Pharmacological studies on the pulmonary vein of the horse. I. Effects of selected spasmogens.

This research investigates the effects of certain substances on the veins in the lungs of horses, to understand how this might contribute to a horse’s asthmatic response. The substances analyzed include histamine, serotonin, and others.

Objective

The objective of the study was to analyze the effects of various spasmogens, substances that cause muscle contraction, on the pulmonary vein of the horse. This was with the intention of better understanding the horse’s respiratory condition, which is similar to human allergic asthma.

Methodology

• Pulmonary vein sections from horses were prepared in vitro, that is, outside of the living body in a controlled environment.
• The effects of histamine, 5-hydroxytryptamine (serotonin), bradykinin, carbachol, and phenylephrine on the veins were studied.
• The capacity of each of these substances to cause contractions in the veins was compared.

Results

• The ranking in terms of the effect these substances had on vein contraction was: 5HT (serotonin) > Histamine > Bradykinin > Phenylephrine > Carbachol. That is, serotonin had the greatest overall effect, followed by histamine, then bradykinin, phenylephrine and carbachol.
• However, histamine consistently produced the most maximal effects.
• Different forms of receptors were identified to mediate the responses to the various substances.
• Distinct levels of tachyphylaxis, a decreased response to repeated application of a drug, were noted for each of the substances tested.

Implications

• The research concluded that the contraction of pulmonary veins brought on by these spasmogens could contribute to the asthmatic responses in horses.
• This is because the contraction could raise the pressure inside the vessels, thereby promoting the formation of edema (a condition characterized by an excess of watery fluid collecting in the cavities or tissues of the body), which would aggravate the asthmatic condition.