Responses of the pig isolated renal artery to transmural electrical stimulation and drugs

1 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. 2 Transmural stimulation of the tissue causes contraction of circular muscle in the arterial wall which produces apparent elongation of the vessel. 3 The effects of transmural stimulation are partially blocked by prazosin and potentiated by propranolol, indicating that noradrenaline acts through both α‐ and β‐adrenoceptors. 4 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 ). 5 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. 6 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.