Skullcap
Botanical Description & Habitat
Scutellaria laterifolia
Family
Labiatae
Common names
| American skullcap | Blue pimpernelle |
| Blue skullcap | Helmet-flower |
| Hood wort | Hooded willow herb |
| Mad dog weed | Pimpernel |
| Side-flowering skullcap |
Habitat
Found in wet, shady places in North America
Description
Has a smooth, erect stem one to three feet high, bearing opposite, coarsely serrated, and ovate leaves. The flowers are pale purple, grow in one-sided racemes, are two-lipped, and bloom from July to September.
Medicinal parts
Whole plant, fresh or dried, gathered in August when fruiting is well-advanced.
Historical Properties & Uses
Skullcap is generally recognized as a mild tonic and nervine, effective for insomnia, excitability, restlessness, and other nervous complaints. It is specifically recommended in cases of sleeplessness due to pain. Much research on this plant has been carried out at several major Russian universities. A typical study finds the plant hypotensive and relaxing, with antispasmodic effects. An anti-epileptic effect is also occasionally reported.
American experience with skullcap dates from the last century, during which the herb was used for neuralgia, convulsions, delirium tremens, insomnia, and restlessness. Strong infusions and decoctions were the rule at that time, but mild preparations are used today. Skullcap is also used to relieve pain and to treat atherosclerosis; it can prevent rises in cholesterol level incurred by diet. The herb is best used in blends of other minor or moderately acting sedatives and tranquilizers, such as valerian root, hops, passion flower, and black cohosh.
Some members of the species Scutellaria, of which skullcap is a member, have been relied upon from ancient times as treatments for allergic and inflammatory diseases. Research has verified those uses, and has demonstrated skullcap antipyretic, hypotensive, hypothermic, and antitumor properties.
Method of Action
Skullcap Species Have Antispasmodic Effects
Skullcap is a component of various popular Japanese "Saiko" prescription drugs. It is usually combined with ginger root, bupleuri root, pinelliae root, and zizyphi fruit.
Research on the individual components as well as combinations of the components has shown skullcap has definite anti-acetylcholine and anti-histamine actions on isolated guinea pig ileum. It also inhibited noradrenaline-induced contractions of isolated guinea pig vas deferens.
While this study found spontaneous activity of isolated rat uterus was enhanced, earlier studies had found just a slight depressant effect on the uterus. Heart rate was slightly reduced. Extracts of skullcap containing the glycosidal fraction have failed to exhibit antispasodic effects, indicating the property must reside in some other fraction. Baicalein and wogonin, two of the main flavonoid glycosides of some species of skullcap, have been screened as to potential antispasmodic effect. The former had very little or no activity, while the latter had slight activity.
Skullcap has Anticholesterolemic Properties
A crude skullcap preparation was found to significantly inhibit rises in serum cholesterol in cholesterol-fed rabbits, while having no effect on the cholesterol levels of normal rabbits, thus indicating it prevents cholesterol absorption and increased choelesterol sequestering and elimination.
Skullcap Has Antipyretic And Hypothermic Properties
Experimental findings using water and alcohol extracts showed skullcap (S. baicalensis) has antipyretic effects. Furthermore, intragastric administration produced a dose-dependent fall in rectal temperature in rats when ambient temperatures were kept below 23 degrees centigrade. The hypothermia appeared to be caused solely by cutaneous vasodilation (as estimated by an increase in cutaneous temperature). At higher temperatures, the response was not observed. Through experimentation it has been found skullcap action is related to the maximal activation of the effectors of heat loss, while the effector of heat production is unaffected. Since baicalin has a definite antipyretic effect, it is likely the hypothermic response also depends on the presence of baicilin. Therefore, only those species of skullcap that contain baicilin would be certain to exhibit this property.
Intraperitoneal administration of aspirin also produces a dose-dependent hypothermia at room temperature and in the cold, and also appears to act through cutaneous vasodilation, with the one difference that aspirin also produced a slight increase in metabolic heat production not observed with skullcap. The antipyretic effect of aspirin, then, possesses at least one drawback not shared by skullcap.
Skullcap Has Hypotensive Properties
The hypotensive action may be related to the cutaneous vasodilation observed in the hypothermia studies discussed above. In anesthetized cats, skullcap preparations produce a fall in arterial pressure which is attributed to a decrease in peripheral resistance in the peripheral vascular beds. It is suggested skullcap inhibits the normal vascular smooth muscle tone by interrupting the descending excitatory impulses from the vasomotor center of the central nervous system.
Skullcap Has Cytotoxic Action
In routine screening tests, it was noticed an ether extract of S. baicalensis was cytotoxic on L1210 cells in vitro. Subsequently, skullcap flavone II, 5,2'-dihydroxy-6, 7,8,6'- tetramethoxyflavone, was isolated and identified as the active constituent. However, the ether extract was seven times stronger than the pure isolated flavone, indicating certain kinds of synergistic substances are contained in the extract. The other flavones of skullcap, including baicalin, baicalein, wogonin, etc., showed not significant cytotoxic activity.
Skullcap Has Anti-Inflammatory Properties
An intensive line of research over the last few years being carried out in Japan has established various flavones from S. baicalenis, including baicalein, baicalin, wogonin and skullcap flavone II, have anti-arthritic and anti-inflammatory actions, even as they occur in 70% methanol extract of whole root.
Evidence has been forthcoming they act, at least in part, by inhibiting arachidonate metabolism in rat polymorphonuclear leukocytes, specifically 5-HETE (5-lipoxygenase product) and HHT (cyclooxygenase product) known to be involved in the various inflammatory processes, such as formation of leukocyte chemotactic substances.
Drug Interactions & Precautions
Possible Interactions
Veratrum alkaloids may potentiate the activity of skullcap up to 50%. The hypotensive effect of this herb may also be potentiated by anorectic drugs, such as fenfluramine, whose effects are mediated by brainstem 5HT.
Skullcap should not be used with methotrimeprazine, a potent CNS depressant analgesic. It should also be noted colchicine may increase sensitivity, or enhance the response to, skullcap.
Additive effects may also occur between the hypotensive property of skullcap and dopamine receptor agonists such as bromocriptine mesylate.
Skullcap may increase the metabolism of digitoxin, oral contraceptives, phenytoin, corticosteroids, fluroxene, methadone, metyrapone, and tetracyclines.
The metabolism of skullcap may be increased by barbiturates, ethanol, diazoxide, loxapine, and vitamin B-6.
Conversely, the metabolism of the herb may be decreased by propoxyphene, troleandomycin, para-aminosalicylic acid (PAS), antihistamines, chloramphenicol, disulfiram, halothane, isoniazid, methylphenidate, phenothiazines, and sulfa drugs.
Skullcap may decrease the absorption and diuretic response to furosemide. It may also inhibit the stimulant effect of glucagon on insulin release by islet of Langerhans cells.
Comments
Skullcap may potentiate the effects of oral anticoagulants to the extent it stimulates the liver to catabolize and excrete cholesterol and its by-products via the biliary route.
The hypotensive property of skullcap may be additive with the CNS depressant activity of the analgesics nalbuphine HCl and propoxyphene HCl. The neuromuscular relaxing action of the herb may also be enhanced by the use of certain aminoglycoside antibiotics, such as clindamycin.
To minimize central nervous system depression and possible synergism, it would be wise to avoid using skullcap with procarbazine antineoplastic drugs.
In the absence of other hard data, it may be assumed observable interactions occur between the many central nervous system drugs and the psychoactive principles in skullcap.
Safety Factors & Toxicity
There is no evidence for toxicity of skullcap at normal doses.
However, the FDA consider it to have caused: confusion, epilepsy, giddiness, stupor and twitching.
Preparation & Administration
Three times a day
Dried plant
1-2 grams
Tea
made from 1/2 tsp dried plant
Fluid extract
1:1 in 25% alcohol, 2-4 ml
Tincture
1:5 in 45% alcohol, 1-2 ml
Note: This Herbal Preparation information is a summary of data from books and articles by various authors. It is not intended to replace the advice or attention of health care professionals.
References
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Scutellaria laterifolia
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