New study supports pain management properties of plant native to Americas

In the study, the researchers found that administering rats and mice with a hydroalcoholic extract of Solidago chilensis Meyen, a goldenrod, decreased responses to pain without causing a sedative effect.

The results were dose-dependent, meaning that more extract was linked to less pain response.

“Our findings indicate that S. chilensis might be an important adjuvant in pain management,” the researchers wrote in their report, published this week in the journal BMC Complementary and Alternative Medicine.

These were based on results of various tests conducted on the rodents, ranging from a writhing test (where researchers observed writher behavior when mice were injected with acetic acid) to a hot plate test (where researchers observed the rodents’ reactions from being placed on hot plates).

“In order to test if S. chilensis also exerts significant effects on the central transmission of pain, we investigated the effects of its extract in models of non-inflammatory pain, such as nociceptive response to heat or a mechanical stimulus,” they explained.

Study details

The researchers used Swiss mice and Wistar rats for their study. The aerial parts of Solidago chilensis, which include everything but the root, were collected from the city of Guararema in the state of Sao Paulo, Brazil.

Plants were immersed in 93% ethanol for one month, after which the hydroalcoholic extract was filtered and concentrated using a rotary evaporator. The resulting liquid was injected into the rodents.

Animals were divided into groups injected with either different doses of the extract (3 mg/kg, 10 mg/kg, or 30 mg/kg), a saline placebo, or a standard pain management drug.

The rodents were put through several tests to gauge reaction to pain, including a writhing test, formalin test, hot plate test, and a hind paw test. To assess whether or not there were any sedative effects, the researchers performed a rota-rod test on the mice.

All researchers were blinded, meaning that they did not know which animal received which injection, except for one, who oversaw administering the extracts and distributing the animals throughout the experiment.

It was the blinded researchers that scored behavior and performed the data analysis.

Oral supplementation?

Though there is a tradition of ingesting the extract orally, the researchers tested the effects of the extract if it were injected intraperitoneally, which means injection straight to a membrane that lines the rodents’ abdomen.

“In our previous study, only topical and intraperitoneal, but not oral, administration of the extract exerted anti-inflammatory effects in rat ear oedema, suggesting that the absorption of its anti-inflammatory component(s) may be affected by the gastrointestinal tract,” they wrote.

“Further studies should address specific compounds of this extract that might have particular pain-related actions, possibly indicating new perspectives to clinical practice,” they added.

Goldenrod in traditional Brazilian medicine

_{^{Solidago chilensis. Photo: Dick Culbert / Flickr}}

In Brazil, goldenrod, specifically S. chilensis, is wildly found and is included as a therapeutic tool for contusion, trauma, and boils by the country’s Medicinal Plant Programs.

In their report, authors of the current study wrote:

“S. chilensis is used topically or by oral administration, depending on the region and according to cultural traditions. Patches from leaves and stems are used for muscle pain or skin lesions.
Infusion, bath, decoction or tincture of S. chilensis flowers or the whole plant macerated are also used for wound healings and boils, purulent infections, inflammation, edema, body pain, chill or rheumatism.”