| Abstrakt: |
Simple Summary: Animal species show marked variations in their cerebrovascular responses to substances that affect blood vessel tone, like noradrenaline, histamine, acetylcholine, 5-hydroxytryptamine, angiotensin II, and bradykinin. These variations may result from the receptor subtype distribution in smooth muscle or endothelial cells, and reflect the interplay of evolutionary and genetic influences for different animal species. Recently, we have investigated whether and how the response to one of these substances, noradrenaline, is related to deviations from an even heart-to-head alignment in an animal's normal posture (which has implications for the gravitational effect on blood flow), for multiple species. Sika deer are even-toed ungulates, closely related to cattle. Close phylogenetic relatives have often been found to show similar cerebrovascular responses, but deer and cattle have a very different heart-to-head alignment. Accordingly, we compared the cerebrovascular responses between sika deer and other ungulates. We found that deer and other even-toed ungulates have similar cerebrovascular responses to histamine, bradykinin, Nω-nitro-L-arginine, and indomethacin (evaluated with cattle), but different responses to noradrenaline and acetylcholine (evaluated with pigs and cattle). We considered that cerebrovascular responses to noradrenaline may positively correlate with gravity (as it affects blood flow in a normal posture) in quadrupedal animals. Gravity may exert species-specific effects on quadrupedal vasoreactivity, reflecting variations in the vertical displacement of the cardiocranial axis from the dorsal plane. Deer show markedly displaced cardiocranial axes compared to their closest phylogenetic relatives, but their relative cerebrovascular responses remain unelucidated. Accordingly, we investigated the responses to noradrenaline (NA), acetylcholine (ACh), 5-hydroxytryptamine (5-HT), histamine, angiotensin (Ang) II, and bradykinin (BK) in cervine basilar arterial rings. NA and 5-HT induced slight contraction, and ACh induced relaxation, which contrasts with the findings reported in pigs and cattle. The cumulative response to ACh was abolished by endothelial denudation and inhibited by Nω-nitro-L-arginine (a nitric oxide synthase inhibitor), atropine (a nonselective muscarinic antagonist), and p-fluoro-hexahydro-sila-difenidol (an M3 antagonist). Pirenzepine (an M1 antagonist) and methoctramine (an M2 antagonist) showed no significant effects. Histamine induced contractions, with its concentration–response curve shifted to the right in parallel by diphenhydramine (an H1 antagonist). However, cimetidine (an H2 antagonist) showed no significant effects. Ang II and BK had no vasomotive effects. NA and ACh induced different cerebrovascular responses in sika deer versus cattle, but histamine and BK did not. Our findings suggest that cerebrovascular responses are influenced by the similarity of animal species and the head and heart positions relative to gravity. [ABSTRACT FROM AUTHOR] |
