The inhibitory material in extracts from the bovine retractor penis muscle is not an adenine nucleotide

Evidence that inhibitory factor extracted from bovine retractor penis is nitrite, whose acid-activated derivative is stabilized nitric oxide

1. Unactivated extracts of bovine retractor penis (BRP) contains 3-7 microM nitrite. Acid-activation of these extracts at pH 2 for 10 min followed by neutralization generates the active form of inhibitory factor (IF; assayed by its vasodilator action on rabbit aorta), and is associated with partial loss of nitrite. 2. Increasing the time of acid-activation at pH 2 from 10 to 60 min with intermittent vortex mixing generates greater vasodilator activity and increases nitrite loss. 3. When acid-activated and neutralized extracts are incubated at 37 degrees C or 30 min or boiled for 5 min, vasodilator activity is lost and nitrite content increased. Reactivation of these samples at pH 2 for 10 min followed by neutralization leads to partial recoveries of vasodilator activity with loss in nitrite content. 4. Addition of sodium nitrite to BRP extracts increases acid-activatable vasodilator activity pro rata. 5. Acid-activation of aqueous sodium nitrite solutions results in less loss of nitrite and generation of less vasodilator activity than BRP extracts. Vasodilatation is only transient and is rapidly abolished on neutralization, whereas responses to acid-activated BRP extracts are more prolonged and activity is stable on ice. 6. Bovine aortic endothelial cells yield vasodilator activity that is indistinguishable from that isolated from BRP. It is activated by acid, stable on ice, abolished by boiling or by haemoglobin, and appears to be due to the generation of nitric oxide (NO) from nitrite. 7. The data provide confirmatory evidence that nitrite in BRP extracts is IF, that acid-activation of BRP extracts yields NO which is responsible for its vasodilator action, and that inactivation occurs by decay of NO to nitrite and nitrate. They further suggest that BRP extracts contain a NO-stabilizing agent which favours conversion of nitrite to NO. 8. The finding that bovine aortic endothelial cells yield an agent indistinguishable from IF suggests that nitrite in endothelial cells may likewise be the precursor of endothelium-derived relaxing factor (EDRF), itself identified as NO.

Endothelium-derived relaxing factor inhibits in vitro platelet aggregation

We studied the effects of endothelium-derived relaxing factor (EDRF), bovine retractor penis muscle inhibitory factor and sodium nitroprusside, three stimulants of guanylate cyclase, on the in vitro aggregation of washed human platelets. Platelet aggregation induced either by collagen or by the thromboxane A2 analogue U46619 was inhibited by all three agents. The anti-aggregatory effect of each agent was inhibited by haemoglobin. The anti-aggregatory effect of EDRF was potentiated by superoxide dismutase. These findings are discussed in relation to a potential role for EDRF in haemostasis.

The mechanisms by which haemoglobin inhibits the relaxation of rabbit aorta induced by nitrovasodilators, nitric oxide, or bovine retractor penis inhibitory factor

The mechanisms by which haemoglobin and methaemoglobin inhibit the vasodilator actions of glyceryl trinitrate, sodium azide, nitric oxide, and the bovine retractor penis inhibitory factor (IF) were studied on rabbit endothelium-denuded aortic rings. Methaemoglobin was less effective than haemoglobin against each vasodilator, it was more effective at inhibiting the relaxation to azide than that to glyceryl trinitrate. Glyceryl trinitrate was neither bound nor inactivated when passed through columns of haemoglobin-agarose or methaemoglobin-agarose. Azide was reversibly bound but less by haemoglobin-agarose than by methaemoglobin-agarose. Inhibition of the vasodilator actions of glyceryl trinitrate is not attributable therefore to a direct interaction with the haemoproteins, although a small part of the inhibition of azide-induced relaxation by methaemoglobin is likely to be due to a direct interaction. Columns of haemoglobin-agarose were more effective than columns of methaemoglobin-agarose in removing nitric oxide from solution. The greater ability of haemoglobin, compared to methaemoglobin, to inhibit vasodilatation induced by nitrovasodilators may therefore reflect the greater ability of haemoglobin to bind nitric oxide which is the active principle of the nitrovasodilators. Neither the acid-activated nor the inactive forms of IF were bound or inactivated when passed through columns of methaemoglobin-agarose. Neither form of IF was retained on passage through columns of haemoglobin-agarose, but the resulting activity in the eluates was less than control, was unstable and, unlike the original activity, decayed rapidly on ice. The greater ability of haemoglobin, compared to methaemoglobin, to inhibit vasodilatation induced by IF might therefore reflect the greater ability of haemoglobin to interact with this vasodilator and inactivate it.

A comparison of the action of the endothelium-derived relaxant factor and the inhibitory factor from the bovine retractor penis on rabbit aortic smooth muscle

The dependence of relaxation of rabbit aortic strips by carbachol and by the inhibitory factor from the bovine retractor penis (BRP) on the presence of endothelium has been compared. Carbachol-induced relaxation is abolished by removing the endothelium, inhibitory factor-induced relaxation is unimpaired. The inhibitory factor, therefore, does not act by releasing an endothelium-derived relaxing factor (EDRF). The effect of inhibitors of eicosanoid metabolism on relaxation was examined. Quinacrine and nordihydroguaiaretic acid abolished the relaxant effect of carbachol and flurbiprofen had no effect. The relaxation produced by the inhibitory factor was unaffected by quinacrine and flurbiprofen while nordihydroguaiaretic acid potentiated the response. No eicosanoid appears, therefore, to be involved in the relaxant effect of the inhibitory factor from the BRP. Methylene blue, a drug reported to inhibit guanylate cyclase, in a concentration of 10 microM selectively abolished the relaxation produced by carbachol. However, at the higher concentration of 30 microM it abolished almost completely the response to inhibitory factor from the BRP and reduced inhibition by sodium nitroprusside. It is not possible from these results to exclude the possibility that the EDRF and the inhibitory factor from the BRP are chemically related.

Mechanisms underlying electrical and mechanical responses of the bovine retractor penis to inhibitory nerve stimulation and to an inhibitory extract

The response of the bovine retractor penis (BRP) to stimulation of non-adrenergic, non-cholinergic (NANC) inhibitory nerves and to an inhibitory extract prepared from this muscle have been studied using intracellular microelectrode, sucrose gap and conventional mechanical recording techniques. Both inhibitory nerve stimulation and inhibitory extract hyperpolarized the membrane potential and relaxed spontaneous or guanethidine (3 X 10(-5) M)-induced tone. These effects were accompanied by an increase in membrane resistance. Following membrane potential displacement from an average value of -53 +/- 7 mV (n = 184; Byrne & Muir, 1984) inhibitory potentials to nerve stimulation were abolished at approximately -30 mV; there was no evidence of reversal. Displacement by inward hyperpolarizing current over the range -45 to -60 mV increased the inhibitory response to nerve stimulation and to inhibitory extract; at more negative potential values (above approximately -60 mV) the inhibitory potential decreased and was abolished (approximately -103 mV). There was no evidence of reversal. Removal of [K+]o reversibly reduced hyperpolarization to nerve stimulation and inhibitory extract. No enhancement was observed. Increasing the [K+]o to 20 mM reduced the inhibitory potential to nerve stimulation but this was restored by passive membrane hyperpolarization. Inhibitory potentials were obtained at membrane potential values exceeding that of the estimated EK (-49 mV). [Cl-]o-free or [Cl-]o-deficient solutions reduced and abolished (after some 20-25 min) the hyperpolarization produced by inhibitory nerve stimulation or inhibitory extract. The inhibitory potential amplitude following nerve stimulation was not restored by passive displacement of the membrane potential from -26 to -104 mV approximately. Ouabain (1-5 X 10(-5) M) reduced then (45-60 min later) abolished the inhibitory potential to nerve stimulation. The effects of this drug on the extract were not investigated. It is concluded that the inhibitory response to nerve stimulation and extract in the BRP may involve several ionic species. However, unlike that in gastrointestinal muscles the NANC response in the BRP is accompanied by an increased membrane resistance and does not primarily involve K+. The underlying mechanisms for the inhibitory response to both NANC nerve stimulation and inhibitory extract appear to be similar, compatible with the view that the latter may contain the inhibitory transmitter released from these nerves in this tissue.

Cyclic GMP mediates neurogenic relaxation in the bovine retractor penis muscle

Field stimulation of the non-adrenergic, non-cholinergic inhibitory nerves to the bovine isolated retractor penis muscle evoked a relaxation that was preceded by a rise in the tissue content of cyclic GMP. There was no change in the content of cyclic AMP. The selective cyclic GMP phosphodiesterase inhibitor, 2-o- propoxyphenyl -8- azapurin -6-one (M&B 22948), elevated the tissue's cyclic GMP content, and potentiated both the relaxation and the rise in cyclic GMP produced by inhibitory nerve stimulation. Sodium nitroprusside and an inhibitory factor extracted from the bovine retractor penis muscle mimicked the effects of inhibitory nerve stimulation in that they each produced relaxation associated with a selective rise in cyclic GMP concentration. Haemoglobin (in the form of erythrocyte haemolysate) and N- methylhydroxylamine , which are known to block guanylate cyclase, blocked the relaxation and the rise in cyclic GMP content produced by inhibitory nerve stimulation, inhibitory factor and sodium nitroprusside. Haemoglobin itself caused a rise in muscle tone and at the same time reduced the cyclic GMP content of the tissue. 8-Bromocyclic GMP, a permeant derivative of cyclic GMP, produced a relaxation of the muscle that, as expected, was not blocked by haemoglobin. Vasoactive intestinal polypeptide, prostaglandin E1 and forskolin each produced relaxation associated with a selective rise in cyclic AMP content. Their effects were not blocked by haemoglobin or N- methylhydroxylamine . It is concluded that inhibitory nerve stimulation in the bovine retractor penis muscle produces a relaxation that is mediated by cyclic GMP, although some substances relax the muscle without affecting cyclic GMP levels. The results are also compatible with the view that the extracts of muscle contain the inhibitory neurotransmitter.

Neurogenic vasodilatation in isolated bovine and canine penile arteries

Field stimulation of isolated, perfused bovine or canine penile arteries produced dilatation, after the adrenergic motor component of the response had been blocked with guanethidine and the vessels had developed a background tone. The vasodilatation was blocked by tetrodotoxin but not by atropine. The vasodilator responses to field stimulation were compared with those produced by ATP, by vasoactive intestinal peptide (VIP), and by the inhibitory factor extracted from the bovine retractor penis muscle. Of the three putative transmitters, the inhibitory factor produced responses that most closely resembled those to field stimulation. Haemoglobin, which blocks non-adrenergic, non-cholinergic inhibitory transmission in the bovine and canine retractor penis muscles, did not impair the vasodilatations produced by ATP or VIP, but slowly reduced or abolished those produced by field stimulation or by the inhibitory factor. Haemoglobin itself produced a powerful constriction of the isolated penile arteries. The results are compatable with the possibility that the inhibitory factor from the bovine retractor penis muscle (which may be the inhibitory transmitter in that muscle) is, or closely resembles, the transmitter of non-adrenergic, non-cholinergic vasodilator fibres in the penile arteries of dog and ox.

The effect of an inhibitory factor from the bovine retractor penis on the gastro-intestinal tract and gall bladder of the guinea-pig

1 The effect of a smooth muscle inhibitory factor extracted from the bovine retractor penis has been examined on a variety of in vitro smooth muscle preparations from the guinea-pig alimentary canal and on the guinea-pig gall bladder. 2 The inhibitory factor caused relaxation of spontaneous and carbachol-induced tone in the taenia coli, the stomach fundal strip and the duodenum and colon. There was little effect on the ileum. Sensitivity was highest in the taenia coli where the response to the inhibitory factor mimicked the response to stimulation of the non-adrenergic, non-cholinergic (NANC) inhibitory nerves. 3 In the taenia coli the inhibitory response to stimulation of the NANC nerves and to ATP was abolished by apamin 5 x 10(-8) M, whereas this or higher concentrations had no effect on the response to the inhibitory factor. This makes it unlikely that the latter is the neurotransmitter in these NANC nerves. 4 The inhibitory factor had no effect on the gall bladder. Inhibitory responses to field stimulation were obtained in this tissue but these were insensitive to tetrodotoxin in concentrations greater than those needed to block the motor cholinergic nerves.

Block of some non-adrenergic inhibitory responses of smooth muscle by a substance from haemolysed erythrocytes

1. A preparation of haemolysed rat erythrocytes (the haemolysate) blocked the relaxations of both the bovine retractor penis and the rat anococcygeus muscles in response to field stimulation of their non-adrenergic inhibitory nerves. The effective concentration range was 5-20 mul./ml. of haemolysate, equivalent to 0.25-1.0 mul./ml. of blood. The active principle in the haemolysate was a non-dialysable, heat-labile material of molecular weight between 50,000 and 100,000 daltons. If, as appeared probable, the active component of the haemolysate was oxyhaemoglobin, its effective blocking concentration was 0.5-2 muM.2. Haemolysate (5-20 mul./ml.) also blocked the relaxation of both the bovine retractor penis and the rat anococcygeus to the inhibitory factor extracted from the bovine retractor penis, an observation supporting the possibility that this inhibitory factor may be the transmitter released by the inhibitory nerves in these tissues. In the bovine retractor penis, haemolysate was also effective in blocking relaxations in response to sodium nitroprusside, but relaxations produced by prostaglandin E(1) or isobutylmethylxanthine were unchanged or only slightly reduced.3. In contrast, in the taenia of the guinea-pig caecum, haemolysate did not block the non-adrenergic inhibitory response to field stimulation, nor the relaxation produced by ATP, although it did block the relaxation produced by the inhibitory factor.4. In spiral strips of isolated rabbit aorta, haemolysate (10 mul./ml.) increased the contraction produced by noradrenaline and blocked the relaxation produced by the inhibitory factor. These were shown to be independent effects.5. Apamin, which blocked the relaxation of the taenia of the guinea-pig caecum elicited by either ATP or field stimulation of its non-adrenergic nerves, was without effect on relaxations of the bovine retractor penis or rat anococcygeus muscles in response to field stimulation of inhibitory nerves or to inhibitory factor.6. These differences in the blocking effects of apamin and haemolysate suggest either that the transmitter in the bovine retractor penis and rat anococcygeus differs from that in the guinea-pig taenia, or, if the transmitter is the same, then its mechanism of action differs.

The effect of ethanol on inhibitory and motor responses in the rat and rabbit anococcygeus and the bovine retractor penis muscles

1 Ethanol (200 mM) reduced the response to inhibitory nerve stimulation in the rat and rabbit anococcygeus and the bovine retractor penis (BRP) muscles. Ethanol also reduced the response to the inhibitory extract from the BRP consistent with the inhibitory factor in these extracts playing some part in the response to inhibitory nerve stimulation. 2 Ethanol's effect on the response to other inhibitory stimuli was examined in the rabbit anococcygeus and the BRP. In the anococcygeus the response to carbachol was reduced, to bradykinin and isobutylmethylxanthine (IBMX) unaltered, and to isoprenaline and adenosine 5'-triphosphate (ATP) potentiated. In the BRP responses to IBMX and sodium nitroprusside were unaltered but in this tissue the response to isoprenaline was reduced. Ethanol's ability to reduce inhibitory responses is, therefore, selective and confined to inhibitory nerve stimulation, inhibitory extract, carbachol, and, in the BRP, isoprenaline. 3 Ethanol reduced the rate of development of inhibition even where the magnitude of the inhibitory response was unaltered. 4 In the rat anococcygeus, ethanol (200 mM) potentiated the response to motor nerve stimulation and to noradrenaline (NA) at low frequencies and low concentrations respectively. Higher ethanol concentrations (400 mM) reduced the response to both motor nerve stimulation and NA. The motor response to carbachol was also reduced. 5 Ethanol (200 mM) itself caused an easily reversible contraction in all three tissues. This was not due to the release of NA but was highly sensitive to the removal of external calcium from the medium. 6 A unified explanation of these varied effects of ethanol based on a reduction in membrane binding of calcium and a reduced efficiency of receptor coupling is suggested.

Some physical and chemical properties of the smooth muscle inhibitory factor in extracts of the bovine retractor penis muscle

1. A method of extracting and partially purifying a smooth muscle inhibitory factor from the bovine retractor penis is described. This consists of extraction in methanol followed by adsorption on an anion exchange resin, elution from the resin with 500 mM-sodium chloride solution and, if necessary, removal of adenine nucleotides by adsorption on alumina. 2. The inhibitory factor exists in a stable pharmacologically inactive form and an unstable pharmacologically active form. Conversion to the active form is by a brief exposure to acid at pH 2.0. 3. The inhibitory factor is insoluble in ether or acetone but soluble in methanol. Anhydrous methanol, however, irreversibly destroys pharmacological activity especially if the inhibitory factor is in the active form. This effect of methanol is prevented by the presence of 20-30-% water. 4. The inhibitory factor binds to an anion exchange resin but not to a cation exchange resin. It can be eluted from the resin by 500 mM-sodium chloride solution. 5. The molecular weight of the inhibitory factor, as judged by the ability to pass ultrafiltration membranes, is about 500. 6. Inhibitory activity is unaffected by the proteases trypsin, subtilisin or pepsin or by leucine aminopeptidase, pyroglutamate aminopeptidase or carboxypeptidase. The inhibitory effect of the extract and the inhibitory response to stimulation of the non-adrenergic, non-cholinergic nerves are also unaffected by the protease inhibitor, aprotinin. The active material, therefore, is unlikely to be a peptide. 7. Inhibitory activity is abolished by exposure of the extracts to periodic acid or sodium periodate. Acetic anhydride in pyridine also abolishes activity but the vehicle pyridine is also effective. 8. Sodium borohydride but not borate abolishes inhibitory activity when added to the acid-activated material at pH 2.0 but has no effect or may even potentiate activity if added to the stable inactive form at pH 9.0. When added to the acid-activated but neutralized material at pH 6.8 it usually abolishes inhibitory activity but occasionally has no effect. 9. These results suggest the smooth muscle inhibitory factor in these extracts is potent and probably novel. It does not appear to be a peptide or a lipid but may contain a carbohydrate as part of the molecule. Its possible physiological role is discussed.

Responses of the isolated anococcygeus muscle of the mouse to drugs and to field stimulation

1. The responses of the isolated anococcygeus muscle of the mouse to drugs and to field stimulation were investigated. 2. Fluorescence micrographs of transverse sections of the muscle revealed fluorescent nerve fibres in control tissues, but not in tissues from mice pretreated with 6-hydroxydopamine. 3. The isolated muscle displayed no spontaneous tone or rhythmic activity. Field stimulation produced frequency dependent contractions which were blocked by phentolamine and by low concentrations of guanethidine (500 nM). Higher concentrations of guanethidine (30 microM) raised muscle tone and, subsequently field stimulation produced frequency dependent relaxations. In muscles from 6-hydroxydopamine pretreated mice neither field stimulation nor guanethidine produced contractions, but when muscle tone was raised by carbachol inhibitory responses to field stimulation were still observed. 4. Contractions of the muscle were produced by noradrenaline (alpha-adrenoreceptors), acetylcholine (muscarinic receptors), 5-hydroxytryptamine, and prostaglandins E1, E2, and F2 alpha. 5. Adenosine 5'-triphosphate (ATP) normally produced muscle contraction, but following incubation of the tissue with indomethacin, ATP produced relaxations of carbachol-induced tone. 6. Vasoactive intestinal polypeptide, but not bradykinin, produced relaxations of tissues in which tone had been raised by carbachol. 7. The isolated anococcygeus muscle of the mouse provides a useful preparation for the study of various aspects of autonomic neurotransmission in smooth muscle.

Actions on the cardiovascular system of an inhibitory material extracted from the bovine retractor penis

1 A partially purified material has been isolated from methanol extracts of the bovine retractor penis muscle. This material exerts biological activity only after treatment with acid and subsequent neutralisation. The active principle in this extract, which appears to be no known autacoid, mimics the response to stimulation of the non-adrenergic, non-cholinergic nerves in the bovine isolated retractor penis muscle. 2 This inhibitory extract did not alter the heart rate or blood pressure of the anaesthetized rat when administered either by intravenous or intra-arterial injection, nor did it have any obvious effect on isolated cardiac muscle. 4 The extract produced relaxation of spiral strips of various arteries isolated from ox, cat, rabbit or rat, in which tone was induced by noradrenaline, K+ of Ba2+. 5 The extract also produced dilatation of the resistance vessels of the rat isolated mesenteric circulation and the rat hindquarters perfused with Krebs solution; tone was induced in these vessels by adrenaline or noradrenaline. 6 Lack of vasodilator activity of the extract in the whole animal appeared to be due to rapid inactivation in the blood, probably by binding to the erythrocytes.

A smooth muscle inhibitory material from the bovine retractor penis and rat anococcygeus muscles

1. A material that powerfully inhibits the bovine retractor penis and rat anococcygeus muscles has been extracted from these muscles. The inhibitory activity is unaffected by atropine 10(-6) M, phentolamine 5 x 10(-6) M or propranolol 5 x 10(-6) M. 2. This inhibitory material exists in two forms, a stable but inactive form and an unstable inhibitory form. As isolated the material is in the stable, inactive form and is converted into the active form by a brief exposure to acid. The optimum for conversion is pH 2.0 and the active form, after neutralization, reverts with time to the inactive but can be reactivated by a further exposure to acid. The reversion to the inactive form is temperature sensitive, and is rapid at 37 degrees C. 3. The inhibitory material, both active and inactive, is irreversibly destroyed by 2 min in a boiling water bath or by exposure to U.V. irradiation. 4. The inhibitory material is not confined to tissues known to possess a non-adrenergic non-cholinergic innervation. Similar activity has been detected in extracts os skeletal and cardiac muscle and of the liver. The poorly innervated rat uterus and the non-innervated human umbilical artery, however, gave only small and variable amounts. The possible relationship of this material to non-adrenergic non-cholinergic nerves is discussed.