Tolazoline HCl (Pridazole, Priscol, Benzalolin, Divascol, Priscoline), the hydrochloride salt of tolazoline, is an imidazolline-based and non-selective competitive α-adrenergic receptor antagonist used as a vasodilator for the treatment of spasms of peripheral blood vessels. In cases of persistent pulmonary hypertension in neonates (PPHN), tolazoline, a pulmonary vasodilator, is prescribed to reduce pulmonary vascular resistance (PVR). Tolazoline exhibits both histamine agonist and mildly alpha-adrenergic blocking properties. Vascular resistance and pulmonary arterial pressure are typically lowered by tolazoline.

Physicochemical Properties

Molecular Formula	C10H13CLN2
Molecular Weight	196.68
Exact Mass	196.076
Elemental Analysis	C, 61.07; H, 6.66; Cl, 18.02; N, 14.24
CAS #	59-97-2
Related CAS #	Tolazoline; 59-98-3
PubChem CID	6048
Appearance	White to off-white solid powder
Density	1.09g/cm3
Boiling Point	338.2ºC at 760mmHg
Melting Point	172-176 °C
Flash Point	158.3ºC
LogP	1.797
Hydrogen Bond Donor Count	2
Hydrogen Bond Acceptor Count	1
Rotatable Bond Count	2
Heavy Atom Count	13
Complexity	169
Defined Atom Stereocenter Count	0
SMILES	N1([H])C([H])([H])C([H])([H])N=C1C([H])([H])C1C([H])=C([H])C([H])=C([H])C=1[H]
InChi Key	RHTNTTODYGNRSP-UHFFFAOYSA-N
InChi Code	InChI=1S/C10H12N2.ClH/c1-2-4-9(5-3-1)8-10-11-6-7-12-10;/h1-5H,6-8H2,(H,11,12);1H
Chemical Name	2-benzyl-4,5-dihydro-1H-imidazole;hydrochloride
Synonyms	Tolazoline; Benzalolin; Divascol; Tolazoline hydrochloride; 59-97-2; Tolazoline HCl; 2-benzyl-4,5-dihydro-1H-imidazole hydrochloride; 2-Benzyl-2-imidazoline hydrochloride; Arterodyl; Tolavad; Pridazole; Priscol; Priscoline
HS Tariff Code	2934.99.03.00
Storage	Powder-20°C 3 years 4°C 2 years In solvent -80°C 6 months -20°C 1 month Note: Please store this product in a sealed and protected environment, avoid exposure to moisture.
Shipping Condition	Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

Biological Activity

Targets	α-adrenergic receptor
ln Vitro	In vitro activity: Tolazoline is a pulmonary vasodilator that is recommended for use in persistent pulmonary hypertension of the newborn (PPHN) to reduce pulmonary vascular resistance (PVR). Tolazoline exhibits both histamine agonist and modest alpha-adrenergic blocking properties. Vascular resistance and pulmonary arterial pressure are typically decreased by tolazoline.[1] Compared to SNP, tolazoline is less broadly effective against all spasmogens that have been studied. However, in human radial arteries, it might be useful in preventing vasospasm mediated by alpha-adrenoceptors.[2]
ln Vivo	Studies have investigated the pharmacologic mechanism of 2-(4'-isothiocyanatobenzyl) imidazoline (IBI) and analogs for interaction with imidazoline receptors (IRs), alpha-adrenergic receptors (alpha-ARs), and calcium channels in cardiovascular muscle systems. IBI differs from tolazoline by substitution of an electrophilic isothiocyanato (NCS) group. Unlike tolazoline, which is a partial alpha-AR agonist, IBI produced an irreversible, slow-onset, and sustained contraction of rat aorta with an median effective concentration (EC50) value of 5 microM, and a maximal contraction (116%) greater than that of phenylephrine (100%) and tolazoline (59%). The IBI-induced contractions were dependent on calcium channels and independent of alpha-ARs or IRs. Similarly, structure-activity relation studies in rat aortic smooth muscles on a series of synthesized IBI analogs indicated that NCS analogs, but not those without the NCS group, exhibited effects by a non-alpha-AR, non-IR, but a calcium channel-dependent mechanism. Thus the presence of an intact IBI ring in these analogs is not a requirement for these activities. Further, IBI inhibited dihydropyridine (DHP, [3H]PN 200-110 and [3H]Bay K 8644) binding to L-type calcium channels of T-tubule membranes in rabbit skeletal muscle. In contrast to nifedipine, IBI and NCS derivatives (nifedipine-NCS, naphazoline-NCS) only partially (50-88%) displaced specific binding of these radioligands. A single site of noncooperative interaction was observed for nifedipine (nH = 0.97), whereas tolazoline-NCS (IBI, nH = 1.46) and nifedipine-NCS (nH = 1.37) exhibited a positive cooperativity in binding to DHP sites. These receptor-binding data indicate that NCS derivatives bind to L-type calcium channels and interact allosterically with DHP-binding sites. Direct binding of the NCS group to specific nucleophilic protein sites of the calcium channel may be responsible for its activation and the subsequent contractile effects of IBI. [1]
Cell Assay	Tolazoline (10(-9)-10(-4) M) or sodium nitroprusside (SNP, 10(-9)-10(-4) M) were cumulatively applied on radial artery rings precontracted submaximally with noradrenaline, endothelin-1, thromboxane analogue, U46619, or potassium chloride. In addition, some rings were pretreated with tolazoline (4 x 10(-6) M) for 30 minutes and the contractile response curve to noradrenaline was assessed in its presence. Results: tolazoline effectively reversed noradrenaline-induced contractions in the radial artery, whereas it failed to produce remarkable relaxations on rings contracted with other spasmogenic agents, while SNP overcame the contractions induced by all spasmogens to a similar extent. In addition, brief pretreatment of radial artery rings with tolazoline significantly inhibited the contractions to noradrenaline. Conclusions: tolazoline is not as broadly effective as SNP against all spasmogens investigated; however, it may be effective in counteracting alpha-adrenoceptor-mediated vasospasm in human radial arteries. [2]
Toxicity/Toxicokinetics	infant TDLo intravenous 48 mg/kg/47H-C GASTROINTESTINAL: ULCERATION OR BLEEDING FROM DUODENUM; GASTROINTESTINAL: ULCERATION OR BLEEDING FROM SMALL INTESTINE Australian Paediatric Journal., 22(221), 1986 [PMID:3767790] human TDLo intravenous 150 ug/kg CARDIAC: CHANGE IN RATE; VASCULAR: OTHER CHANGES; SKIN AND APPENDAGES (SKIN): SWEATING: OTHER Folia Medica, 27(729), 1941 rat LD50 oral 1200 mg/kg Drugs in Japan, 6(511), 1982 rat LD50 intraperitoneal 100 mg/kg Drugs in Japan, 6(511), 1982 rat LD50 intravenous 85 mg/kg Drugs in Japan, 6(511), 1982
References	[1]. J Cardiovasc Pharmacol . 1998 May;31(5):721-33. [2]. Ann Thorac Surg . 2006 Jan;81(1):125-31.
Additional Infomation	Tolazoline hydrochloride is a member of benzenes. A vasodilator that apparently has direct actions on blood vessels and also increases cardiac output. Tolazoline can interact to some degree with histamine, adrenergic, and cholinergic receptors, but the mechanisms of its therapeutic effects are not clear. It is used in treatment of persistent pulmonary hypertension of the newborn. See also: Tolazoline (has active moiety). The radial artery is increasingly being used in coronary revascularization as an alternative conduit to a saphenous vein graft. Its perfect endothelial capacity provides a high patency rate comparable with the internal mammary artery (IMA). However, its spastic characteristics cause difficulties during its intraoperative preparation and may lead to early postoperative graft failure. Thus, treatment and/or prevention of radial artery spasm with an effective vasodilator agent is essential for its longevity. Endogenous vasoconstrictors, including noradrenaline, endothelin-1, and thromboxane A2, are likely to play a role in the pathogenesis of graft spasm. In the present study, we evaluated the vasorelaxant effect of tolazoline, a nonselective alpha-adrenoceptor blocker, against the contractions induced by various spasmogenic agents in an isolated human radial artery.[2]

Solubility Data

Solubility (In Vitro)

DMSO: 33.3~39 mg/mL (169.5~198.3 mM) Water: ~39 mg/mL (~198.3 mM) Ethanol: 39 mg/mL

Solubility (In Vivo)

Solubility in Formulation 1: ≥ 2.5 mg/mL (12.71 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution. For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL. Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution. Solubility in Formulation 2: ≥ 2.5 mg/mL (12.71 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution. For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly. Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution. Solubility in Formulation 3: ≥ 2.5 mg/mL (12.71 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution. For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly. Solubility in Formulation 4: 100 mg/mL (508.44 mM) in PBS (add these co-solvents sequentially from left to right, and one by one), clear solution; with ultrasonication.  (Please use freshly prepared in vivo formulations for optimal results.)

Preparing Stock Solutions		1 mg	5 mg	10 mg
	1 mM	5.0844 mL	25.4220 mL	50.8440 mL
	5 mM	1.0169 mL	5.0844 mL	10.1688 mL
	10 mM	0.5084 mL	2.5422 mL	5.0844 mL

*Note: Please select an appropriate solvent for the preparation of stock solution based on your experiment needs. For most products, DMSO can be used for preparing stock solutions (e.g. 5 mM, 10 mM, or 20 mM concentration); some products with high aqueous solubility may be dissolved in water directly. Solubility information is available at the above Solubility Data section. Once the stock solution is prepared, aliquot it to routine usage volumes and store at -20°C or -80°C. Avoid repeated freeze and thaw cycles.