We are using arteries from humans for myographical studies, but we have problems during contraction when we use phenylphrine (PE)? But, the arteries contract normally when we use KCl.
All vessels are not equal when it comes to their ability to constrict to PE; some arteries are much more responsive to PE than others. It depends on the amount of adrenergic receptor expressed on the smooth muscle cells, and on the amount of sympathetic innervation of the artery studied (although, I am not 100% sure that the level of sympathetic innervation directly correlates with the expression level of adrenergic receptors...).
In your context (cancer feeding arteries or umbilical cord), I am not so sure that PE is physiologically relevant, I would try other agonists. I was quickly looking into the literature and found this paper where they show that arterioles within a prostate tumor do not constrict to PE:
I would try other agonists (ET1, AngII, 5-HT, PGI2 etc.) but your choice depends on your hypothesis, what is it that you would like to test on these vessels? Are you studying a pathway in particular or do you "just" want to see the overall contractile ability of these vessels?