The hyperin and tannin content of H. perforatum is higher at growth temperatures above 14 degrees C. (tannin, 15.06% of dry weight) than below (13.42%). Both hyperin and rutin content is higher in dry conditions (1.25% and 2.32% respectively) than wet conditions (no figure given and 1.89%, respectively). Hyperin content is highest at 7pm (84). Total tannin content is highest when the buds are forming, just prior to flowering, in June (85,86).

Higher amounts of flavonoids, including rutin, quercetin, and hyperin occur in plants of northern slopes with few generative shoots (87). Flavonoid content (rutin, hyperin, quercetin, and quercitrin) is highest in the leaves of St. John's wort, and is at maximum concentration during full bloom. In the flowers, the content of flavonoids is highest at the start of flowering, falling sharply during flowering (88).

St. John's wort (flowers) had the highest content of flavonoids (11.71%) of any of 223 species tested (89).

Pharmacology
Extracts of the flowering tops of Hypericum perforatum have shown a variety of effects in the laboratory, including psychotropic activity, wound and burn-healing activity, bactericidal effect against pathogens in pyelitis and cystitis, anti-viral effects, sunscreen activity (disputed), antidepressive activity, and diuretic, anthelmintic, and mildly uterotonic activity (90, 91, 92). Although much more work needs to be done to validate the use of St. John's wort for the many uses it finds in clinical and common practice, there are a few laboratory studies which corroborate its use for some of these conditions and point the way for further research.

Following is a summary of the laboratory work that has been conducted on the pharmacological effects of St. John's wort extract or oil.

Anti-depressive and Psychotropic Activity
Among the most common psychiatric illnesses today are depression, mania, (abnormal elation with irritability), bipolar affective disorder, characterized by swings between depression and mania, and schizophrenia. One of the best-known (but contoversial) theories hypothesizes that depression is caused by deficiency or decreased effectivness of norepinephrine and serotonin, acting as nerve-impulse transmitting substances (neurotransmitters), in particular nerve pathways. One method for treating depression uses the monoamine oxidase (MAO) inhibitors which retard one of the enzymes responsible for monoamine (a precursor) breakdown, increasing the concentration of neurotransmitters in the central nervous system (93, 94).

Because of St. John's wort's history of use for psychiatric conditions, it was tested for MAO inhibiting activity. Suzuki, et al. (1984), in an international effort, first demonstrated that xanthones, common in the Guttiferae (the family of St. John's wort) and the Gentianaceae (Gentian family), inhibit both type A and B monoamine oxidase. Among these is the compounds isogentisin, which has been found in some species of Hypericum, but not H. perforatum (95, 96). A further study by the same group found that hypericin from H. perforatum irreversibly inhibits type A and B MAO in vivo. The authors stress, however, that although this study is suggestive, no definite conclusion can be drawn yet regarding St. John's wort's antidepressant activity (97).

A standardized (hypericin) extract of H. perforatum has been tested in various animal models generally used for determining antidepressant activity, and has been found to enhance the exploratory activity of mice in a foreign environment, extended the narcotic sleeping time dose-dependently, and has shown reserpine antagonism and decreased aggressive behavior in socially isolated male mice (98).

Muldner and Zoller (1984), in a clinical trial with 6 depressive women, 55-65 years old, measured smetabolites of noradrenaline and dopamine in the urine, and found that after taking a standardized hypericin extract, there was a significant increase in 3-methoxy-4-hydroxyphenylglucol, a marker for the beginning of an antidepressive reaction. The same research team, working with 15 women taking a standard hypercin extract, demonstrated an improvement in symptoms of anxiety, dysphoric mood, loss of interest, hypersomnia, anorexia, depression (worse in the morning), insomnia, obstipation, psychomotoric retardation, and feelings of worthlessness. They reported no side-effects (99).

Wound and Burn Healing
In a number of studies St. John's wort extracts have demonstrated anti-bacterial and wound-healing activity. For instance, two widely prescribed Russian preparations of Hypericum, novoimanine and imanine, have been tested for Staphylococcus aureus infection in vivo and in vitro, and been found to be more effective than sulfonilamide (100, 101, 102). Hyperforin, a bicyclic tetraketone from H. perforatum, is reported to be a main antibiotic constituent of novoimanine (103).

One German patent mentions that an ointment containing an extract of St. John's wort flowers shortened healing time of burns and showed antiseptic activity (104). According to the report, first degree burns healed in 48 hours when treated with the ointment, while second and third degree burns healed without keloid (a type of scar tissue) formation three times faster than burns treated by conventional methods.

Other reports include that a freeze-dried St. John's-wort extract suppressed inflammation and leukocyte infiltration in vivo (105), and that St. John's wort oil has been used in commercial products as a sun screen. However, reports of its efficacy in this latter regard are contradictory (106, 107).

Anti-viral Effects
International interest increased in St. John's wort after researchers from New York University medical center and the Weizmann Institute of Science in Israel demonstrated that two compounds from the plant strongly inhibit a variety of retroviruses in vitro and in vivo (108). Several points bear citing from their report:

• "When the compounds interact with the infecting particles shortly after in vivo administration, disease is completely prevented."
• "Preliminary in vitro studies with pseudohypericin indicate that it can reduce the spread of HIV."
• The total yield of hypericin and psuedohypericin from H. triquetrifolium Turra was 0.04%.
• The compounds were still effective when administered orally or i.p. within 1 day of infection.
• No serious toxic side effects were noticed after testing over 800 mice with the compounds. Administration of the compounds did not result in abnormalities in any of a wide variety of clinical tests performed on the animals.
• Hypericin shows toxicity to some human cells at very high concentrations (>10 ug/ml, or lower for some cell types). Pseudohypericin is less toxic. Fortunately, the compounds show remarkable antiviral potency "after one administration of a relatively small dose of the compounds."
• "The compounds directly inactivate the virions or interfere with assembly or shedding of assembled viral particles."
• "The compounds can cross the blood-brain barrier" (important for HIV infection).

Clinical Applications
Clearly, the potential scope of clinical application of St. John's wort is extensive. However, if one narrows the focus down to those activities that are most mentioned, such as anti-bacterial, anti-phlogistic, diuretic, and anti-depressive, specific clinical applications become more restricted.

In modern European medicine, St. John's wort extracts are included in many over-the-counter and prescription drugs for mild depression, and have clinical application for bed-wetting and nightmares in children. The extract is included in diuretic preparations, and the oil is taken internally by the teaspoon to help heal gastritis, gastric ulcers, and inflammatory conditions of the colon (using a retention enema) (110). The oil is also used extensively in burn and wound remedies, externally.

Table 2, taken from the German Health Department's official monograph on St. John's wort (1984), summarizes the current clinical applications of the plant (105,106).

Herb source: flowers of Hypericum perforatum, "gathered during the time of blooming or of the dried parts above the ground, as well as their preparations, in effective dosages."

Clinical applications: Internally: "psychovegetative disturbances, depressive states, fear and/or nervous disturbances. Oily hypericum preparations during dyspeptic disturbances." Externally: "Oily hypericum preparations for the treatment or after treatment of sharp or abrasive wounds, myalgias (muscular pain) and first degree burns."

Contraindications: "None known." Side effects: "Photosensitization is possible, especially in light skinned people." Interference with other drugs: "None known." Dosage schedule: Average daily dose recommended is 2-4 grams of the powdered herb, or 0.2-1.0 g hypericin as a powdered extract. Method of use: "Cut or powdered plant, liquid and solid forms for oral administration. "Liquid and semi- solid forms for external use." Effects: Mild anti-depressant action (monoamineoxidase [MAO] inhibitor), oily preparations have antiphlogistic activity. "Diuretic activity,...direct effect on smooth musculature."

Toxicity
Besides its long history of use as a medicinal plant, St. John's wort is also known as a photosensitizing plant that can cause sickness and even death in grazing animals (when large amounts are eaten), particularly cattle, sheep, horses, and goats, but also rabbits and rats111. This toxic activity of St. John's wort was first noted in the literature by Cirillo (1787), and since then, there have been many papers published, and the effect mentioned numerous times (112). The plant, however, does not seem to be a major threat to livestock, because the first symptoms of Hypericum intoxication includes loss of appetite, which makes the absorption of the photodynamic pigment, hypericin, self-limiting (113).

In the case of Hypericum toxicity, the compound hypericin is absorbed from the intestine and concentrates near the skin. When the skin of the animal is exposed to sunlight, an allergic reaction takes place. Oxygen is necessary for the photodynamic hemolysis, leading to tissue damage. In the absence of sunlight, a reaction will not occur, and the compound does not show particular toxicity. (114, 115) This first type of reaction is called 'primary photosensitization' (116). Another, more serious type, is secondary photosensitization, where the liver and other internal organs can be damaged (117).

Cattle appear to be more sensitive to the phototoxicity of hypericin than sheep. In one test with cattle, a single dose of 1 g per kg bodyweight of dried Hypericum showed no photosensitization or changes in liver enzymes, but 3-4 g did. If humans were as sensitive to hypericin as cattle, this dose would correlate to 59 gms for a 130 lb individual. Importantly, hypericin does not seem to be accumulative. (118)