Abstract
Pig isolated renal arteries contract in response to addition of noradrenaline, 5-hydroxytryptamine, histamine, angiotensin II, vasopressin and carbachol, whereas cholecystokinin, adenosine, and inosine produce relaxation. Transmural stimulation of the tissue causes contraction of circular muscle in the arterial wall which produces apparent elongation of the vessel. The effects of transmural stimulation are partially blocked by prazosin and potentiated by propranolol, indicating that noradrenaline acts through both alpha- and beta-adrenoceptors. Guanethidine (10(-5) M) reduces the size of responses to transmural stimulation in the presence of both prazosin (10(-6) M) and propranolol (10(-7) M). Both saralasin (10(-7) M), and desensitization of angiotensin II receptors by prolonged contact with the peptide, produced a reduction in response to transmural stimulation, indicating that angiotensin II may be involved in neurotransmission. This effect was blocked by tetrodotoxin. Transmural stimulation produces relaxation of renal arteries in the presence of maximal doses of saralasin, prazosin, and propranolol, suggesting that a third unidentified substance is also released from autonomic nerves.
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