinoaortic-denervated rats may also have involved alpha 1-adrenoceptors. The bradycardia induced by the alpha 2-agonist in both groups of rats involved preferentially central alpha 2-adrenoceptors but also partially stimulated alpha 1-adrenoceptors. Phenylephrine, at a dose of 10-60 micrograms, induced a rise in blood pressure and a bradycardiac response while 90 micrograms produced a biphasic pressure response (early transient rise followed by a fall) as well as bradycardia in both sham-operated and sinoaortic-denervated animals. Phenylephrine activated alpha 1-adrenoceptors in every case, but the fall in blood pressure and the bradycardia also involved alpha 2-adrenoceptors. The responses were significantly higher in the sinoaortic-denervated rats than in the sham-operated. Our findings suggest that arterial baroreceptor reflexes can modify the effects of alpha-agonists initiated in the central nervous system. Sinoaortic denervation preparations enable one to unmask the depressor response to clonidine and also demonstrate the true magnitude of the phenylephrine response.

Decreased beta-adrenoceptor-mediated vasodilation in aorta from aged rats: possible involvement of a stimulatory GTP-binding protein.

KCl-contracted aortic rings from 18-month-old rats, in contrast with those from 2-month-old rats, showed a substantial reduction in the relaxant effects of the non-selective beta-adrenoceptor agonist, isoproterenol, and of the selective beta 2-adrenoceptor agonist, clenbuterol, without changes in the relaxant actions of forskolin (an activator of the adenylate cyclase), 3-isobutyl-1-methyl-xanthine (a phosphodiesterase inhibitor) or acetylcholine (an endothelium- and cyclic GMP-dependent vasodilator). The relaxant responses induced by adenosine and 2-Cl-adenosine were also reduced in aged aortas. Isoproterenol and cholera toxin (an inhibitor of GTPase activity of the stimulatory GTP-binding protein) reduced cAMP production in aortas from 18-month-old rats. It is suggested that a decrease in the function of the stimulatory GTP-binding protein may contribute at least in part to the impairment in the vasodilation induced by activation of beta-adrenoceptors in aortas from aged rats.

Role of dopamine1-receptors in mediating renal responses to furosemide in the rat.

1. Dopamine (DA) infusion enhanced the diuresis, natriuresis and kaliuresis evoked by furosemide, but this increase was significantly lower in the presence of SCH 23390, a selective DA1-dopaminergic antagonist. 2. Water, Na+ and K+ excretion induced by furosemide were reduced by haloperidol, and SCH 23390, whereas they were not affected by +/- sulpiride, a preferentially DA2-dopaminergic antagonist. 3. The treatments used did not modify the mean blood pressure during the experiments. 4. Our data show that renal responses to furosemide are attenuated by the DA1-dopaminergic antagonist. It is possible that endogenous DA, stimulating DA1 receptors in the rat kidney may be an important factor involved in the Na+, K+ and water excretion evoked by furosemide.

Effects of clenbuterol treatment on the responses to vasodilators in urethane-anaesthetized rats.

Seven or 14 days of treatment with the beta 2-adrenoceptor agonist clenbuterol, 0.3 mg kg-1, s.c., twice daily, increased the basal mean blood pressure in normotensive urethane-anaesthetized rats. The elevated pressure values were maintained until 48 h after the end of the 14 day treatment. Clenbuterol treatment decreased the vasodilatory responses to the beta-adrenoceptor agonist isoprenaline and adenosine, agents which act through an increase in intracellular cyclic AMP. Decreased responses were maintained until 48 h after a 14 day treatment with clenbuterol. On the other hand, its administration to rats for 14 days did not modify the vasodilator responses to acetylcholine or sodium nitroprusside, two agents that exert their effects by enhancing cyclic GMP. The increase in mean blood pressure in urethane-anaesthetized rats after clenbuterol treatment may be a consequence of a reduced vasodilator beta 2-adrenoceptor-mediated response to circulating catecholamines.

Endothelium and Ca2+ in the prostaglandin F2 alpha potentiation of vasoconstrictor responses.

Prostaglandin F2 alpha (PGF2 alpha), at a concentration that did not induce vascular contraction (10(-9) and 10(-10) M), potentiated the dose-response curves to norepinephrine (NE) in rat mesenteric ring segments only when the endothelium was present. Moreover, PGF2 alpha, in both unrubbed mesenteric artery and mesenteric vascular bed, was able to increase the contraction to NE as well as the ratio of the amplitude of two NE-induced contractions under previously standardized conditions, in the absence of extracellular calcium. In addition, without extracellular Ca2+, PGF2 alpha increased in both tissues the refilling of Ca2+ induced by 80 mM KCl plus 1.5 mM Ca2+. The mechanism of this potentiation is unknown, but it may be related to cellular events including the intracellular Ca2+ mobilization. This study suggests that the endothelium plays a necessary role in PGF2 alpha potentiation of vasoconstrictor response, possibly through the release of an endothelial vasoconstrictor factor which probably increases the Ca2+ bioavailability for the contraction.

Desensitization of the beta-2 adrenoceptor-mediated vasodilation in rat aorta after prolonged treatment with the beta-2 adrenoceptor agonist clenbuterol.

Administration to rats of the selective beta-2 adrenoceptor agonist (+/-)-clenbuterol (CLEN) (0.3 mg.kg-1 s.c., twice daily for 14 days) decreased the relaxant responses to the beta adrenoceptor agonist (-)-isoproterenol (IS) and to CLEN in KCl-contracted aortic rings. The treatment did not modify the vasodilation induced by forskolin (a direct activator of the catalytic subunit of the adenylate cyclase), 3-isobutyl-1-methylxanthine (a phosphodiesterase inhibitor), adenosine or acetylcholine. IS increased (cAMP) cyclic AMP levels dose-dependently in rat aorta, and this effect was reduced markedly in arteries from CLEN-treated rats. By contrast, the treatment did not modify the forskolin-induced cAMP production. The contractile response to (-)-norepinephrine (NE) was inhibited in the presence of IS or CLEN in control aortic rings. However, this modulatory effect was not seen in arteries from CLEN-treated rats. Preincubation of the arteries with either cholera toxin (an activator of the stimulatory guanine nucleotide binding protein, Gs) or forskolin reduced NE-induced vasoconstriction to the same extent in aortic rings from both control and CLEN-treated rats. The chronotropic response to NE in rat atria (beta-1-mediated) was not affected by the treatment. These results suggest that prolonged administration of CLEN to rats induced desensitization of beta-2 adrenoceptor-mediated vascular relaxation by alterations at the level of the beta-2 adrenergic receptor, but not in the mechanisms related to Gs, adenylate cyclase or in those distal to cAMP production.

Diuretic and natriuretic effect of a brain soluble fraction that inhibits neuronal Na+,K(+)-ATPase.

The separation by Sephadex G-50 of two subfractions, peak I and II, from the brain soluble fraction has been previously described. These fractions were able to stimulate and inhibit synaptosomal membrane Na+,K(+)-ATPase, respectively (Rodríguez de Lores Arnaiz and Antonelli de Gómez de Lima, Neurochem. Res. 11, 933-948, 1986). Experimental evidence indicates that the alteration of Na+,K(+)-ATPase activity may result in changes of renal and cardiovascular parameters. In the present study, we have analyzed the effect of peak I and II fractions prepared from rat cerebral cortex on water and sodium excretion and on heart rate and arterial pressure in normotensive anesthetized rats. It was observed that water and sodium excretion were not modified by the administration of peak I fraction but that they were increased by peak II fraction. The cardiovascular parameters were not significantly modified by either of the fractions. The results indicate that brain soluble factor (s) which is (are) present in peak II fraction may modify some aspects of renal physiology after systemic administration.