In vitro studies of the carotid rete mirabile of Artiodactyla.

The carotid rete of Artiodactyla, an intracranial arterial plexus which supplies blood to the brain, has intrigued investigators for a long time. This study was designed to examine the responsiveness of isolated retial arteries (250-700 microns in external diameter) of goat, pig, and cattle. The findings in these arteries were compared to those observed in cerebral arteries (250-650 microns in external diameter) of the same animal species. The magnitude of the arterial responses to potassium chloride varied with the resting tension applied to the tissue. The two types of vessels exhibited similar resting tension values (0.3 g) for maximal tension development in response to potassium chloride; however, the ability of retial vessels to contract in the presence of potassium chloride was consistently smaller than that of cerebral arteries. The contractile response of retial arteries to norepinephrine (10(-9) to 10(-4) M), tyramine (10(-8) to 10(-3) M), and field electrical stimulation (2-16 Hz) was negligible. The same retial arteries exhibited dose-dependent contractions in response to 5-hydroxytryptamine (10(-9) to 10(-5) M) and histamine (10(-9) to 3 X 10(-4) M). Cerebral arteries exhibited larger responses to the vasoactive agents than retial arteries. Our findings indicate that retial arteries have a small vasomotor activity in response to adrenergic stimulation or to vasoactive agents. Therefore, the carotid rete of Artiodactyla may have a low ability to change resistance to blood flow under neural or hormonal influences.