Preliminary pharmacological characterization of ovine mesenteric vasculature.

Spirally cut strips of ovine mesenteric vein and artery were studied in isolated organ baths. No qualitative differences were observed in the autonomic and autacoid reactivity of these blood vessels. Both arterial and venous preparations responded in a dose-related manner to 5HT greater than or equal to adrenaline greater than phenylephrine greater than histamine. The responses of venous and arterial strips to 5HT were antagonized by methysergide while mepyramine inhibited histamine-induced contractions. Phentolamine competitively inhibited adrenaline on arteries. Vascular preparations, incubated with mepyramine (2 X 10(-7) M) and contracted half-maximally with 5HT, responded with relaxations to the higher doses of histamine. Specific H2-agonists, impromidine and dimaprit also caused relaxations of half-maximally contracted venous and arterial strips. Impromidine was approximately 500-5000 times more potent than histamine and dimaprit. Trimetaquinol effectively relaxed both venous and arterial preparations while isoproterenol had either no effect or produced weak contractions/relaxations. This investigation suggested the presence of (i) both excitatory and inhibitory receptors for histamine, (ii) D-tryptaminergic receptors mediating contractile effects of 5HT, and (iii) a predominance of alpha-adrenergic receptors, in the mesenteric vasculature of sheep.